AD01CTS ‐ ADVANCED CONSTRUCTION TECHNOLOGY AND SERVICES Alfrendo Satyanaga
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AD01CTS ‐ADVANCED CONSTRUCTION TECHNOLOGY AND SERVICES
Alfrendo Satyanaga
Lecture 2 – Concrete Frame
Concrete Applications
• Residential and commercial buildings • Bridges, flyovers, culverts • Dams, tunnels, water tanks • Swimming pools • Roads, runways, pipes • Foundations, piles, sewers • Offshore platforms • Nuclear power stations, radiation shields etc. • Fire and corrosion protection of steel structures
Concrete Fact
• The most used man‐made material• The 2nd most used material• Total value of concrete infrastructure > 17 trillion US dollars
• Annual consumption of concrete in the world– 18 billion ton/year (as of 2015)– About 3 tons per person– More than 10x that of steel
Advantages of Concrete
• Ease of production from local materials(cost benefit)
• Good compressive strength• Protection of embedded steel (fireresistance)
• Mouldability to achieve any shape andsize (flexibility of application)
• A durable material in principle
Advantages of Concrete
• Require less energy to produce thanother construction materials
• Aesthetic possibilities through the useof color, texture and shape
• A material with tailorable properties
Disadvantages of Concrete
• A brittle material with very low tensilestrength and tensile ductility.
• Low strength‐to‐weight ratio (even incompression)
• Prone to chemical attack• Undergoes irreversible shrinkage due tomoisture loss
• Creep significantly under an appliedload
What is Concrete?
• Concrete is made by mixing:
– Cement
– Fine aggregates
– Coarse aggregates
– Water
Concrete Admixture
• An additional material, known as admixture, is
sometimes added to modify certain properties of
concrete
Concrete Admixture
Absorption
Internal impervious
Pores partially filled
Free moisture
Oven dry mass, WD
Air dry-moisture condition,
Wm
Saturated surface dry-
moisture condition,
WSSD = WD +WP
Moist-moisture condition,
Wm
Absorption
D
DSSDW
WWA
• Absorption (A) is the moisture content
when the aggregates are in saturated
surface dry condition (SSD)
Free Moisture
D
DmWWWM
• Free moisture is the moisture content
(M) in excess of the SSD condition
AMmoistureFree
Aggregates in Concrete
Functions of Aggregates in Concrete
• Reduce costs
• Modify properties of concrete
• Reduce dry shrinkage
Admixtures
• Admixtures are substances that are introduced into a batch of concrete, during or immediately before its mixing, in order to alter or improve the properties of the fresh or hardened concrete or both
Use of Admixtures
• To improve the workability of the fresh concrete
• To reduce water content for a given workability thereby increasing the strength
• To increase the durability of hardened concrete
• To retard setting time or to increase it
Use of Admixtures
• To impart colour to concrete• To maintain volume stability by reducing or offsetting shrinkage during concreting
• To increase concrete resistance to freezing and thawing
Reinforced Concrete
• Basically made of two materials: plain concrete and steel bars embedded in concrete.
• The tensile strength of concrete is only about 10 % of the compressive strength assumed does not resist any tensile forces.
• Reinforcement is designed to carry the tensile strength.
Reinforce Concrete
• Proper bonding is required to prevent slip of the bars
• Proper concrete mixtures are needed to provide adequate impermeability of the concrete against water intrusion and bar corrosion
Stress‐Strain Relationship
• As the load is applied, at first strain increases linearly with stress and the concrete behaves as an elastic material.
• After that the curve is no longer linear and the concrete behaves more like plastic material.
• In the plastic range, if the load is removed, the deformation would not recover.
Stress‐Strain Curve for Concrete
Concrete Strength
• Concrete generally increases its strength with age.
• A typical variation in strength of an adequately cured Portland Cement Conrete as suggested by BS8110 is:
• BS 8110 does not permit the use of strengths greater than the 28‐day value in calculations
Duration 7 days 1 month 2 months 3 months 6 month 1 year
Strength (N/mm2)
20 30 33 35 36 37
Durability of Concrete
The durability of concrete is influenced by:
• The exposure conditions
• The concrete quality
• The cover to the reinforcement
• The width of any cracks
Specification of Concrete
• Concrete of a given strength is identified by
its “grade”
• For example Grade 25 concrete has a
characteristic cube crushing strength of 25
N/mm2 after 25 days of curing.
