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CONTENTS
Volume 6, Number 3, April 1998
 

Abstract
This paper present an analysis which may be used to obtain a rational design of a system of inclined piles used in preventing downhill creep of unsaturated clay formations. It uses two simple and relatively easy to measure parameters (an estimate of the maximum downhill creep together with a knowledge of the depth of the so called active zone) to calculate the required section size and the optimal spacing (pitch) of the piles for a desired efficiency of the system as a whole. Design charts are provided to facilitate the process.

Key Words
saturated and unsaturated clays, downhill creep, piles, rainfall, pitch

Address
Poorooshasb HB, Saga Univ, Inst Lowland Technol, Saga 840, Japan
Saga Univ, Inst Lowland Technol, Saga 840, Japan
Concordia Univ, Montreal, PQ, Canada

Abstract
The test results from non-destructive and destructive field testing of a three-span deteriorated reinforced concrete slab bridge are used as a vehicle to examine the reliability of available tools for finite-element analysis of in-situ structures. Issues related to geometric modeling of members and connections, material models, and failure criteria are discussed. The results indicate that current material models and failure criteria are adequate, although lack of inelastic out-of-plane shear response in most nonlinear shell elements is a major shortcoming that needs to be resolved. With proper geometric modeling, it is possible to adequately correlate the measured global, regional, and local responses at all limit states. However, modeling of less understood mechanisms, such as slab-abutment connections, may need to be finalized through a system identification technique. In absence of the experimental data necessary for this purpose, upper and lower bounds of only global responses can be computed reliably. The studies reaffirm that success of finite-element models has to be assessed collectively with reference to all responses and not just a few global measurements.

Key Words
abutment, actual structures, analytical modeling, bridge, correlation study, destructive testing, deteriorated bridges, field testing, finite element analysis, geometric modeling, linear analysis, non-destructuctive testing, nonlinear analysis, piper cap, reinforced concrete slab bridge, slab-abutment connection, slab-pier cap connection, system identification, truck load testing

Address
Ho IK, CICI Corp, Taipei, Taiwan
CICI Corp, Taipei, Taiwan
Univ Cincinnati, Dept Civil & Environm Engn, Cincinnati, OH 45221 USA

Abstract
The objective of the paper is to present a method whereby the time required for a steel structure to sustain the effects of a prescribed temperature rise according to real fire curves can be calculated. The method is divided into two parts. The first part deals with the post-yield behaviour of steel structures at elevated temperatures. It takes into account the variation of the properties of steel material with temperature in an incremental elastoplastic analysis SC, that the safety factor of the structure under certain fire conditions can be assessed. The second part deals with the heat transfer problem of bare steel members in real fire. Factors affecting the heat transfer process are examined and a model for predicting the temperature variation with time under real fire conditions is proposed. This model results in more accurate temperature predictions for steel members than those obtained from previously adopted model.

Key Words
fire, temperature prediction, elastoplastic analysis, steel

Address
Wong MB, Monash Univ, Dept Civil Engn, Melbourne, Vic 3004, Australia
Monash Univ, Dept Civil Engn, Melbourne, Vic 3004, Australia
Monash Univ, Dept Mech Engn, Melbourne, Vic 3004, Australia

Abstract
This paper deals with the non-axisymmetric dynamic response of an imperfectly bonded buried orthotropic pipeline subjected to longitudinal wave (P-wave) excitation. An infinite cylindrical shell model, including the rotary inertia and shear deformation effects, has been used for the pipeline. For some cases comparison of axisymmetric and non-axisymmetric responses have also been furnished.

