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CONTENTS
Volume 1, Number 2, May 2004
 

Abstract
The flexural ductility of solid rectangular reinforced concrete beams has been studied quiternextensively. However, many reinforced concrete beams are neither solid nor rectangular; examples includernT-, -, - and box-shaped beams. There have been few studies on the flexural ductility of nonrectangularrnreinforced concrete beams and as a result little is known about the possible effect of sectionalrnshape on flexural ductility. Herein, the effect of sectional shape on the post-peak flexural behaviour ofrnreinforced normal and high-strength concrete beams has been studied using a newly developed analysisrnmethod that employs the actual stress-strain curves of the constitutive materials and takes into account thernstress-path dependence of the stress-strain curve of the steel reinforcement. It was revealed that thernsectional shape could have significant effect on the flexural ductility of a concrete beam and that thernflexural ductility of a T-, -, - or box-shaped beam is generally lower than that of a solid rectangularrnbeam with the same overall dimensions and the same amount of reinforcement provided. Based on thernnumerical results obtained, a simple method of ensuring the provision of a certain minimum level ofrnflexural ductility to non-rectangular concrete beams has been developed.

Key Words
flexural ductility; high-strength concrete; reinforced concrete beams.

Address
Department of Civil Engineering, The University of Hong Kong, Hong Kong

Abstract
We present in this work a coupled phenomenological chemo-mechanical model thatrnrepresents the degradation of concrete-like materials. The chemical behaviour is described by thernnowadays well known simplified calcium leaching approach. And the mechanical damage behaviour isrndescribed by a continuum damage model which involves the gradient of the damage quantity. Therncoupled nonlinear problem at hand is addressed within the context of the finite element method. For thernequation governing the calcium dissolution-diffusion part of the problem, special care is taken to treat thernhighly nonlinear calcium conductivity and solid calcium functions. The algorithmic design is based on arnNewton-type iterative scheme where use is made of a recently proposed relaxed linearization procedure.rnAnd for the equation governing the damage part of the problem, an augmented Lagrangian formulation isrnused to take into account the damage irreversibility constraint. Finally, numerical simulations arerncompared with experimental results on cement paste

Key Words
calcium leaching; continuum damage mechanics; gradient damage formulation; continuumrnthermodynamics; finite element method.

Address
?aboratoire d Analyse des Materiaux et ntification, Institut Navier, 6 et 8, Avenue Blaise Pascal, CiternDescartes, Marne-la-Vallee Cedex 2, Francern?RSN/DIR/Pg, BP 17, 92262 Fontenay-aux-Roses Cedex, France

Abstract
A two-dimensional nonlinear finite element model is developed to simulate time-dependentrncracking of reinforced concrete members under service loads. To predict localized cracking, the crackrnband model is employed to model individual crack opening. In conjunction with the crack band model, arnbond-interface element is used to model the slip between concrete and reinforcing steel permitting largernslip displacements between the concrete element nodes and the steel truss element nodes at crackrnopenings. The time-dependent effects of concrete creep and shrinkage are incorporated into the smearedrncrack model as inelastic pre-strains in an iterative solution procedure. Two test examples are shown tornverify the finite element model with good agreement between the model and the observed test results.

Key Words
concrete; cracking; creep; shrinkage; time; finite element.

Address
School of Civil and Environmental EngineeringrnThe University of New South Wales, UNSW Syudney, 2052. Australia

Abstract
A coupled damage-viscoplasticity model is presented for the analysis of localisation and sizerneffects. On one hand, viscosity helps to avoid mesh sensitivity because of the introduction of a lengthrnscale in the model and, on the other hand, enables to represent size effects. Size effects were analysed byrnmeans of three-point bending tests. Correlation between the fracture energy parameter measuredrnexperimentally and the density fracture energy modelling parameter is discussed. It has been shown thatrnthe dependence of nominal strength and fracture energy on size is determined by the ligament length inrncomparison with the width of the fracture process zone.

Key Words
damage viscoplasticity; fracture energy; size effect; localisation

Address
URGC Structures , INSA de Lyon, Villeurbanne France ,rnTU Delft, Faculty of Civil Engineering and Geosciences, Delft, The NetherlandsrnURGC Structures , INSA de Lyon, Villeurbanne, France

Abstract
Several extensions to the Thelandersson phenomenological model for concrete under transientrnhigh temperatures are explored. These include novel expressions for the temperature degradation of thernelastic modulus and the temperature dependency of the coefficient of the free thermal strain. Furthermore,rna coefficient of thermo mechanical strain is proposed as a bi-linear function of temperature. Goodrnqualitative agreement with various test results taken from the literature is demonstrated. Further extensionsrninclude the effects of plastic straining and temperature dependent Poisson? ratio. The models performancernis illustrated on several simple benchmark problems under uniaxial and biaxial stress states.

Key Words
concrete; transient temperature effects; transient creep; load induced thermal strain; restraint stresses.

Address
?anish Technological Institute, P.O. Box 141, DK-2630 Taastrup, Denmarkrn??epartment Civil Engineering, University of Glasgow, Rankine Building, Oakfield Avenue,rnGlasgow G12 8LT, U.K.

Abstract
A relatively simple multiple-vertical-line-element macro model has been incorporated into arnstandard computer code DRAIN-2D. It was used in blind predictions of seismic response of cantilever RCrnwalls subjected to a series of consequent earthquakes on a shaking table. The model was able to predictrnpredominantly flexural response with relative success. It was able to predict the stiffness and the strengthrnof the pre-cracked specimen and time-history response of the highly nonlinear wall as well as to simulaternthe shift of the neutral axis and corresponding varying axial force in the cantilever wall. However, failingrnto identify the rupture of some brittle reinforcement in the third test, the model was not able to predictrnpost-critical, near collapse behaviour during the subsequent response to two stronger earthquakes. Thernanalysed macro model seems to be appropriate for global analyses of complex building structures withrnRC structural walls subjected to moderate/strong earthquakes. However, it cannot, by definition, be usedrnin refined research analyses monitoring local behaviour in the post critical region.

Key Words
nonlinear analysis; seismic analysis; reinforced concrete walls; macro model; benchmark study.

Address
University of Ljubljana, Faculty of Civil and Geodetic Engineering,rnJamova 2, SI-1000 Ljubljana, Slovenia


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