• For normal dense aggregate reinforced
concrete use grades of 30, 35, 40
Typical Properties of Structural Concrete
PropertiesCompressive strength (MPa) 35Flexural strength (MPa) 6Tensile strength (MPa) 3Modulus elasticity (GPa) 28Tensile strain at failure 0.001Cofficient of thermal expansion (/oC) 10 x 10‐6Ultimate shrinkage strain (%) 0.05 – 0.1Density
Normal weight (kg/m3) 2300Light weight (kg/m3) 1800
Environmental Impact of Concrete
Enormous raw material and energy consumption • Global concrete demand > 18 billion tons annually as of 2006
• 1 ton of cement clinker requires 1.7 tons of non‐fuel raw materials
• Cement production is 10x more energy intensive than general economy and is account for 2% of global primary energy use (4000‐7500 MJ per tonne of cement)
• Land scarring
Environmental Impact of Concrete
CO2 emission and climate change • Production of 1 ton of cement clinker generates equal amount of greenhouse gas
• Cement production accounts for 5‐10% of global CO2 emissions
Surface runoff Urban heat island
Shrinkage
• As concrete hardens there is a reduction in volume.
• This shrinkage is liable to cause cracking of the concrete.
• It also has the beneficial effect of strengthening the bond between the concrete and the steel reinforcement.
Thermal Expansion
• Day‐to day thermal expansion of concrete can be greater than the movements caused by shrinkage.
• When the tensile stresses caused by shrinkage or thermal movement exceed the strength of concrete, cracking will occur.
• To control the crack widths, steel reinforcement must be provided close to the concrete surface.
Workability & Consistency
• It is desirable that freshly mixed concrete be relatively easy to transport, place, compact and finish without harmful segregation. A concrete mix satisfying these conditions is said to be workable.
• It is determined to a large extent by measuring the “consistency” of the mix. Consistency is the fluidity or degree of wetness of concrete.
Factors Affecting Workability
• Method and duration of transportation.• Quantity and characteristics of cementingmaterials.
• Aggregate grading, shape and surface texture.• Quantity and characteristics of chemicaladmixtures.
• Amount of water.• Amount of entrained air.• Concrete & ambient air temperature.
Bleeding
• Bleeding is the tendency of water to rise to the surface of freshly placed concrete.
• It is caused by the inability of solid constituents of the mix to hold all of the mixing water as they settle down.
Working Life of Concrete Structure
Concrete Structural Form
• Flat slab• Ribbed slab• Waffle slab• Band beam and slab• Deep beam and slab• Hybrid concrete construction• Precast• Tunnel form
Flat Slab
• A reinforced concrete slab supported directly by concrete column without the use of beams
Flat Slab
• Common used in construction
Flat Slab with Drop Panels & Column Heads
Use of drop panels:• Increase shear strength of slab• Increase negative moment capacity of slab• Stiffen the slab and hence reduce deflectionUse of column heads:• Increase shear strength of slab• Reduce the moment in the slab by reducing the clear or effective span
Benefit of Flat Slab
• Flexibility in room layout• Saving in building height; most economic forms of construction
• Shorter construction time• Ease of installation of M & E services• Prefabricated welded mesh• Buildable score• Can incorporate all edge protection and provide robust working platform (health & safety)
Flat Slab
HDBFlat slab with drop panel
Waffle Slab
• A type of slab that has two‐directional reinforcement on the outside of the material, giving it the shape of the pockets on a waffle.
Waffle Slab
LibraryTriangular waffle slab in Louis Khan gallery, Italy
Construction with Waffle Slab
LodytelCommunication
Development Centre, Spain
It was the first building to use the Holedeck pods for waffle sytem.
Chattrapati ShivajiTerminal,India
It is recognized for its innovative column design which also
consists waffle design.
Metropol Parasol,Italy
It is the world’s largest structure which is made up of waffle
system.
