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CONTENTS
Volume 19, Number 6, April20 2005
 

Abstract
The split Hopkinson pressure bar (SHPB) technique is widely used to characterize the dynamic mechanical response of engineering materials at high strain rates. In this paper, attendant problems associated with testing 70 mm diameter concrete specimens are considered, analysed and resolved. An adaptation of a conventional solid circular striker bar, as a means of achieving reliable and repeatable SHPB tests, is then proposed. In the analysis, a pseudo one-dimensional model is used to analyse wave propagation in a non-uniform striker bar. The stress history of the incident wave is then obtained by using the finite difference method. Comparison was made between incident waves determined from the simplified model, finite element solution and experimental data. The results show that the simplified method is adequate for designing striker bar shapes to overcome difficulties commonly encountered in SHPB tests. Using two specifically designed striker bars, tests were conducted on 70 mm diameter steel fibre reinforced concrete specimens. The results are presented in the paper.

Key Words
split Hopkinson pressure bar; dynamic characteristics of concrete; strain rate effect; finite difference method; impact.

Address
Pengjun Zhao; Centre for Protective Technology, National University of Singapore, Department of Civil Engineering, 10 Kent Ridge Crescent, Singapore 119260
Tat-Seng Lok; School of Civil and Environmental Engineering, Nanyang Technological University, Block N1, Nanyang Avenue, Singapore 639798

Abstract
The objective of this research was to determine the Vlasov soil parameters for quadratically varying elasticity modulus Es(z) of the compressible soil continuum and discuss the interaction affect between two close plates. Interaction problem carried on for uniformly distributed load carrying plates. Plate region was simulated by Kirchhoff plate theory based (mixed or displacement type) 2D elements and the foundation continuum was simulated by displacement type 2D elements. At the contact region, plate and foundation elements were geometrically coupled with each other. In this study the necessary formulas for the Vlasov parameters were derived when Young

Key Words
Kirchhoff plate; Vlasov foundation; soil parameters; finite elements.

Address
Istanbul Technical University, Faculty of Civil Engineering, 34469 Maslak, .Istanbul, Turkey

Abstract
In this paper, a full-scale K-joint specimen was tested to failure under cyclic combined axial and in-plane bending loads. In the fatigue test, the crack developments were monitored step by step using the alternating current potential drop (ACPD) technique. Using Paris?law, stress intensity factor, which is a fracture parameter to be frequently used by many designers to predict the integrity and residual life of tubular joints, can be obtained from experimental test results of the crack growth rate. Furthermore, a scheme of automatic mesh generation for a cracked K-joint is introduced, and numerical analysis of stress intensity factor for the K-joint specimen has then been carried out. In the finite element analysis, J-integral method is used to estimate the stress intensity factors along the crack front. The numerical stress intensity factor results have been validated through comparing them with the experimental results. The comparison shows that the proposed numerical model can produce reasonably accurate stress intensity factor values. The effects of different crack shapes on the stress intensity factors have also been investigated, and it has been found that semi-ellipse is suitable and accurate to be adopted in numerical analysis for the stress intensity factor. Therefore, the proposed model in this paper is reliable to be used for estimating the stress intensity factor values of cracked tubular K-joints for design purposes.

Key Words
tubular K-joints; alternating current potential drop (ACPD); stress intensity factor; J-integral; crack shapes; semi-ellipse.

Address
School of Civil Engineering, Yantai University, Yantai City, 264005, P.R. China

Abstract
Concrete filled steel tubular columns (CFT) are widely used in civil engineering works, especially in large scale of works because of high strength, deformation, toughness and so on. On the other hand, as a kind of strengthening measure for seriously damaged reinforced concrete piers of viaduct in Hansin-Awaji earthquake of Japan in 1995, reinforced concrete piers were wrapped with steel plate. Then, a new kind of structure appeared, that is, reinforced concrete filled steel tubular column (RCFT). In this paper, compression test and bending-shearing test on RCFT are carried out. The main parameters of experiments are (1) strength of concrete, (2) steel tube with or without rib, (3) width-thickness ratio and (4) arrangement of reinforcing bars. According to the experimental results, the effect of parameters on mechanical characteristics of RCFT is analyzed clearly. At the same time, strength evaluation formula for RCFT column is proposed and tested by experimental results and existed recommendations (AIJ 1997). The strength calculated by the proposal formula is in good agreement with test result. As a result, the proposed evaluation formula can evaluate the strength of RCFT column properly.

Key Words
reinforced concrete filled steel tubular column; compression test; bending-shearing test; load-carrying capacity; ductility ratio; strength; evaluation formula.

