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CONTENTS
Volume 18, Number 4, October 2004
 

Abstract
In this study, theoretical and experimental results are presented which were obtained during an investigation of the influence of the P-D effect that was caused by the simultaneous changing of the axial load P of the column and the lateral displacement D in the external beam-column joints. The increase or decrease of D was simultaneous with the increase or decrease of the axial compression load P and caused an additional influence on the aseismic mechanical properties of the joint. A total of 12 reinforced concrete exterior beam-column subassemblies were examined. A new model, which predicts the beam-column joint ultimate shear strength, was used in order to predict the seismic behaviour of beam-column joints subjected to earthquake-type loading plus variable axial load and P-D effect. Test data and analytical research demonstrated that axial load changes and P-D effect during an earthquake cause significant deterioration in the earthquake-resistance of these structural elements. It was demonstrated that inclined bars in the joint region were effective for reducing the unfavourable impact of the P-D effect and axial load changes in these structural elements.

Key Words
beam-column frame; beams (supports); columns (supports); connections; cyclic loads; earthquake resistant structures; hinges (structural); joints (junctions); reinforced concrete; reinforcing steel; shear strength; structural analysis.

Address
Aristotle University of Thessaloniki, Division of Structural Engineering, P. O. Box 482, 541 26, Thessaloniki, Greece

Abstract
In this study, a newly developed unconditionally stable explicit method is employed to solve momentum equations of motion in performing pseudodynamic tests. Due to the explicitness of each time step this pseudodynamic algorithm can be explicitly implemented, and thus its implementation is simple when compared to an implicit pseudodynamic algorithm. In addition, the unconditional stability might be the most promising property of this algorithm in performing pseudodynamic tests. Furthermore, it can have the improved properties if using momentum equations of motion instead of force equations of motion for the step-by-step integration. These characteristics are thoroughly verified analytically and/or numerically. In addition, actual pseudodynamic tests are performed to confirm the superiority of this pseudodynamic algorithm.

Key Words
unconditional stability; explicit method; pseudodynamic test; error propagation.

Address
Department of Civil Engineering, National Taipei University of Technology, Taipei 106, Taiwan, Republic of China

Abstract
Remotely Operated Vehicle of 6000-meters is a new conceptual equipment made to replace the manned systems for investigating the deep-sea environment, and all of the ROV systems in operational condition strongly depend on the connecting cables. In this point of view dynamics of the ROV cable system is very important for operational and safety aspects as a cable generally encounters great tension. Researches have been executed on this problem, and most of papers have been mainly focused on the operational condition of ROV system in deep sea. This paper presents the dynamic cable response analysis during ROV launching condition rather than the operational one in order to provide the design guide of a ROV cable system in this circumstance, considering the coupling effects between cable and wave-induced ship motion. To obtain the variations of cable tensions during a ROV launching, a pre-stressed harmonic response analysis was carried out. Wave-induced tensions of the cable during ROV launching were obtained in real sea states using FE modeling, and the basic design guide of a ROV cable system was obtained.

Key Words
ROV cable system; coupling motion; dynamic cable response; pre-stressed harmonic response analysis; head and beam seas; significant wave.

Address
Kyu Nam Cho; Dept. of Naval Architecture and Ocean Engineering, Hongik Univ., Jochiwon, Chungnam 339-701, Korea
Ha Cheol Song; Research Institute of Marine Systems Eng., Seoul Nat. Univ.,
San 56-1, Shillim-dong, Kwankak-gu, Seoul 152-744, Korea
Do Chun Hong; Korea Research Institute of Ships and Ocean Engineering, 171, Jang-dong, Yusung-gu, Daejeon 305-343, Korea

Abstract
This paper explores the potential use of neural networks (NNs) in the field of contact mechanics. A neural network model is developed for predicting, with sufficient approximation, the contact lengths between the elastic layer and two elastic circular punches. A backpropagation neural network of three layers is employed. First contact problem is solved according to the theory of elasticity with integral transformation technique, and then the results are used to train the neural network. The effectiveness of different neural network configurations is investigated. Effect of parameters such as load factor, elastic punch radii and flexibilities that influence the contact lengths is also explored. The results of the theoretical solution and the outputs generated from the neural network are compared. Results indicate that NN predicted the contact length with high accuracy. It is also demonstrated that NN is an excellent method that can reduce time consumed.

Key Words
contact length; elasticity; elastic layer; elastic punch; neural network.

