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CONTENTS
Volume 4, Number 5, October 2004
 

Abstract
Strength of reinforced concrete beams can easily be increased by the use of externally bonded CFRP composites. However, the mode of failure of CFRP strengthened beam is usually brittle due to tension-shear failure in the concrete substrate or bond failure near the CFRP-Concrete interface. In order to improve the ductility of CFRP strengthened concrete beams, critical variables need to be investigated. This experimental and analytical research focused on a series of reinforced concrete beams strengthened with CFRP composites to enhance the flexural capacity and ductility. The main variables were the amount of CFRP composites, the amount of longitudinal and shear reinforcement, and the effect of CFRP end diagonal anchorage system. Sixteen full-scale beams were investigated. A new design guideline was proposed according to the effects of the above-mentioned variables. The experimental and analytical results were found to be in good agreement.

Key Words
CFRP; CFRP anchorage system; flexural strength; ductility.

Address
Department of Civil and Environmental Engineering, Syracuse University, Syracuse, NY 13244, U.S.A.

Abstract
A new reduction method of residual stress in welding joint is proposed where welded metals are shaken during welding. By an experiment using a small shaker, it can be shown that tensile residual stress near the bead is significantly reduced. Since tensile residual stress on the surface degrades fatigue strength for cumulative damage, the proposed method is effective to reduction of residual stress of welded joints. The effectiveness of the proposed method is demonstrated by the response analysis using one mass model with nonlinear springs.

Key Words
welding; residual stress; vibration; X-ray diffraction method.

Address
Tokyo Metropolitan College of Technology, 1-10-40, Higashi-Ohi, Shinagawa-ku, Tokyo 140, Japan

Abstract
A numerical model based on the finite element technique is adopted to investigate the behavior and strength of thin-walled I-section beam-columns. The model considers both the material and geometric nonlinearities. The model results were first verified against some of the currently available experimental results. A parametric study was then performed using the numerical model and interaction diagrams for the investigated beam-columns have been presented. The effects of the web depth-to-thickness ratio, flange outstand-to-thickness ratio and bending moment-to-normal force ratio on the ultimate strength of thin-walled I-section beam-columns were scrutinized. The interaction equations adopted for beam columns design by the NAS (North American Specifications for the design of cold formed steel structural members) have been critically reviewed. An equation for the buckling coefficient which considers the interaction between local buckling of the flange and the web of a thin-walled I-section beam-column has been proposed.

Key Words
beam column; buckling coefficient; flange outstand; local buckling; interaction diagram; slenderness; thin walled section.

Address
Adel Helmy Salem; Structural Engineering Department, Ain Shams University, Cairo, EgyptrnEzzeldin Yazeed Sayed-Ahmed; University of Qatar, Civil Engineering Dept., Doha Qatar, PO Box 2713, Qatar (on leave from the Structural Engineering Department, Ain Shams University, Cairo, Egypt)rnAhmed Abdelsalam El-Serwi and Mohamed Mostafa Korashy;rnStructural Engineering Department, Ain Shams University, Cairo, Egypt

Abstract
Nearly 400 composite railway bridge decks of a new kind belonging to the trough type with U-shaped cross section have been constructed in Belgium over the last fifteen years. The construction of these bridge decks is rather complex with the preflexion of precambered steel girders, the prestressing of a concrete slab and the addition of a 2nd phase concrete. Until now, they have been designed with a classical computation method using a pseudo-elastic analysis with modular ratios. Globally, they perform according to the expectations but variability has been observed between the measured and the computed camber of these bridge decks just after the transfer of prestressing and also at long-term. A statistical analysis of the variability of the relative difference between the measured camber and the computed camber is made for a sample of 36 bridge decks using no less than 10 variables. The most significant variables to explain this variability at prestressing are the ratio between the maximum tensile stress reached in the steel girders during the preflexion and the yield strength and the type of steel girder. For the same sample, the long-term camber under permanent loading is computed by two methods and compared with measurements taken one or two years after the construction. The camber computed by the step-by-step method shows a better agreement with the measured camber than the camber computed by the classical method. The purpose of the paper is to report on the statistical analysis which was used to determine the most significant parameters to consider in the modeling in order to improve the prediction of the behaviour of these composite railway bridge decks.

Key Words
camber; composite bridge; high strength concrete; hot-rolled girder; numerical modelling; prestressing; statistical analysis; welded girder.

Address
Department of Civil Engineering, CP194/4, Universite Libre de Bruxelles, rnA.Buyl Avenue, 87, B-1050 Brussels, Belgium

Abstract
Lateral sway is most likely to control the design of semi-rigid steel frames where the frame arrangements do not include any form of bracing. This paper investigates the sway behaviour of semi-rigid regular steel frames i.e., frames having the same arrangement of beam and column sections at all levels, and hence proposes some design charts for the prediction of sway that eliminate the need for doing any numerical modelling. Schueller

Key Words
ANSYS; connection stiffness; corresponding regular frame; finite element analysis; flexibility factor; multi-storey frames; semi-rigid connection; sway.

Address
M. Ashraf and D. A. Nethercot; Dept. of Civil and Environmental Engineering, Imperial College London, London SW7 2BU, U.K.rnB. Ahmed; Department of Civil Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh


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