CIDECT 2W Final Report

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Final Report

HOLLOW SECTION COLUMNSEMBEDDED IN CONCRETE

CIDECT Project 2W

München, August 2007

Prof. Dr.-Ing. Ö. Bucak University of Applied Sciences

Munich, Germany

Karlstr. 680333 München, GermanyTelefon +49 89 1265 2642Telefax +49 89 1265 2699



Hollow sections columns embedded in concrete

Final Report

Title of the research: HOLLOW SECTIONS COLUMNS EMBEDDED IN

CONCRETE

Sponsors: CIDECT

V & M

Research Programme: CIDECT 2W

Application for research by: Vallourec & Mannesmann TubesV&M Deutschland GmbHDüsseldorf, Germany

Coordinator: Dipl.-Ing. O. Josat

Research carried out by:

Prof. Dr.-Ing. Ö. BucakUniversity of Applied SciencesKarlstr. 680333 München

Germany

Date: August 2007



Hollow sections columns embedded in concrete page 1

CIDECT project 2W UNIVERSITY OF APPLIED SCIENCES, MUNICH

List of contents

1. Introduction and background ........................................................................... 2

2. Aim of the project .............................................................................................. 3 3. Test programme ................................................................................................ 4

4. Test results ........................................................................................................ 7

5. Evaluation ........................................................................................................ 15

6. Summary .......................................................................................................... 21

7. Literature .......................................................................................................... 23





1. Introduction and background

Architectural trends today show an increase in the use of hollow section members,for both building and bridge structures. This is primarily due to their advantageouscharacteristics for structural as well as aesthetic aspects of design as compared toconventional open-section members. Much advancement was made, but there arestill areas which need some improvements. In investigations carried out in the scopeof ECSC-Project 7210-SA/511 [1], the design embedded length of open sectionscould be reduced to 40 up to 50 % of the previously allowed values.

It is proven in Munich by Heimershof, that for circular and rectangular timber

sections, a smaller embedded length is adequate for design.The lower embedded length and the corresponding economic benefits not onlyreduce the volume of earth excavation, but also the foundation dimensions. Also,erection of such columns is simplified.

More advantages are expected in areas where the ground water level is very high.

At present, hollow sections are designed very conservatively, which presents adisadvantage in the use of hollow sections as a result of deeper foundationrequirements than for other sections. Appropriate turnovers may be expected, whencolumns of steel structures made of hollow sections are just as economicallydesigned as columns made of open sections.

This research project may be considered as an extension of

• CIDECT Research Project 2J [3] and

• ECSC Project 7210-SA/511 [1] for rolled open sections

to hollow sections.





2. Aim of the project

This research programme considers the following aspects: • Investigation whether the existing design formulae determined for open

sections can also be used (with possible modifications) for circular andrectangular hollow sections

• Theoretical work (financial support of the German Research Foundation, DFG,is applied for) substantiates the low number of tests.

• Especially for circular hollow sections, a more favourable mechanism of loadshedding and failure is expected, where the embedded length to be selected

or designed is reduced again, in comparison to open sections.

• Including the modified design formulae in existing standards.

In the framework of these tests additional information about the load carryingbehaviour of these elements will be achieved using strain and deformationmeasurements. With this, a more detailed view about

• Failure mode

• Strain distribution inside and outside of the foundation

• Distribution of forces

• Crack pattern

will be possible.





3. Test programme

To cover a wide range of profile sizes and embedded lengths as well as varying d/tand b/t ratios the specimens listed in Table 3-1 and in Table 3-2 have been testedduring that research.

Hollow sectiondimensions

[mm]

Foundation

[m]

Embedded length

[mm]

Ø 219.1 x 6.30.80 x 1.00 x 1.07

0.80 x 1.00 x 1.17

320550

650

Ø 273.0 x 8.0 0.80 x 1.00 x 1.15400500

Ø 323.9 x 10.00.80 x 0.80 x 1.300.80 x 0.80 x 1.80

500650800

Ø 406.4 x 12.5 0.80 x 1.00 x 1.50700600

Table 3-1: Test specimens made of CHS

Hollow sectiondimensions

[mm]

Foundation

[m]

Embedded length

[mm]

100 x 100 x 6.30.60 x 0.80 x 1.000.50 x 0.50 x 1.00

200300400

200 x 200 x 8.00.80 x 1.00 x 1.050.70 x 0.70 x 1.00

350400500

260 x 260 x 11.0 0.80 x 1.00 x 1.20 400600

400 x 400 x 16.01.40 x 1.40 x 1.501.40 x 1.40 x 1.80

650800

Table 3-2: Test specimens made of RHS

Figure 3-1 shows the test set-up and the arrangement of the LVDT schematically.The performed positions of the strain gauges can be seen in Figure 3-2. All tests are

done in horizontal position. The load was introduced by jacks at the free ends of thesections. The foundation was fixed in the test rig. For all the tests the displacementbehaviour was recorded and the crack pattern was also marked on the foundation.