Address
Wei Hua; Department of Civil and Environmental
Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551, Japan (Faculty of Civil Engineering, Shenyang University of Technology)
Hai-Jun Wang; Faculty of Civil Engineering, Shenyang University of Technology, No.58, Xinghua South Street, Tiexi District, Shenyang 110023, China
Akira Hasegawa and Yukitake Shioi; Department of Environmental and Civil Engineering, Hachinohe Univ. of Technology, 88-1 Ohbiraki, Hachinohe 031-8501, Japan
Shoji Iwasaki and Yutaka Miyamoto; Department of Civil and Environmental Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551, Japan

Abstract
This paper presents a practical method to evaluate the effective length factors for columns in multi-storey unbraced frames based on the concept of storey-based elastic buckling by means of decomposing a multi-storey frame into a series of single-storey partially-restrained (PR) frames. The lateral stiffness of the multi-storey unbraced frame is derived and expressed as the product of the lateral stiffness of each storey. Thus, the stability analysis for the multi-storey frame is conducted by investigating the lateral stability of each individual storey, which is facilitated through decomposing the multi-storey frame into a series of single-storey PR frames and applying the storey-based stability analysis proposed by the authors (Xu and Liu 2002) for each single-storey PR frame. Prior to introducing decomposition approaches, the end rotational stiffness of an axially load column is derived and rotational stiffness interaction between the upper and lower columns is investigated. Three decomposition approaches, characterized by means of distributing beam-to-column rotational-restraining stiffness between the upper and lower columns, are proposed. The procedure of calculating storey-based column effective length factors is presented. Numerical examples are then given to illustrate the effectiveness of the proposed procedure.

Key Words
column effective length; lateral stability; multi-storey unbraced frame; storey-based buckling.

Address
Department of Civil Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1

Abstract
The bending stress formula that taking into account the transverse deformation is developed for plane-curved, untwisted isotropic beams subjected to loadings that result in deformations in the plane of curvature. In order to account the transverse Poisson contraction effect, a new constitutive relation between force resultants, moment resultants, mid-plane strains and deformed curvatures for a curved plate is derived in a 6 ?6 matrix form. This constitutive relation will provide the fundamental basis to the analyses of curved structures composing of isotropic or anisotropic materials. Then, the bending stress formula of a curved isotropic beam can be deduced from this newly developed curved plate theory. The stress predictions by the present analysis are compared to those by the analysis that neglected the Poisson contraction effect. The results show that the Poisson effect becomes more significant as the Poisson ratio and the curvature are getting larger.

Key Words
curved beam; curved plate; bending stress; Poisson ratio.

Address
Department of Mechanical Engineering, Chinese Culture University, No. 55, Hua-Kang Rd., Taipei, Taiwan

Abstract
The strong need of verifying theories formulated for semi-active control through applications to real structures is due to the fact that theoretical research on semi-active control systems is not matched by a corresponding satisfactory experimental activity. This paper shows how a smart system including magnetorheological devices as damping elements can be implemented in a large-scale structural model, by describing in detail the kind of electronics (dedicated hardware and software) adopted during the experimental campaign. It also describes the most interesting results in terms of reduction of the seismic response (either experimental or numerical) of the semi-actively controlled structure compared to a passive operating control system, and in terms of the evaluation criteria proposed in the benchmark for seismically excited controlled buildings. The paper also explains how to derive from the classical theory of optimal control the adopted control logic, based on a clear physical approach, and provides an exhaustive picture of the time delays characterizing the control sequence.

Key Words
semi-active control; magnetorheological dampers; large scale tests.

Address
Department of Structural Analysis and Design, School of Engineering, University of Napoli Federico II, Via Claudio n. 21 - 80125 Napoli, Italy

Abstract
In this work, thermo-elastic stability behavior of laminated cross-ply elliptical cylindrical shells subjected to uniform temperature rise is studied employing the finite element approach based on higher-order theory that accounts for the transverse shear and transverse normal deformations, and nonlinear in-plane displacement approximations through the thickness with slope discontinuity at the layer interfaces. The combined influence of higher-order shear deformation, shell geometry and non-circularity on the prebuckling thermal stress distribution and critical temperature parameter of laminated elliptical cylindrical shells is examined.

Key Words
laminated shell; cross-ply; thermal buckling; critical temperature; non-circular; higher-order; finite element; elliptical cross-section.

Address
B. P. Patel; Indian Institute of Technology Delhi, New Delhi-110 016, India
K. K. Shukla; Motilal Nehru National Institute of Technology, Allahabad-211 004, India
Y. Nath; Indian Institute of Technology Delhi, New Delhi-110 016, India


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