Optimization of HOLLOW CORE SLABS

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ACKNOWLEDGMENTS

I would like to express my deepest appreciation to my supervisor in Strängbetong, Mr. Henrik Vinell,

for his time, motivation, patience, continuous advising and support during those months. I strongly

believe that his ideas and way of thinking, are of the most important things I gained from this

experience. Without his guidance and persistent help this project would not have been possible.

I would like to express my sincere gratitude to my thesis supervisor at KTH Royal Institute of

Technology, Professor Johan Silfwerbrand, for bringing me in contact with Strängbetong and hence

giving me the opportunity to work with this topic. Additionally, I am thankful for his help and

comments on this report, but also for teaching me about the important field of theory and

methodology on research.

I also wish to thank the employees in the office of Strängbetong in Stockholm for answering my

questions, creating a nice working environment and making me feel comfortable from the first day.

Many thanks to the employees of Strängbetong in the factory in Kungsör, for sharing with me their

knowledge, providing me with useful material and being willing to answer all my questions.

This thesis was completed during a pandemic, under very special circumstances. I would like to thank

my family and friends for their support during this difficult period.

Stockholm in September 2020,

Konstantinos Apostolou

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Abstract [en]

The Swedish precast concrete company ‘Strängbetong’ produces a variety of Hollow Core slabs, with

a standard width of 1200 mm. Quite often, the HC units are subjected to longitudinal cutting1, which

takes place in the factory by a diamond blade, in order to achieve narrower elements. This results in a

considerable material waste since the rest part of the HC unit cannot always be utilized. Regarding the

cutting process, it requires a significant amount of time that slows down the production. Moreover,

extra workhands are needed, while other factors such as the transfer and crash of unwanted pieces,

contribute to a higher cost for the factory. Approximately 12% of the HC elements produced by

Strängbetong are fillers. Aiming to achieve a more efficient and sustainable production, the reduction

of the number of fillers is of vital importance.

This thesis project investigates if a line producing smaller width elements would be more profitable.

The study starts by investigating the most common width that HCs are cut, with the aim to create a

line according to this width2. Then, the most promising width is determined, taking into account the

possible alternatives and fillers’ width trends that have been found. To estimate accurately the

possible cost saving, the impact of the smaller width line on the production and the possible increase

of thru put3, the production of the factory in Kungsör, is simulated on MATLAB. Firstly, the current

situation is simulated (8 lines, 1200-mm-wide) in order to evaluate the current efficiency. Then, the

studied scenario is simulated (7 lines 1200-mm-wide and one 813-mm-line), to evaluate the

advantages of this alteration. Both simulations start by imposing the HC production load of 2019. This

thesis is completed by a repetition of the simulations, where the input data are modified, in an effort to

calculate accurately the possible cost saving as a function of designers’ adaption to the 813-mm-line.

The results show that if an 813-mm-line were used instead of a 1200-mm-line during 2019, the

possible cost saving would be at least 1.0 million SEK annually. The suggested line leads to a more

sustainable production, as concrete and steel waste can be decreased by 51.6% and 50.3%,

respectively. A significant amount of time due to less longitudinal cutting can be saved while there is

a slight increase of thru put. Moreover, the results show that the factory will be able to handle the

pressure on the production, despite the decrease by 1/8 of the physical production capacity of 1200

mm units. Finally, if the designers adapt fast to the new width alternative, the possible cost saving

would rise significantly. If it is possible to design 1 out of 5 future fillers as a full-width element, cost

saving can reach 1.4 million SEK annually.

1 Elements produced at a width smaller than the full width (1200 mm), are mentioned as ‘fillers’ in the HC production. In

Sweden, usually those elements are mentioned as ‘passelement’. 2 This that it is examined, is the modification of a full width line to a line with a smaller standard width. It should not be

confused with the creation of an extra casting bed. 3 The term ‘thru put’ stands for the number of production cycles per day.

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Sammanfattning [sv]

Den svenska betongelementtillverkaren Strängbetong producerar olika typer av håldäck med en

standardbredd på 1200 mm. Ganska ofta blir håldäckselementen föremål för längdsågning som

genomförs i fabriken med en diamantsåg med syftet att erhålla smalare element. Detta leder till ett inte

försumbart materialsvinn eftersom den avsågade delen inte alltid kan användas. Beträffande sågningen

kräver den en betydande tidsåtgång som fördröjer produktionen. Vidare krävs ytterligare arbetskraft

medan andra faktorer som transport och krossning bidrar till högre kostnader för fabriken. Cirka 12 %

av Strängbetongs håldäcksproduktion utgörs av så kallade passelement. För att nå en mer effektiv och

hållbar produktion är det angeläget att minska antalet passelement.

I detta examensarbete studeras om en linje som produceras smalare element skulle vara lönsam.

Studien inleds med att undersöka de vanligaste bredderna som håldäckselementen sågas i med syftet

att skapa en linje för den bredden. Därefter bestäms den mest lovande bredden genom att beakta

möjliga alternativ och identifierade trender kring passelementens bredder. För att noggrant kunna

uppskatta de möjliga kostnadsbesparingarna, en smalare linjes inverkan på produktionen och en

möjlig ökning av volymen (antalet produktionscyklar per dag) så har produktionen i Kungsörfabriken

simulerats med hjälp av MATLAB. Först studerades den rådande situationen (8 st 1200 mm breda

linjer) för att uppskatta dagens effektivitet. Därefter simulerades ett studerat scenario (7 st 1200 mm

breda linjer och en med bredden 813 mm) för att utvärdera fördelarna med denna förändring. Båda

simuleringarna utgår från 2019 års produktionsbelastning. Examensarbetet avslutas med en

upprepning av simuleringarna, nu med modifierade ingångsdata, i ett försök att korrekt beräkna

möjliga kostnadsbesparingar där hänsyn tas till konstruktörernas kännedom om den 813 mm breda

linjens existens.

Resultaten visar att ifall en 813 mm bred linje hade använts i stället för en av 1200 mm-linjerna under

2019 så hade kostnadsbesparingarna uppgått till minst 1,0 miljon kronor årligen. Den föreslagna linjen

leder till en mer hållbar produktion eftersom betong- och stålsvinn kan reduceras med 51,6 resp. 50,3

%. En betydande tidsbesparing kan göras på grund av mindre längdsågning samtidigt som volymen

ökar något. Dessutom visar resultaten att fabriken förväntas kunna hantera det ökade trycket på

produktionen trots att kapaciteten för 1200 mm breda element minskar med 1/8. Slutligen ifall

konstruktörerna snabbt börjar tillvarata det nya alternativet så skulle de möjliga

kostnadsbesparingarna kunna öka i hög grad. Om det vore möjligt att dimensionera 1 av 5

passelement som ett fullbreddselement så skulle kostnadsbesparingarna kunna uppgå till 1,4 Mkr per

år.

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Contents

1. Introduction ...................................................................................................................................... 7

1.1 General information .................................................................................................................. 7

1.2 Description of the problem ........................................................................................................ 8

2. Background Information .................................................................................................................. 9

2.1 Types of HC slabs ..................................................................................................................... 9

2.2 Regulations for longitudinal cutting of HC units ...................................................................... 9

2.3 The difficulty of re-using scrap elements ................................................................................ 11

2.4 Efficiency of a new width line ................................................................................................ 12

3. Methodology .................................................................................................................................. 13

3.1 Data analysis of produced HC units ........................................................................................ 13

3.2 Data analysis of fillers by type of element .............................................................................. 13

3.3 Grouping of width frequencies by cutting zones .................................................................... 14

3.4 Relation between fillers’ width and actual need ..................................................................... 15

3.5 Possible widths of a new line based only on fillers’ characteristics ....................................... 15

3.6 The choice of the new line’s width ......................................................................................... 16

3.7 Required time for longitudinal cutting of HC units ................................................................ 17

3.8 Simulation of the production ................................................................................................... 18

3.8.1 Simulation of the current situation (8x1200 mm system) ..................................................... 20

3.8.2 Simulation of the studied scenario (7x1200 mm and an 800-mm-line)................................ 21

3.8.3 Estimation of the daily required time for longitudinal cut of fillers ..................................... 24

3.8.4 Parameters concerning waste and cost calculations.............................................................. 25

3.8.5 Evaluating thru put ................................................................................................................ 27

3.8.6 Evaluating production’s pressure when a full-width line is modified .................................. 28

3.9 Estimation of cost saving, considering designers’ adaption to the 813-mm-line.................... 29

4. Results ............................................................................................................................................ 30

4.1 Data analysis of produced HC units ........................................................................................ 30

4.2 Data analysis of fillers by type of element .............................................................................. 33

4.3 Grouping of width frequencies by cutting zones .................................................................... 36

4.4 Relation between fillers’ width and actual need ..................................................................... 39

4.5 Possible widths of a new line based only on fillers’ characteristics ....................................... 41

4.6 The choice of the new line’s width ......................................................................................... 43

4.7 Required time for longitudinal cutting of HC units ................................................................ 49

4.8 Simulation of the production ................................................................................................... 49

4.8.1 Efficiency of the production in the current situation ............................................................ 50

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4.8.2 Simulation of the studied case (system of 7x1200-mm, 1x800-mm) ................................... 53

4.8.3 Reduction of material waste in the case of the 800-mm-line................................................ 55

4.8.4 Possible cost saving in the case of the 800-mm-line ............................................................ 56

4.8.5 Possible increase of thru put in the case of the 800-mm-line ............................................... 59

4.8.6 Pressure on the production in the case of the 800-mm-line .................................................. 62

4.9 Possible cost saving vs the adaption to the new width line ..................................................... 64

5. Conclusions and suggestions for future research ........................................................................... 66

5.1 Conclusions ............................................................................................................................. 66

5.2 Suggestions for future research ............................................................................................... 67

6. References ...................................................................................................................................... 68

7. Appendix ........................................................................................................................................ 69

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1. Introduction

1.1 General information

Hollow Core slabs (HC slabs) are an alternative type of slab that offers many advantages and is

gaining popularity, especially across Northern Europe and the United States. HC slabs are prestressed

precast concrete elements manufactured using long line casting pallets. Longitudinal voids, or cores,

run throughout a HC slab, resulting in a significant reduction of raw material consumption and self-

weight of the slabs, while they provide ready-made ducts for services. With the prestress and low self-

weight, longer spans can be achieved for the same loads or greater loads for the same depths.

Moreover, higher erection speed of a building is achieved, as HC slabs are factory made. Site work is

significantly reduced, and construction process is not vulnerable to weather conditions. HC slabs are

cast in long beds, and then length-cutting with diamond blades takes place (IPHA 2020).

Picture 1-1. A hollow core slab (from Strängbetong)

Strängbetong is the major Hollow Core producer in Sweden. HC slabs are produced in three of the

company’s factories: in Kungsör, Veddige and Långviksmon. The company produces a variety of

types of HC slabs (with regard to thickness and number of cores), of a standard width 1200 mm. The

factory in Kungsör leads the production of HC slabs, with 8 casting beds, 143 m long.

Even though the use of HC slabs is accompanied with certain benefits, their design, production and

use are always a field under study. Innovative ideas have already been a subject under research with

the intention of making the HC production more efficient. Additionally, as the use of HC slabs has

been increased, recommendations and alterations of the design guidelines of HC slabs are often an

issue under discussion.

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1.2 Description of the problem

As mentioned before, HC slabs can provide certain advantages against other types of slabs. However,

as the width of the HC slabs is fixed at 1200 mm, one understands that the structural elements are

often subjected to further cut, in order to fit projects’ specific needs. Apart from cutting for making

specific angles on elements, or other cuts for details, length-cutting usually takes place (a HC unit is

cut longitudinally in its long dimension). Elements subjected to length-cutting are mentioned as

‘fillers’4 in the HC production.

Length-cutting of HC units increases the material waste significantly, as it is not always possible to

use the other side of the HC slab, when a 1200-mm-wide element has to be cut. Moreover, there is a

slowdown of the production, due to the time needed to cut an element. Apart from the cost deriving

from the material waste, there is an additional cost for the factory for transferring and destroying the

unwanted pieces, while the removal of those elements from the beds requires time and workhands.

The environmental impact is higher, due to the material waste and the additional CO2 emissions from

the produced unwanted pieces.

In this report, it is examined if a new casting bed of a standard width smaller than 1200 mm will result

to more efficiency in the HC production. Firstly, the width that would lead to the highest possible

efficiency is investigated. Then, the production is simulated and the possible cost saving is studied, as

also the impact of a new width line on the production, based on the HCs produced during 2019 in the

factory in Kungsör. Following this, more simulations are made, to predict the possible cost saving

considering designers’ adaption to the new width line.

4 The Swedish term is ‘Passelement’.

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2. Background Information

2.1 Types of HC slabs

There are in total six alternative depths of HC elements that are produced by Strängbetong today.

Moreover, there are alternatives in the design patterns of cores for specific depths, which leads to nine

types of HC slabs in total. The technical characteristics of each type are depicted below. A more

detailed description of each type is given in the Appendix A1.

Table 2-1. Technical characteristics of the available HC types.

Type Thickness

(depth)

(mm)

Width

(mm)

Number

of cores

Number of

strands

Cross-section

area

(m2)

Weight

(kg /m)

HD/F 120/20 F155 200 1197 6 7 0.124 310

HD/F 120/20 F125 200 1197 6 7 0.160 399

HD/F 120/22 F155 220 1197 6 7 0.147 368

HD/F 120/22 F125 220 1197 6 7 0.172 430

HD/F 120/27 F184 265 1197 5 8 0.165 411

HD/F 120/27 F155 265 1197 5 8 0.211 527

HD/F 120/32 F236 320 1197 4 11 0.178 445

HD/F 120/38 F218 380 1197 4 14 0.214 534

HD/F 120/40 F172 400 1197 5 16 0.234 585

2.2 Regulations for longitudinal cutting of HC units

When a HC unit needs to be cut, it is important to cut at a point so that the strands (body) will not be

affected. Affecting the body of the HC unit, will lead to lower capacity of the element and many other

problems during the production stage. Hence, a distance from the strands is always required. There are

two general regulations (Eriksson 2014) that are followed when a HC unit needs to be cut:

1. Cut of a HC unit according to allowable zones for cutting (SE-HDF00-525) (old regulation)

According to that regulation, an engineer is allowed to cut a HC unit in a zone around the middle of

the core, while he is recommended to cut in the smallest possible cross-section area. This regulation is

used more often.

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Figure 2-1. Zones where it is allowed to cut a HC unit according to the old regulations.