Figure 3-1: Test set-up

Figure 3-2: Positions of the strain gauges (schematically)





Figure 3-3: Layout of the reinforcement (schematically)

The embedded part of the hollow sections was filled with concrete only at a few testspecimens. All embedded parts of the other test specimen weren’t filled withconcrete. The reinforcement was chosen that the hollow sections are covered byloops. Figure 3-3 shows a sketch of the reinforcement layout. The concrete qualitywas C20/25 acc. to ENV 1992-1-1:1991 for all the tests. Due to economic reasonsthe ends of the hollow sections are open and not closed. The section was closed by

a timber section during the concreting.

The design of the foundation was made according to existing standards.

More information and some exemplary pictures are given in the attachments.





4. Test results

42 test specimens had been tested during the investigation. This resulted in 16ultimate load tests for circular hollow sections (CHS) and 26 tests for rectangular hollow sections (RHS).

In Table 4-1 the results for RHS are given. In this table all geometrical dimensions of the hollow sections, the embeddings and the embedding lengths (see Figure 4-1) aregiven. Together with this, the maximum loads Pmax and the resulting moments Mmax and stresses σ in the hollow sections are given. In addition, information concerningthe fabrication of the test specimens and the failure modes can be found in this table.It can be seen that in some cases the reinforcement was modified or concrete was

also filled into the hollow sections.

The same data are given for circular hollow sections, too. You can see them in Table4-2.

For all test specimens a load deflection curves have been plotted. An example isgiven in Fig. 4-2 for test specimen CHS 219.1 x 6.3 (No. 10). Fig. 4-3 shows thecracked foundation of this test at the end.

An example for the production and testing of an RHS specimen is given in the Attachments for specimen RHS 100 x 100 x 6.3 (specimen No. 9).

load 1

reaction

force

(support)

Concrete

f1

load 2

f2

load 1

reaction

force

(support)

Concrete

f1

load 2

f2

Figure 4-1: Schematic test set-up and denomination of embedding f1 and f2





T a b l e 4 . 1 :

T e s t r e s u l t s f o r r e c t a n g

u l a r h o l l o w

s e c t i o n s





T a b l e 4 . 2 :

T e s t r e s u l t s f o r c i r c u

l a r h o l l o w

s e c t i o n s





Figure 4-2: load deflection curves of test specimen CHS 219.1 x 6.3(specimen No.10)





Figure 4-3: Test specimen CHS219.1 x 6.3 (No. 10)after the test





Summarizing the test results according their sizes the following statements can begiven:

RHS 100x6.3

In the tests with this tube dimension only short fissures have occurred. In some teststhere occurred no fissures in the foundation. In these cases a complete plasticizationof the hollow section has occurred before a damage of the foundation took part. Evenwith the shortest embedding length (200 mm) the tubes are fixed in the foundation.

In particular tubes with short fissures no increase of the maximum load could befound. In the case of tubes with a concrete filling the ultimate load could be increasedcompared to hollow sections without concrete filling.

The reduction of the foundation dimensions had practically no bearing on the failure.

The crack propagation for all specimens was a little bigger and thus consequentlyinduced longer fissures. Nevertheless, the plastic deformation failure of the hollowsection ruled the ultimate load.

RHS 200x8

Yielding of the quadratic hollow section could be observed in all the samples here.Fissures have appeared in the foundation block. These fissures started from thequadratic hollow profile edge such as in case of RHS 100.

On the 50 cm embedding length side only very short fissures were observed. Tubedeformation and buckling of the compression chord were larger than on the 35 cmembedding length side.

There was no difference between the cracking load of a tube filled with concrete andthe cracking load of a tube that wasn’t filled with concrete. Both tubes had the samefixing length. In the case of the concrete filled tube no buckling of the tube occurred.

In the case of specimens with reduced foundation dimensions and reducedpercentage of reinforcement deep cracks have occurred on both sides of thefoundation.

