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CONTENTS
Volume 27, Number 6, December10 2007
 

Abstract
Applying the method calculating creep of Concrete Filled steel Tube (CFT) members based on the Elastic Continuation and Plastic Flow theory for concrete creep with the finite element method, the paper develops a new numerical method for the creep of CFT arch bridges considering effects of bending moment. It is shown that the method is feasible and reasonable through comparing the predicted stresses and deflection caused by the creep with the results obtained by the method of Gu et al. (2001) based on ACI209R model and experimental data of an actual CFT arch bridge. Furthermore, nine CFT arch bridges with different types are calculated and analyzed with and without the effects of bending moment. As a result, the bending moment has considerable influences on long-term deformations and internal forces of CFT arch bridges, especially when the section of arch rib is subjected to a large bending moment.

Key Words
creep; CFT; arch bridge; eccentric compression; Finite Element Method (FEM).

Address
Y.F. Wang, B. Han, J.S. Du and K.W. Liu; School of Civil Engineering and Architecture, Beijing Jiaotong University, Beijing 100044, P. R. China

Abstract
An experimental study to evaluate a redundancy capacity in simple span two plate-girder bridges, which are generally classified as a non-redundant load path structure, has been performed under the condition that one of the two girders is seriously damaged. The bottom lateral bracing was selected as an experimental parameter and two 1/5-scale bridge specimens with and without bottom lateral bracing have been prepared. The loading tests were first performed on the intact specimens without cracked girder within elastic range. Thereafter, the ultimate loading tests were conducted on the damaged specimens with an induced crack at the center of a girder. The test results showed that the cross beams and concrete deck redistributed partly the applied load to the uncracked girder, but the lateral bracing system played a significant role of the load redistribution when a girder was damaged. The redundancy was evaluated based on the test results and an appropriate redundancy level was evaluated when the lateral bracing was provided in a seriously damaged simple span two-girder steel bridge.

Key Words
redundancy; simple span two-girder bridge; bottom lateral bracing; fractured girder; load redistribution.

Address
Yong-Myung Park and Woom-Do-Ji Joe; Department of Civil Engineering, Pusan National University, 30 Jangjeon-dong, Geumjeong-gu, Busan 609-735, Korea
Min-Oh Hwang and Tae-Yang Yoon; Civil Engineering Research Team, Research Institute of Industrial Science and Technology, 79-5 Youngcheon, Dongtan, Hwaseong, Gyeonggi-do 445-813, Korea

Abstract
The probability and the reliability-based seismic performance evaluation procedure proposed in the FEMA-355F was applied to a reinforced concrete moment frame building in this study. For the FEMA procedure, which was originally developed for steel moment frame structures, to be applied to other structural systems, the capacity should be re-defined and the factors reflecting the uncertainties related to capacity and demand need to be determined. To perform the evaluation procedure a prototype building was designed per IBC 2003, and inelastic dynamic analyses were conducted applying sitespecific ground motions to determine the parameters for performance evaluation. According to the analysis results, distribution of the determined capacities turned out to be relatively smaller than that of the demands, which showed that the defined capacity was reasonable. It was also shown that the prototype building satisfied the target performance since the determined confidence levels exceeded the objectives for both local and global collapses.

Key Words
reinforced concrete special moment frame; seismic capacity; confidence; performance evaluation.

Address
Taewan Kim and Jinkoo Kim; Department of Architectural Engineering, SungKyunKwan University, Cheoncheon-dong, Jangan-gu, Suwon, Korea

Abstract
This article is concerned with the presentation of a time-domain BEM approach applied to the solution of the scalar wave equation for 2D problems. The basic idea is quite simple: the basic variables of the problem at time tn (potential and flux) are computed with the results related to the potential and to its time derivative at time tn.1 playing the role of ?initial conditions?. This time-marching scheme needs the computation of the potential and its time derivative at all boundary nodes and internal points, as well as the entire discretization of the domain. The convolution integrals of the standard timedomain BEM formulation, however, are not computed; the matrices assembled, only at the initial time interval, are those related to the potential, flux and to the potential time derivative. Two examples are presented and discussed at the end of the article, in order to verify the accuracy and potentialities of the proposed formulation.

Key Words
time-domain BEM; scalar wave equation; step-by-step BEM analysis.