Ribbed Slab
• A pre‐stressed concrete flat half slab with concrete up strands (rib) that are purposely designed to provide the necessary stiffness to the slab for handling
Advantages of Ribbed and Waffle Slab
• Flexible• Relatively light, therefore less foundation costs and longer spans are economic
• Speed of construction• Fairly slim floor depths• Robustness• Excellent vibration control• Thermal mass• Good for services integration• Durable finishes• Fire resistance
Disadvantages of Ribbed and Waffle Slab
• Construction requires strict supervision and skilled labour.
• The casting forms or moulds required for pre‐cast units are very costly and hence only economical when large scale production of similar units are desired.
• Headroom is reduced , hence increased storey height.
• Due to waffle ceiling , it creates problem in lighting facilities and hanging pipes or ducts.
Ribbed and Waffle Slab
• Commonly used as both ceiling and floor slab. They are used in the areas which has huge spans.
• It is often used for industrial, commercial buildings, airports, parking garages, bridges, residences and other structures requiring extra stability.
• The main purpose of employing this technology is for its strong foundation characteristics of crack and sagging resistance. Waffle slab also holds a greater amount of load compared with conventional concrete slabs.
Construction Technique
1.Arranging the Framework
2.Fixing the Connectors
3.Fixing the Framework
4.Providing a horizontal
connector
5.Placing the
Pods
Construction Technique
6.Fixing pods to the connectors
7.Removing framework
8.Removing connectors
9.Removing pods
10.Providing stacking
Band Beam and Slab
• Beam and slab construction involves the use of one or two way spanning slabs onto bems spanning in one or two directions
• Band beams are shallow, wide beams that minimise the overall structural depth.
Deep Beam and Slab
• Deep beam provide a stiff floor capable of long spans, and able to resist lateral loads.
• To limit the formation of flexural cracks along the sides
• Beam can be designed as T or L beams using the slab as a flange
Advantages & Disadvantages of Beam and Slab Construction
Advantages:• Traditional effective solution.• Long spans.• Fast lead time as formwork can be made on site.Disadvantages:• Penetrations through beams for large ducts difficult to handle.
• Slow construction.• Greater floor‐to‐floor height.
Pos‐Tensioned Slab
Wedge action producing a frictional grip on the wires. Direct bearing from rivet or bolt heads formed at the end of the wires. Looping the wires around the concrete.
Pos‐Tensioned Slab
Unbonded Tendon
• Unbonded tendons are protected by a layer of grease inside a plastic sheath.
Unbonded Tendon
• Single strand coated with corrosion inhibiting grease and encased in polyethylene sheathing
• PT force is transferred to the concrete by the anchors provided at the ends
Strand
• Strand is made from seven cold drawn high carbon steel wires.
• Seven individuals wires, with six wires helically wound to a long pitch around a centre wire.
• All strands should be grade 1860 Mpa
• Strand is mostly available in two nominal size 12.7mm&15.7mm diameter
Unbonded Tendon
Unbonded Tendon
Bonded Tendon
• Bond is achieved throughout the length of the tendon by a cementitious matrix called grout
• Post‐tension force along the tendon is a function of the deformation of the concrete
Advantages of Bonded Tendon
• Higher flexural capacity.• Good flexural crack distribution.• Good corrosion protection.• Flexibility for later cutting of penetrations.• Easier demolition.
Bonded Tendon
Advantages of Post‐Tension Slab
Longer span Overall structural cost Reduced floor to floor height. Deflection &cracks control Waterproof slabs Early formwork stripping Materials handling Fast construction
Cost Saving of Post‐Tension Slab
Disadvantages of Post‐Tension Slab
Since there are a number of tendons and wires spread inside the post tension slab, it can result in corrosion.
Complexity of work.
Poor workmanship can lead to accidents.
Application of Post‐Tension Slab
It used to fabricate large members, such as long –span bridge decks of the box – girder type by prestressing together a number of smaller precast units The chief merit of post –tensioning is that it allows the use of curved and stopped‐off cables Post‐tensioning is variably used for strengthening concrete dams, circular prestressing of large concrete tanks & biological shields of nuclear reactors.