In addition to that, a deformation of the hollow sections could be observed. Therewas only a slight buckling on the side with the reduced reinforcement. On theopposite side the upper chord buckled on the top side and on the flanges.

The maximum loads of the quadratic hollow sections were the same on both sides.The stronger reinforcement resulted however in a rigid fixed support, which inducedlarge final deformation of the hollow section.

RHS 260x11

Compared to the hollow sections described above only little plastic deformationsoccurred with these samples. The tubes were loose at the bearing point and the tubewas extracted (approximately 10 mm) in the case of foundations with an embedding

length of 40 cm. On the upper side of the profile the tube was pushed in the concrete.





Foundation cracking was very pronounced in all the specimens with thesedimensions. Furthermore, the samples with the shortest embedding length (40 cm)showed flattening and flaking along the reinforcement. Also in the samples that had aembedding length of 60 cm, the concrete flaked on the edges and in the transition

from top of the edge to foundation.

The concrete filling in the tube did not affect the ultimate load of the test specimensdue to the fact that the failure of these samples was caused by failure of theembedment and of the foundation and not by yielding of the hollow section.

RHS 400x16

Also with the attempts of this tubing dimension marks on top of the tubes at thetransition hollow section to foundation arose at the normal reinforced sides. Thiscould be determined at all examined embedding lengths. Furthermore one of these

pipes within the embedded length was coated. This pipe at the modified reinforcedside with a embedding length of 65 cm wasn’t able to resist the attacking loadcompletely. It was pulled out of the concrete foundation.

At all other embedding lengths of these pipes fissures in the concrete were onlydetermined. There hasn’t been any flaking at the foundation.

CHS 219.1x6.3

As expected, the tube yielding of the circular hollow section CHS 219.1x6.3 made of

S235JRH was higher than by other samples with the same dimensions. The higher yielding produced a strong buckling in that sample.

In the tests with concrete filled sections the concrete core inhibits tube buckling.

In the case of foundations with an embedding length of 55 cm the cracks in thefoundations were not significant. In the case of embedding lengths of 65 cm therewere no apparent fissures. On the other hand long and deep fissures until the border of the foundation occurred in the tests with embedding lengths equal to 32 cm. Pullout of the hollow section did not occur but buckling at an embedded length of 32 cm.

CHS 273x8

In nearly all cases using the circular hollow section Ro 273x8 the basic failure modewas yielding of the profile. Thus, tube buckling occurred on both embedding lengthsused for the tests.

In the case of concrete filled tubes, the buckling was constrained. However, in thecases of concrete filled specimens the cracks in the foundations occurred at first.

Fissures on the concrete foundations occurred both on the side with 40 cm fixinglengths and on the side with 55 cm fixing lengths. The samples with the shortestfixing length (40 cm) showed loosening and when the tube was not filled with

concrete the profile was extracted (ca. 6 mm).





CHS 323,9x10

Also with these attempts chipping off the foundation could always be determined on

the modified reinforced side. One of the tubes embedded in concrete on the modifiedreinforced side was still coated thereby. This tube could take up only very smallloads. It was pulled out of the foundation. That’s what we have expected. However,resulting from the selected experimental setup, thereby the attempt on the normalreinforced side could not load up to its actual maximum failure. At all normal reinforced side’s only fissures at the concrete surface were determined.No failure at the tubes could be determined. Also no material failure loads on thenormal reinforced sides are determined at all selected embedding lengths aspreviously mentioned. This is because of the selected experimental setup.

CHS 406.4x12.5

The failure mode with these tubing dimensions was with priority concrete failure.Flakings could be determined on the modified reinforced side. Only fissures could bedetermined at the normal reinforced side. At the concreted pipes no buckling or other failure modes could be determined.





5. Evaluation

Additional to the tests, which have been carried out, the necessary fixing lengthsaccording to Koch [2] are calculated. Koch’s evaluation applied on I-profiles, whichare fixed in reinforced concrete.