(Strängbetong handbook, SE-HDF00-525), (full document on the Appendix A2)

2. Cut of a HC unit at a recommended width (SE-HDF00-521) (new regulation)

This regulation defines the exact points that an engineer is allowed to cut, for each type of HC

element. The regulation allows the designers to cut only in the middle of the cores. This regulation is

used less often, but it is gaining popularity year by year, especially across the new designers.

Figure 2-2. Recommended cutting widths, leading to the lowest cross section area.

(Strängbetong handbook, SE-HDF00-521), (Full document on the Appendix A3)

Cutting a HC unit in a cutting zone (SE-HDF00-525) is more time consuming, as most of the times,

the element is not cut exactly in the middle of the core, leading to a higher cross-section area that

needs to be cut by the diamond blade. Moreover, it is more difficult to combine fillers in the

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production, in order to reduce the waste. However, even when two fillers are placed beside each other

to reduce waste, it is very common that the diamond blade may need to cut twice in order to create the

required widths. Hence, cutting a HC unit according to that regulation slows down the production and

makes the employees’ job more difficult. In addition, when an element is cut at a point far from the

middle of the core, the blade during the cutting tends to turn towards the core center, something that

increases difficulty and time, while it is quite common that the diamond blade will have to cut twice to

succeed an acceptable result.

Cutting a HC unit in an exact point – which is the middle of the core (SE-HDF00-521), leads to

cutting in the lowest cross-section areas and consequently to the lowest possible slowdown of the

production. The blade is strained less and the cutting procedure is more efficient. In addition, it is

easier for the production planners to place HC fillers beside each other in order to reduce waste. In

that case, two HC fillers can be cut, by only one pass of the diamond blade.

2.3 The difficulty of re-using scrap elements

For a filler to be produced, a full-width element is subjected to longitudinal cutting. The production

planners try to utilize the rest of the casting bed (towards the transverse direction), by placing a filler

there. In that way, material is saved, capacity is increased and with one pass of the diamond blade, two

fillers are cut. This is easier when elements are cut according to the new regulations of cutting (SE-

HDF00-521), because elements are cut in specific widths and as a result, it is easier to find an element

that matches the dimensions. However, it is not always possible to place a filler on the other side of

the element, resulting to a scrap element.

Generally, the scrap elements are utilized when this is possible. Elements that are possible to use

again, are stored in the factory and their technical details and other characteristics are marked. When

an order of a filler can be covered by an element of those on storage, then, instead of casting, the scrap

element is utilized. However, for many reasons, it is very difficult to utilize scrap elements, and hence

one understands the importance to reduce scrap elements produced by longitudinal cutting.

Firstly, it is quite difficult to match an order with a scrap element of those in storage, as the technical

details have to match (dimensions, HC type, etc.). Secondly, storage of fillers is difficult for the

production, as it requires extra workhands and a significant amount of space. Furthermore, elements

most often include design details, something that increases the difficulty of finding a stored element

which is compatible. More problems can derive in the re-use of scrap elements e.g. regarding the

lifting of those elements on site. One way of lifting fillers is by using lifting wires locked on specific

positions of the filler, which can be a problem when an element is re-used.

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The above shows that it is quite difficult to use a scrap element, and consequently, it is of vital

importance to reduce the produced scrap elements, for a more efficient production.

2.4 Efficiency of a new width line

The efficiency of the width of a new line is generally depended on the following factors:

1. The biggest possible percentage of fillers that the new width line can cover. This can be done

in two ways: directly and indirectly.

• Directly, if the element fits exactly to the actual need (less common).

• Indirectly, when a new element is used in combination with cast-in-situ concrete joints

(more common).

2. By avoiding the highest possible length cutting. Usually, it implies that covering the biggest

possible percentage of fillers leads to avoid the highest possible length cutting.

3. By reducing to the lowest possible, the material waste. This occurs in various ways:

3.a When the line covers the highest percentage of fillers, so there is no need for cutting of HC

units (factor 1).

3.b By reducing the material waste from the future fillers, after the new line is made. A new

line with standard width X < 1200 mm can lead to big reduction of material waste, when fillers

with width smaller than the width of line X, are cast and cut on this line and not on a 1200-

mm-line.

4. By increasing thru put. It implies that if a new line covers the highest possible percentage of

fillers (factor 1), less time for longitudinal cutting is required and thru put is increasing.

Moreover, by reducing units that need cutting on a 1200-mm-line, by casting and cutting them

on the new line X (factor 3.b), thru put is increasing to the highest possible. In other words, if

the cases of cutting on a 1200-mm-line are limited only to the fillers that have a width bigger

than X, the thru put is increasing.

5. By decreasing the factory’s additional costs due to the production of scrap elements. When a

scrap element is produced, the factory has to transfer and crash it or store it for future use,

resulting to an extra cost.

6. By reducing in-situ casting to the highest possible.

7. By reducing the environmental impact. By reducing the material waste (factor 3) to the highest

possible, a more environmentally friendly production is achieved, while CO2 emissions5 are

decreasing too.

5 When a HC unit is cut in the long dimension and the one side of the HC unit is not utilized, more concrete is produced

than what is actually needed. From this aspect, there are additional CO2 emissions.

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3. Methodology

During the first part of this report (subchapters 3.1 – 3.5), the width of a new line that seems to be

more beneficial was investigated. The main idea was to choose the width of a new line according to

the width that fillers are usually longitudinally cut. Hence, the study aimed to discover the width that

HC fillers are cut more often. As a first step, the geometrical characteristics of the fillers from the

previous years’ production, were analysed. Then, a more extended study was made, by analysing

those fillers by elements’ type. The results were grouped properly, in order to be able to make

conclusions. Following this, the relationship between fillers’ width and the actual need on a project,

was studied. Finally, the possible widths for a new line were discussed, based only on fillers’

characteristics. Other important aspects regarding fillers were also studied.

3.1 Data analysis of produced HC units

At this chapter, the data history of the produced HC units of the years 2010-2019 at the three factories,

was analysed using the software MATLAB. Firstly, by company’s history, the number of HC units

that are cut (fillers), was estimated.

Then, in order to investigate if there is any trend in the width that HC fillers are cut more often, the

frequency of each width for the range of 1 – 1196 mm was calculated. Graphs were made, to show the

widths that HC fillers tend to be cut more often.

The changes of the width frequencies’ graphs over the years were explained by the following two

regulations regarding cutting (Eriksson 2014):

1. Cut of a HC unit according to allowable zones for cutting (SE-HDF00-525) (old regulation).

2. Cut of a HC unit at a recommended width (SE-HDF00-521) (new regulation).

Finally, a graph was made, that shows how many designers follow the new regulation year by year,

based on the width that HC fillers are cut.

3.2 Data analysis of fillers by type of element

In this chapter, the width frequencies and additionally, the total cutting length for each width, are

calculated. Due to the fact that the recommendations about cutting of HC fillers change depending on

the type of the HC unit, but also because even when the old rules are used, the cutting point is strongly

influenced by the position of the strands (which are different depending on the HC type), fillers are

studied separately, regarding their HC type.

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The type of HC unit that produces most of the fillers was found. Then, based on the data of the

production 2015-2019 and for all three factories, the width frequencies were plotted, per type of

element, in order to show any trends.

It is important to notice that the way that designers choose to cut a HC unit, changes over the years.

The later years, more and more designers adapt to the new regulations of cutting at specific points –

the centres of the cores. Hence, the analysis counts only the production of the years 2015-2019 and

not the previous years. Including, for example, the year 2012 in the analysis, would insert an error in

the results, because the way that engineers design, has changed significantly since then. From the

other side, even if the year 2019 is the most representative regarding the cutting rules at the moment, it

is necessary to include the production of other years in the analysis in order to avoid errors due to

specific project demands.

3.3 Grouping of width frequencies by cutting zones

The plotted width frequencies vary, due to the fact that many engineers cut an element according to

the old rules. Hence, a width frequency diagram has peaks for widths that are very similar. For

example, it can be seen in the results that there are peaks in a width of 592 mm and 600 mm. This

difference is very small and it happens mainly due to the fact that engineers do not follow the same

cutting rules. It is considered that those differences represent the same need.

In order to have a clearer and more representative image so as to make conclusions about the width

trends, it was necessary to group the results of the widths that fillers are usually cut. This was made

according to the cutting zones of the old rules (Appendix A2). The table below shows the allowable

cutting zones for the first three cores of each type, according to which the frequencies were grouped.

Table 3-1. Grouping of data – zones of cutting for each type of HC unit

Type of slab HD/F 120/20 HD/F 120/22 HD/F 120/27 HD/F 120/32 HD/F 120/38 HD/F 120/40

1st core (mm) 1013-1116 1013-1116 995-1107 937-1112 963-1112 1010-1087

2nd core (mm) 824-940 824-940 772-872 659-821 680-800 786-859

3rd core (mm) 635-751 635-751 548-649 376-538 397-517 562-635

After grouping the data, the amount of fillers that are cut at each core for all HC types, was presented.

The total cutting length in meters and the percentage to the total cutting length, were calculated.

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3.4 Relation between fillers’ width and actual need

At this part, a discussion was made about the relationship between the final width that fillers are cut

and the actual need for a project. The width that an element is longitudinally cut, is not the same with

the actual need on a project, due to the fact that engineers are not allowed to cut a HC element at every

point. Moreover, cast-in-situ concrete joints are necessary beside fillers, especially when two fillers

are placed beside each other in a project. Hence, the position that an engineer decides to cut an

element, is influenced by more factors.

In general, the first part of this chapter investigates the most common widths that HC units are cut,

with the purpose to create a line with this width. Producing elements that depict, to the nearest

possible, the actual need on a project and as a result, do not require big cast-in-situ concrete joints,

will reduce the construction costs and make designers’ jobs easier. Thus, a discussion was made, in

order to find the link between the filler’s width and the actual need. When the width of the new line is

to be decided, this relationship is counted for finding the most cost-effective solution.

3.5 Possible widths of a new line based only on fillers’ characteristics

At this part, the possible widths of the new line, that seem to be more beneficial, were presented.

Conclusions at this point, were based only on aspects such as the width frequencies that fillers are

usually cut and the corresponding cutting length at each width. Moreover, the relationship between the

cutting width and the actual need, was counted in the decision.

Other aspects, that are of interest for the efficiency of the new width line, are not possible to be

estimated accurately at this point. For example, the possible reduction of the material waste (and

consequently the possible environmental benefits), the possible increase in thru put, the time saved

due to less longitudinal cutting and the reduction of other additional costs due to fillers’ production,

are some of the factors that cannot be estimated accurately at the moment.

This happens because various practices are followed during the HC production, in order to reduce

material waste and speed up the production. In order for someone to calculate accurately the above-

mentioned factors, one has to simulate the production firstly. For example, in order to calculate

accurately the material that is wasted, it is important to take into account the fillers that are placed

beside other fillers, and how much material is wasted in that case.

The same implies for other aspects such as the possible increase in thru put. In order for someone to

have a more representative and accurate picture, a simulation of the production should take place,

where one can understand better the impact of a different line on the production.

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Even factor 2 (from chapter 2.4), which refers to the cutting length, cannot be answered accurately, by

only considering the geometrical characteristics of the fillers. This is because the final cutting length is

not exactly equal to the sum of the length of the fillers. For example, when two fillers are placed

beside each other on the casting bed, to reduce waste, the cutting length is equal to the length of the

longer filler.

3.6 The choice of the new line’s width

The width of the new line was determined in this chapter. Any decisions were made by taking account

the width frequencies, the corresponding cutting length for each width and the possible alterations that

can be made in a 1200-mm-line.

It is noted that the decision regards only the factory in Kungsör, the one with the highest HC

production. The factory hall has eight casting beds which are 1200 mm wide and 143 meters long, and

there is no space in the hall for the creation of an extra casting bed. Hence, the decision of the new

width, is for modifying one of the eight existing casting beds.

In the first part of this subchapter, the basic principles regarding splitting of a 1200-mm-line to

smaller standard widths, were explained. Then the basic principles regarding the chamfer were

presented and a decision was made for which one is of preference. A table showing the possible

alterations of a full width line by the provider company for machinery and equipment was described.

The percentages of fillers for each HC type were compared with the available alternatives.

Alternatives that are not available for the HC type that produces the highest percentage of fillers, were

rejected. Then, an extended comparison of the alternatives that are compatible with the most common

HC type were made, based on the following criteria:

• Amount of fillers cut at each width. The results about width frequencies and trends on these,

as they had derived from the previous chapters, were used.

• Possible direct reduction of longitudinal cutting.

• Possible reduction of the material waste and additional costs for the factory.

• Speed up of the production and the general impact of any alternative on the production.

A more qualitive comparison was made between criteria that include production aspects. This is

because during the production, various practices are followed for reducing waste or speeding up the

production, for which, an accurate calculation was done later by simulating the production.

Additionally, one extra criterion that was included in the choice of the width of the new line, was the

increase of the possibility to avoid cutting elements in the future, when a new width line will be

17

available. This is an aspect from the designers’ point of view, regarding the span combinations that a

new width element can offer when the HC elements are placed on a project. More specifically, a

comparison was made, about the possible combinations that new width elements together with 1200

mm wide elements can offer, to cover a span6.

Finally, since some of the used HC types are not available for the chosen width alternative, it was

necessary to change the core pattern in some of these cross-sections, in order to make the 800-mm-

line available for all the depths. Moreover, one extra HC type was introduced.

3.7 Required time for longitudinal cutting of HC units

The delay of the production due to longitudinal cutting at the current situation, but also the possible

increase of thru put in the case of an 800-mm-line, and other aspects that involve time, are calculated

when the production is simulated. For those calculations, the required time for longitudinal cutting of

a HC element is needed. This time varies for every HC type and is strongly depended on the cross-

section area that is cut.

At this subpart, a mean value was calculated for every type of HC unit. This time, in other words, is

the speed that the diamond blade longitudinally cuts a HC element. It does not involve the time

needed for starting the blade or the time needed for positioning of the blade before each element.

The data of the time needed for every longitudinal cut, as also the corresponding cutting length, are

kept on blade’s database. The data from the factory in Kungsör for the year 2016 are used, to estimate

the average time in minutes/meter of HC type.

It should be mentioned that those data have a very high variation. This is because many factors

influence the time needed to cut an element. A main reason for this variation is the difference in the

cross-section that is cut each time. However, the point of cutting, in order to find the time needed as a

function of the cross-section, is not kept. The only data kept are the time needed in seconds, the

corresponding longitudinal cutting in meters and the depth of the element that is cut. This means, that

there is no information either for the core pattern – data of different HC types with the same depth are

mixed. This inserts a type of error which is inevitable.

