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CONTENTS
Volume 20, Number 6, August20 2005
 

Abstract
A reliability analysis method is proposed in this paper through a combination of the advantages of the response surface method (RSM), finite element method (FEM), first order reliability method (FORM) and the importance sampling updating method. The accuracy and efficiency of the method is demonstrated through several numerical examples. Then the method is used to estimate the serviceability reliability of cable-stayed bridges. Effects of geometric nonlinearity, randomness in loading, material, and geometry are considered. The example cable-stayed bridge is the Second Nanjing Bridge with a main span length of 628 m built in China. The results show that the cable sag that is part of the geometric nonlinearities of cable-stayed bridges has a major effect on the reliability of cable-stayed bridge. Finally, the most influential random variables on the reliability of cable-stayed bridges are identified by using a sensitivity analysis.

Key Words
reliability analysis; failure probability; response surface method (RSM); importance sampling; serviceability limit state; Monte Carlo simulation (MCS); cable-stayed bridges; geometric nonlinearity.

Address
Department of Bridge Engineering, Tongji University, Shanghai, 200092, China

Abstract
In this work, the mechanism of damping and its theoretical evaluation for layered aluminium cantilever structures jointed with a number of equispaced connecting bolts under an equal tightening torque have been considered. Extensive experiments have been conducted on a number of specimens for comparison with numerical results. Intensity of interface pressure, its distribution pattern, dynamic slip ratio and kinematic coefficient of friction at the interfaces, relative spacing of the connecting bolts, frequency and amplitude of excitation are found to play a major role on the damping capacity of such structures. It is established that the damping capacity of structures jointed with connecting bolts can be improved largely with an increase in number of layers maintaining uniform intensity of pressure distribution at the interfaces. Thus the above principle can be utilized in practice for construction of aircraft and aerospace structures effectively in order to improve their damping capacity which is one of the prime considerations for their design.

Key Words
interface pressure; dynamic slip ratio; relative spacing; damping capacity.

Address
Department of Mechanical Engineering, National Institute of Technology, Rourkela-769008, Orissa, India

Abstract
Seismic random responses due to the wave passage effect are extensively investigated by using the pseudo excitation method (PEM). Two examples are used. The first is very simple but also very informative, while the second is a realistic suspension bridge. Numerical results show that the seismic responses vary significantly with wave speed, especially for low velocity or large span. Such variations are not monotonic, especially for flexible structures. The contributions of the dynamic and quasi-static components depend heavily on the seismic wave velocity and the natural frequencies of structures. For the lower natural frequency cases, the dynamic component has significant effects on the dynamic responses of the structure, whereas the quasi-static component dominates for higher natural frequencies unless the wave speed is also high. It is concluded that if insufficient data on local seismic wave velocity is available, it is advisable to select several possible velocity values in the seismic analysis and to choose the most conservative of the results thus obtained as the basis for design.

Key Words
wave passage effect; earthquake; random vibration; extended structures.

Address
Y. H. Zhang and J. H. Lin; State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian, 116023, China
F. W. Williams and Q. S. Li; Department of Building and Construction, City University of Hong Kong, Kowloon, Hong Kong

Abstract
A general step-by-step simulation for the time-dependent analysis of segmentally-erected prestressed concrete box-girder bridges is presented. A three dimensional finite-element model for the balanced-cantilever construction of segmental bridges, including effects of the load history, material nonlinearity, creep, shrinkage, and aging of concrete and the relaxation of prestressing steel was developed using ABAQUS software. The models included three-dimensional shell elements to model the box-girder walls and Rebar elements representing the prestressing tendons. The step-by-step procedure allows simulating the construction stages, effects of time-dependent deformations of materials and changes in the structural system of the bridges. The structural responses during construction and throughout the service life were traced. A comparison of the developed computer simulation with available experimental results was conducted and good agreement was found. Deflection of the bridge deck, changes in stresses and strains and the redistribution of internal forces were calculated for different examples of bridges, built by the balanced-cantilever method, over thirty-year duration. Significant time-dependent effects on the bridge deflections and redistribution of internal forces and stresses were observed. The ultimate load carrying capacities of the bridges and the behavior before collapse were also determined. It was observed that the ultimate load carrying capacity of such bridges decreases with time as a result of time-dependent effects.

Key Words
segmental bridges; box-girder ; prestress; long-term deformations; time-dependent analysis; balanced-cantilever construction; redistribution of stresses; ultimate load.

Address
S. Hedjazi and A. Rahai; Department of Civil and Environmental Engineering, Amirkabir University, Tehran, Iran
K. Sennah; Civil Engineering Department, Ryerson University, Toronto, Ontario, Canada

Abstract
Hybrid coupled shear walls in tall buildings are known as efficient structural systems to provide lateral resistance to wind and seismic loads. Multiple hybrid coupled shear walls throughout a tall building should be joined to provide additional coupling action to resist overturning moments caused by the lateral loading. This can be done using a coupling beam which connects two shear walls. In this study, experimental studies on the hybrid coupled shear wall were carried out. The main test variables were the ratios of coupling beam strength to connection strength. Finally, this paper provides background for rational design guidelines that include a design model to behave efficiently hybrid coupled shear walls.

Key Words
steel coupling beams; connection failure; shear yielding; flexure yielding; hybrid coupled shear walls.

Address
Wan-Shin Park and Hyun-Do Yun; School of Architecture, Chungnam National University, Daejeon 305-764, Korea
Jae-Yong Chung; Department of Architecture, Hongik University, Seoul 121-791, Korea
Yong-Chul Kim; School of Architecture, Chungnam National University, Daejeon 305-764, Korea

Abstract
Based on the improved first order Taylor interval expansion, a new interval analysis method for the static or dynamic response of the structures with interval parameters is presented. In the improved first order Taylor interval expansion, the first order derivative terms of the function are also considered to be intervals. Combining the improved first order Taylor series expansion and the interval extension of function, the new interval analysis method is derived. The present method is implemented for a continuous beam and a frame structure. The numerical results show that the method is more accurate than the one based on the conventional first order Taylor expansion.

Key Words
interval parameter; interval parameter structure; interval analysis; interval extension of function.

Address
Jie Wu and You Qun Zhao; College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Su Huan Chen; Department of Mechanics, Nanling Campus, Jilin University, Changchun 130022, China

Abstract
The present study is an experimental investigation into the behaviour of high strength concrete square short columns subjected to biaxial bending moments and strengthened by GFRP laminates. The main objectives of the study are: to evaluate the improvement in the structural performance of HSC short square columns subjected to small biaxial eccentricity when strengthened by externally applied FRP laminates, and to investigate the optimum arrangement and amount of FRP laminates to achieve potential enhancement in structural performance especially ductility. The parameters considered in this study are: number of FRP layers and arrangement of wraps. The load eccentricity is kept corresponding to e/t = 0.125 in two perpendicular directions to the columns principal axes, and the wraps are applied in single or double layers (partial or full wrapping). In the present work, test results of five full scale concrete columns are presented and discussed. The study has shown that FRP wraps can be used successfully to enhance the ductility of HSC columns subjected to biaxial bending by 300%.

Key Words
RC columns; biaxial bending; strengthening; rehabilitation; advanced composite materials; fiber reinforced plastics (FRP).

Address
O. A. Hodhod; Structural Engineering Department, Cairo University, Giza, Egypt
W. Hassan; Department of Strength of Materials and Quality Control, HBRC, Giza, Egypt
M. S. Hilal; Structural Engineering Department, Cairo University, Giza, Egypt
H. Bahnasawy; Department of Strength of Materials and Quality Control, HBRC, Giza, Egypt


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