| doi:10.3850/978-981-08-6218-3_CC-Fr009 |
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A STUDY ON LOAD CARRYING CAPACITY OF CIRCULAR CFTS USING SIX INTERNATIONAL DESIGN METHODS
H. Raghuvanshia and P. K. Guptab
Department of Civil Engineering, Indian Institute of Technology, Roorkee, Uttarakhand, India.
aharsragh@gmail.com
bpkgupfce@iitr.ernet.in
EXTENDED ABSTRACT
Composite forms of constructions provide better utilization of the materials at hand as they make use of the desired qualities of the constituent materials. Steel concrete composite construction is the earliest development in the era of composite construction engineering and yet there exists a need to carry out further research in this field, to get the best optimisation of material utilization for structural purposes. Concrete filled tubes (CFTs) are one of the steel concrete composite which are gaining prominence worldwide due to their inherent advantages. At present, there are quite a few design methods available internationally for the design of CFTs. Present study focuses on design of circular CFTs using six internationally recommended design methods and finally compares the results on the basis of ultimate load carrying capacity predictions by the individual methods under consideration. Design methods on the basis of following codes of practice have been considered for the purpose of this study :-
(a) EN 1994-1-1(Eurocode 4).
(b) AISC LRFD(Load and resistance method used by American Institute of Steel Constructions).
(c) ACI 318(Code of Practice of American Concrete Institute).
(d) NBR 8800(Brazilian Code of Practice).
(e) CAN/CSA- S16.1 M 94(Canadian Code of Practice).
(f) Egyptian Code of Practice.
As part of the study ‘Microsoft Excel’ based design sheets were prepared for automated design results. Based on these sheets a ‘comparison sheet’ was developed taking the prediction of ultimate load carrying capacity and design load carrying capacity as the comparison parameters. Some available experimental results were then compared with these theoretical results. These experiments were carried out at the institute as a part of an earlier study on CFTs. Based on the comparison of theoretical and experimental results following observations were made :-
(a) ANSI/AISC LRFD gives the best prediction of ultimate compressive strength. However, if material safety factors are neglected then NBR 8800 gives the best estimation and EC4 gives the second best estimation of ultimate compressive strength. NBR 8800 follows the similar method as that of EC4 and the difference lies in the empirical formula used to predict the concrete secant modulus for which NBR 8800 gives higher value than EC4.
(b) Both EC4 and NBR 8800 give a very non conservative design capacity of the section and thus the sections so designed are the most economical when compared to other codes under reference.
(c) Egyptian Code of practice gives the most conservative values, both, for the estimation of ultimate load carrying capacity as well as the design load carrying capacity, hence the design by this code is least economical when compared to all other codes.
(d) Canadian code considers only the design values which are relatively non conservative.
(e) ACI 318 uses higher safety factors as compared to AISC LRFD.
Based on this study it was found that NBR 8800 and EC4 give the best estimation of ultimate capacity of a circular CFT. AISC LRFD method gives the second best estimation while Egyptian method gives the most conservative and non economical results.