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CONTENTS
Volume 21, Number 3, October20 2005
 

Abstract
This article deals with the reconstruction of an impact force. This requires to take measurements from the impacted structures and then to deconvolve those signals from the impulse response function. More precisely, the purpose of the work described here is to analyse the method of deconvolution and the problems that it implies. Thus, it is highlighted that the associated deconvolution problem depends on the location of the measurement points: it is possible or not to reconstruct the force of impact in function of the location of this point. Then, the role of the antiresonances is linked up with this problem. The singular value decomposition is used to understand these difficulties. Numerical predictions are compared and validated with experiments.

Key Words
inverse problem; impact force history; deconvolution; antiresonances.

Address
Laboratoire MŽcanique MatŽriaux Structures, Universite Claude Bernard Lyon 1, 82 Bd Niels Bohr, Domaine Scientifique de la Doua, 69622 Villeurbanne Cedex, France

Abstract
Based on the random vibration theory, a response spectrum method is developed for seismic response analysis of linear, multi-degree-of-freedom structures under multi-support excitations is developed. Various response quantities, including the mean and variance of the peak response, the response mean frequency, are obtained from proposed combination rules in terms of the mean response spectrum. This method makes it possible to apply the response spectrum to the seismic reliability analysis of structures subjected to multi-support excitations. Considering that the tedious numerical integration is required to compute the spectral parameters and correlation coefficients in above combination rules, this paper further offers simplified procedures for their computation, which enhance dramatically the computational efficiency of the suggested method. The proposed procedure is demonstrated for tow numerical examples: (1) two-span continuous beam; (2) two-tower cabled-stayed bridge by using Monte Carlo simulation (MC). For this purpose, this paper also presents an approach to simulation of ground motions, which can take into account both mean and variation properties of response spectrum. Computed results based on the response spectrum method are in good agreement with Monte Carlo simulation results. And compared with the MSRS method, a well-developed multi-support response spectrum method, the proposed method has an incomparable computational efficiency.

Key Words
multi-support excitation; response spectrum method; random vibration; seismic reliability analysis.

Address
Jian-hua Li; Department of Civil and Environmental Engineering, University of Missouri-Columbia,
Columbia, MO 65211, USA
Jie Li; School of Civil Engineering, Tongji University
, Siping Road 1239, Shanghai, 200092, P.R. China

Abstract
When a thin-walled multicell box girder is subjected to an eccentric load, the distortion becomes an important global response in addition to flexure and torsion. The three global responses appear in a combined form when a conventional shell element is used thus it is not an easy task to examine the three global responses separately. This study is to propose an analysis method using conventional shell element in which the three global responses can be separately decomposed. The force decomposition method which was designed for a single-cell box girder by Nakai and Yoo is expanded herein to multicell box girders. The eccentric load is decomposed in the expanded method into flexural, torsional, and multimode distortional forces by using the force equilibrium. From the force decomposition, the combined global responses of multicell box girders can be resolved into separate responses and the distortional response which is of primary concern herein can be obtained separately. It is shown from a series of extensive comparative studies using three box girder bridge models that the expanded method produces accurate decomposed results. Noting that the separate consideration of individual global response is of paramount importance for optimized multicell box girder design, it can be said that the proposed expanded method is extremely useful for practicing engineers.

Key Words
independent distortional analysis; shell analysis; force decomposition; expanded method; multicell box girders.

Address
Nam-Hoi Park and Young-Jong Kang; Department of Civil and Environmental Engineering, Korea University, 5-1, Anam-Dong, Sungbuk-Ku, Seoul 136-701, South Korea
Hee-Joong Kim; Department of Civil Engineering, Keimyung University, 1000, Shindang-Dong, Dalseo-Ku, Daegu 704-701, South Korea

Abstract
This paper evaluates the effective width of composite steel beams with precast hollowcore slabs numerically using the finite element method. A parametric study, carried out on 27 beams with different steel cross sections, hollowcore unit depths and spans, is presented. The effective width of the slab is predicted for both the elastic and plastic ranges. 8-node three-dimensional solid elements are used to model the composite beam components. The material non-linearity of all the components is taken into consideration. The non-linear load-slip characteristics of the headed shear stud connectors are included in the analysis. The moment-deflection behaviour of the composite beams, the ultimate moment capacity and the modes of failure are also presented. Finally, the ultimate moment capacity of the beams evaluated using the present FE analysis was compared with the results calculated using the rigid – plastic method.

