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Volume 14, Number 3, March 2013
 

Abstract
Current design standards do not provide adequate guidelines for the fire design of cold-formed steel compression members subject to flexural-torsional buckling. Eurocode 3 Part 1.2 (2005) recommends the same fire design guidelines for both hot-rolled and cold-formed steel compression members subject to flexural-torsional buckling although considerable behavioural differences exist between cold-formed and hot-rolled steel members. Past research has recommended the use of ambient temperature cold-formed steel design rules for the fire design of cold-formed steel compression members provided appropriately reduced mechanical properties are used at elevated temperatures. To assess the accuracy of flexural-torsional buckling design rules in both ambient temperature cold-formed steel design and fire design standards, an experimental study of slender cold-formed steel compression members was undertaken at both ambient and elevated temperatures. This paper presents the details of this experimental study, its results, and their comparison with the predictions from the current design rules. It was found that the current ambient temperature design rules are conservative while the fire design rules are overly conservative. Suitable recommendations have been made in relation to the currently available design rules for flexural-torsional buckling including methods of improvement. Most importantly, this paper has addressed the lack of experimental results for slender cold-formed steel columns at elevated temperatures.

Key Words
cold-formed steel columns; flexural-torsional buckling; column tests; elevated temperatures; fire design

Address
Faculty of Built Environment and Engineering, Queensland University of Technology, Brisbane, Australia

Abstract
Corrosion is important reason for the deterioration of the bond between reinforcing steel and the surrounding concrete. Corrosion of the steel mainly depends on its microstructure. Smooth S220, ribbed S420 and S500 grade reinforcing steels were used in the experiments. Samples were subjected to accelerated corrosion. Pullout tests were carried out to evaluate the effects of corrosion on bond strength of the specimens. S500 grade steel which has tempered martensite microstructure showed lower corrosion rate in concrete than S220 and S420 steels which have ferrite+perlite microstructure. S500 grade steel showed highest bond strength among the other steel grades in concrete. Bond strength between reinforcing steel and concrete increased with increase in the strength of steel and concrete. It also depends on whether reinforcing bar is ribbed or not.

Key Words
Bond strength; corrosion; tempcore steel; accelerated corrosion; concrete

Address
G. Kurklu : Faculty of Engineering(Civil), Kocatepe University, Afyonkarahisar, Turkey
M.S. Başpinar : Faculty of Technology (Metallurgy and Material Sci.), Kocatepe University, Afyonkarahisar, Turkey
A. Ergun : Technical Education Faculty (Construction Sci.Education Dept.), Kocatepe University, Afyonkarahisar, Turkey

Abstract
Distortional and local buckling are important factors that influences the bearing capacity of steel-concrete composite box-beam. Through theoretical analysis of distortional buckling forms, a stability analysis calculation model of composite box beam considering rotation of steel beam top flange is presented. The critical bending moment calculation formula of distortional buckling is established. In addition, mechanical behaviors of a steel beam web in the negative moment zone subjected separately to bending stress, shear stress and combined stress are investigated. Elastic buckling factors of steel web under different stress conditions are calculated. On the basis of local buckling analysis results, a limiting value for height-to thickness ratio of a steel web in the elastic stage is proposed. Numerical examples are presented to verify the proposed models.

Key Words
steel-concrete composite box-beam; distortional buckling; local buckling; negative moment

Address
Lizhong Jiang, Linlin Sun : Department of Civil Engineering and Architecture, Central South University, Changsha, 410075, China
Jingjing Qi : School of Civil Engineering, Hunan University of Science and Technology, Xiangtan, 411201, China
Andrew Scanlon 3Department of Civil and Environmental Engineering : Penn State University, PA, 16802, USA

Abstract
This paper presents the behavior and design of axially loaded normal and steel fiber reinforced concrete in-filled steel tube (SFRCFT) columns, to examine the contribution of steel fibers on the compressive strength of the composite columns. Non-linear finite element analysis model (FEA) using ANSYS software has been developed and used in the analysis. The confinement effect provided by the steel tube is considered in the analysis. Comparisons of the analytical model results, along with other available experimental outputs from literature have been done to verify the structural model. The compressive strength and stiffness of SFRC composite columns were discussed, and the interpretation of the FEA model results has indicated that, the use of SFRC as infill material has a considerable effect on the strength and stiffness of the composite column. The analytical model results were compared with the existing design methods of composite columns – (EC4, AISC/LRFD and the Egyptian code of Practice for Steel Construction, ECPSC/LRFD). The comparison indicated that, the results of the FEA model were evaluated to an acceptable limit of accuracy. The code design equations were modified to introduce the steel fiber effect and compared with the results of the FEA model for verification.

Key Words
Composite structures; finite element; steel fibers; reinforced concrete; tubular columns; confined concrete

Address
Civil Engineering Department, Faculty of Engineering, Benha University (Shoubra district) Cairo, Egypt

Abstract
This paper deals with the applicability of a new extended layerwise optimization method for thermal buckling load optimization of laminated composite plates. The design objective is the maximization of the critical thermal buckling of the laminated plates. The fibre orientations in the layers are considered as design variables. The first order shear deformation theory (FSDT) is used for the finite element solution of the laminates. Finally, the numerical analysis is carried out to show the applicability of extended layerwise optimization algorithm of laminated plates for different parameters such as plate aspect ratios and boundary conditions.

Key Words
laminated plates; thermal buckling load; finite element solution; extended layerwise optimization method; optimization

Address
Karadeniz Technical University, Faculty of Technology, Department of Civil Engineering, Trabzon, Turkey

Abstract
In this paper, a simplified approach based on critical temperature for fire resistance design of steel-concrete composite beams is proposed. The method for determining the critical temperature and fire protection of the composite beams is developed on the basis of load-bearing limit state method employed in current Chinese Technical Code for Fire safety of Steel Structure in Buildings. Parameters affecting the critical temperature of the composite beams are analysed. The results show that at a definite load level, section shape of steel beams, material properties, effective width of concrete slab and concrete property model have little influence on the critical temperature of composite beams. However, the fire duration and depth of concrete slab have significant influence on the critical temperature. The critical temperatures for commonly used composite beams, at various depth of concrete and fire duration, are given to provide a reference for engineers. The validity of the practical approach for predicting the critical temperature of the composite beams is conducted by comparing the prediction of a composite beam with the results from some fire design codes and full scale fire resistance tests on the composite beam.

Key Words
steel-concrete composite beam; fire-resistance design; load level; critical temperature

Address
Guo-Qiang Li : College of Civil Engineering, Tongji University, Shanghai, 200092, P.R. China
State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092,
P.R. China
Wei-Yong Wang : College of Civil Engineering, Chongqing University, Chongqing, 400045, P.R. China


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