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CONTENTS
Volume 34, Number 6, April20 2010
 

Abstract
A mathematical model and its analytic solution for the analysis of stress-strain state of a linear elastic two-layer beam is presented. The model considers both slip and uplift at the interface. The solution is employed in assessing the effects of transverse and shear contact stiffnesses and the thickness of the interface layer on behaviour of nailed, two-layer timber beams. The analysis shows that the transverse contact stiffness and the thickness of the interface layer have only a minor influence on the stress-strain state in the beam and can safely be neglected in a serviceability limit state design.

Key Words
composite beam; slip; uplift; analytical solution; elasticity; parametric study.

Address
Ales Kroflic: University of Ljubljana, Faculty of Civil and Geodetic Engineering, Jamova 2, SI-1115 Ljubljana, Slovenia
Igor Planinc: University of Ljubljana, Faculty of Civil and Geodetic Engineering, Jamova 2, SI-1115 Ljubljana, Slovenia
Miran Saje: University of Ljubljana, Faculty of Civil and Geodetic Engineering, Jamova 2, SI-1115 Ljubljana, Slovenia
Bojan cas: University of Ljubljana, Faculty of Civil and Geodetic Engineering, Jamova 2, SI-1115 Ljubljana, Slovenia

Abstract
In this paper, a nonlinear finite element procedure is presented for the dynamic analysis of reinforced concrete shell structures. A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), was used. A 4-node flat shell element with drilling rotational stiffness was used for spatial discretization. The layered approach was used to discretize the behavior of concrete and reinforcement in the thickness direction. Material nonlinearity was taken into account by using tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach was incorporated. The low-cycle fatigue of both concrete and reinforcing bars was also considered to predict a reliable dynamic behavior. The solution to the dynamic response of reinforced concrete shell structures was obtained by numerical integration of the nonlinear equations of motion using Hilber-Hughes-Taylor (HHT) algorithm. The proposed numerical method for the nonlinear dynamic analysis of reinforced concrete shell structures was verified by comparison of its results with reliable experimental and analytical results.

Key Words
reinforced concrete; shell structures; layered approach; material nonlinearity; low-cycle fatigue; hilber-hughes-taylor algorithm.

Address
T.-H. Kim: Civil Engineering Research Team, Daewoo Institute of Construction Technology, 60 Songjuk-dong, Jangan-gu, Suwon, Gyeonggi-do 440-210, Korea
J.-G. Park: Department of Civil and Environmental Engineering, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do 440-746, Korea
J.-H. Choi: Department of Civil Engineering, Hankyong National University, 67 Sukjong-dong, Ansung, Gyeonggi-do 456-749, Korea
H.M. Shin: Department of Civil and Environmental Engineering, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do 440-746, Korea

Abstract
In classical higher-order discontinuous boundary element formulation for two-dimensional elastostatics, interpolation functions for different boundary variables (i.e., boundary displacements and tractions) are assumed to be the same. However, there is a derivational relationship between these variables. This paper presents a boundary element formulation, called Mixed Boundary Element Formulation, for two dimensional elastostatic problems in which above mentioned relationship is taking into account. The formulations are performed by using discontinuous first and second-order mixed boundary elements. Based on the formulations presented in this study, two computer softwares are developed and verified through some example problems. The results show that the present formulation is credible.

Key Words
boundary element method; discontinuous mixed boundary element; two dimensional elastostatics.

Address
M.H. Severcan: Department of Civil Engineering, Nigde University, 51100 Merkez, Nigde, Turkey
A.K. Tanrikulu: Department of Civil Engineering, Cukurova University, 01330 Balcali, Adana, Turkey
A.H. Tanrikulu: Department of Civil Engineering, Cukurova University, 01330 Balcali, Adana, Turkey
I.O. Deneme: Department of Civil Engineering, Aksaray University, 68100 Merkez, Aksaray, Turkey

Abstract
The aim of this paper concerns with the nonlinear analysis of cable-stayed bridges including the vibration effect of cable stays. Two models for the cable stay system are built up in the study. One is the OECS (one element cable system) model in which one single element per cable stay is used and the other is MECS (multi-elements cable system) model, where multi-elements per cable stay are used. A finite element computation procedure has been set up for the nonlinear analysis of such kind of structures. For shape finding of the cable-stayed bridge with MECS model, an efficient computation procedure is presented by using the two-loop iteration method (equilibrium iteration and shape iteration) with help of the catenary function method to discretize each single cable stay. After the convergent initial shape of the bridge is found, further analysis can then be performed. The structural behaviors of cable-stayed bridges influenced by the cable lateral motion will be examined here detailedly, such as the static deflection, the natural frequencies and modes, and the dynamic responses induced by seismic loading. The results show that the MECS model offers the real shape of cable stays in the initial shape, and all the natural frequencies and modes of the bridge including global modes and local modes. The global mode of the bridge consists of coupled girder, tower and cable stays motion and is a coupled mode, while the local mode exhibits only the motion of cable stays and is uncoupled with girder and tower. The OECS model can only offers global mode of tower and girder without any motion of cable stays, because each cable stay is represented by a single straight cable (or truss) element. In the nonlinear seismic analysis, only the MECS model can offer the lateral displacement response of cable stays and the axial force variation in cable stays. The responses of towers and girders of the bridge determined by both OECS- and MECSmodels have no great difference.

Key Words
cable-stayed bridge; cable stays; catenary; OECS; MECS.

