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CONTENTS
Volume 14, Number 2, February 2013
 

Abstract
Flexural behavior of thin walled steel-concrete composite sections as cross sections for beams is investigated by conducting an experimental study supported by applicable analytical predictions. The experimental study consists of testing up to failure, simply supported beams of effective span 1440 mm under two point loading. The test specimens consisted of composite box and channel (with lip placed on tension side and compression side) sections, the behavior of which was compared with companion empty sections. To understand the role of shear connectors in developing the composite action, some of the composite sections were provided with novel simple bar type and conventional bolt type shear connectors in the shear zone of beams. Two RCC beams having equivalent ultimate moment carrying capacities as that of composite channel and box sections were also considered in the study. The study showed that the strength to weight ratio of composite beams is much higher than RCC beams and ductility index is also more than RCC and empty beams. The analytical predictions were found to compare fairly well with the experimental results, thereby validating the applicability of rigid plastic theory to cold-formed steel concrete composite beams.

Key Words
composite beam; empty beam; shear connector; flexural strength; ductility

Address
T. Valsa Ipe,Merchant Mohd Zafar Iqbal : Faculty of Civil Engineering, MSRIT, Bangalore India
H. Sharada Bai : Faculty of Civil Engineering, UVCE Bangalore India
K. Manjula Vani : Faculty of Civil Engineering, JNTUH Hyderabad India

Abstract
This paper deals with multiobjective optimization of symmetrically laminated composite angleply annular sector plates subjected to axial uniform pressure load and thermal load. The design objective is the maximization of the weighted sum of the critical buckling load and fundamental frequency. The design variable is the fibre orientations in the layers. The performance index is formulated as the weighted sum of individual objectives in order to obtain the optimum solutions of the design problem. The first-order shear deformation theory is used for the mathematical formulation. Finally, the effects of different weighting factors, annularity, sector angle and boundary conditions on the optimal design are investigated and the results are compared.

Key Words
laminated annular sector plates; multiobjective optimization; buckling; frequency

Address
Karadeniz Technical University, Of Faculty of Technology, Of, Trabzon, Turkey

Abstract
The concrete-filled steel tube (CFT) columns have several benefits of high load-bearing capacity, inherent ductility and toughness because of the confinement effect of the steel tube on concrete and the restraining effect of the concrete on local buckling of steel tube. However, the experimental research into the behavior of square CFT columns consisting of high-strength steel and high-strength concrete is limited. Six full scale CFT specimens were tested under flexural moment. The CFT columns consisted of high-strength steel tubes (fy=325MPa, 555MPa, 900MPa) and high-strength concrete (fck=80MPa and 120MPa). The ultimate capacity of high strength square CFT columns was compared with AISC-LRFD design code. Also, this study was focused on investigating the effect of high-strength materials on the structural behavior and the mathematical models of the steel tube and concrete. Nonlinear fiber element analyses were conducted based on the material model considering the cyclic bending behavior of high-strength CFT members. The results obtained from the numerical analyses were compared with the experimental results. It was found that the numerical analysis results agree well with the experimental results.

Key Words
concrete-filled steel tube; high-strength steel; high-strength concrete; experimental research; nonlinear fiber element analysis

Address
Kyung-Soo Chung, Jin-Ho Kim : Steel Structure Research Division, RIST, 180-1 Songdo-Dong, Yeonsu-Gu, Incheon 406-840, Republic of Korea
Jung-Han Yoo : School of Architecture, Seoul National University of Science &Technology, 232 Gongreung-ro, Nowon-gu, Seoul, 139-743, Republic of Korea

Abstract
This study analytically evaluated the seismic performance of wind-designed diagrid tall steel buildings in regions of moderate/low seismicity and strong winds. To this end, diagrid tall steel buildings with varying wind exposure and slenderness ratio (building height-to-width ratio) conditions were designed to satisfy the wind serviceability criteria specified in the Korean Building Code and the National Building Code of Canada. A series of seismic analy ses were then performed for earthquakes having 43- and 2475- year return periods utilizing the design guidelines of tall buildings. The analyses demonstrated the good seismic performance of these wind-designed diagrid tall steel buildings, which arises because significant overstrength of the diagrid system occurs in the wind design procedure. Also, analysis showed that the elastic seismic design process of diagrid tall steel buildings might be accepted based on some wind exposures and slenderness ratios.

Key Words
moderate/low seismicity; tall steel buildings; diagrid; wind design; seismic performance

Address
Seonwoong Kim : Disaster Prevention Research Team, DAEWOO E&C, Suwon, Korea
Kyungkoo Lee : Dept. of Architectural Engineering, Dankook University, Yongin, Korea

Abstract
The major objective of this paper is to evaluate the behavior and ultimate resisting capacity of circular CFT columns. To consider the confinement effect, proper material models with respect to the confinement pressure are selected. A fiber section approach is adopted to simulate the nonlinear stress distribution along the section depth. Material nonlinearity due to the cracking of concrete and the yielding of the surrounding steel tube, as well as geometric nonlinearity due to the P-

Key Words
circular CFT; confinement effect; ultimate resisting capacity; nonlinear FEM; short column

Address
Ji-Hyun Kwak, Hyo-Gyoung Kwak : Steel Structure Research Division, Research Institute of Industrial Science and Technology, Yeonsu, Incheon 406-840, Korea
Jin-Kook Kim : Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Yuseong, Daejeon 305-701, Korea

Abstract
A hybrid double skin concrete filled (HDSCF) circular steel tube column is proposed in this study. The yield strength of the outer steel tube is larger than 690MPa and the inner tube has less strength. In order to achieve efficiency with the high strength outer tube, a feasibility study on reducing the thickness of the tube below the specified design codes for CFTs was conducted based on an experimental approach. The experiment also took variables such as thickness of the inner tube, hollow ratio, and strength of concrete into consideration to investigate the behavior of the HDSCF column. In order to estimate the applicability of design equations for CFTs to the HDSCF column, test results from CFT and HDSCF columns with design codes were compared. It was found that the axial compressive performance of the proposed HDSCF column is equivalent to that of the conventional CFT member irrespective of design variables. Furthermore, the design equation for a circular CFT given by EC4 is applicable to estimate the ultimate strength of the HDSCF circular steel tube column.

Key Words
double skin; 690MPa; hybrid; CFT; confinement

Address
Jin-Kook Kim : Steel Structure Research Division, Research Institute of Industrial Science and Technology,
Yeonsu, Incheon 406-840, Korea
Hyo-Gyoung Kwak and Ji-Hyun Kwak : Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Yuseong, Daejeon 305-701, Korea


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