Address
Karadeniz Technical University, Civil Engineering Dept., 61080, Trabzon, Turkey

Abstract
A proposed incremental model for the solution of a general class of convex programming problems is introduced. The model is an extension of that developed by Mahmoud et al. (1993) which is limited to linear constraints having nonzero free coefficients. In the present model, this limitation is relaxed, and allowed to be zero. The model is extended to accommodate those constraints of zero free coefficients. The proposed model is applied to solve the elasto-static contact problems as a class of variation inequality problems of convex nature. A set of different physical nature verification examples is solved and discussed in this paper.

Key Words
inequality problems; convex programming problems; contact problems; finite element.

Address
College of Engineering, Zagazig University, Zagazig, Egypt

Abstract
Anchorage devices play an important role in post-tensioned bridge structures since they must sustain heavy loads in order to permit the transfer of the prestressing force to the structure. In external prestressing, the situation is even more critical since the anchorage mechanisms, with the deviators, are the only links between the structure and the tendons throughout the service life of the structure. The behaviour of anchorage devise may be studied by using the finite element method. To do so, each component of the anchorage must be adequately represented in order to approximate the anchor mechanism as accurately as possible. In particular, the modelling of the jaw/tendon device may be carried out using the real geometry of these two components with an appropriate constitutive contact law or by replacing these components by a single equivalent. This paper presents the numerical study of a mono-strand anchorage device. The results of a comparison between two different representations of the jaw/tendon device, either as two distinct components or as a single equivalent, will be examined. In the double-component setup, the influence of the wedge configuration composing the jaw, and the influence of lubrication of the anchor, will be assessed.

Key Words
anchorage device; contact; finite element; jaw/tendon device; lubrication; yielding; stress and strain distribution; wedge penetration.

Address
D. Marceau; Department of Applied Sciences, University of Quebec at Chicoutimi, Quebec, Canada, G7H 2B1
M. Fafard and J. Bastien; Department of Civil Engineering, Laval University, Quebec, Canada, G1K 7P4

Abstract
This paper addresses the behavior and strength of structural walls with a concrete compressive strength exceeding 69 MPa. This information also enhances the current database for improvement of design recommendations. The objectives of this investigation are to study the effect of axial-load ratio on seismic behavior of high-strength concrete flexural walls. An analysis has been carried out in order to assess the contribution of deformation components, i.e., flexural, diagonal shear, and sliding shear on total displacement. The results from the analysis are then utilized to evaluate the prevailing inelastic deformation mode in each of wall. Moment-curvature characteristics, ductility and damage index are quantified and discussed in relation with axial stress levels. Experimental results show that axial-load ratio have a significant effect on the flexural strength, failure mode, deformation characteristics and ductility of high-strength concrete structural walls.

Key Words
high-strength concrete; structural walls; ductility; axial loads; strength; earthquake-resistant structures.

Address
Seung-Hun Kim; Technical Division, LG Engineering & Construction Corp., Seoul 100-722, Korea
Ae-Bock Lee and Byung-Chan Han; School of Architecture, Chungnam National University, Daejeon 305-764, Korea
Sang-Su Ha; STRESS, Hanyang University, Seoul 133-791, Korea
Hyun-Do Yun; School of Architecture, Chungnam National University, Daejeon 305-764, Korea

Abstract
Many types of passive control devices have been recognized as effective tools for improving the seismic resistance of structures. A lot of past research has been carried out to study the response of structures equipped with energy-absorbing devices by assuming that the behavior of the beam-column systems are linearly elastic. However, linear theory may not be adequate for beams and columns during severe earthquakes. This paper presents the results of research on the nonlinear responses of structures with and without added passive devices under earthquakes. A new material model based on the plasticity theory and the two-surface model for beams and columns under six components of forces is proposed to predict the nonlinear behavior of beam-column systems. And a new nonlinear beam element in consideration of shear deformation is developed to analyze the beams and columns of a structure. Numerical results reveal that linear assumption may not be appropriate for beams and columns under seismic loadings, especially for unexpectedly large earthquakes. Also, it may be necessary to adopt nonlinear beam elements in the analysis and design process to assure the safety of structures with or without the control of devices.

Key Words
structural control; energy absorber; seismic resistance; nonlinear analysis.

Address
C. S. Tsai; Dept. of Civil Engineering, Feng Chia University, Taichung, 407, Taiwan, R.O.C.
Kuei-Chi Chen; Graduate Institute of Civil & Hydraulic Eng., Feng Chia University, Taichung, 407, Taiwan, R.O.C.

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