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Behaviour of reinforced and concrete-encased composite columns subjected to biaxial bending and axial load

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Behaviour of reinforced and concrete-encased composite columnssubjected to biaxial bending and axial load

Text of Behaviour of reinforced and concrete-encased composite columns subjected to biaxial bending and...

  • Building and Environment 43

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    presented. In the proposed procedure, nonlinear stressstrain relations are assumed for concrete, reinforcing steel and structural steel

    materials. The compression zone of the concrete section and the entire section of the structural steel are divided into adequate number of

    structures, such as buildings and bridges. A composite

    stress block for the concrete compression zone in the

    experimental results for L-shaped and channel shaped

    load using Whitneys stress block [9] in the compressionzone of the concrete section. Rodriguez and Ochoa [10] andFatis [11] have suggested numerical methods for the

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    Corresponding author. Tel.: +90 322 338 6762; fax: +90 322 338 6702.

    computation of the failure surface for reinforced concretesections of arbitrary shape. Hong [12] has proposed asimple approach for estimating the strength of slender

    0360-1323/$ - see front matter r 2007 Elsevier Ltd. All rights reserved.

    doi:10.1016/j.buildenv.2007.02.010

    E-mail addresses: [email protected] (C. Dundar), [email protected]

    (S. Tokgoz), [email protected] (A.K. Tanrikulu), [email protected]

    (T. Baran).column is a combination of concrete, structural steel andreinforcing steel to provide an adequate load carryingcapacity of the member. Thus, such composite memberscan provide rigidity, usable oor areas and cost economyfor mid-to-high buildings. Many experimental and analy-tical studies have been carried out on reinforced andcomposite members in the past years. Furlong [1] hascarried out analytical and experimental studies on re-inforced concrete columns using well-known rectangular

    reinforced concrete sections. Dundar [5] has studiedreinforced concrete box sections under biaxial bendingand axial load. Rangan [6] has presented a method tocalculate the strength of reinforced concrete slendercolumns including creep deection due to sustained loadas an additional eccentricity and the method comparedwith ACI 318-Building Code Method [7]. Dundar andSahin [8] have researched arbitrarily shaped reinforcedconcrete sections subjected to biaxial bending and axialthe Moment Magnication Method. The proposed procedure was compared with test results of 12 square and three L-shaped reinforced

    concrete columns subjected to short-term axial load and biaxial bending, and also some experimental results available in the literature for

    composite columns compared with the theoretical results obtained by the proposed procedure and a good degree of accuracy was

    obtained.

    r 2007 Elsevier Ltd. All rights reserved.

    Keywords: Reinforced concrete column; Composite column; Biaxial loading; Ultimate strength; Stressstrain models

    1. Introduction

    Reinforced and concrete-encased composite columns ofarbitrarily shaped cross section subjected to biaxialbending and axial load are commonly used in many

    analysis. Brondum-Nielsen [2] has proposed a method ofcalculating the ultimate strength capacity of crackedpolygonal concrete sections using rectangular stress blockin the concrete compression zone of the section underbiaxial bending. Hsu [3,4] has presented theoretical andsegments in order to use various stressstrain models for the analysis. The slenderness effect of the member is taken into account by usingBehaviour of reinforced and consubjected to biaxial b