The reference value there is the “elastic length” of the steel profiles in the bearingpoint. The determination of the elastic length is simplified as follows:

bC

I E L S S

E ⋅

⋅⋅=

4(1)

whereb

E C B= ,

7

S

B

E E = ⇒ 45,2 S E I L =

ES Young's modulus of steelEB Young's modulus of concreteIS Moment of inertia of steel profile

b Width of the section

C Bedding modulus in half space

If 3,0≤ pl

D

V

V (2)

hence

4

h

b L

M

M f E

pl

D⋅⋅≥α (3)

E E L f L α ≤≤5,1 (4)

If 3,0≥ pl

D

V

V (5)

hence

E L f ⋅≥α (6)

where 3=α for uncoated profiles in bearing point

4=α for coated profiles in bearing point

Another condition results from the concrete pipe pressing’s limitation on the leadingedge of the fixed support:

d

d

V

M p p p f ⋅++⋅≥ 33,543,533,2 2 (7)

where´b

V p

R

d

⋅= β

(8)





For open sections the value of b` will be calculated with b´ = b + 0.5*h. In this the b isthe width of the flange and h is the height of the open section. On the save side wedecide to calculate b´ for RHS with the width of the profile and for the CHS with thediameter of the profile.

Figure 5-1: Calculation for b´ for that project

The calculated embedding length according to Koch [2], the embedding lengthobtained by tests and the rates Mmax/Mpl and tested ratios (embedding length/tubedimensions) are listed in the following table. The red marked fields show thereby nogood conformity with the calculated embedding length according to Koch [2]. Thatmeans this embedment length is shorter than the calculated minimal embedmentlength. Yellow marked fields indicate a small deviation from the calculatedembedding length according to Koch [2]. Green marked fields indicate a good to verygood conformity to the clamping calculated embedding length according to Koch [2].

The results from table 5.1 are pictured in diagram 5.1 for a better understanding of the results from table 5.1. On the abscissa the embedding length relative to the

elastic bedding is shown. On the coordinate y is shown the relative from Mmax to Mpl.This diagram includes the column determ. f . This embedded length f is the minimumvalue of the equations 3, 4 and 7 in comparison to the embedded length in the tests.

The black lines in diagram 5.1 shows the limit of the relative from embedding lengthto the “elastic length” for α = 3 for I-profile sections without a coating in theembedding length and α = 4 for I-profiles sections with a coating in the embeddinglength according to Koch.





T a b l e 5 . 1 :

C a l c u l a t e d e m b e d d i n g l e n g t h a c c o r d i n g t o K o c h

i n a c c o r d a n c e w i t h t h e e m b

e d d e d t e s t l e n g t h









0 , 4 5

0 , 5 5

0 , 6 5

0 , 7 5

0 , 8 5

0 , 9 5

1 , 0 5

1 , 1 5

1 , 2 5

1 , 3 5

0 , 5

0

1 , 0

0

1 , 5

0

2

, 0 0

2 , 5

0

3 , 0

0

3 , 5

0

4 , 0

0

4 , 5

0

5 , 0

0

5 , 5

0

6 , 0

0

f / L

m a x M / M P l

1 0 0 x 1

0 0 x 6 , 3

2 0 0 x 2

0 0 x 8

2 6 0 x 2

6 0 x 1 1

Ø 2

1 9

, 1 x 6 , 3

Ø 2

7 3

, 0 x 8

4 0 0 x 4

0 0 x 1 6

Ø 4

0 6

, 4 x 1 2 , 5

Ø 3

2 3

, 9 x 1 0

4 0 0 x 4

0 0 x 1 6

1 c

1 d

1 b

1 a

D i a g r a m

m 5 . 1 :

T e s t r e s u l t s f o r t h e

e m b e d d i n g l e n g t h

α = 3

α

= 4





Notes to theDiagramm

1a modified reinforcement + coating→ destroying of the foundation + pull out of the hollow section

1bno increase of the load necessary due to the early

destroying of test 1a (just little fissures on testspecimen at the side of 1b)

1c to little embedding length and reducedreinforcement→ destroying of the foundation

1dno increase of the load necessary due to the early

destroying of test 1c (just little fissures on test

specimen at the side of 1d)





6. Summary

All of the specimens (16 RHS specimen and 26 CHS specimen) have beenconcreted and tested. The different measurements of the specimen can see in thefollowing table.

All test datas are recorded, documented, tabulated and evaluated. Thedocumentation of the test datas is available as Appendix to this report.

