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CONTENTS
Volume 1, Number 1, February 2004
 

Abstract
Computer-based analysis tools for forensic assessment of reinforced concrete structures arernpresented. The analysis tools, mostly in the form of nonlinear finite element procedures, are based on thernconcepts and formulations of the Modified Compression Field Theory. Relevant details regarding theirrnformulation are provided. Development of realistic constitutive models and corroboration of the analysisrnprocedures, through comprehensive experimental programs, are discussed. Also presented are graphicsbasedrnpre- and post-processors, which are of significant aid in structural modeling, input of data, andrninterpretation of analysis results. The details and results of a case study, illustrating the application andrnvalue of such analytical tools, are also discussed.rn

Key Words
analysis; distressed; failure; finite elements; reinforced concrete; repair; shear; structures, software.

Address
Department of Civil Engineering, University of Toronto, 35 St. George Street, Toronto, Ontario, Canada M5S 1A4rn

Abstract
In this study, a design process for reinforced concrete structures using the nonlinear FEMrnanalysis is developed. Instead of using the nonlinear analysis to evaluate the required performance afterrndesign process, the nonlinear analysis is applied before designing the reinforcement arrangement inside thernRC structures. An automatic reinforcement generator for computer aided reinforcement agreement is developedrnfor this purpose. Based on a nonlinear FEM program for analyzing the reinforced concrete structure, arnsmart fictitious material model of steel is proposed which can self-adjust the reinforcement to the requiredrnamount at the cracking location according to the load increment. Using this tool, the reinforcement ratiornrequired at design load level can be decided automatically. In this paper, an example of RC beam withrnopening is used to verify the proposed process. Finally, a trial design process for a real size undergroundrnRC LNG tank is introduced.rn

Key Words
nonlinear analysis; FEM; RC structures; computer aided design.

Address
An Xuehui; School of Civil Engineering, Tsinghua University, ChinarnMaekawa Koichi; Department of Civil Engineering, The University of Tokyo, Japan

Abstract
A methodology is presented for computing stresses in structural concrete members exposedrnto fire. Coupled heat and moisture migration simulations are used to establish temperature, pore pressure,rnand liquid-saturation state variables within near-surface zones of heated concrete members. Particularrnattention is placed on the use of coupled heat and multiphase fluid flow simulations to study phenomenarnsuch as moisture-clogging. Once the state variables are determined, a procedure for combining the effectsrnof thermal dilation, mechanical loads, pore pressure, and boundary conditions is proposed and demonstrated.rnCombined stresses are computed for varying displacement boundary conditions using data obtained fromrncoupled heat and moisture flow simulations. These stresses are then compared to stresses computed fromrnthermal analyses in which moisture effects are omitted. The results demonstrate that moisture migrationrnhas a significant influence on the development of thermal stresses.rn

Key Words
fire; pore pressure; slip-flow; relative permeability; thermal stress; effective stress.

Address
University of Florida, Department of Civil & Coastal Engineering, P.O. Box 116580, Gainesville, FL 32611, U.S.A.

Abstract
The influence of the fracture process zone (FPZ) on the fracture properties is one of thernhottest topics in the field of fracture mechanics for cementitious materials. Within the FPZ in front of arntraction free crack, cohesive forces are distributed in accordance with the softening stress-separationrnconstitutive relation of the material. Therefore, further crack propagation necessitates energy dissipation,rnwhich is the work done by the cohesive forces. In this paper gf, the local fracture energy characterizingrnthe energy consumption due to the cohesive forces, is discussed. The computational expression of gf inrnthe FPZ can be obtained for any stage during the material fracture process regarding the variation of FPZ,rnwhether in terms of its length or width. Gfa, the average energy consumption along the crack extensionrnregion, has also been computed and discussed in this paper. The experimental results obtained from thernwedge splitting tests on specimens with different initial notch ratios are employed to investigate thernproperty of the local fracture energy gf and the average value Gfa over the crack extension length. Thesernresults can be used to indicate the influence of the FPZ. Additionally, changes in the length of the FPZrnduring the fracture process are also studied.rn

Key Words
energy dissipation; fracture process zone; softening law; fracture energy.

Address
Yanhua Zhao and Shilang Xu; Department of Civil Engineering, Dalian University of Technology, Dalian, ChinarnZongjin Li; Department of Civil Engineering, Hong Kong University of Science & Technology, Hong Kong, Chinarn

Abstract
The paper is devoted to present the Continuum Strong Discontinuity Approach (CSDA) andrnto examine its capabilities for modeling cracking of concrete. After introducing the main ingredients ofrnthe CSDA, an isotropic continuum damage model, which distinguishes tension and compression states, isrnused to implicitly induce a projected traction separation-law that rules the cracking phenomena. Criteriarnfor onset and propagation of material failure and specific finite elements with embedded discontinuitiesrnare also briefly sketched. Finally, some representative numerical simulations of cracking, in plain andrnreinforced concrete specimens, using the CSDA are presented.rn

Key Words
concrete; crack modeling; strong discontinuity; continuum damage.

Address
ETS Enginyers de Camins, Canals i Ports de Barcelona, Technical University of Catalonia (UPC),rnCampus Nord UPC, Edifici C-1, C/Jordi Girona 1-3, 08034 Barcelona, Spainrn

Abstract
This paper presents a numerical model for simulating the nonlinear response of reinforcedrnconcrete (RC) shear walls subject to cyclic loadings. The material behavior of cracked concrete isrndescribed by an orthotropic constitutive relation with tension-stiffening and compression softening effectsrndefining equivalent uniaxial stress-strain relation in the axes of orthotropy. Especially in making analyticalrnpredictions for inelastic behaviors of RC walls under reversed cyclic loading, some influencing factorsrninducing the material nonlinearities have been considered. A simple hysteretic stress-strain relation ofrnconcrete, which crosses the tension-compression region, is defined. Modification of the hysteretic stressstrainrnrelation of steel is also introduced to reflect a pinching effect depending on the shear span ratio andrnto represent an average stress distribution in a cracked RC element, respectively. To assess thernapplicability of the constitutive model for RC element, analytical results are compared with idealizedrnshear panel and shear wall test results under monotonic and cyclic shear loadings.rn

Key Words
pinching effect; shear walls; cyclic behavior; average stress-strain; nonlinear analysis.

Address
Department of Civil and Environmental Engineering, KAIST,rn373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korearn

Abstract
The article reports data on, and numerical modelling of, beams exhibiting points of inflectionrnand subjected to sequential loading. Both tests and analysis point to inadequacies in current codes ofrnpractice. An alternative design methodology, which is strongly associated with the notion that contraflexurernpoints should be designed as \"internal supports\", is shown to produce superior performance even though itrnrequires significantly less secondary reinforcement than advocated by codes.rn

Key Words
structural concrete; nonlinear finite-element modelling; points of inflection; sequential loading;

Address
I. Jelic; Arup, 155 Avenue of the Americas, New York 10013 USArnM.N. Pavlovic; Department of Civil and Environmental Engineering, Imperial College, London SW7 2AZ, UKrnM.D. Kotsovos; Department of Civil Engineering, National Technical University of Athens, Zographou, Athens 15780, Greecern


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