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CONTENTS
Volume 4, Number 3, June 2004
 

Abstract
A mechanics model is developed in this paper for concrete-filled steel CHS (circular hollow section) beam-columns. A unified theory is described where a confinement factor (ξ) is introduced to describe the composite action between the steel tube and the filled concrete. The predicted load versus deformation relationship is in good agreement with test results. The theoretical model was used to investigate the influence of important parameters that determine the ultimate strength of concrete-filled steel CHS beam-columns. The parametric and experimental studies provide information for the development of formulas for the calculation of the ultimate strength of the composite beam-columns. Comparisons are made with predicted beam-columns strengths using the existing codes, such as LRFD-AISC-1999, AIJ-1997, BS5400-1979 and EC4-1994.

Key Words
composite columns; beam-columns; composite actions; constraining factor; concrete; design; hollow sections; columns; member capacity.

Address
Lin-Hai Han and Guo-Huang Yao;rnCollege of Civil Engineering and Architecture, Fuzhou University, Gongye Road 523, Fuzhou, Fujian, Province, 350002, P. R. ChinarnXiao-Ling Zhao; rnDepartment of Civil Engineering, Monash University, Clayton, VIC 3168, Australia

Abstract
The commonly used seismic design procedures to evaluate the maximum effect of both horizontal components of earthquakes, namely, the Square Root of the Sum of the Squares (SRSS) and the 30-percent (30%) combination rules, are re-evaluated. The maximum seismic responses of four threedimensional moment resisting steel frames, in terms of the total base shear and the axial loads at interior, lateral and corner columns, are estimated as realistically as possible by simultaneously applying both horizontal components. Then, the abovementioned combination rules and others are evaluated. The numerical study indicates that both, the SRSS rule and the 30% combination method, may underestimate the combined effect. It is observed that the underestimation is more for the SRSS than for the 30% rule. In addition, the underestimation is more for inelastic analysis than for elastic analysis. The underestimation cannot be correlated with the height of the frames or the predominant period of the earthquakes. A basic probabilistic study is performed in order to estimate the accuracy of the 30% rule in the evaluation of the combined effect. Based on the results obtained in this study, it is concluded that the design requirements for the combined effect of the horizontal components, as outlined in some code-specified seismic design procedures, need to be modified. New combination ways are suggested.

Key Words
seismic inelastic response; three-dimensional moment resisting steel frames; horizontal components; time history analysis; multi degree of freedom systems.

Address
Alfredo Reyes-Salazar, Jose A. Juarez-Duarte, Arturo Lopez-Barraza and Juan I. Velazquez-Dimas; Facultad de Ingenieria, Universidad Autonoma de Sinaloa, Ciudad Universitaria, Culiacan, Sinaloa, CP 80040, Mexico

Abstract
This paper presents a study on the structural behaviour of modular steel scaffolds through both experimental and numerical investigations. Three one-storey and three two-storey modular steel scaffolds were built and tested to failure in order to examine the structural behaviour of typical modular steel scaffolds. Details of the tests and their test results were presented in this paper. Moreover, an advanced non-linear analysis method was employed to evaluate the load carrying capacities of these scaffolds under differentrnsupport conditions. Comparisons between the experimental and the numerical results on the structural behaviour of these modular steel scaffolds were also presented. Moreover, the restraining effects of external supports in practical situations were also studied through finite element methods. The predicted load carrying capacities and deformations at failure of these models under partially restrained conditions were found to be close to the experimental results. A codified design method for column buckling with modified slenderness ratios was adopted for practical design of modular steel scaffolds.

Key Words
modular steel scaffolds; structural instability; partially restrained supports; modified slenderness ratios; column buckling design.

Address
W.K. Yu; Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China

Abstract
This paper presents a moment-curvature method that accounts for the strength deterioration of steel at elevated temperature in estimating the response of steel beams exposed to fire. A modification to the EC4 method is proposed for a better estimation of the temperature distribution in the steel beam supporting a concrete slab. The accuracy of the proposed method is verified by comparing the results with established test results and the nonlinear finite element analysis results. The beam failure criterion based on a maximum strain of 0.02 is proposed to assess the limiting temperature as compared to the traditional criteria that rely on deflection limit or deflection rate. Extensive studies carried out on steel beams with various span lengths, load ratios, beam sizes and loading types show that the proposed failure criterion gives consistent results when compared to nonlinear finite element results.

Key Words
elevated temperature; fire safety design; limiting temperature; moment-curvature method; steel beam; limit state design.

Address
H.X. Yu and J.Y. Richard Liew; Department of Civil Engineering, National University of Singapore, Blk E1A, 1 Engineering Drive 2, Singapore 117576

Abstract
Comparison of behaviour of shear connections by means of shear-connection strips (perfobond and comb-shaped strips) and headed studs under static and repeated loading, possible failure modes of concrete dowels and ways of the quantitative differentiation of some failure modes are described in the paper. The article presents a review of knowledge resulting from the analysis of shear-connection effects based on tests of perfobond and comb-shaped strips carried out in the laboratories of the Faculty of Civil Engineering of the Technical University of Kosice (TU of Kosice) in Slovakia and their comparison with results obtained by other authors.rn

Key Words
composite steel and concrete structures; perfobond strip; comb-shaped strip; failure modes; concrete dowel; push-out test; repeated load.

Address
Marian Rovnak and Antonia Duricova;rnTechnical University of Kosice, Faculty of Civil Engineering, Vysokoskolska 4,rnSK-042 00 Kosice, Slovakia


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