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CONTENTS
Volume 2, Number 1, March 1994
 

Abstract
A unified theory has recently been developed for reinforced concrete structures (Hsu 1993), subjected to the four basic actions - bending, axial load, shear and torsion. The theory has five components, namely, the struts-and-ties model, the equilibrium (or plasticity) truss model, the Bernoulli compatibility truss model, the Mohr compatibility truss model and the softened truss model. Because the last three models can satisfy the stress equilibrium, the strain compatibility and the constitutive laws of materials, they can predict not only the strength, but also the load-deformation history of a member. In this paper the five models are summarized to illustrate their intrinsic consistency.

Key Words
axial load; bending moment; compatibility; constitutive laws; equilibrium; reinforced concrete; shear; structural design; torsion; truss models.

Address
Department of Civil and Environmental Engineering, University of Houston, Houston, Texas, U.S.A.

Abstract
This paper proposes a new four node degenerated shell element. In the formulation of the new element, the assumed covariant shear strains are used to avoid the shear locking problem, and the assumed covariant membrane strains are applied to alleviate the membrane locking problem and also to improve the membrane bending performance. The assumed covariant strains are obtained from the covariant strain field defined with respect to the element natural coordinate system. This formulation enables us to obtain a shell element, which does not produce spurious singular modes, avoids locking phenomena, and excels in calculation efficiency. Several examples in this paper indicate that, despite its simplicity, the achieved accuracy and convergence are satisfactory.

Key Words
assumed strain degenerated shell element; shear locking; membrane locking; covariant; natural coordinate line; membrane bending.

Address
Department of Civil Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea

Abstract
A plasticity-based concrete model is proposed. The failure surface is elliptic in the σ-τ stress space. Independent hardening as well as softening is assumed in tension, compression, and shear. The nonlinear inelastic action initiates from the origin in the σ-ε (τ-γ) diagram. Several parametesr are incorporated to control hardening/softening regions. The model is incorporated into a nonlinear finite element program along with other classical models. Several examples are solved and the results are compared with experimental data nd other failure criteria. "Reasonable results" and stable solutions are obtained for different types of reinforced concrete oriented structures.

Key Words
concrete model; plasticity; failure surface; independent hardening/softening; ellipse; nonlinear finite element; reinforced concrete.

Address
Dept. of Civil Engineering, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia

Abstract
Based on the transfer matrix approach and integral transforms, a solution method is developed for the stress analysis of axisymmetrically loaded transversely isotropic elastic media with generalized interlayer and support conditions. Transfer functions (Green

Key Words
stress analysis; anisotropy; elastic layers; transfer matrix.

Address
Department of Civil and Environmental Engineering, Clarkson University, Potsdam, NY 13676, USA

Abstract
A cable is considered as a system of helical wires and a core with distributed dry friction forces at their interfaces. Deformations of the cable subjected to a uniform bending are analyzed. It is shown that there is a critical bending curvature when a slip at the wire-core interface occurs. It originates at the neutral axis of the cross section of the cable and then spreads symmetrically over the cross section with the increase of bending. The effect of slippage on the cable stiffness is investigated. This model is also used to analyze a cable under the quasi-static cyclic bending. Explicit expression for the hysteretic losses per cycle of bending is derived. Numerical examples are given to show the influence of dry friction and helix angle on the bending stiffness and hysteretic losses in the cable.

Key Words
cables; bending; dry friction; slip; hysteretic losses.

Address
Department of Mechanical Engineering, The University of Calgary, Alberta, Canada

Abstract
It is well recognized that structures designed to resist strong ground motions should be able to withstand substantial inelastic deformations. A simple procedure has been developed in this paper to monitor the dynamic earthquake response (time-history analysis) of both steel and concrete multistorey buildings in the inelastic range. The building is treated as a shear beam model with three degrees of freedom per floor. The entire analysis has been programmed to run on a microcomputer and can output time histories of displacements, velocities, accelerations and member internal forces at any desired location. A record of plastic hinge formation and restoration to elastic state is also provided. Such information can be used in aseismic analysis and design of multistorey buildings so as to control the damage and optimize their performance.

Key Words
asymmetry; multi-storey building; hysteresis model; inelastic response; aseismic design.

Address
School of Civil Engineering, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4001, Australia

Abstract
This paper describes the formulation and application of a dynamic model for a conventional rail track subjected to arbitary loading functions that simulate wheel/rail impact forces. The rail track is idealized as a periodic elastically coupled beam system resting on a Winkler foundation. Modal parameters of the track structure are first obtained from the natural vibration characteristics of the beam system, which is discretized into a periodic assembly of a specially-constructed track element and a single beam element characterized by their exact dynamic stiffness matrices. An equivalent frequency-dependent spring coefficient representing the resilient, flexural and inertial characteristics of the rail support components is introduced to reduce the degrees of freedom of the track element. The forced vibration equations of motion of the track subjected to a series of loading functions are then formulated by using beam bending theories and are reduced to second order ordinary differential equations through the use of mode summation with non-proportional modal damping. Numerical examples for the dynamic responses of a typical track are presented, and the solutions resulting from different rail/tie beam theories are compared.

Key Words
railway track; dynamics; impact loading; modal analysis.

Address
Department of Civil Engineering, Royal Military College, Kingston, Ontario, Canada, K7K 5L0
Department of Civil Engineering, Queen

Abstract
A method for computing the elastic buckling prestressing force of a post-tensioned composite steel-concrete tee-beam is presented. The method is based on a virtual work formulation, and incorporates the restraint provided by the concrete slab to the buckling displacements of the steel beam. The distortional buckling solutions are shown to be given by a quadratic equation. The application of the analysis to calculation buckling strengths is given, based on codified rules for beam-columns. Conclusions are then drawn on the importance of distortional buckling when a post-tensioned composite beam is stressed during jacking.

Key Words
buckling; composite beams; distortion; post-tensioning; prestressing.

Address
Department of Structural Engineering, The University of New South Wales, Kensington, Australia

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