Address
J. A. M. Carrer; Programa de Pos-Graduacao em Metodos Numericos em Engenharia, Universidade Federal do Parana, CEP 81531-990, Curitiba, PR, Brasil
W. J. Mansur; Programa de Engenharia Civil, COPPE/UFRJ, Caixa Postal 68506, CEP 21945-970, Rio de Janeiro, RJ, Brasil

Abstract
Though extensive research has been carried out for the ultimate strength of steel reinforced concrete (SRC) members under static and cyclic load, there was only limited information on the applied analysis models. Modeling of the inelastic response of SRC members can be accomplished by using a microcosmic model. However, generally used microcosmic model, which usually contains a group of parameters, is too complicated to apply in the nonlinear structural computation for large whole buildings. The intent of this paper is to develop an effective modeling approach for the reliable prediction of the inelastic response of SRC columns. Firstly, five SRC columns were tested under cyclic static load and constant axial force. Based on the experimental results, normalized trilinear skeleton curves were then put forward. Theoretical equation of normalizing point (ultimate strength point) was built up according to the load-bearing mechanism of RC columns and verified by the 5 specimens in this test and 14 SRC columns from parallel tests. Since no obvious strength deterioration and pinch effect were observed from the loaddisplacement curve, hysteresis rule considering only stiffness degradation was proposed through regression analysis. Compared with the experimental results, the applied analysis model is so reasonable to capture the overall cyclic response of SRC columns that it can be easily used in both static and dynamic analysis of the whole SRC structural systems.

Key Words
steel reinforced concrete (SRC); applied model; ultimate bearing strength; skeleton curve; hysteresis rule.

Address
Xilin Lu and Ying Zhou; State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092, P. R. China

Abstract
Nowadays computers can perform symbolic computations in addition to mere number crunching operations for which they were originally designed. Symbolic computation opens up exciting possibilities in Structural Mechanics and engineering. Classical areas have been increasingly neglected due to the advent of computers as well as general purpose finite element software. But now, classical analysis has reemerged as an attractive computer option due to the capabilities of symbolic computation. The repetitive cycles of simultaneous . equation sets required by the finite element technique can be eliminated by solving a single set in symbolic form, thus generating a truly closed-form solution. This consequently saves in data preparation, storage and execution time. The power of Symbolic computation is demonstrated by six examples by applying symbolic computation 1) to solve coupled shear wall 2) to generate beam element matrices 3) to find the natural frequency of a shear frame using transfer matrix method 4) to find the stresses of a plate subjected to in-plane loading using Levy?s approach 5) to draw the influence surface for deflection of an isotropic plate simply supported on all sides 6) to get dynamic equilibrium equations from Lagrange equation. This paper also presents yet another computationally efficient and accurate numerical method which is based on the concept of derivative of a function expressed as a weighted linear sum of the function values at all the mesh points. Again this method is applied to solve the problems of 1) coupled shear wall 2) lateral buckling of thin-walled beams due to moment gradient 3) buckling of a column and 4) static and buckling analysis of circular plates of uniform or non-uniform thickness. The numerical results obtained are compared with those available in existing literature in order to verify their accuracy.

Key Words
symbolic computation (Computer Algebra); coupled shear wall; natural frequency; flexural stiffness; geometric stiffness; mass matrix; differential quadrature; mesh points.

Address
S. Rajasekaran; Infrastructure Engineering, PSG College of Technology, Coimbatore - 641004, Taminadu, India

Abstract
Tests were conducted on two partially pre-stressed concrete solid beams subjected to combined loading of bending, shear and torsion. The beams were designed using the Direct Design Method which is based on the Lower Bound Theorem of the Theory of Plasticity. Both beams were of 300 ? 300 mm cross-section and 3.8 m length. The two main variables studied were the ratio of the maximum shear stress due to the twisting moment, to the shear stress arising from the shear force, which was varied between 0.69 and 3.04, and the ratio of the maximum twisting moment to the maximum bending moment which was varied between 0.26 and 1.19. The required reinforcement from the Direct Design Method was compared with requirements from the ACI and the BSI codes. It was found that, in the case of bending dominance, the required longitudinal reinforcements from all methods were close to each other while the BSI required much larger transverse reinforcement. In the case of torsion dominance, the BSI method required much larger longitudinal and transverse reinforcement than the both the ACI and the DDM methods. The difference in the transverse reinforcement is more pronounce. Experimental investigation showed good agreement between design and experimental failure loads of the beams designed using the Direct Design Method. Both beams failed within an acceptable range of the design loads and underwent ductile behaviour up to failure. The results indicate that the Direct Design Method can be successfully used to design partially prestressed concrete solid beams which cater for the combined effect of bending, shear and torsion loads.

Key Words
beams; direct design method; bending; torsion; shear; prestressed concrete; partially prestressed concrete; concrete structures.

Address
A. S. Alnuaimi; Department of Civil and Architectural Engineering, College of Engineering, Sultan Qaboos University, Muscat, Sultanate of Oman

Abstract
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Key Words
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Address
Reza Attarnejad and Amir K. Ghorbani-Tanha; School of Civil Engineering, University of Tehran, P.O. Box 1365-4563, Tehran, Iran


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