A filter was used to reject the extreme values and consequently obtain more representative results.

According to this, all the values smaller than 0.4 minutes/meter or higher than 4.5 minutes/meter,

were rejected.

6 A span can be used in two cases: The parallel dimension with the strands of HC units, when those are placed to cover an

area, and the transverse dimension, by adding the width of the HC units. Here, the 2nd is implied.

18

3.8 Simulation of the production

During the production of HC slabs, units are placed in such a way in the casting bed, so as that the

cost for the factory will be the smallest possible. This cost includes the material waste (concrete and

steel), the time and workhands needed for longitudinal cutting, the handling, transfer and crash of the

scrap elements, but also the slowdown of the production and the reduction of thru put.

Hence, the concrete waste for example, cannot be accurately calculated by looking only on the fillers’

dimensions; one has to take into account the way that each element is placed on the casting bed. Other

examples that are also influenced by the way that elements are placed on the bed, are the total casting

length of a casting program, or the total longitudinal cutting. In order for someone to study those

aspects with high accuracy, one has to take into account the position of elements on the bed.

Figure 3-1. The placement of the HC fillers on the bed influences the cost calculations and the efficiency of the production.

For example, the longitudinal cutting in the case shown above is equal to the length of the longer filler.

Figure 3-1 shows a common case of fillers placed on the casting bed. Fillers are placed beside each

other, to reduce the material that is wasted and increase the capacity of the casting bed. Moreover, by

placing fillers beside each other, there is less use of the diamond saw, because for one pass of the

blade, two elements are cut. Apart from fillers, HC units with diagonal cuts are placed in such a way

to reduce waste.

The data of the produced HC elements, apart from the technical details (length, width, HC type,

thickness, etc.), also contain the casting date, the casting bed, the casting program and the order of the

unit on the casting bed. In addition, each filler which is positioned beside another element is marked

19

with a note ‘SPLIT’7. By that information, it is easy to understand the placement of elements and

estimate the above-mentioned aspects.

However, it is quite common to not follow a strict numbering of the elements on the bed for many

reasons. Quite often, when a casting bed contains fillers, the numbering starts with the full-width

elements and thereafter the fillers follow (which is not the actual positioning on the bed, fillers are

positioned in a way to reduce waste). In that case, the only possible way for someone to understand

the actual position of fillers on the bed, and hence estimate the exact waste, is by studying each

casting program’s report8.

Another practice that it is followed during the casting, for reducing concrete waste, is that when an

element fails to be cast correctly (or any other problem), the workers directly pause the casting

machine, instead of letting it cast the whole length of the element. The system pushes another element,

the casting of which, directly starts. The scrap element is noted in the system as ‘DISCARDED’;

however, the initial length is still shown in the data (not the actual cast length). The same notation is

used even if the element has been fully cast, but some problems occur.

As mentioned before, when two fillers are placed beside each other, the shorter element is noted in the

system as ‘split’. However, sometimes, when two fillers are cast beside each other, and there is an

error in the longer one, there are cases where this filler is not mentioned as a scrap element. The

shorter filler is still noted as ‘split’. In that case, if someone does not study in detail the casting

program report, it is likely to underestimate the concrete waste, thinking that the other side of the

shorter filler was utilized. In fact, the other side gives a scrap element that should be counted in the

waste calculations. In other words, a filler that is noted as ‘SPLIT’, does not imply that the other side

of the filler has been necessarily utilized.

The above-mentioned shows that in order to calculate accurately aspects such as the concrete waste,

one has to look at each casting program’s report. As the total production is of interest, the production

is simulated9. With a simulation, split fillers can be matched and a higher accuracy in calculations is

succeeded. Moreover, other aspects such as the estimation of pressure (load) on the system, or the

possible increase of thru out, make the simulation of the production of vital importance.

Consequently, in this chapter, the HC production in Kungsör is simulated with the use of MATLAB in

order to study the efficiency of the production. Then, the simulation is modified, to study the

7 Usually, the shorter of the two elements is noted as split. If they have the same length, then the narrower of them. 8 It is possible though to understand the way that fillers are placed on a bed by only looking at the elements’ dimensions, in

simple cases. 9 By a simulation, in other words, elements are reordered in a casting program in a way that the efficiency will be the

highest possible, as the production planners do on the factory.

20

efficiency of the case of an 800-mm-line instead of a 1200-mm-line. Hence, two basic systems were

created:

• Simulation of the production when there are eight lines, 1200 mm wide (current situation)

• Simulation of the production in the case of seven lines of 1200 mm and one line of 813 mm

(the studied scenario).

For the simulation, production’s data of the year 2019 from the factory in Kungsör were used. This

year’s production was one of the highest, while it is considered the most representative for the

following years, due to the high adaption to the new cutting regulations (SE-HDF00-521).

3.8.1 Simulation of the current situation (8x1200 mm system)

For every working day of the factory in Kungsör in 2019, all the produced HC units from the database

are sorted by the casting program they belong to. Then for each casting program, HC units were sorted

by their casting program order10. Due to the fact that a strict numbering is not followed and in order to

understand how many fillers were possible to be placed beside others to make the production more

efficient, for each filler it is checked if it is possible to be placed beside another element (of the same

casting program). This was done by implementing an algorithm with the following rules, in priority:

• If two fillers have the same length and their width is 1200 mm in total, then they are placed

beside each other.

• If two fillers do not have the same length, but their total width is 1200 mm in total, the shorter

filler is marked as a split element. Then an irritative procedure takes place, to see if it is

possible to place one more filler from the same casting program, beside the longer one

(following the shorter filler).

• If two fillers are of the same length, but their width in total is smaller than 1200 mm, then the

fillers are placed beside each other. However, in that case, different rules apply. The cutting

length is equal to the length of the two fillers, and there is a concrete waste between them. The

time needed for longitudinal cutting is higher in that case.

• If two fillers X and Y have a width of 1200 mm in total, but there is the possibility to place the

e.g. Y beside another filler Z of the same casting program, even if the total width of the new

match YZ, is less than 1200 mm, but the saving in material is much higher (because of a

significant length difference between X and Y), then Y and Z are matched together.

• For each match of fillers, it is checked if any other combination of fillers on the bed can lead to

a more efficient production (e.g. less waste).

10 Casting program order is the position of the element on the casting bed.

21

• HC elements with diagonal cuts, were placed in a way so as to reduce waste (angles of both

full width elements and fillers are matched).

The above steps are parts of an irritative procedure between the elements of the same casting program,

where in the end they converge to the most efficient placement. Elements with status ‘DISCARDED’

are then excluded of the analysis, as many of them are not cast in their full length and another element

is pushed by the system. Including those elements while e.g. in reality only 1 meter can be cast in a

10-meter-long element, can insert high errors in the simulation. As only the efficiency regarding the

impact of fillers is of interest, excluding those elements is on the safe side and gives more accurate

results. However, aspects such as the general material waste of the factory cannot be calculated; any

results about material waste, concern only the waste due to production of fillers.

By comparing each simulated casting program to the corresponding casting program report, it is

estimated that only 1.24% of the simulated casting programs deviates from the actual situation.

3.8.2 Simulation of the studied scenario (7x1200 mm and an 800-mm-line)

In the previous chapters, the optimal width, if a full-width line is to be modified, was investigated.

The results, based on the most common widths that HC fillers are usually cut and the available

alternatives, showed that an 813-mm-line is the most promising option. However, certain aspects,

such as the material saving or the possible increase in thru put due to less cutting, were not possible to

be estimated.

In order to study the cost benefits of an 813-mm-line for the factory, and also the impact in the

production, the simulation of the system of 8x1200 mm lines was modified to a 7x1200 and 1x813

mm lines system. For the simulation, MATLAB was used with the data of the HC production of 2019

in Kungsör, so as to be able to compare with the current situation and draw conclusions.

The following modifications of the created simulation (8x1200 mm system), in combination with

certain assumptions, took place:

• One of the existing casting beds in Kungsör is modified from 1200 mm to 813 mm. As a

result, in the new situation, only seven lines can be used for casting 1200-mm wide elements.

• The modified casting bed is the 8th in position, the one in the end of the hall. In this line, 813

mm wide elements will be produced in combination with fillers of a width smaller than 813

mm. One understands that the most of longitudinal cutting in the new situation will take place

in the new line, hence it is chosen to modify the last -in position- bed in the hall, with the aim

to not influence the production in the other seven lines. Moreover, from this bed smaller

22

elements will be produced; the impact of transferring these elements is lower. Hence, choosing

to produce elements in the 8th line – the one which is the most remote in the factory11 – is

advantageous for the production.

• The total HC production for the year 2019 in Kungsör is imposed to the new system. However,

elements with a status ‘DISCARDED’ are not included. When an element fails to be cast

correctly, it is cast again some days after. Hence, including ‘DISCARDED’ elements will lead

to more load on the new system, as elements appear twice, which is not the case. However, it

should be mentioned that not including casting failures on the new system, gives an advantage

for the efficiency of the new system12.

• It is initially assumed in the simulation, that the number of working days in the new system, is

the same with that in the current situation. Moreover, it is assumed that the maximum number

of casting beds each day in the new situation cannot exceed the number of casting beds of each

day, in the current situation.

• It is assumed that the 8th line (the 813-mm-wide line) can be cast at a maximum of once per

working day. This is conservative, in fact, under certain circumstances, this line can be cast

twice per day.

• It is assumed that elements of a width in a range of 800-822 mm, would be designed at 813

mm if the new line is available. Hence, for those elements, no longitudinal cutting will take

place. The designer, in other words, will take advantage of the 813 mm option.13

The load (the total production of HC elements) is imposed to the new system on the following steps:

• Initially, the daily production according to the casting date of the current situation, cast at all

beds apart from that on the 8th line, is imposed to the 7x1200 mm lines of the new system.

However, only full-width elements and fillers wider than 822 mm are put in those lines. Fillers

narrower than 822 mm will be placed in the 8th line of the new system.

• Up to this point, the daily production that was cast on the 8th line of the current situation, is not

imposed in the new simulation, as there is no space for this. The physical capacity for 1200-

mm-wide elements has decreased by 1/8, as the 8th line will be used for narrower elements.

11 Units from each line, are transferred to the end of the hall, in a space between the 4th and the 5th line. Hence, the 1st and

the 8th line, are the most remote in the production hall. 12 The results will show a higher efficiency than the expected. 13 This is very conservative. In fact, most of the elements that now are cut at a width range of 772-872 mm, are believed to

be designed as 813 mm wide elements, if the designers had that option. Apart from this, if a new width line is available,

designers will utilize this new dimension in the possible combinations to avoid cutting elements. Hence, there will be an

increasing number of elements designed at 813 mm and a decrease of fillers at other widths. This assumption does not take

this into account.

23

• Due to the fact that fillers are moved from the full-width casting programs to the 813-mm-

wide line, a significant amount of space is available in the former one. This is utilized by

placing full-width elements of the 8th casting bed of the current situation to those lines14.

The above will result in a reorder of the elements on the lines. Until this point, the elements that have

been reordered on the 7x1200 mm wide lines of the new simulation, are only full-width elements and

fillers wider than 822 mm. Moreover, until this point, all the elements that have been imposed, have

the same casting date as in the current situation.

The simulation is based on placing the HC elements on the lines, according to the date that they have

been cast in the current situation. Since the capacity of 1200-mm-wide elements is decreased by 1/8,

and also, the casting of the 8th line requires that there will have been collected enough elements to cast

an 143-meters-long casting bed, one understands that many elements in the new situation will be

reordered in a way so that they will be cast in a different day than the one in the current situation.

It would be preferable to make this simulation according to the date that orders arrive in the company

or, better, the day that elements have to be delivered. However, those dates are not available, and as a

result, the casting date of the element in the current situation is used.

It would be against the external validity of the whole study to impose the load on the system without

taking a dating system into account. In other words, placing the whole HC production of the year 2019

without any limitation regarding the casting date of elements, would result in a more efficient

production than the actual.

The simulation continues by imposing the load of the rest of elements, that have not been imposed

until this point, in the new lines’ system. This occurs according to the following:

• As mentioned before, all elements with a width equal or smaller than 822 mm, are moved from

the casting program they belonged to, on the 8th line. This load is imposed to the 8th line, when

there are enough fillers of a specific HC type, so as to cast a 143-meters-long line. One

understands that there will be a waiting time for those elements to be cast. The simulation

takes into account a limitation on this waiting time. It is set that there will not be a time

difference of the elements being cast on the same day of the new 8th line in the new system,

higher than 15 working days (according to the casting date of elements on the current

situation). This is a reasonable assumption for the way that elements in the 8th line will be cast

when the 813-mm-line will be available. The production planner will have to wait before

14 If elements are moved from the casting program they belong to in the current situation, they are always moved to a new

casting program which is of the same HC type.

24

casting a bed, for enough elements of a specific HC type to be collected. It is considered that a

waiting time of 15 working days before the delivery date reflects the reality; however, as the

delivery date is not available, the current casting date is used.

• It is highlighted that the 8th line is assumed to be cast once per day. This means if e.g. there

have been collected enough elements to cast two beds, the 2nd one will be cast the next

working day.

• If there are not enough elements to complete a 143-meters-long line in 15 working days

waiting period, and the collected elements result to a casting length of e.g. 110 meters, the load

is imposed on the line.

• An irritative procedure takes place in order to fill all the space of the seven lines that has

derived by taking away all elements with width ≤ 822 mm. Firstly, elements of the 8th casting

program of the current situation are distributed among the seven lines system of the new

situation. Secondly, a reorder of the production takes place, to reduce the casting programs –

of the new system – to the highest possible.

• For the elements on the seven lines, it is set as a time limitation, that all elements are cast in a

maximum period of ten working days from the casting date of the current situation.

3.8.3 Estimation of the daily required time for longitudinal cut of fillers

The time needed to longitudinally cut HC elements was found according to the method described in

section 3.7. This is, in other words, the speed that the diamond blade can achieve for each HC type.

The total required time for length-cutting of each casting program, is calculated based on that speed.

According to the production employees, before each filler, the blade needs about 2 minutes for

positioning. Moreover, at the beginning of each casting program containing fillers, the saw requires

about 10 minutes as a starting time.