H o l l o w s e c t i o n F o u n d a t i o n E m b e d d in g

d i m e n s i o n s s t e e l g r a d e d i m e n s i o n s l e n g t h[ m m ] [ m ] [ m m ]

2 0 0

3 0 0

4 0 0

3 0 04 0 0

3 5 05 0 0

4 0 04 0 0

4 0 06 0 0

4 0 06 0 0

8 0 0

8 0 0

6 5 0

6 5 0

3 2 0

5 5 0

6 5 0

4 0 05 5 0

6 5 05 0 0

8 0 08 0 0

7 0 0

6 0 0

1 . 4 0 x 1 . 4 0 x 1 . 5 0

4 0 0 x 4 0 0 x 1 6

0 . 8 0 x 1 . 0 0 x 1 . 2 0

0 . 8 0 x 1 . 0 0 x 1 . 2 0

2 6 0 x 2 6 0 x 1 1 S 3 5 5 J 2 H

1 0 0 x 1 0 0 x 6 . 3 S 3 5 5 J 2 H

2 0 0 x 2 0 0 x 8 . 0 S 3 5 5 J 2 H

0 . 8 0 x 1 . 0 0 x 1 . 5 0

0 . 8 0 x 1 . 0 0 x 1 . 3 0

0 . 8 0 x 1 . 0 0 x 1 . 8 0

0 . 6 0 x 0 . 8 0 x 1 . 0 0

0 . 5 0 x 0 . 5 0 x 1 . 0 0

0 . 8 0 x 1 . 0 0 x 1 . 0 5

1 . 4 0 x 1 . 4 0 x 1 . 8 0

0 . 8 0 x 1 . 0 0 x 1 . 1 5

0 . 8 0 x 1 . 0 0 x 1 . 0 70 . 8 0 x 1 . 0 0 x 1 . 1 7

0 . 7 0 x 0 . 7 0 x 1 . 0 0

S 3 5 5 J R H

∅ 2 7 3 . 0 x 8 . 0

∅ 4 0 6 . 4 x 1 2 . 5 S 3 5 5 J 2 H

S 3 5 5 J 2 H

∅ 3 2 3 . 9 x 1 0 . 0 S 3 5 5 J 2 H

S 2 3 5 J 2 H∅ 2 1 9 . 1 x 6 . 3





In a first evaluation the formula of Koch [2] for open sections was used. The resultsfound were reasonable and leads to the impression that the reduced embeddinglength for open sections calculated with this formula can also be used for hollowsections, too.

Nevertheless further investigations should be done in order to examine and correctthe approach of b'. This factor considers the concrete stress at the junction hollowsection to foundation at the embedding. The chosen b’ in this project seems to be tooconservative for hollow and circular sections. But the definition of b´ should beinvestigated in another research project.





7. Literature

[1] ECSC project 7210-SA/511“Steel Columns Embedded in Concrete Foundations”, Final Report 1992

[2] Koch E.:Zum Tragverhalten von in Stahlbeton eingespannten Stahlprofilen, Von der Fakultät für Bauingenieur- und Vermessungswesen angenommeneDissertation, Universität Karlsruhe, 2000

[3] Bergmann, R.:"Verbundstützen – Bemessung", Vortrag beim Seminar Verbundbau 2 an der FH München am 26./27. November 1998

[4] Mang, F., Bucak, Ö.:Columns of RHS Clamped in Concrete Foundation, CIDECT Final ReportProject 2J, Universität Karlsruhe, 1978

[5] Puthli, R.:Hohlprofilkonstruktionen in Stahl nach DIN V ENV 1993(EC3) und DIN 18800(11.90), ca. 230 Seiten, Werner Verlag GmbH & Co., KG, Düsseldorf, 1997

Standards and design guides

EN 10025Hot rolled products of non-alloy structural steels; Technical delivery conditions(includes amendment A1:1993); German Version EN 10025:1990

DIN 1045Beton und Stahlbeton; Bemessung und Ausführung, 2001

V ENV 1992-1-1Eurocode 2: Design of concrete structurs - Part 1: General rules and rules for buildings; German version ENV 1992-1-1:1991

V ENV 1994-1-1Eurocode 4: Design of composite steel and concrete structures; part 1-1: Generalrules and rules for buildings; German version ENV 1994-1-1:1992

EN 10210Hot finished structural hollow sections of non-alloy and fine grain structural steels- Part 1: Technical delivery requirements; German version EN 10210-1:1994Part 2: Tolerances, dimensions and sectional properties; German version EN10210-2:1997



Hollow sections columns embedded in concrete Attachment 1


E x a m p l e f o r t h e c a l c u l a t i o n o f t h e r e i n f o r c e m e n t





Reinforcement cage for RHS 100 x 100 x 6.3





Concreted specimen RHS 100 x 100 x 6.3 (in the formwork)

Test specimen RHS 100 x 100 x 6.3 (specimen No. 9) during the test






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