Application of Post‐Tension Slab
Sangyong E&C applied the post-tension methodto construct bridges inclined at 52 degrees at its highest, which is 10 times more inclined than the leaning tower of pisa (5.5˚). The team adopted a tension method whereby post-tension is installed on a 600 mm thick bearing wall and wire is stretched from inside.
Application of Post‐Tension Slab
DYWIDAG Tendons Stabilize Pier Underpinning above Singapore’s new Downtown Line• A post-tensioned, 7m wide, 2.5m deep and 24m
long transfer beam was built directly underneath the pile cap that horizontally linked the two diaphragm walls
Application of Post‐Tension Slab
"One Raffles Quay" Prime Office Building, Marina Bay, Singapore• For the column free floor plate of the lower South Tower, a post‐tensioned design proved to be more economical.
• Post‐tensioned beams span 19.5 m from the central core wall into the perimeter columns, with the maximum height being kept at 900 mm
Application of Post‐Tension Slab
Elevated Expressway from Airport Road to Tampines Avenue 10, Singapore 2 km Long, 45 m span Under construction
Hybrid Concrete Construction
A method of construction which integrates precast concrete and cast in‐situ concrete to make best advantage of their different inherent qualities. The accuracy, speed and high‐quality finish of precast components can be combined with the economy and flexibility of cast in‐situ concrete
Hybrid Concrete Construction
Hybrid concrete construction can incorporate all the benefits of precasting, (e.g. form, finish, colour, speed, accuracy, prestressing, high‐quality, assured covers and dense and properly cured covercrete) with all the benefits of in‐situ construction (e.g. economy, flexibility, moulability, continuity and robustness).
Hybrid Concrete Construction
Caisson/ ceiling of Manchester HQ• 2,000 large precast concrete coffer units, weighing up to 6.5 tonnes each, onto steel beams and then adding a topping of in‐situ concrete.
Hybrid Concrete Construction
Yishun community hospital near Khoo TeckPuat Hospital • To minimize dust and noise
Tunnel Form
A formwork system that allows the contractor to cast walls and slabs in a cellular structure form
The end walls and facades are easily completed with thermally insulated units that can be clad as required.
Tunnel Form
Tunnels can be between 8 – 11 m long and 2.4 – 6.8 m width.
Advantages of Tunnel Form
Fast and economic construction. Example: earthquake recovery housing
project in Turkey 40,000 units completed in 5 months.
Advantages of Tunnel Form
Easy to use Smooth concrete surface Doors, windows, electrical pipes ready in
place Wide range of building types No height limitations
Innovations in Concrete
Ultra‐high performance concrete
Flowing concrete
Self compacting concrete
Fibre reinforced concrete
Nano concrete
Ultra‐high Performance Concrete
High strength, ductile material formulated
by combining portland cement, silica fume,
quartz flour, fine silica sand, high‐range
water reducer, water and steel or organic
fibers.
Ultra‐high performance concrete
Ultra‐high performance concrete
For bunker construction in Iran
Flowing Concrete
Economical ready mix concrete that allow
maximum flowability without sacrificing
strength by adding water at the jobsite.
Self Compacting Concrete
Flowing concrete mixture that is able to
consolidate under its own weight.
It is suitable for difficult conditions and in
sections with congested reinforcement.
It can minimize hearing‐related damages on
the worksite that are induced by vibration of
concrete.
Fibre‐Reinforced Concrete
Concrete containing fibrous material which
increases its structural integrity. It contains
short discrete fibres that are uniformly
distributed and randomly oriented. Fibers
include steel fibers, glass fibers, synthetic
fiber and natural fibers – each of which lend
varying properties to the concrete.
Fibre‐Reinforced Concrete
Welded wire mesh fiber reinforced
concrete
Glass fiberreinforced concrete
Steel fiberreinforced concrete
Nano Concrete
A concrete made with portland cement particles that are less than 500nm as a cementing agent.
Currently cement particle sizes range from a few nano‐meters to a maximum of about100 micro meters.
Benefits of Nano Concrete
Lower cost per building site.
Concrete with high initial and final
compressive and tensile strengths.
Concrete with good workability.
Nano Concrete
Jubillee church in rome, Italy – self cleaning concrete
THANK YOU
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