Generally, it is difficult to estimate accurately the daily required time, as it is depended on many

different factors (similarly to the speed for cutting). Even if the cutting speed for each HC type is

found, the total time for cutting a filler, can be considerably different between fillers of the same HC

type, depending on the point of cutting and the difficulties that can occur. Cutting of fillers according

to SE-HDF00-521 (the new cutting regulations, according to which, a filler is cut only in the middle

of cores), is generally easier and difficulties or delays are less common. The difficulty and

consequently the probability of delay in the cutting process increases when the cutting point deviates

from the middle of the core. When the deviation is significant, apart from the extra time needed due to

the higher cross-section, more problems can occur due to the fact that the blade tends to turn towards

the center of the core. Sometimes, a second pass of the blade is taking place, to achieve the desirable

25

result. This extra time is taken into account by increasing the calculated time by 40% (Eriksson

2014).15

The time needed for each casting program is obtained according to the following:

𝐶𝑢𝑡. 𝑡𝑖𝑚𝑒 = 2 𝑚𝑖𝑛 + 𝑐𝑢𝑡𝑡𝑖𝑛𝑔 𝑙𝑒𝑛𝑔𝑡ℎ × 𝑏𝑙𝑎𝑑𝑒 𝑠𝑝𝑒𝑒𝑑 [if cutting point < 70 mm from center]

𝐶𝑢𝑡. 𝑡𝑖𝑚𝑒 = 2 𝑚𝑖𝑛 + 1.4 × 𝑐𝑢𝑡𝑡𝑖𝑛𝑔 𝑙𝑒𝑛𝑔𝑡ℎ × 𝑏𝑙𝑎𝑑𝑒 𝑠𝑝𝑒𝑒𝑑 [if cutting point ≥ 70 mm from center]

𝑇𝑜𝑡𝑎𝑙 𝑐𝑢𝑡𝑡𝑖𝑛𝑔 𝑡𝑖𝑚𝑒 𝑜𝑓 𝑎 𝑐𝑎𝑠𝑡𝑖𝑛𝑔 𝑏𝑒𝑑 = 10 𝑚𝑖𝑛 + ∑(𝑐𝑢𝑡𝑡𝑖𝑛𝑔 𝑡𝑖𝑚𝑒 𝑜𝑓 𝑒𝑎𝑐ℎ 𝑓𝑖𝑙𝑙𝑒𝑟)

Consequently, the daily cutting time is equal to the total cutting time of all the casting beds that

contain fillers, that particular day.

3.8.4 Parameters concerning waste and cost calculations

This subchapter focuses on the procedure followed in order to calculate all the factors that contribute

to the final cost of the production. A cost estimation of the production took place for both simulations,

and the cost saving by modifying one full-width line derived from the difference of the former one.

The cost calculations concern only aspects due to the production of fillers. For example, the estimated

concrete waste, regards only the scrap elements that were not used when full-width elements were

longitudinally cut; it should not be confused with the total waste produced by the factory. In order to

find the total production waste, more information is needed which is not available (e.g. the actual

casting length of an element, whose production was stopped due to a problem16). From the other side,

since the aim is to discover if a smaller-width line is more profitable, taking into account the waste

and additional costs made only by the production of fillers leads to a more objective comparison.

Below (Figure 3-2), the procedure followed in order to estimate the cost, is presented. From each

simulation, the amount of scrap elements and their corresponding volume of concrete and steel for

both cases have been derived. It should be noted though that certain assumptions took place in the

new simulation (7x1200-mm,1x813-mm), aiming to approach to the highest possible, the situation

when an 813-mm-line will be available:

• For all fillers with width < 800 mm, it is assumed that 25% of them will be possible to be

placed beside other fillers to save material. For all fillers with width >822 mm (hence cast at

15 On the referring report, every calculation of cutting time that it is not made according to SE-HDF00-521, is increased by

40%. After contact with the production planners, since this thesis report calculates the speed of the blade by data of cuts at

various points (not only in the middle), it is chosen to increase by 40%, only the time for cuttings that take place at a point

more than ± 70 mm from the center of the core. 16 Elements noted as ‘disregarded’.

26

the 7x1200 mm lines), it was assumed that it will not be possible to place other fillers beside

them. However, it should be mentioned that this is a conservative assumption.

• Since the simulation is based on data of 2019, it is assumed that all fillers that were cut at a

width in the range of 800-82217, would be produced as 813-mm-wide elements. Hence, for

those fillers, it is considered that there will not be any longitudinal cutting or waste.

The final cost is calculated by using the values presented in Figure 3-2. It should be mentioned that a

casting team consists of four persons, while the removal of each filler from the casting bed is

estimated at 10 minutes.

Figure 3-2. The followed procedure for the estimation of cost.

17 A very conservative assumption. It is believed that more fillers would be designed as 813-mm-elements. But it is of

preference to make a conservative study of the possible cost saving, and hence eliminate the possibility to overestimate the

advantages of a smaller-width line. During the last part of this thesis, the case where more elements are designed according

to the 813-mm-line, is also presented.

27

3.8.5 Evaluating thru put

The possible increase in thru put is one of the main factors for determining if the modification of a

1200-mm-line to an 800-mm-line is profitable. By an increase of thru put, it is implied that for the

same production time, more beds will be cast. Hence, thru put contributes to the possible cost-saving

of a smaller-width line.

However, estimating accurately thru put is difficult. Even if the time saved with the introduction of the

smaller-width line can be estimated, thru put is depended on many other factors that are difficult to

strictly determine. Some of those factors are mentioned below:

• During a production cycle, problems can occur that will lead to delays, which are impossible

to predict or simulate. Those delays decrease thru put.

• Production planners can always do a reorder of the production, to maximize thru put. This

reorder can also be made for cases when a problem has been occurred. One understands that it

is impossible to simulate that factor.

• The maximum number of casting beds that can be achieved daily, is strongly dependent on the

order of casting programs, the work that elements require (e.g. cutting of details) and the

possibility to take advantage of the night hours for curing. Those aspects are difficult to

include in the estimation of thru put; they are either unknown (e.g. required work) or including

them is not on the conservative side.

• Curing time is one of the basic parts of a production cycle. Even if elements’ thicknesses are

known, more factors that influence this, cannot be predicted (e.g. variation in temperature).

From the above, one understands that thru put cannot be strictly estimated, like the other factors which

contribute to the possible cost saving. Below, the two approaches that were made, are described.

However, it should be mentioned that in terms of the methodology of science, the robustness of the

simulation regarding thru put is low; a small change in the assumptions implies a considerable change

in the results. For this reason, it is chosen to refer to thru put separately from the possible cost-saving

resulting from the other factors, whose accuracy is significantly higher.

Description of the two methods followed to estimate thru put:

• Initially, the total amount of time saved is calculated. By considering that curing can be made

during night hours, and that a production cycle without curing lasts 5 hours, thru put is

calculated by dividing the time saved by 5 hours. This is a very rough approach, followed

mainly in production. The confounding factors resulting to an overestimation are that it is not

always possible to take advantage of the night hours. Moreover, by this method, if e.g. a small

28

amount of time is saved in a particular day, this amount of time is counted, while in fact no

increase of thru put is made. A confounding factor resulting to an underestimation, is that

production planners can order the production in such a way that they could cast more beds.

This method does not count this aspect.

• In an effort to calculate thru put more accurately, simulation searches for days where the saved

time is higher than 2.5 hours (placement of wires and casting). For such days, it is assumed

that curing can take place overnight and it is checked if the following day, there is enough time

to continue with the cutting process and remove the elements from the casting bed. If the

above conditions are fulfilled, thru put is increased by 1 bed. However, if the day, due to the

reorder of the production, has a negative time difference, thru put is decreased by 1 bed. This

method is more conservative and it is considered more reliable. Still some confounding factors

exist, such as the way that the production has been reordered.

3.8.6 Evaluating production’s pressure when a full-width line is modified

If a 1200-mm-line is modified to an 813-mm-line, the physical production capacity of 1200-mm

elements is reduced by 1/8 (there are eight casting beds, 1200 mm wide, in the current situation).

From the one hand, the longitudinal cutting on the 7x1200 mm lines of the studied scenario is

decreased significantly, hence faster production cycles will be achieved. From the other hand, there

are days that the production of 1200-mm elements is high; the fact that there will be seven available

lines for casting those elements (instead of eight), could be a problem for the production (regarding

the additional pressure on those lines).

Thus, the additional pressure on the seven lines producing 1200-mm-elements is examined, to

conclude if the factory will actually be able to handle such a situation. For that purpose, an indicator (a

factor) is defined for each working day, as the daily number of casting programs divided by the

number of casting beds.

𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑖𝑛𝑑𝑖𝑐𝑎𝑡𝑜𝑟 =𝑑𝑎𝑖𝑙𝑦 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 1200 𝑚𝑚 𝑐𝑎𝑠𝑡𝑖𝑛𝑔 𝑝𝑟𝑜𝑔𝑟𝑎𝑚𝑠

𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝑐𝑎𝑠𝑡𝑖𝑛𝑔 𝑙𝑖𝑛𝑒𝑠

This is considered a reliable method to evaluate the pressure on the system, however, due to the fact

that pressure is influenced by the day that it is decided to cast a program, the results should also be

seen as a total. Moreover, the whole simulation analysis is based on the casting date of elements in the

current situation which is considered a big advantage for the reliability of this evaluation.

29

3.9 Estimation of cost saving, considering designers’ adaption to the 813-

mm-line

The method that was used to estimate the possible cost saving due to the introduction of the 813-mm-

line leads to conservative results. This happens because the simulation was based on the production

data of 2019, where designers did not have the option of the 813-mm line and consequently, they

designed based only on 1200 mm wide elements. Regarding the simulation, only the elements that

during 2019 were cut at a range of 800-822 mm, were assumed to fit exactly in an 813-mm line and

hence do not need longitudinal cutting. One understands that this is very conservative; fillers cut at

e.g. 780 mm during 2019, most probably would be designed as 813-mm wide full width elements if

this were possible. Moreover, if two width choices are available (1200 mm, 813 mm), it will be easier

for the designers to make more combinations when they decide how to place the HCs, and hence

avoid to some extent, the longitudinal cutting of further elements (cast-in-situ concrete joints can also

be utilised for this purpose).

Hence, more simulations took place, where the input data of 2019 were slightly modified, depending

to the percentage of fillers that will be designed as 1200-mm or 813-mm wide elements. This was

made by creating a vector of the total number of fillers produced in 201918 on MATLAB. Then a

random choice was made, modifying some of the fillers with width < 800 mm or > 822 mm to full

width elements, depending on the degree of adaption considered at each simulation. The percentage of

the adaption to the new situation, was implemented by setting a corresponding step in an irritative

loop of that vector, for each simulation.

18 Without the fillers of a width at 800-822 mm, which are already counted as 813-mm-wide elements.

30

4. Results

4.1 Data analysis of produced HC units

By analysing the data history of the HC production, important outcomes are made. For example, by

company’s history one can estimate the number of units that are longitudinally cut (fillers), and by

further investigation, one can discover the most common widths that HC units are cut and if there is

any trend in those widths. This is made by plotting the frequency of fillers being cut at each width

(width frequencies).

Firstly, an analysis of the HC production for the years 2010-2019 is made, and the results are

illustrated below. In total, 532614 HC units were tested, from which, 65740 were longitudinally cut

(fillers). Thus, fillers are 12.34% of the total HC production of 2010-2019. With the use of MATLAB,

graphs were made, to see at which width the fillers are usually cut (width frequencies). The results are

depicted below.

Figure 4-1. Number of HC units that are longitudinally cut (fillers) and their corresponding widths.

(production 2010-2019, all factories)

The figure above depicts the most common widths that the HC units are cut. For example, the highest

peak means that 2202 units were cut at 816 mm.

As it is seen, there are general trends on the widths of fillers. The results show that most of the HC

units are cut at specific widths: the majority of them seems to be cut around 800 mm wide, followed

by a trend of units cut at almost 600 mm wide.

31

It is interesting to notice the differences over the years. During the years 2010-2017, the width of the

fillers varies more, comparing to the later years (2018-2019). For example, Figure 4-2 shows that

there are a lot of units cut at 790 mm and 800 mm, while Figure 4-3 shows that the HC units are

usually cut at specific widths (e.g. 816 mm).





32

The reduction in the width variation during 2018 – 2019, is explained due to the new regulation about

cutting of HC units, that is followed by engineers mainly after 2017, which defines the exact width

that a HC unit should be longitudinally cut (Figure 2-2). Cutting at those specific widths leads to the

smallest cross-section area and consequently to less work for the diamond saw.

As it is seen from the graph below, during the last years more and more engineers follow the new

rules of cutting at a specific width, instead of cutting in a zone (old rules). In 2019, almost 50% of HC

units were cut according to the new rules.

Figure 4-4. Percentage of fillers cut according to the new rules per year.


49.99

23.1

10.79.48.3

50.01

76.9

89.390.691.7

0

10

20

30

40

50

60

70

80

90

100

2015 2016 2017 2018 2019

PER

CEN

TAG

E (%

) O

F FI

LLER

S

YEAR

% Length-cut at a specific point (new rules) %Length-cut in a cutting zone (old rules)

33

4.2 Data analysis of fillers by type of element

Even though there are differences over the years, the most common widths of fillers (the general

trends) do not differ. Because the recommended cutting widths (new cutting rules) vary depending on

the type of HC unit, it is important to analyse the fillers by their type. Moreover, the width that a HC

unit is cut is strongly dependent on the position of the strands. As the position of the strands varies

between the HC types, an analysis of the HC fillers by their type is necessary for making conclusions.

Firstly, it is important to notice that specific types of HC units are used much more than others. Figure

4-5 shows that almost half of the fillers are of a specific type (type HD/F 120/27, 265 mm thick). The

width frequency of fillers for each type is illustrated below, for the years 2015 – 2019 (Figure 4-6).

Moreover, for each type, the cutting length in meters is calculated (Figure 4-7).

Figure 4-5. Fillers by their type. Almost half of the total fillers are of type HD/F120/27 (thickness 265 mm).

(production 2015-2019, all factories).

HD/F 120/2019.2%

HD/F 120/225.1%

HD/F 120/2747.6%

HD/F 120/3217.8%

HD/F 120/386.7%

HD/F 120/403.4% Other

0.2%

Type of fillers (2015-2019)

HD/F 120/20

HD/F 120/22

HD/F 120/27

HD/F 120/32

HD/F 120/38

HD/F 120/40

Other

34

Figure 4-6. Width frequency, per type of HC unit.


35

Figure 4-7. Cutting length per width, for each type of HC element.


36

From the figures above, one can notice peaks that differ very slightly. For example, for the elements

of thickness 265 mm, there is a peak at 816 mm and there is also a peak at 820 mm. This is due to the

fact that the recommendations of the suggested cutting widths are not always followed by engineers.