Key Words
orthotropic, axisymmetric, buried, dynamic response, imperfect bond, cylindrical shell

Address
Dwivedi JP, Banaras Hindu Univ, Inst Technol, Dept Mech Engn, Varanasi 221005, Uttar Pradesh, India
Banaras Hindu Univ, Inst Technol, Dept Mech Engn, Varanasi 221005, Uttar Pradesh, India

Abstract
A method that determines the minimum stiffness of baracing to achieve non-sway buckling conditions at a given story level of a multi-column elastic frame is proposed. Condensed equations that evaluate the required minimum stiffness of the lateral and torsional bracing are derived using the classical stability functions. The proposed method is applicable to elastic framed structures with rigid, semirigid, and simple connections. It is shown that the minimum stiffness of the bracing required by a multi-column system depends on: 1) the plan layout of the columns; 2) the variation in height and cross sectional properties among the columns; 3) the applied axial load pattern on the columns; 4) the lack of symmetry in the loading pattern, column layout, column sizes and heights that cause torsion-sway and its effects on the flexural bucking capacity; and 5) the flexural and torsional end restrains of the columns. The proposed method is limited to elastic framed structures with columns of doubly symmetrical cross section with their principal axes parallel to the global axes. However, it can be applied to inelastic structures when the nonlinear behavior is concentrated at the end connections. The effects of axial deformations in beams and columns are neglected. Three examples are presented in detail to show the effectiveness of the proposed method.

Key Words
buckling, bracing, building codes, columns, construction types, computer applications, frames, loads, P-Delta effects, reinforced concrete, seismic loads, steel, stability

Address
Aristizabal-Ochoa JD, Natl Univ, Sch Mines, Medellin AA 75267, Colombia
Natl Univ, Sch Mines, Medellin AA 75267, Colombia

Abstract
In this paper, the first-order ordinary differential constitutive equations of endochronic theory are incorporated into finite element formalism. A theoretical investigation is performed on the ratchetting effect of a stepped beam subjected to steady tension and cyclic bending. Experimental data of lead alloy found in literature are used for comparison. Those data reveal that the endochronic prediction yields more adequate results than those predictions using the plasticity models with isotropic hardening or kinematic hardening, as employed by Hardy, et al. (1985).

Key Words
endochronic theory, finite element formalism, stepped beam, cyclic bending

Address
Pan WF, Natl Cheng Kung Univ, Dept Engn Sci, Tainan 70101, Taiwan
Natl Cheng Kung Univ, Dept Engn Sci, Tainan 70101, Taiwan
Natl Pingtung Polytech Inst, Dept Civil Engn, Pingtung 91207, Taiwan

Abstract
The computation size and accuracy in the boundary element method are mutually coupled and strongly influenced by the formulations in boundary discretization and integration. This aspect is studied numerically for two-dimensional elastodynamic problems in the frequency-domain. The localized nature of error is observed in the computed results. A boundary discretization criterion is examined. The numer of integration points in the boundary integration is studied to find the optimum number for accuracy. Useful information is obtained concerning the optimization in boundary discretization and integration.

Key Words
boundary element method, boundary discretization, element integration

Address
Fu TM, Univ Cincinnati, Dept Civil & Environm Engn, Cincinnati, OH 45221 USA
Univ Cincinnati, Dept Civil & Environm Engn, Cincinnati, OH 45221 USA

Abstract
In this study an improved design method for the traditional A-type(or V-type) offshore template platform system was proposed to mitigate the vibration induced by the marine environmental loadings and the strong ground motions of earthquakes. A newly developed material model was combined into the structural system and then a nonlinear dynamic analysis in the time domain was carried out. The analysis was focused on the displacement and rotation induced by the input wave forces and ground motions, and the mitigation effect for these responses was evaluated when the viscoelastic damping devices were applied. The wave forces exerted on the offshore structures are based on Stokes fifth-order wave theory and Morison equation for small body. A step by step integration method was modified and used in the nonlinear analysis. It was found that the new design approach enhanced with viscoelastic dampers was efficient on the vibration mitigation for the structural system subjected to both the wave motion and the strong ground motion.


Key Words
offshore structure, dynamic analysis, viscoelastic material, vibration mitigation, seismic mitigation

Address
Lee HH, Natl Sun Yat Sen Univ, Dept Marine Environm, Kaohsiung 80424, Taiwan
Natl Sun Yat Sen Univ, Dept Marine Environm, Kaohsiung 80424, Taiwan


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