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CONTENTS
Volume 14, Number 5, May 2013
 

Abstract
A composite box-girder with corrugated steel webs has been used in civil engineering practice as an alternative to the conventional pre-stressed concrete box-girder because of several advantages, such as high shear resistance without vertical stiffeners and an increase in the efficiency of pre-stressing due to the accordion effect. Many studies have been conducted on the shear buckling and flexural behavior of the composite box-girder with corrugated steel webs. However, the torsional behavior is not fully understood yet, and it needed to be investigated. Prior study of the torsion of the composite box-girder with corrugated steel webs has been developed by assuming that the concrete section is cracked prior to loading and doesn

Key Words
torsion; corrugated steel webs; composite structure; non-linear analysis; box-girder bridge

Address
1 Hee-Jung Ko, Jiho Moon, Hak-Eun Lee: School of Civil, Environmental & Architectural Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 136-701, South Korea; 2 Yong-Woo Shin: Civil Engineering Team, Daewoo E&C, 57 Sinmunno 1-ga, Jongno-gu, Seoul 110-713, South Korea

Abstract
The Big Bang-Big Crunch (BB-BC) optimization algorithm is developed for optimal design of non-linear steel frames with semi-rigid beam-to-column connections. The design algorithm obtains the minimum total cost which comprises total member plus connection costs by selecting suitable sections. Displacement and stress constraints together with the geometry constraints are imposed on the frame in the optimum design procedure. In addition, non-linear analyses considering the P-

Key Words
Big Bang-Big Crunch algorithm; meta-heuristics; semi-rigid connections; steel frames; optimum design

Address
1 A. Rafiee, A. Hadidi: Department of Civil Engineering, University of Tabriz, Tabriz, Iran; 2 S. Talatahari: Marand Faculty of Engineering, University of Tabriz, Tabriz, Iran

Abstract
This paper presents the structural behavior of CFRP (carbon fiber reinforced polymer) strengthened CFT (concrete-filled steel tubes) columns under axial loads. Circular and square specimens were selected to investigate the retrofitting effects of CFRP sheet on CFT columns. Test parameters are cross section of CFT, D/t (B/t) ratios, and the number of CFRP layers. The load and ductility capacities were evaluated for each specimen. Structural behavior comparisons of circular and rectangular section will be represented in the experimental result discussion section. Finally, ultimate load formula of CFRP strengthened CFT will be proposed to calculate the ultimate strength of CFRP strengthened circular CFT. The prediction values are in good agreement with the test results obtained in this study and in the literature.

Key Words
concrete-filled steel tubes (CFT); composite column; confinement effect; carbon fiber sheet; FRP

Address
1 Jai Woo Park: Gayoon Construction Co., Ltd., Seoul, Korea; 2 Sung Mo Choi: The University of Seoul, Department of Architecture Engineering, Seoul, Korea

Abstract
The primary objectives of this paper are to describe the buckling patterns and to determine the squash load of steel plate-concrete (SC) walls. The major variables in this study were the width-thickness (B/t) ratio and yield strength of surface steel plates. Six SC walls were tested, and the results include the maximum strength, buckling pattern of steel plates, strength of headed studs, and behavior of headed studs. Based on the test results, the effects of the B/t ratio on the compressive strength are also discussed. The paper also presents recommended effective length coefficients and discusses the effects of varying the yield strength of the steel plate, and the effects of headed studs on the performance of SC structures based on the test results and analysis.

Key Words
buckling; steel plate-concrete structure; B/t ratio; effective length factor; headed studs; SC structures

Address
1 Byong-Jeong Choi, Cheol-Kyu Kang: Department of Plant Architectural Engineering, Kyonggi University, 154-42 Gwanggyosan-ro, Yeongtong-Gu, Suwon-Si, Kyonggi-Do 443-760, Republic of Korea; 2 Won-Ki Kim: Department of Architectural Engineering, Hoseo University, 20 Hoseo-ro 79bean-gil, Baebang-Eup, Asan-Si, Chungcheongnam-Do 336-795, Republic of Korea; 3 Woo-Bum Kim: Department of Architectural Engineering, Kongju National University, 56 Gongjudaehak-ro, Gongju-Si Chungcheongnam-Do 314-701, Republic of Korea

Abstract
Bending behavior of reinforced concrete slabs encased over shallow I-sections at different levels of compression heads were investigated in present study. 1500 mm long I-sections were used to create composite slabs. Compression heads of monolithic experimental members were encased at different levels into the concrete slabs. Shear connections were welded over some of the I-sections. The testing was carried out in accordance with the principles of four-point loading. Results revealed decreasing load bearing and deflection capacities of composite beams with increasing encasement depths into concrete. Mechanical properties of concrete and reinforcing steel were also examined. Resultant stresses calculated for composite beams at failure were found to be less than the yield strength of steel beams. Test results were discussed with regard to shear and slip effect.

Key Words
composite beam; shear connectors; ultimate behavior; collapse mechanism

Address
(1) Selçuk Emre Gőrkem: Erciyes University, Biosystems Engineering Department, Kayseri, Turkey;
(2) Metin Hűsem: Karadeniz Technical University, Civil Engineering Department, Trabzon, Turkey.

Abstract
In this study we have considered the governing nonlinear equation of an eccentrically reinforced cylindrical shell. A new analytical method called He\'s Variational Approach (VA) is used to obtain the natural frequency of the nonlinear equation. This analytical representation gives excellent approximations to the numerical solution for the whole range of the oscillation amplitude, reducing the respective error of angular frequency in comparison with the variation approach method. It has been proved that the variational approach is very effective, convenient and does not require any linearization or small perturbation. Additionally it has been demonstrated that the variational approach is adequately accurate to nonlinear problems in physics and engineering.

Key Words
eccentrically reinforced cylindrical shell; stringer shell; nonlinear vibration; variational approach; Runge-Kutta

Address
1 Mahmoud Bayat: Young Researchers and Elites club, Science and Research Branch, Islamic Azad University, Tehran, Iran; 2 Iman Pakar, Mahdi Bayat: Department of Civil Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran


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