Differences of such a range are considered to represent the same need.

As it is seen from the graphs above, the point that a HC filler is cut, is strongly dependent on the type

of HC unit. This happens mainly due to the fact that the cutting regulations change for each type.

More specifically, the point where an engineer decides to cut an element, is strongly dependent on the

core pattern and the position of the strands (from which, the cutting regulations have derived).

Usually the width frequency of HC units implies the cutting length. However, they are not perfectly

correlated. It can be said that as the thickness of the element increases, there is a trend to

(longitudinally) cut shorter elements. One possible explanation for this, is that designers try to avoid

cutting long HC units of a high thickness, as it has a high impact for the factory. Hence, for the same

number of fillers, the length cutting that corresponds to a longitudinal cut of a thin element is slightly

higher than that of a thick element.

It is important to notice how much higher length cutting takes place in specific HC types. The 265-

mm-thick elements produce more than the double of length cutting produced by the following two

most common types, together (types 200-mm-thick and 320-mm-thick, Figure 4-5). Moreover, the HC

elements of type HD/F 120/27, HD/F 120/20 and HD/F 120/32 produce the 84.6% of the total fillers

(production 2015-2019).

More comments can be added, such as that the width variation is lower on fillers that have a big

thickness (320 mm, 380 mm and 400 mm). This happens because designers try to avoid cutting heavy

HC elements in points different than those indicated by the new instructions (centres of cores), as this

would be very time-consuming for the production.

4.3 Grouping of width frequencies by cutting zones

As mentioned above, there are slight differences in the width frequencies, that in fact represent the

same need. In order to be able to draw conclusions about the most common cutting widths, the data

are grouped.

After grouping the width frequencies of the fillers by zones, the results show that most of the length-

cut takes place at the 2nd core of the HC elements with thickness 265 mm. More specifically, 15.42%

of the total fillers or 14.9% of the total cutting length takes place at this point. Other very common

cutting points are the 3rd core of the same type of slab (11.09% of fillers), the 1st core of the same type

37

of slab (8.95% of fillers) and the 2nd core of the HC slab of thickness 320 mm (8.54% of fillers). The

results are presented in more detail below.

Figure 4-8. Percentage of fillers per cutting point (core), per type of HC element.

(data from production 2015-2019)

Figure 4-9. Length cutting of fillers per cutting point (core), per type of HC element.


0

2

4

6

8

10

12

14

16

18

Freq

uen

cy (

% o

f to

tal f

iller

s)

Cutting frequency

Cut on 1st core

Cut on 2nd core

Cut on 3rd core

66

82

.3

11

94

.0

22

41

7.5

17

72

4.7

73

28

.2

20

11

.0

98

61

.78

27

25

.96

37

81

7.4

4

24

35

9.7

1

11

37

6.2

9

39

26

.23

10

55

0.3

7

39

23

.18

27

16

9.3

1

52

88

.69

26

83

.95

46

69

.20

0

5000

10000

15000

20000

25000

30000

35000

40000

Len

gth

in m

Length cutting

Cut on 1st core

Cut on 2nd core

Cut on 3rd core

38

Figure 4-10. Percentage of total length-cut per point of cutting (core), per type of HC element.


Figure 4-11. The most common cutting zones and the percentage of fillers cut at this zone.

(Type HD/F 120/27 on the left side, HD/F 120/32 on the right side)

2.63

0.47

8.81

6.97

2.88

0.79

3.9

1.1

14.9

9.6

4.5

1.5

4.15

1.54

10.68

2.08

1.06

1.84

0

2

4

6

8

10

12

14

16

% o

f to

tal l

engt

h c

utt

ing

Percentage of total length cutting

Cut on 1st core

Cut on 2nd core

Cut on 3rd core

39

4.4 Relation between fillers’ width and actual need

As it has already been mentioned above, company’s data about the width of fillers, do not represent

the actual need. Those numbers show where a HC unit is finally cut and do not represent the actual

width that is needed in a certain project. The choice of where to cut a HC unit, is strongly dependent

on the position of the strands and also the area of the cross-section at that point. This is explained

better with the example shown in Figure 4-12, on the most used HC element type (HD/F 120/27,

thickness 265 mm). When there is a need for a HC unit 920 mm wide, engineers are not able to cut at

that point, because the strands are located there. Cutting at that point, would affect the strands and the

web, leading to lower load-carrying capacity. Also, the cross-section area at that point is the biggest

possible. Instead, engineers choose to cut exactly on the middle of the previous core and fill the

remaining space with in-situ concrete. In the same way, at a need of an 880 mm unit, engineers decide

to cut in the middle of the previous core in order to reduce the cutting cross-section area, leading to

less work for the diamond saw.

Figure 4-12. Example of the actual need and the point where the unit is finally cut.

(Cross section HD/F 120/27)

As a result, the most common cutting zone (15.42% of fillers at the 2nd core of the HD/F 120/27)

means that the actual need of elements is always higher than 772 mm (the lower limit of the zone) and

smaller than the position of the middle of the next core (otherwise the HC unit would be cut in the

next core).

The zone of the 2nd core of this element ranges from 772 mm to 872 mm. However, even elements at

the lower limit of the zone (e.g. 780 mm) correspond to an actual need bigger than 800 mm, if one

considers that according to the rules, a joint of at least 40 mm is usually required beside a filler.

(Strängbetong 2018)

40

The width of cast-in-situ longitudinal concrete joints varies, depending on the thickness of the HC

element. The maximum cast-in-situ concrete joint without placement of reinforcement19, for every

cross-section, is defined in the regulations (Appendix A3). For the element of type HD/F 120/27, the

maximum width of the concrete joint can reach 177 mm. Hence, for the cut with the highest width

frequency (816 mm), the actual need on a project can reach 993 mm.

Figure 4-13. The actual needs are not the same with the point of cutting. Cutting at the 2nd core means that the actual need

is bigger, potentially until the middle of the core at the left. (Cross-section HD/F 120/27, to the left results based on

production of 2015-2019, to the right based on production 2018-2019.)

Moreover, from Figure 4-13, one can conclude that even if the regulations changed at 2017 (instead of

cutting in an allowed zone, an engineer has to cut exactly in the middle), the percentages are almost

the same, while cutting at the 2nd core of this type of element is becoming even more popular year by

year (Figure 4-14).

Figure 4-14. The increasing trend of cutting at the 2nd core of HD/F 120/27.

19 Designers usually avoid the option of cast-in-situ concrete joints with reinforcement.

10.02

16.3

14.32

17.65 17.88

2015 2016 2017 2018 2019Per

cen

tage

(%

) to

to

tal f

iller

s

Year

CUT AT THE 2ND CORE OF ELEMENTS HD/F 120/27

41

4.5 Possible widths of a new line based only on fillers’ characteristics

Given the results shown above, one can suggest certain widths of a new line, that seem to be more

beneficial than others. Of course, these conclusions derive by considering only the geometrical

characteristics of the fillers. Conclusions at this point, include only aspects such as the width

frequency of fillers, corresponding cutting length and the relationship between fillers’ dimensions and

actual need. The choice of the width of a new line is based mainly on the type of element that is

generally used more often and consequently produces the most fillers.

Considering the above, one can come to the following outcomes:

• An 800-mm-line seems the most ideal, since the majority of fillers are cut approximately 800

mm wide, so a line of this width will cover the needs represented by fillers cut at this width.

Consequently, it will lead to a significant reduction of the material waste and longitudinal

cutting. However, the possible reduction in the material waste or the length cutting, cannot be

accurately estimated, without a simulation of the production.

• A 600-mm-line can be a good alternative, for the same reasons as for the 800-mm-line.

However, significantly more elements are cut at a width of 800 mm than 600 mm, hence the

800-mm-line is preferable.

• Since the majority of fillers are cut 800 mm wide (e.g. the highest peak at 816 mm), and

considering the relationship between the width of a filler and the actual need, it can be said that

the biggest actual need is for elements strictly bigger than 800 mm (or even 820 mm).

However, in the case of constructing a 900-mm-line, this line would not cover many needs that

are represented as a cut at 816 mm. For example, for a need of 880 mm, which at the current

case is presented as a filler with a width 816 mm, the option of a 900-mm-line would lead to

further longitudinal cutting of HC elements.

42

Figure 4-15. An example of a filler cut at 818 mm while the actual need is smaller than 900 mm (841 mm).

Figure 4-16. An example of a filler cut at 816 mm while the actual need is higher than 900 mm (920 mm).

43

4.6 The choice of the new line’s width

In this section, the final decision of the width that the new line should have, is presented. It is

important to notice that the decision is made for the factory in Kungsör (the one with the higher HC

production). There is no space for an extra casting bed in the factory hall (for a 9th bed – there are

eight casting beds in the current situation). What it is examined is the change of one of the existing

1200-mm-lines, to a line that will produce HC units with a smaller standard width.

Firstly, the possible alterations of a 1200-mm-line are presented (Elematic, Split slabs 2019).

According to Elematic20, two basic principles are followed regarding splitting, when a 1200-mm-line

is converted to production of smaller width elements. Depending on the slab type, the two choices are:

• Replacing one core with the center side form.

• Placing the center side form between cores. In that case, the cores next to the center side form

need to be made more narrow.

20 Elematic is the provider company for the HC production machinery, equipment and installation.

Figure 4-17. Center side form between cores.

(Example of a 200 mm thick HC unit, with 6 cores) (provided by Elematic)

Figure 4-18. Center side form replaces one core.

(Example of a 200 mm thick HC unit, with 7 cores) (provided by Elematic)

44

The basic principles regarding the chamfer, are that the chamfer can be made in the center side of the

slab by:

• Center side form (without a center rail): This option will not give a perfect chamfer, while

there will be some burrs on the one side. This occurs because cement paste is going under the

center side form.

• Center rail: This option is promising a perfect and clean chamfer (a finishing of the HC unit

similar to the chamfer that the 1200-mm-wide elements have). However, this option requires a

rail to be welded on the bed.

Figure 4-19. Chamfer without a center rail.

Figure 4-20. Chamfer when a center rail is welded on the bed.

Due to the fact that there are projects where HC slabs are visible after the construction, the option of a

center rail welded on the casting bed, is chosen. This option leads to elements with a better aesthetic

result and is of preference. The option of a center side form, without a center rail, would limit the

designers when they use the new width elements on projects where the elements are not hidden.

Below, the possible alterations, per type of HC element are mentioned, as they are given by Elematic.

All sizes mentioned have a tolerance of +0/-5 mm for width. There are different options, depending on

the type of HC unit. For example, in order to create 800 mm wide HC units of a 200 mm cross section

of six cores, this can be done by dividing the bed in two fillers, one of 800 mm wide and one 400 mm

wide. In that scenario, both sides on the bed are utilised. However, for a HC unit 265 mm thick with 5

cores, only the one side is cast, resulting to only a unit 800 mm wide. The option of 800 mm wide

units in the e.g. HC type 320 mm thick with four cores is not available. This happens because the

splitting of units is made either on the middle of the cores or between two cores. The core pattern of

this type is such that it is not possible to split the unit there. The only available widths for this HC

type, are one unit 900 mm wide or two units 600 mm wide. It should be noticed that the sizes

45

mentioned in the table are approximations and for more accurate values, one should contact the

company about the width of interest.

Table 4-1. Available alterations of a 1200-mm-line. (Units in millimetres, N/A=Not available, x = Not relevant) (Elematic,

Available split and narrow sizes for the extruder P7/E9 2019)

The decision of the width of the new line is based on the outcomes from the previous chapters in

combination with the available widths per HC type from the table above. As has been already

mentioned, the HC type HD/F 120/27 (5/265 according to the table notations) produces 47.6 % of the

total amount of HC fillers. Hence, it is important that the chosen width will cover this HC type. The

table shows that this type is compatible with split elements 1000 mm wide, 800 mm wide (the highest

trend) and 2x600 mm wide units (the 2nd highest trend). This type of HC unit is not compatible with

elements 900 mm wide; hence the 900-mm-line is rejected.

The fillers that are cut at around 800 mm wide, are significantly more that those cut at around 600 mm

wide. Creating a 600-mm-line, would result in a significant reduction of the fillers that need to be cut

and subsequently, to a big reduction of material waste. However, as the 1st trend is for fillers cut at

around 800 mm, the 600-mm-line would not cover those demands. Hence, a big amount of HC units

would still require longitudinal cutting from the 1200 mm wide elements, leading to a lot of material

waste and slowdown of the production.

From the other side, by creating an 800-mm-line, the 1st trend of HC fillers would be covered. An

800-mm-line would lead to the highest possible direct reduction of units that need longitudinal

cutting. Moreover, when an 800-mm-line is available, units with a width smaller than 800 mm (e.g.

590 mm – the 2nd higher trend) can be cast and cut at this line, and not on the 1200-mm-lines. This is

not the case, when a 600-mm-line is available, because the 800 mm units would need to be cast and

46

cut on a 1200-mm-line. Thus, apart from the material saved by making a casting bed with a width

similar to that of the 1st trend, a significant amount of material can be saved by placing narrower

fillers (e.g. 590 mm) on the 800-mm-line. This gives a big advantage in favour of the 800-mm-line.

The impact of the 800-mm-line is explained further in the chapter where the production is simulated.

However, it can be added at this point, as an advantage of the 800-mm-line, that 800 mm wide

elements, which is the 1st trend, cannot be covered in any other scenario and if a 600-mm-line is to be

made, casting the 800 mm wide fillers from the 1200-mm-lines is inevitable. In contrast, elements of

the 2nd trend can be covered by the 800-mm-line, while placing two elements 600 mm wide beside

each other, on a 1200-mm-line and then cut those elements, to reduce concrete waste, is always an

available option.

One can support the 600-mm-line of the fact that if the 600-mm-line is chosen, both sides of the bed

will be utilized. In other words, the maximum physical capacity of the bed (1200 mm wide at the

current situation) is fully utilized from the production point of view. However, this is not considered

an advantage for the production, due to the fact that when a 600-mm-line is created, all the fillers

wider than 600 mm, will have to be cast and cut in the seven lines of 1200 mm. The 1st trend is for

fillers wider than 600 mm and in combination with the fact that the physical production capacity of

1200 mm wide elements is reduced by 1/8, the load of the 7x1200 mm lines will be increased

significantly. A lot of longitudinal cutting would still occur in those seven lines, while additionally

they would have to handle the load of 1200 mm wide elements that will not be produced in the 8th

line. Hence, even if both sides of a 600-mm-line are utilised, a line of this width is not the most

beneficial from the production point of view21.