    Cengiz Dundar, Serkan Tokgoz

    Civil Engineering Department, Cuku

    Received 3 February 2006; received in revised

    Abstract

    An experimental investigation of the behaviour of reinforced co

    and slender reinforced and composite columns of arbitrarily sh(2008) 11091120

    ete-encased composite columnsding and axial load

    . Kamil Tanrikulu, Tarik Baran

    a University, 01330 Adana, Turkey

    26 January 2007; accepted 2 February 2007

    te columns and a theoretical procedure for analysis of both short

    d cross section subjected to biaxial bending and axial load are

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  • ARTICLE IN PRESSEnvreinforced concrete columns with arbitrarily shaped crosssection using nonlinear stressstrain relationship for thematerials. Saatcioglu and Razvi [13] have presented anexperimental research to investigate the behaviour of highstrength concrete columns conned by rectilinear reinfor-cement under concentric compression. Furlong et al. [14]have examined several design procedures for ultimatestrength analysis of reinforced concrete columns andcompared with many short and slender experimentalcolumns under short-term axial load and biaxial bending.Morino et al. [15] have presented a series of experimentalresults on short and slender square composite columns.Roik and Bergmann [16] have proposed a simplied designmethod based on the strength interaction curve andreported test results for short and slender compositecolumns with unsymmetrical square and rectangularshaped cross sections. Virdi and Dowling [17] havepresented a numerical method and test results for squarecomposite columns to predict the ultimate strengthcapacity of the composite column members under biaxialbending and axial load. Mirza [18] has examined the effectsof variables, such as the connement effect, the ratio ofstructural steel to gross area, the compressive strength ofconcrete, the yield strength of steel and the slendernessratio, on the ultimate strength of composite columns.Mirza and Skrabek [19] have carried out a statisticalanalysis on the variability of ultimate strength capacity ofslender composite beam-columns. Munoz [20] and Munozand Hsu [21,22] have presented an experimental and atheoretical study based on the nite differences method,including connement effect for the concrete, on squareand rectangular cross sections of short and slendercomposite columns under biaxial load. Weng and Yen[23] have investigated the differences between the ACI [7]and AISC [24] approaches for the design of concrete-encased composite columns. Lachance [25], Chen et al. [26]and Sfakianakis [27] have proposed a numerical analysismethod for short composite columns of arbitrarily shapedcross section.Connement provided by lateral ties increases the

    ultimate strength capacity and ductility of reinforcedconcrete columns under combined biaxial bending andaxial load. Strength and ductility gain in concrete areobtained by many connement parameters e.g., thecompressive strength of concrete, longitudinal reinforce-ment, type and the yield strength of lateral ties, tiespacing, etc. Because of such parameters, determinationof mechanical behaviour of conned concrete is not as easyas unconned concrete. Some researchers for instance,Kent and Park [28], Sheikh and Uzumeri [29], Saatciogluand Razvi [30], Chung et al. [31] have presented astressstrain relationship to describe the conned concretebehaviour.The main objective of this paper is to present an iterative

    computing procedure for the rapid design and ultimate

    C. Dundar et al. / Building and1110strength analysis of arbitrarily shaped both short andslender reinforced, and concrete-encased composite mem-bers having arbitrarily located reinforcing steel bars andstructural steel elements subjected to biaxial bending andaxial load. For this aim a computer program has beendeveloped which considers various conned or unconnedconcrete stressstrain models for the concrete compressionzone for both short and slender reinforced and compositecolumns. Thus, results of the ultimate strength analysis,with various concrete models, can be compared with eachother.In the experimental part of the study, 12 square and

    three L-shaped short and slender reinforced concretecolumns were tested to determine the ultimate strengthcapacity, load-deection behaviour, load-axial strain be-haviour and connement effect of column members. Thetest results were compared with the theoretical resultsobtained by the developed computer program which usesvarious stressstrain models for the conned concrete orunconned concrete in the compression zone of themember.Finally, the theoretical results obtained using the

    proposed procedure were also compared with the testresults available in the literature for short and slendercomposite columns.

    2. Experimental program

    An experimental investigation of the behaviour ofreinforced concrete columns under short-term axial loadand biaxial bending is presented. The primary objective ofthis investigation was to examine the ultimate strengthcapacity and load-deection behaviour of short and slenderreinforced concrete columns and to compare the test resultsof ultimate strength capacities of specimens with the resultsobtained by the proposed theoretical procedure usingvarious stressstrain models for the materials. For thisreason, reinforced concrete specimens were designed withdifferent length, dimension and cross section with differentdiameter and arrangement of longitudinal and lateralreinforcements.

    2.1. Test specimens

    The experimental program includes 15 reinforced con-crete columns. Five specimens are short square tiedcolumns (C1C5), seven specimens are slender square tiedcolumns (C11C14, C21C23) and the other three areL-shaped section slender tied columns (LC1LC3). Thecross section details and dimensions of each specimen areshown in Fig. 1.The reinforced concrete column specimens were cast

    horizontally inside a formwork in Structural Laboratory atCukurova University, Adana. Maximum 20mm diameterlocal aggregate and Normal Portland Cement were used inall concrete batches. Three standard cylinder specimens(150mm in diameter by 300mm long) were cast from each

    ironment 43 (2008) 11091120column specimen concrete mix and cured under the samecondition as the column specimen in the Structural

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    5) C14

    6 mm

    17.5

    (C21