Key Words
effective width; precast; hollowcore slabs; finite element; modelling; composite design; steel; concrete.

Address
Ehab El-Lobody; Department of Structural Engineering, Faculty of Engineering, Tanta University, Tanta, Egypt
Dennis Lam; School of Civil Engineering, University of Leeds, Leeds, LS2 9JT, U.K.

Abstract
The Element-free Galerkin Method has become a very popular tool for the simulation of mechanical problems with moving boundaries. The internally applied Moving Least Squares interpolation uses in general Gaussian or cubic weighting functions and has compact support. Due to the approximative character of this interpolation the obtained shape functions do not fulfill the interpolation conditions, which causes additional numerical effort for the application of the boundary conditions. In this paper a new weighting function is presented, which was designed for meshless shape functions to fulfill these essential conditions with very high accuracy without any additional effort. Furthermore this interpolation gives much more stable results for varying size of the influence radius and for strongly distorted nodal arrangements than existing weighting function types.

Key Words
interpolation; Moving Least Squares; meshless discretization; boundary conditions

Address
Institute of Structural Mechanics, Bauhaus-University, Weimar, Marienstr. 15, D-99423 Weimar, Germany

Abstract
This paper presents results of an experimental study to evaluate a new retrofit technique for strengthening shear deficient short concrete beams and columns. In this technique a mortar jacket reinforced with expanded steel meshes is used for retrofitting. Twelve short reinforced concrete specimens, including eight retrofitted ones, were tested. Six specimens were tested under a constant compressive axial force of 15% of column axial load capacity based on original concrete gross section, Ag , and the concrete compressive strength, f c\'. Main variables were the spacing of ties in original specimens and the volume fraction of expanded metal in jackets. Original specimens failed before reaching their nominal calculated flexural strength, Mn , and had very poor ductility. Strengthened specimens reached their nominal flexural strength and had a ductility capacity factor of up to 8 for the beams and up to 5.5 for the columns. Based on the test results, it can be concluded that expanded steel meshes can be used effectively to strengthen shear deficient concrete members.

Key Words
expanded steel mesh; concrete; short column; ductility; shear strength; retrofit; strengthening.

Address
Reza Morshed; Department of Civil Engineering, Yazd University, Yazd, P.O. Box 89195-741, Iran
Mohammad Taghi Kazemi; Department of Civil Engineering, Sharif University of Technology, Tehran, P.O. Box 11365-9313, Iran

Abstract
Multi-span beams carrying multiple point masses are widely used in engineering applications, but the literature for free vibration analysis of such structural systems is much less than that of single-span beams. The complexity of analytical expressions should be one of the main reasons for the last phenomenon. The purpose of this paper is to utilize the numerical assembly method (NAM) to determine the exact natural frequencies and mode shapes of a multi-span uniform beam carrying multiple point masses. First, the coefficient matrices for an intermediate pinned support, an intermediate point mass, left-end support and right-end support of a uniform beam are derived. Next, the overall coefficient matrix for the whole structural system is obtained using the numerical assembly technique of the finite element method. Finally, the natural frequencies and the associated mode shapes of the vibrating system are determined by equating the determinant of the last overall coefficient matrix to zero and substituting the corresponding values of integration constants into the related eigenfunctions respectively. The effects of in-span pinned supports and point masses on the free vibration characteristics of the beam are also studied.

Key Words
single-span beam; multi-span beam; numerical assembly method (NAM); natural frequency; mode shape.

Address
Hsien-Yuan Lin; Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-Sen University,70 Lien-hai Rd. Kaohsiung 804, Taiwan, Republic of China
Ying-Chien Tsai; Department of Mechanical Engineering, Cheng Shiu University, Kaohsiung, Taiwan 800,
Republic of China

Abstract
A big progress has been made for moving force identification from bridge dynamic responses in recent years. Current knowledge and the potentials on moving force identification methods are reviewed in this paper under main headings below: background of moving force identification, experimental verification in laboratory and its application in field.

Key Words
moving force identification; vehicle-bridge interaction; dynamic response; review.

Address
Ling Yu; Blasting and Vibration Department, Changjiang River Scientific Research Institute, Wuhan, Hubei, 430010, P. R. China (Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, P. R. China)
Tommy H.T. Chan; Department of Civil and Structural Engineering, The Hong Kong Polytechnic University,
Hung Hom, Kowloon, Hong Kong, P. R. China


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