The main disadvantage of an 800-mm-line, is that even if the most common HC element is compatible

with this width (5/265 according to the table notations), this line is not compatible with all the HC

types that Strängbetong produces today. In contrast, the choice of 2x600 mm line, is compatible with

all the HC types. This can be overcome by changing the core pattern for some types that the 800-mm-

line is not compatible at the moment. This implies a change in the structural properties22 of some

elements, but this will only occur for fillers; the full width elements will remain the same.

The table below shows the HC types that are used by Strängbetong today. As it can be seen, only two

HC types are not compatible with the 800-mm-line. These are the types HD/F 120/32 and the type

21 Further discussion about the impact of a new width line is made on the chapter about simulation of the production. 22 An increasing number of cores in a HC type will result to less self-weight and different structural behaviour.

47

HD/F 120/38,23 of 4 cores each. In order to make the 800-mm-line available for all depths of fillers,

the design patterns for these cross-sections change to 5/320 and 5/380 correspondingly (5 cores each).

Table 4-2. Compatible HC types for an 800-mm- line and necessary modifications.

HC types used today

(Strängbetong notation)

HC types used today

(Elematic notation)

Compatible with the

800-mm-wide line

Recommended cross-

sections, compatible

with the 800-mm-line

HD/F 120/20 6/200 Yes 6/200

HD/F 120/22 6/220 Yes 6/220

HD/F 120/27 5/265 Yes 5/265

HD/F 120/32 4/320 No 5/320

5/350

HD/F 120/38 4/380 No 5/380

HD/F 120/40 5/400 Yes 5/400

In addition, for giving designers more freedom, one more HC type is recommended to be added in the

available HC types. Quite often, the HD/F 120/32 is not structurally adequate, resulting to use the

HD/F 120/38, which is 60 mm thicker. Hence, the HC type 5/350 is recommended, as a solution in

between, which is a 350 mm thick slab of 5 cores.

More reasoning can be done in favour of the 800-mm-line over the 600-mm-line. When designers

decide the placement of HC units, they try to avoid cutting full-width units (1200 mm). There are

many factors that influence this, such as the architectural design, but generally designers try to place

HC elements in such a way that they will cut the least possible. In that cases, the cast-in-situ joints are

utilised (without reinforcement) to give designers more options. When a 600-mm-line is available,

designers can take advantage of 600 mm wide elements, to make combinations of HC units that will

cover the span and will not need to longitudinally cut full-width elements. But, a 600 mm wide unit

limits those combinations, as 2x600 mm units have the same width as a full width element at the

moment. In contrast, in the case that designers are able to use 800 mm elements, those elements can

give more combinations. Firstly, those combinations can be made by using 1x800 mm unit in

combination with the 1200 mm wide units and cast-in-situ concrete joints (this holds also in the case

of 600 mm elements). The advantage of the 800 mm wide units is that they can give one more

23 It should be noticed that this type of HC element is not used very often.

48

combination by placing 2x800 mm units beside each other, which is not the case for the 600 mm

units.

Figure 4-21. The 800 mm wide units offer more combinations to the designers, when the placement of HC elements is

decided. The example does not include cast-in-situ concrete joints, but of course they are used, to avoid cutting full width

elements.

From this aspect, the 900-mm-line is the most advantageous, as it can provide even more

combinations than the 800-mm-line. For example, placing 3x900 mm wide units beside each other,

gives a width of 2700 mm, while 3x800 mm wide units beside each other are equal to 2x1200 mm

wide units. Moreover, 900 mm wide elements can capture odd spans, which is not the case for the

800-mm-line or the 600-mm-line. However, because the 900-mm-line is not available for the HC type

that produces the most of fillers and because the 1st trend of fillers’ width includes needs below 900

mm, this option is not chosen.

For all the reasons mentioned above, the 800-mm-line is chosen, where only the one side of the

casting bed will be cast. A center rail has to be welded to the casting bed, while it is necessary to

change some HC types, according to Table 4-2. Examples of detailed drawings of the new cross-

sections are presented in Appendix B1. After contacting Elematic, the final width of those elements is

813 mm.

49

4.7 Required time for longitudinal cutting of HC units

Diamond blade’s data from the year 2016 from the factory in Kungsör are used to estimate the time

needed for longitudinal cutting of HC elements. This time includes only the time that is needed for

cutting; the time needed to start the diamond blade or positioning of the blade before each element, is

not counted yet. The table below depicts the estimated time in minutes/meter for each of the used HC

depths.

Table 4-3. Required time for length cutting.

Thickness of HC unit (mm) Time needed for length cutting (minutes/meter)

200 0.83

220 0.85

265 0.92

320 1.46

380 1.68

400 1.81

4.8 Simulation of the production

During the HC production, elements are placed in such a way to make the production more efficient.

The efficiency of the production includes the reduction of the material waste, time and workhands

needed for longitudinal cutting of fillers, the increase in the capacity of casting beds and thru put, as

also the reduction of additional costs due to the production of scrap elements.

In order for those aspects to be studied with high accuracy, the production is simulated; HC elements

are positioned on the casting beds, as the production planners place them, for achieving the highest

possible efficiency.

So, the HC production of the year 2019 in Kungsör is simulated with the software MATLAB.

Initially, the current situation is simulated (eight casting beds 1200-mm-wide) in order to evaluate the

efficiency of the production at the moment. Then, the simulation is modified to a system of seven

casting beds 1200-mm-wide and one casting bed 813-mm-wide24, so as to evaluate the efficiency in

the case of a smaller width line and its impact on the production.

24 Referred as 800-mm-line below, for simplicity.

50

4.8.1 Efficiency of the production in the current situation

A simulation of the current situation (eight lines, 1200-mm wide), for the HC units of 2019 in

Kungsör, was made. A code was created to place the units in the position they were cast on the bed

and consequently calculate the efficiency with higher accuracy. The accuracy of the simulation of the

current situation is estimated at 98.76%.25 The main results are presented below:

• In total, 33795 HC elements were produced. This number is only for units that were

successfully cast; it does not contain units noted as ‘disregarded’.

• The annual casting length is estimated at 256.1 km.

• From this production, 4428 are fillers.

• The total longitudinal cutting of fillers is 25.1 km.26

• The annual estimated waste27, in terms of casting bed’s surface, is 7977 m2.

• The concrete waste28 due to longitudinal cutting of HC elements is 1133.2 m3.

• The steel waste due to longitudinal cutting is 47.9 tones.

• The total scrap material for transport and crash is 2881 tones.

• The annual required time for longitudinal cutting is estimated at 820 hours.

• Only due to length-cutting, at least 2776 scrap elements of varying width were produced.

• For the year 2019, 1943 beds were cast, from which, 595 did not contain any filler.

• For the studied year, at least eight beds/day were casted in 176 of the total working days, while

there were 57 working days with seven beds/day or less.

• The factory in Kungsör worked in total 233 days29 in year 2019 (for HC production).

• In the best scenario, 11 beds per day are cast.

Figure 4-22 shows the daily casting length, and the corresponding longitudinal cutting. The daily

casting length is calculated only by the elements that were successfully cast; elements that for any

reason are noted as ‘disregarded’ are not included in the daily casting length. This means that the sum

of casting beds for each day is slightly higher than that shown below, depending on the number of

elements that are failed to be cast properly.

25 By checking the casting program report of 100 castings, only one is expected to deviate from the simulation. 26 Fillers placed beside others to reduce waste and longitudinal cutting, are taken into account. 27 Considering only the surface of scrap elements due to longitudinal cutting. 28 Concrete waste that derives only from longitudinal cutting. The total concrete waste in the factory is higher, if one

considers other aspects that contribute to the waste e.g. failures during casting of elements. 29 Generally, the number of days that at least one of the 3 factories for HC production (Kun – Lån – Ved) worked, is 251,

for the year 2019. In the results, all working days are counted according to this dating system (referred as ‘general dating

system’ – working days from all factories). Hence, any reference of working day is according to the general dating system

(of 251 working days) and for some of the days of this dating system, the factory in Kungsör did not work. The total

number of days that there was HC production in Kungsör, is 233. For example, working day no. 233 for the factory in

Kungsör, is the working day no. 251 according to the general dating system, which is the 20 of December 2019.

51

Figure 4-22. Daily casting length and longitudinal cutting, in meters, Kungsör, 2019 (8x1200-mm-lines).

As it is seen from the figure above, the daily casting length varies significantly. The highest peak

(work. day 230, 25th of November 2019) shows that the total casting length is 1510.8 meters and the

corresponding cutting length of fillers is 111.4 meters. However, it is not common to reach that high

values of casting length in a day. The graph shows that during days near the capacity, HC production

reaches 1350-1400 meters of daily casting, which is strongly dependent on the amount of longitudinal

cutting in that day.

Figure 4-23 shows the number of casting beds per day and as it is seen, the highest number succeeded

during 2019, was eleven beds/day. In the same way to the daily casting length, the number of beds is

highly dependent on the percentage of fillers in the daily production. Moreover, other factors such as

the HC types of casting beds, influence the number of beds that can be cast daily (e.g. if a daily

production contains many casting beds of the HC type HD/F 120/40, which is 400 mm thick, more

time for curing of concrete is needed, delaying the thru put).

52

Figure 4-23. Number of casting beds per day, Kungsör, 2019.

It is important to notice that the number of casting bed per day varies significantly throughout the

year. Even in periods of very high demand (high production), there are days that the number of casting

beds is low. For example, the graph above shows that around the working day 150 (14th of August

2019), even if it seems that the demand is high (10-11 casting beds/daily), there are days with low

number of casting beds (e.g. 9th of August, with six casting beds). From this, one can support that the

factory is not working in its full capacity and it can cope with a higher pressure on the production (e.g.

a slight increase in the beds cast annually). Especially in a case that elements’ orders are received in a

longer-term period, and thus the production planners can take advantage of the days with low

production to cast the additional load then, one understands that the factory can cope smoothly with a

higher production.

As mentioned above, during the studied year, in 57 of the total working days, which is the 24.5%, the

daily number of casting beds is equal to seven beds/day or less. In the case that one of the lines is

modified from a 1200-mm-line to an 800-mm-line, the physical capacity for production of full-width

elements is reduced by 1/8; only seven casting beds can be used for 1200-mm-wide elements. Since

almost a quarter of the working days had a production ≤ 7 beds/day, one understands that a big portion

of the production will not be influenced – in terms of capacity – if one casting bed is not producing

53

1200-mm-wide elements. However, this is a very general approach, since the fillers on those seven

lines will be produced in the 8th line in the new situation, and as a result, there will be more space in

those lines and an increase in thru put (faster production due to less longitudinal cutting).

Moreover, the results show that fillers are 13.1% of the total HC production of 2019 in Kungsör. In

the case of an 800-mm-line instead of a 1200-mm-line, the physical capacity for full width elements

will be decreased by 1/8. Since:

1

8= 0.125 = 12.5% 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑜𝑡𝑎𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦

and moreover, in the 13.1% of fillers, some of them will still be cast in the 7x1200-mm-lines, as they

have a width ≥ 813 mm, one understands that the percentage of fillers that will be cast in the 8th line,

is similar to the capacity of one line; hence it seems that modifying the width of one line, will not have

a big influence in the system’s capacity, there will just be a reorder of the production.30

4.8.2 Simulation of the studied case (system of 7x1200-mm, 1x800-mm)

In order to understand the advantages, estimate the efficiency and the possible cost saving when a

smaller width line is used, a new simulation takes place. The simulation is based on the one created

for studying the efficiency in the current situation, where one line is modified from 1200 mm to 813

mm. Hence, for the studied scenario (7x1200, 1x813-mm-wide lines), the HC production of the year

2019 in Kungsör is rearranged to the new system, according to the following rules:

• All 1200-mm-wide elements can be cast only on the 7x1200-mm-wide lines.

• All fillers wider than 822 mm31, will be cast on the 7x1200-mm-wide lines.

• All elements narrower than 822 mm, will be cast in the 8th line. However, only the fillers that

now have a width smaller than 800 mm are assumed to be longitudinally cut if the 813-mm-

wide line is available. Hence, only fillers narrower than 800 mm or wider than 822 mm are

counted for the waste calculations.

• In the simulation of the new situation, it is assumed that for 25% of the fillers < 800 mm, it

will be possible to place them beside other fillers. For the fillers > 822 mm, it is assumed that

the rest of the casting bed is wasted.

30 Of course, there are many more factors that are important for the achieved capacity, such as the amount of longitudinal

cutting. Further discussion is made in the following chapters. 31 It is assumed than fillers that are cut in a width of 800-822 mm during 2019, would be designed as 813 mm wide

elements, if an 813-mm-wide line was available. This is very conservative though, as in the case of an 813-mm-line, more

fillers will be designed as 813-mm-wide elements to avoid longitudinal cutting.

54

Given those assumptions and imposing the production load of year 201932, the following results are

found:

• The annual casting length of the 7x1200-mm-lines, that have to handle the load of the 1200-

mm elements and the fillers > 822 mm, is estimated at 239.9 km.

• The total casting length of the 8th line is estimated at 21.7 km.

• Based on the data of 2019, the capacity of the 8th line is low. By simulating the line to be cast

once per working day, the line is used only 182 of the 233 working days.

• In the new system (7x1200-mm,1x813-mm), 21 km of longitudinal cutting are expected in

total.

• Fillers, whose length cutting is avoided due to the 813-line, have a total length of 5 km. This

value is considered low, and this is because the data used for the simulation, are from the

current case where the 813-mm-wide units are not an option. In fact, this number is expected

to be much higher when the line is available.

• The total required time for longitudinal cutting of fillers is estimated at 652 hours.

• The fillers that are cast on the 7x1200-mm-lines after the reorder (in other words, fillers of a

width > 822 mm) are 1317. This is 29.7 % of the total amount of fillers.

Figure 4-24. An example of the simulation created for both systems, based on the data of 2019 in Kungsör.

32 The production is rearranged in the studied case, according to the casting date of the current situation.

55

4.8.3 Reduction of material waste in the case of the 800-mm-line

In this subchapter, the waste is calculated for both the current situation and the case where a 1200-

mm-line is modified to an 800-mm-line. More specifically, a comparison between the concrete and

steel waste of the two cases takes place, as also the amount of scrap pieces and the total material that

has to be transported and crashed, in each case.