Address
P.H. Wang: Department of Civil Engineering, Chung-Yuan University, Chung-Li, Taiwan, R.O.C.
M.Y. Liu: Department of Civil Engineering, Chung-Yuan University, Chung-Li, Taiwan, R.O.C.
Y.T. Huang: Department of Civil Engineering, Chung-Yuan University, Chung-Li, Taiwan, R.O.C.
L.C. Lin: Department of Civil Engineering, Chung-Yuan University, Chung-Li, Taiwan, R.O.C.

Abstract
Pointing to the design requirement of prestressed space grid structure being the target cable force, the pretension scheme decision analysis method is studied when there\'s great difference between structural actual state and the analytical model. Based on recursive formulation of cable forces, the simulative recursive system for pretension process is established from the systematic viewpoint, including four kinds of parameters, i.e., system initial value (structural initial state), system input value (tensioning control force scheme), system state parameters (influence matrix of cable forces), system output value (pretension accomplishment). The system controllability depends on the system state parameters. Based on cable force observation values, the influence matrix for system state parameters can be calculated, making the system controllable. Next, the pretension scheme decision method based on cable force observation values can be formed on the basis of iterative calculation for recursive system. In this way, the tensioning control force scheme that can meet the design requirement when next cyclic supplemental tension finished is obtained. Engineering example analysis results show that the proposed method in this paper can reduce a lot of cyclic tensioning work and meanwhile the design requirement can be met.

Key Words
prestress; space grid structure; pretension process; cable force; recursive system.

Address
Zhen Zhou: Key Laboratory of RC & PC of Ministry of Education, Southeast University, Nanjing 210096, PR China; International Institute for Urban Systems Engineering, Southeast University, Nanjing 210096, PR China
Shao-ping Meng: Key Laboratory of RC & PC of Ministry of Education, Southeast University, Nanjing 210096, PR China; International Institute for Urban Systems Engineering, Southeast University, Nanjing 210096, PR China
Jing Wu: Key Laboratory of RC & PC of Ministry of Education, Southeast University, Nanjing 210096, PR China; International Institute for Urban Systems Engineering, Southeast University, Nanjing 210096, PR China

Abstract
Near-fault ground motion with directivity or fling effects is significantly influenced by the rupture mechanism and substantially different from ordinary records. This class of ground motion has large amplitude and long period, exhibits unusual response spectra shapes, possesses high PGV/PGA and PGD/PGA ratios and is best characterized in the velocity and the displacement time-histories. Such ground motion is also characterized by its energy being contained in a single or very few pulses, thus capable of causing severe damage to the structures. This paper investigates the characteristics of near-fault pulse-like ground motions and their implications on the structural responses using new proposed measures, such as, the effective frequency range, the energy rate (in time and frequency domains) and the damage indices. The paper develops also simple mathematical expressions for modeling this class of ground motion and the associated structural responses, thus eliminating numerical integration of the equations of motion. An optimization technique is also developed by using energy concepts and damage indices for modeling this class of ground motion for inelastic structures at sites having limited earthquake data.

Key Words
near-fault; pulse-like ground motion; frequency content; energy rate; inelastic response; ductility; damage index; critical excitation.

Address
Abbas Moustafa: Department of Civil Engineering, Minia University, Minia 61111, Egypt
Izuru Takewaki: Department of Urban & Environmental Engineering, Graduate School of Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan

Abstract
In order to consider high-order effects on the actual limit state function, a new response surface method is proposed for structural reliability analysis by the use of high-order approximation concept in this study. Hermite polynomials are used to determine the highest orders of input random variables, and the sampling points for the determination of highest orders are located on Gaussian points of Gauss-Hermite integration. The cross terms between two random variables, only in case that their corresponding percent contributions to the total variation of limit state function are significant, will be added to the response surface function to improve the approximation accuracy. As a result, significant reduction in computational cost is achieved with this strategy. Due to the addition of cross terms, the additional sampling points, laid on two-dimensional Gaussian points off axis on the plane of two significant variables, are required to determine the coefficients of the approximated limit state function. All available sampling points are employed to construct the final response surface function. Then, Monte Carlo Simulation is carried out on the final approximation response surface function to estimate the failure probability. Due to the use of high order polynomial, the proposed method is more accurate than the traditional second-order or linear response surface method. It also provides much more efficient solutions than the available high-order response surface method with less loss in accuracy. The efficiency and the accuracy of the proposed method compared with those of various response surface methods available are illustrated by five numerical examples.

Key Words
structural reliability analysis; Hermite polynomial; high-order response surface; Gaussian points.

Address
Hong-Shuang Li: School of Aeronautics, Northwestern Polytechnical University, Xi\'an 710072, P.R. China
Zhen-Zhou Lu: School of Aeronautics, Northwestern Polytechnical University, Xi\'an 710072, P.R. China
Hong-Wei Qiao: School of Aeronautics, Northwestern Polytechnical University, Xi\'an 710072, P.R. China

Abstract


Key Words


Address
Pengzhen Lu: School of Civil Engineering, Southwest Jiaotong University, Chengdu, 610031, PR China
Renda Zhao: School of Civil Engineering, Southwest Jiaotong University, Chengdu, 610031, PR China

Abstract


Key Words


Address
Jia-Jang Wu: Department of Marine Engineering, College of Maritime, National Kaohsiung Marine University, No.482, Jhongjhou 3rd Road, Cijin District, Kaohsiung City 80543, Taiwan (ROC)

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