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Journal of Constructional Steel Research . -. .. . .

An experimental study on elliptical concrete filled columns under axial compression N. Jamaluddin a. D. Lam b.*, XH. Dai '.I. Ye " Fccvity 01 Civil ondEnvimnmenm1 Engineoing, Tun Hussein Onn Onhrmily olMolqvria. Malaysia

School af .Engineerin& Dwr@ md Trdmology. univmlty oJBr@furd, Bradford, LIK ' Dwomnunr @Enginnetin& Lanrano Univmity, lonrmter. Uh!

A R T I C L E I N F O

Article history: Received 15 FcbrualyZO13 Acccprrd 3 Apdl2013 Avallabie imline 4 May 2013

Ke,w'or.d.~: Conmete filled tubc mlumn Uliplical rstion Slenderneri mtio stltTnes3 Slrenafh Self-almpactha concrctc

A B S T R A C T

This Daller "resents the exoerimental results and abservation of eUiuticd collcrete filled tube (UT) columns . . . ruhjectr.d ro dxlll curnprrr5ivr load. A ls,ral of tlvmN5u ?lllptlcdl ibT spe~lnlelll lncludlng !nth INZ in0 slrnder rtlnlpmltc columns .!re rzrlea lo lnlltlre lo inu?ille,al+ Ihe Jxlal ~nnlpresrive lwhdvlnur V.uloll5 column lengths, secTiona1 sizes and iniill concrete strength are rlsed to quantify the influence of tnemher geometry .id canrtlruent material propenies on the smctwal hehaviour of elliptical LFI columns. As there i s no desim guidance currentlv available in anv Code of I'ractice. this studv ~ravldes a review of the - - . . rurrznt deslgn rules for concrete filleo clrcubl hollow rerooll5 in tt.mrnde 4 ltC4). Ntw ?qclanonP hlwd on the tbru~oie 4 pt?v~sLns ~ O T ~ O ~ C I P I P hlled orcul~r llallow wnlanr were proposed anu tnsrcl to pwdcl the capacities of elliptical CFI columns.

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1. Intmduction

The composite CFT column i s well renowned for i t s strenmh. zood ductility an2 energy absorption capacity in earthquake. type of columiis has aim bee11 proven to be economical due to rapid coo- struction, as the external steel tubes may act as permanent and inte- gral lormworks which lead to reduction in labour costs, materials and con~t r~c t ion time.The orielntation of steel and concrete materials in a CFI column is also beneficial in terms of enhancinz the columns'

Extensive ipsearches have been carried oul on sho11 EHS columns 13-IOj. These included experimenls on typical steel hollow sections with different wall thicknesses, normal to high concrete infill strength, various loading caes including loadingcompositely, loading on concrete cove only and loading through steel section only. From these studies, the elect of the strength of concrete infill and wall thickness of steel hollow sections on the structural bebaviour has been highlighted. Furthermore the comparison and analyses showed that the effecl of steel tube wall thickness was esveciallv sensitive

stityness and bending strength, as the steel tube has ;greater elastic in composite columns with nonnal strength concreke as the capacily modulus owinp. to the [act that the element i s situated furthest from of the columns depends on the elfen of confinement that i s provided - the centroid ofthe cross section [I]. by the steel tube. when the concrete strength increases, the influence

Elliptical hollow section (EHS) is a relalively new cross-section that of wall thickness becomes less significant. h a been introduced in the UK by CORUS. I t offers an additional choice Researches on the ultimate strengths of elliptical carried out by to structural desienen for its structural eficiencv and lo the architects the authors with the souare and circular CFT colu~nns carried out bv lor its appearance. This section may provide greater bending capacity Lam and Williams [4],'and Ciakoumelis and Lam 11 11 showed that commred to thecircular hollow section with identical areaand weinht the circular CFT columns were better than ellivtical CFI columns due to its strong and weakaxis directions (21. However, currently there is limited undentandineconcer~line the structural behaviour of ellioti- - - cal CFT columns. Presently, the design lor the compressive members with elliptical section shape h a not been covered by any Code of Practice, Specificatio~i or Standard. However due to the incleases in the use of such hollow section shape, broad study has been conducted to pmvide all insight to the behaviour of this form of sll'uctules.

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due to the circular hollow section providing stronger confinement to the concrete core, higher axial load may be achieved by elliptical CFT columns as compared to square and rectangular CFT columns. This attributes to the curved section shape of the elliptical tube that offers more circumferential tension which in turn provides a higher confinement to the collcrete core.

Funher investigation on elliptical CFTcolum~is carried out by Yang et al. 1121 indicated that the wall thickness oithe lube did affect the axial compressive behaviour of this type of composite columns. In- clined shear failure on the concl-ete infill was observed in composite columns with smaller wail thickness olthe steel sections due to less

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