For the current situation (8x1200-mm-lines), the elements have been placed exactly as they are placed

during the production and any estimation of waste is deriving from that simulation. However, the

elements that were noted as ‘disregarded’ are not included in the calculations. For the studied case, the

HC production of the year 2019 has been rearranged on the lines as explained above, and for all waste

parameters, it is assumed a possibility 25% of fillers with width < 800 mm, to be placed beside other

fillers.

Figure 4-25 shows the estimated material waste for the current situation and the expected waste when

a 1200-mm-line is modified to an 813-mm-line. As it is seen, the reduction in the number of scrap

elements is not significant. This is due to two main reasons:

• Firstly, the study is based on the HC data of 2019, when the 813-mm-line is not an option for

designers. Many fillers are longitudinally cut at a point where it would be possible to avoid

cutting and instead, using an 813-mm-wide element if that option existed. Since only 1200-

mm-lines were available for the production, using those HC data for the simulation leads to a

higher estimation of scrap pieces than expected (e.g. a filler cut 790 mm wide, gives a scrap

element of 23 mm width according to the simulation. In the reality, it is most possible that

there will not be a need for cutting; design the element as an 813-mm-wide element).

• Secondly, all fillers wider than 822 mm, are placed on the 7x1200-mm-lines and it is assumed

that no filler will be placed beside them. This increases the estimated scrap elements

significantly. In fact, the space beside those elements can be used for placing narrower fillers.

However, not considering this aspect is on the conservative side, as it will not be always

possible to utilize that space. For example, in cases of heavy pressure on the 7x1200-mm-lines,

the possibility to place fillers beside others in that beds, is lower.

Even if the decrease in the amount of scrap pieces is not significant, the decrease of the material waste

is exceptional. The steel waste is reduced by 51.6% and the concrete waste by 50.3%. The total

scrap material in tones, deriving from those two, which has to be handled in the hall, transported and

crashed, is reduced almost to the half.

56

Figure 4-25. Comparison of the material waste between the current situation and the studied case.

There are two basic explanations for the high reduction of material:

• In the current situation, the most common width that fillers are cut is around 800 mm (e.g. 816

mm), while it is quite common to not be able to place a filler beside this element. By creating a

line that can cover this need (the 813-mm-line), there is a direct reduction of the wasted

material.

• The ability to cast and longitudinally cut elements narrower than 800 mm (e.g. units 590 mm

wide), in the 813-mm-line, instead of a 1200-mm-line, leads to a significant reduction of

waste.

The results shown above refer only to the waste due to longitudinal cutting of fillers and not in the

general waste. Other aspects, such as the concrete waste due to casting failures, are not included in

the comparison.

4.8.4 Possible cost saving in the case of the 800-mm-line

At this subchapter, the possible reduction in the production cost, when a 1200-mm-line is converted to

an 813-mm-line, is presented. A cost estimation of the current production is taking place, and then the

expected cost if a smaller width line is available, is calculated. The possible saving that can be

achieved, derives from the cost comparison of the two cases.

The parameters that influence the cost of the production are:

• The amount of concrete waste.

563.4

23.2

2737

1431.8

1133.2

47.9

2776

2880.9

0.0 500.0 1000.0 1500.0 2000.0 2500.0 3000.0 3500.0

Concrete waste (m3)

Steel waste (tones)

Pieces of waste (amount)

Total material for crash andtransport (tones)

Mater ia l Waste , the 8x1200mm System vs the 7x1200+813mm system (Kungsor , prod.2019)

Current situation (8x1200 mm lines) New situation (7x1200 mm + 1x813 mm lines)

57

• The amount of steel waste.

• The amount of scrap pieces that have to be handled in the hall. Each scrap piece that has to be

handled, requires time, workhands (one person operating the machine), while there are also

machine costs.

• The total volume of material that has to be transported and crashed.

• Costs related to the time needed for cutting. This involves:

➢ One person operating the diamond saw and the machine costs (of diamond saw).

➢ The additional cost that comes from the rest of the casting team, that waits during the

time of longitudinal cutting (three persons).

• The speed up of the production due to less longitudinal cutting. If less fillers need to be cut,

the production cycles are faster (cleaning of casting beds – placement of reinforcement –

casting etc.) and as a result, it is possible to cast more beds in a day. This aspect is not counted

at the cost calculations at this point; an extended discussion is made in the section 4.8.5.

Figure 4-26 shows the estimated annual cost for the current situation and the studied alternative, for

the factory in Kungsör, based on the HC production data of 2019. The total cost for the above-

mentioned factors, in the current situation is estimated at 3.205.000 SEK, while in the case of an 813-

mm-line instead of a 1200-mm-line, the total cost is expected at 2.199.000 SEK. Hence, the cost due

to fillers is reduced by 31.4% and the expected cost saving is estimated at 1.006.000 SEK

annually.

Figure 4-26. Estimated annual cost, comparison between the current case and the studied scenario, based on production

data of 2019 in Kungsör.

58

The higher contribution to the total cost, according to Figure 4-26, comes from the team waiting while

the cutting process takes place. The 2nd highest contribution comes from the waste of concrete,

followed by the cost due to longitudinal cutting. The 1st and the 3rd factor are related to the time

needed for longitudinal cutting and thus, one understands the importance to reduce the time of using

the diamond saw. The 2nd contribution (concrete waste), as also the steel waste, are related to the

percentage of casting bed’s width that it is utilized. Even if they are important, they follow factors

related to time for cutting. Other factors, such as the handling of pieces in the hall or the crash of

waste, are not so important contributors. It is concluded that the optimal solution comes from a

combination of reduction in the time needed for length-cutting and increase of the utilized ratio of a

casting bed.

By modifying a full width line to an 813-mm-line, the reduction of concrete waste is the factor with

the higher contribution on the possible cost saving. More specifically, the saving due to the reduction

of concrete waste constitutes the 36.8% of the total cost saving. The 2nd most important factor seems

to be the cost for the team waiting when length-cutting occurs (19.6%), followed by the steel waste

(17.2%).

The possible saving regarding the handling of wasted pieces in the hall is not significant; this is

because the study is made based on the HC data of 2019. Studying the case of the 813-mm-line by

using these data results to an overestimation of the scrap pieces. In reality, it is expected that if an

813-mm-line is made, scrap pieces will be decreased further, and the cost saving will be higher than

the one presented above.

To conclude, it should be mentioned that the results above are considered conservative and in fact, a

higher cost saving can be expected. From the one side, elements with status ‘DISREGARDED’ are

not included in the simulation, and thus the simulation of the 7x1200+1x813 mm system leads to a

higher efficiency, regarding this aspect. From the other side, the efficiency of a new width line, is

studied by using HC data of a production where the new width line was not an option. This leads to a

lower calculated efficiency than the one expected, when an 813 mm line is available. Moreover, the

simulation of the 7x1200+1x813 mm system follows certain assumptions that decrease the estimated

efficiency. For example, it was assumed that all fillers < 800 mm, will be cast in the 8th line. However,

there is always the option for the production planners to place e.g. 2x592 mm wide elements, beside

each other in a 1200-mm-line, to save material, if the load on the 7x1200-mm-lines is low on specific

days. Another conservative assumption is that the 8th line was simulated to be cast only once per

working day. In fact, in cases of thin HC types (e.g. HD/F 120/20, 200 mm thick), it is possible to cast

the line twice per day.

59

4.8.5 Possible increase of thru put in the case of the 800-mm-line

Since the total longitudinal cutting of HC elements will decrease with the introduction of the 813-mm-

line, a significant amount of time will be saved, resulting to faster production cycles.33 In this chapter,

the possibility to cast more beds at the given production time is studied, or in other words, the possible

increase of thru put.

Generally, it is difficult to estimate the thru put, as it is dependent on many different factors. A cycle

of casting a bed, can at the best scenario last approximately 12 hours (the curing time is included). The

most thin HC types need at best about 7 hours for curing. Even if the saved time due to less

longitudinal cutting can be estimated, other factors that influence the thru put cannot be strictly

defined. For example, for a day that a significant amount of time is saved, the ability to cast one extra

bed, apart from the time saved and the type of HC slab, is also dependent on the availability of a

casting bed (which in turn is dependent on the curing of the previous castings) and/or the possibility to

take advantage of the night hours for curing. Moreover, the increase in thru put is very strongly

dependent on the daily production, the difficulty of casting the previous casting programs, as also, the

order of the casting programs. Considering the above, one understands that these factors are not

known or cannot be simulated.

Initially, the daily amount of time that is saved is calculated for the two simulations. The simulations

show that:

• For the current case (8x1200-mm-lines), longitudinal cutting requires 820 hours annually.

• For the studied case (7x1200,1x813-mm), longitudinal cutting would require 652 hours

annually.

Figure 4-27 depicts the daily required time for longitudinal cutting of fillers, for both systems. The

daily average time needed for the current situation is 3.5 hours, while for the studied case is estimated

at 2.8 hours. Figure 4-28 depicts the required time for the two systems, but only for the 1200-mm-

lines. As it is seen, the difference is higher, as most of the longitudinal cutting in the new case

(7x1200,1x813-mm), takes place in the 8th line. The daily average of the 7x1200-mm-lines in the new

system is estimated at 1.4 hours.

Hence, based on the production data of 2019 in Kungsör, 169 hours are saved annually. If one

assumes that curing can be done at night hours, and also given that the placing of wires, the casting,

33 A production cycle is defined as the overall process of casting a bed. It includes the cleaning of the casting bed,

placement of wires, the concrete phase, as also the marking of details, curing of concrete, cutting of elements (transverse,

longitudinal and cutting of details) and finally the removal of elements from the casting bed.

60

transverse cutting and removal of elements from the casting bed require around 5 hours34, then thru

put can be roughly estimated at 34 casting beds/annually.

However, certain errors exist if the thru put is calculated in this way, leading to a higher value than the

actual. The 169 hours that are saved, are not equally distributed in the working days. For example, if

15 minutes are saved in a working day, those 15 minutes are included in the total amount, but no

actual increase in thru put can take place.

In a more accurate approach, it can be said that thru put is increased by one bed, when the daily time

difference between the two simulations is higher than 2.5 hours. This assumes that curing of the bed

will be done during the night, while it will be possible to remove the elements the following day. By

this method, an increase of the thru put is estimated, at approximately 23 beds/annually.

To conclude, simulations do not show a significant increase in thru put. A significant amount of time

is saved, but thru put is also dependent on other factors that are difficult to predict. The actual increase

of thru put can be higher than the one estimated, due to the fact that the simulations are based on the

production of 2019, where the 813-mm-line was not an option and a lot of full-width elements were

subjected to length-cutting. «How fast» will designers adapt to the new case and how many fillers can

be designed as 813-mm-wide elements, are main contributors for succeeding a higher thru put in the

future.

Regarding the 8th line in the new situation, is should be noted that apart from the fillers’ cutting that

will be avoided, a significant amount of time is saved due to the fact that fillers are collected in only

one bed and then cutting takes place. It is more time-consuming if fillers are distributed between the

eight lines since the diamond blade needs 10 minutes to start before every casting program. Placing

the majority of fillers in the same casting bed, is an advantage of the production, as the diamond blade

can work without significant interruptions, and hence the required time is decreased and thru put is

boosted.

It is also important to notice that the load of the production in 2019, results in a use of the 8th line at

only 182 of the 233 working days. By considering that the 8th line is simulated to be cast only once per

day, the use of the 8th line is low as it is estimated to not work at approximately 22% of the working

days.

34 Generally, it can be said that only the placement of wires and the casting, requires approximately 2 hours. For example,

the 1st casting of the day starts around 5:00 and it is completed around 7:00, where curing follows.

61

Figure 4-27. Total time needed to longitudinally cut elements, for both cases (production 2019, Kungsör). The high

difference after day no.182, is because the 8th line is not used. All the load of fillers < 822 mm from the production in 2019

in Kungsör, has been cast on the 8th line by working day no.182. The 8th line, given that data, is empty the last 51 days of

the simulation.

Figure 4-28. The time needed to longitudinally cut fillers in the 1200-mm-lines of both cases (production 2019, Kungsör).

62

4.8.6 Pressure on the production in the case of the 800-mm-line

As it is shown above, less longitudinal cutting due to the introduction of the 800-mm-line will lead to

faster production cycles. However, regarding only the 1200-mm-wide elements, their physical

production capacity will be decreased by 1/8. Only seven lines will have to handle the load of the

1200-mm-wide elements in the new situation. Even if there will be some time gained, an additional

pressure will be created in the 7x1200-mm-lines of the new system in particular days, which is

considered to be the only drawback of introducing the 800-mm-line. More specifically, for days with

more than seven casting programs, the ‘loss’ of one full-width casting bed (1200 mm), will result

more load on the seven lines and hence will demand a ‘tighter’ casting schedule of the previous

casting programs, in order for the daily production to work normally.

At the current situation, each 1200-mm-wide casting bed has to handle 243 beds annually. With the

alteration of one 1200-mm-wide line to an 813-mm-wide line, each 1200-mm-bed will have to handle

approximately 252 beds annually. This is not a significant increase and of course, in the new case,

casting cycles will be faster due to that fillers < 800 mm that demand cutting, will be placed on the 8th

line. However, this increased load on the 1200-mm-lines can be demanding in certain periods.

The pressure on the 1200-mm-lines is studied by defining an indicator as the number of casting

programs that correspond to each line for each working day. Hence, if this indicator is equal to 1, this

means that there are eight casting programs that have to be handled by eight lines in the current

situation, or seven casting programs that have to be handled by seven lines in the new case. One

understands that for the working days that this indicator is ≤ 1, the production runs very smoothly.

The ability of the system35 at the current case is 1.375 (maximum number of beds/day in the Figure 4-

29), which is translated to eleven casting programs being handled by eight lines. During 2019, this

happened mainly during only one period (working days 150-162 according to the Figure 4-29, which

is the period August 14th – August 28th).

The reduction by 1/8 of the 1200-mm-lines in the studied case, shows that this indicator reaches 1.43,

which is equivalent to ten casting programs being handled by seven lines. This is a pressure that the

production has never been tested before, and as Figure 4-29 shows, ten of the total working days are

expected to run under that pressure in the new case, according to the simulation. This is not expected

to be a problem when such a high value of the pressure on the system occurs in a particular day, while

the following days have a significantly lower pressure, because the production planners can distribute

the load between these working days for a smoother production. However, if these values of pressure

35 The ability is defined as the maximum daily number of casting beds achieved during 2019 in Kungsör. Under certain

circumstances, this number can be higher.

63

are reached at a sequence of working days, it can be a problem for the production. The circles on

Figure 4-29 show those cases.

Figure 4-29. The pressure on the production, defined as the daily number of casting programs per line.

(based on data of HC production of 2019 in Kungsör)

It is controversial if the factory will be able to handle the load those particular days, and it is very

difficult to predict as it is dependent on many factors. For example, factors that seem to be decisive for

this, are the amount of cutting that still will take place on the seven lines and the curing time of the

casting programs. According to Figure 4-28, a significant amount of time is saved, that can balance

this additional pressure, however it is not possible to make a safe comparison.

To conclude, even if the pressure on the production those particular days cannot finally be handled by

the factory, this should not be taken into account against the 813-mm-line, due to the following

reasons:

• Production planners can avoid this high load on the seven lines of the new system, by casting

some of the beds on days with lower pressure. In other words, a rearrangement of the

production can be made.

• The days with such a high pressure are very few compared to the total number of working

days.

64

• The graph above is made by using data of the year 2019, where designers designed based only

on 1200 mm full width elements. If a new width is available, designers are expected to adapt

to this choice, and thus gradually, the use of the 8th line will increase, dropping the pressure on

the seven lines.

4.9 Possible cost saving vs the adaption to the new width line

During the previous subchapter, the possible cost saving by modifying a 1200-mm-line to an 813-mm-

line was calculated, using the HC production of 2019. The results have shown that the possible saving

is estimated at 1.006.000 SEK per year. However, this is considered conservative.

Firstly, this amount was calculated by considering that only the fillers that were cut at a range of 800-

822 mm in 2019, will be designed as 813-mm-wide elements, when the new line will be available.

One understands that e.g. a filler cut at 780 mm, would probably be designed as an 813-wide-element,

if this option exists.

Secondly, by creating smaller width elements, designers will be able to make more combinations

when they decide the way of placing the HCs, in an effort to avoid cutting full-width elements. This

aspect was discussed thoroughly in subchapter 4.6, but it was not taken into account in the simulation

of the 813-mm-line, since data of 2019 were used.

With the purpose to estimate the possible cost saving when designers start taking advantage of the

813-mm-line, various simulations took place. The simulations initially started by setting a small

number of fillers to be designed as 813-mm elements and estimating the total cost saving. Then a

higher number was set, to count for the case where designers will avoid length-cutting, by combining

the two choices of full width elements (1200 mm, 813 mm) for covering their needs.

Figure 4-30 shows the possible cost saving, by percentage of the fillers that will be designed as full-

width elements. Hence, if for example, only 1 out of 20 fillers can be designed as an 813 mm element,

the possible cost saving can reach 1.057.000 SEK annually.

65

Figure 4-30. The expected cost saving, per degree of adaption to the new 813-mm-line.

It can be concluded that the estimated amount by using the data of 2019, depicts the cost saving

directly after when the 813-mm-line will be made. Gradually, designers will start adapting to the new

width line. It is believed that quite soon, a 10% of fillers will be designed as 813-mm-wide elements,

which leads to a cost saving of 1.209.000 SEK annually. If combinations of the two width choices are

utilized to avoid cutting, saving increases considerably. If only 15% of fillers are designed as 813-

mm elements and 5% fillers are designed as 1200 mm elements (which means that 1 out of 5

fillers is avoided), cost saving is expected to reach 1.398.000 SEK annually.

1006000

1057000

1107000

1166000

1188000

1209000

1225000

1295000

1316000

1398000

1000000 1100000 1200000 1300000 1400000 1500000

Data of 2019

2.5% increase of 813 mm elements

5% increase of 813 mm elements

7.5% increase of 813 mm elements

7.5% increase of 813 mm and 1% of 1200 mm elements


7.5% increase of 813 mm and 3% of 1200 mm elements


10% increase of 813 mm and 5% of 1200 mm elements

15% increase of 813 mm and 5% of 1200 mm elements

POSSIBLE COST SAVING (SEK)PERCENTAGE OF FILLERS

DEGISNED AS FULL WIDTH ELEMENTS

66

5. Conclusions and suggestions for future research

5.1 Conclusions

This thesis project shows that the modification of one of the existing 1200-mm-wide casting beds of

the factory in Kungsör to an 813-mm line is accompanied with certain benefits, resulting to a more

profitable production. By the introduction of the smaller width line, the material waste is decreasing

significantly. Based on the hollow core production of 2019, the concrete waste is expected to be

reduced by 50.3% (570 m3) while the steel waste by 51.6% (24.7 tonnes). The reduction of the wasted

material has even higher economic benefits for the company since the total wasted material for

transport and crash is dropping significantly. Moreover, the introduction of the 813-mm line is

accompanied with certain environmental advantages, as it will lead to a more sustainable production

and less CO2 emissions. The total amount of longitudinal cutting of HC units will be decreased,

resulting to a more efficient production. The total cost saving for the factory in Kungsör is estimated

at 1.006.000 SEK annually. However, this estimation is based on the data of 2019, where the 813-mm

line was not an option and consequently, it is believed to be conservative. In fact, this amount of cost

saving is expected directly after the introduction of the new width line. Gradually, designers will adapt

to the new width line; more fillers will be designed as full width units and a higher amount of

longitudinal cutting will be avoided. The study shows that if there is an increase of only one out of

five future fillers designed as full width elements, the possible cost saving can reach 1.4 million SEK

annually. This cost saving does not include the possible increase of thru put due to faster production

cycles, where an increase is also expected. About the decrease of the physical production capacity of

1200-mm units in the factory in Kungsör, an additional pressure on the seven 1200-mm lines can

occur under certain periods, due to the high demand for 1200-mm units. However, the additional

pressure is expected in very particular days and hence it is not considered a drawback for the

introduction of the 813-mm line.

It should be noted that the study focuses on the production of the factory in Kungsör. That factory has

eight casting lines of a 143 m length. The results show that it is profitable to convert one of those

existing lines to an 813-mm line. However, the other two factories that produce HC units (factories in

Veddige and Långviksmon) have fewer but longer casting beds. Hence, certain aspects such as the

pressure on the production if a modification is made, vary significantly between the factories. The

physical production capacity of 1200 mm units in the factory in Kungsör is reduced by 12.5% (which

is close to the amount of fillers of the total production). This is not the case for the other two factories,

where the modification of one of the existing lines would have a different impact on the pressure of

the production. Thus, the suggested solution for modifying a 1200-mm line to an 813-mm line in the

67

factory in Kungsör, should not be inferred for the other two factories; one should investigate further

the impact on the production for the factories in Veddige and Långviksmon. However, if the creation

of an extra casting bed is under discussion in those two factories, the results regarding the most

promising width options can be used.

5.2 Suggestions for future research

The results have shown that the capacity of the 813-mm line will be low enough, especially directly

after the introduction of the line. By making very conservative assumptions, the results show that the

813-mm line will not be used for 22% of the total working days. It would be interesting to examine if

that capacity could be utilized for producing 813-mm wide units for the other factories of

Strängbetong (e.g. the factory in Veddige), and if such an idea would be profitable, as transfer costs

are included.

As the width of the precast HC units is fixed, longitudinal cutting of HCs will always be an issue for

the precast companies. Some research on this field has already been made and certain ideas exist.

Companies providing machinery equipment for precast producers, such as Elematic, suggest

modifications of the extruders used today, for producing smaller width elements. More specifically,

Elematic has announced a modified version of the standard extruder that is equipped with a special

nozzle, that promises the casting of two HC slabs of different width in the same production line

(Elematic, Adjustable Extruder solves the major challenge of all American precasters 2020). This

modification can provide slabs in widths of a certain range between 600-2400 mm. It would be

interesting and very profitable for the precast companies to examine if HC slabs of a narrower width

than 600 mm can be produced. Moreover, since the needs for units of such a width are very specific, it

would be ideal to be given the ability of casting only a part of the length of a production line or being

able to alter the casting width along the production line.

Fillers’ high width variation (Figure 4-1) shows that even if a new width line is introduced, there will

always exist needs on projects that will not be covered by the available width options. Of course,

making available a second width alternative (813 mm units) will give the designers more alternatives

in order to be able to make more combinations and hence avoid future fillers. Cast-in-situ concrete

joints are also utilised to avoid further cutting of HC units. However, designers are usually limited to

cast-in-situ concrete joints without reinforcement, which are of a limited width while they are

increasing the cost and work needed on site. Alternative solutions of cast-in-situ concrete joints that

can ideally cover a wider span, be more economic or require less work on site, would offer the

designers more span combinations and thus the need for fillers could be decreased, resulting to higher

production savings for the precast companies.

68

6. References

1. Commission, FIB. Special design considerations for precast prestressed hollow core floors.

International Federation For Structural Concrete, 2000.

2. Elematic. Adjustable Extruder solves the major challenge of all American precasters.

Concreteissues.com, 2020.

3. Elematic. Available split and narrow sizes for the extruder P7/E9. Finland: Elematic, 2019.

4. Elematic. Split slabs. Finland: Elematic, 2019.

5. Eriksson, Per. “Kostnader för längdsågning i Håldäck.” Strängbetong, Sweden, 2014.

6. IPHA. International Prestressed Hollowcore Association. Edited by International Prestresed

Hollowcore Association. 2020. https://hollowcore.org/hollowcore/why-hollowcore/.

7. PCI. Manual for the Design of Hollow Core Slabs and Walls - Third Edition.

Precast/Prestressed Concrete Institute, 2015.

8. Srl, Nordimpianti System. “Hollow core slabs in new widths.” www.nordimpianti.com. 2016.

9. Strängbetong. “Föreskrivna Breddmått.” In Strängbetong Handbook. Sweden, 2018.

69

7. Appendix

Appendix A1- ‘Technical characteristics of the available HC types’

Appendix A2- ‘Allowable zones for cutting of HC elements’

Appendix A3- ‘Recommended cutting widths’

Appendix B1- ‘Drawing examples of split elements’

70 213 65 218 65 218 65 213 70

1197

4029

545

380

25

3325

829

320

1197

61 230 47 236 47 236 47 231 61

3518

941

265

150 224 224 224 224 151

1197

20184

126 189 189 189 189 189 126

1197

220

20

126 189 189 189 189 189 126

1197

2515

025

200

155 34 20

HD/F 120/20 F155

Tvärsnittsarea=0.124 m²Elementvikt=310 kg/mFogvikt=17 kg/mYtvikt inkl. fog=272 kg/m²

HD/F 120/27 F184



HD/F 120/22 F155

HD/F 120/32 F236


HD/F 120/38 F218


42ø140

26

1197

3931

744

400

HD/F 120/40 F172


73.5 16352

17252

17252

17252

163 73.5

150 224 224 224 224 151

1197

20155

265

5815

057

HD/F 120/27 F155


3515

035

155 3442ø140

126 189 189 189 189 189 126

1197

100 20

0

20ø125


HD/F 120/20 F125

39 kg 49 kg

Igjutning Massa/m

Igjutning Massa/m

72 kg

Igjutning Massa/m

140 kg 144 kg

Igjutning Massa/m

111 kg 118 kg

Igjutning Massa/m

121 kg 122 kg

Igjutning Massa/m

49 kg

Igjutning Massa/m

31 kg

Igjutning Massa/m

39 kg 49 kg

KungsörLångviksmonVeddige








PRODUKTSTANDARD UTGÅVA

Elementtvärsnittför HD/F 120/20, /22, /27, /32, /38 och /40

4H

2018-02-13

SE-HDF00-101

ELEMENT

kdapo

Text Box

Appendix A1

HD/F 120/20 F155

HD/F 120/27 F184

HD/F 120/32 F236

HD/F 120/38 F218

HD/F 120/40 F172

81 103 73 116 73 116 73 116 73 116 73 103 81

81 184

257

373

446

562

635

751

824

940

1013

1116

90 112 123 100 123 101 123 100 123 112 90

90 202

325

425

548

649

772

872

995

1107

85 175 118 162 118 162 118 175 85

85 260

377

540

657

820

937

1112

85 149 163 120 163 120 163 149 85

85 234

397

517

680

800

963

1112

110 77 151 73 151 73 151 73 151 77 110

110

187

338

411

562

635

786

859

1010

1087

HD/F 120/27 F155

HD/F 120/22 F155

HD/F 120/20 F125

81 103 73 116 73 116 73 116 73 116 73 103 81

81 184

257

373

446

562

635

751

824

940

1013

1116

81 103 73 116 73 116 73 116 73 116 73 103 81

81 184

257

373

446

562

635

751

824

940

1013

1116

90 112 123 100 123 101 123 100 123 112 90

90 202

325

425

548

649

772

872

995

1107

min. 30

Faktor som avgör inom vilka zonersom håltagning kan tillåtas:

1.) Linornas täckskikt mot hål-snittet ska vara det samma sommot underkant platta.

Tillåtna zoner för håltagningi HD/F 120/20, /22, /27, /32, /38 och /40

3A

2019-05-28

SE-HDF00-525

ELEMENT PRODUKTSTANDARD UTGÅVA

kdapo

Text Box

Appendix A2

HD/F 120/20 F155HD/F 120/20 F125

HD/F 120/32 F236

HD/F 120/38 F218

HD/F 120/40 F172

1197

1197

1197

1197

1197

309 876 498 687 1065

368 816 592 592 1040

451 734 1016

451 734 1017

368 816 592 592 1040

133

177

213

253

267

Max breddmått föroarmerad igjutning

Sågning i ytterkanalbör undvikas eftersomden smala plattdelenblir oanvändbar

Föreskrivna bredderför sågade HD/F-plattorHD/F-profiler

HD/F 120/22 155

1197 309 876 498 687 1065 146

(213)*

* HD/F 120/32 F179

HD/F 120/27 F184HD/F 120/27 F155

Föreskrivna breddmått (sågning mitt i hålkanaler) tillämpas för:1.Samtliga byggnader och håldäck fritt bil

Faktorer:1.) För att tillfredställande gjutfog ska kunna utföras krävs minst 40 mm frittavstånd till nästa intillliggande platta.

Föreskrivna breddmåttför sågade HD/F-plattor

2D

2018-02-13

SE-HDF00-521

ELEMENT PRODUKTSTANDARD UTGÅVA

kdapo

Text Box

Appendix A3

Figure 7-1. Technical characteristics of an 813-mm-wide ‘split’ element, according to Elematic. This HC

type is not produced by Strängbetong.

Figure 7-2. Example of an 813-mm-wide ‘split’ element made from a 1197 mm full width element (HD/F 120/27). The dimensions are approximated; the exact technical details and final dimensions should be agreed with Elematic.

Appendix B1

TRITA-ABE-MBT-20725

Optimization of HOLLOW CORE SLABS

Documents