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CivilComp Proceedings
ISSN 17593433 CCP: 86
PROCEEDINGS OF THE ELEVENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING Edited by: B.H.V. Topping
Paper 158
MultiLayer ViscoElastic Creep Model for TimeDependent Analysis of Concrete Structures P.L. Ng, J.Y.K. Lam and A.K.H. Kwan
Department of Civil Engineering, The University of Hong Kong, China P.L. Ng, J.Y.K. Lam, A.K.H. Kwan, "MultiLayer ViscoElastic Creep Model for TimeDependent Analysis of Concrete Structures", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Civil, Structural and Environmental Engineering Computing", CivilComp Press, Stirlingshire, UK, Paper 158, 2007. doi:10.4203/ccp.86.158
Keywords: concrete, cracking, creep, finite element method, shrinkage, viscoelasticity.
Summary
Timedependent analysis of concrete structures is crucial for the assessment of possible longterm shrinkage and creep movements, identification of highly stressed regions at different time, recognition of areas which are prone to cracking, and evaluation of alternative construction schemes and concrete placement scheduling so as to mitigate the shrinkage cracking problem [1,2]. For general structures, the timedependent analyses are most suitably conducted using the finite element method. In accordance with the conventional concrete creep models (including the prevalent codified formulations, for example, Model Code 1990 [3]), when the stresses in concrete vary with time, the corresponding creep strains at any time have to be determined as the summation of individual creep responses due to stress increments in preceding time intervals [4,5]. However, such summation process entails the memorisation of stress histories for all finite elements, thus leading to prohibitive computer storage requirements and computational effort demand for large analysis problems.
In the present study, a new viscoelastic creep model is developed for concrete, whereby the concrete creep is modelled by a set of rheological elements and the creep strain is expressed in terms of a set of remnant creep strains carried by viscoelastic units. By connecting specially designed viscoelastic units in parallel, the proposed model possesses a multilayer configuration. In this paper, the associated governing equations and mathematical derivations are expounded. The proposed model successfully circumvents the need of memorising the stress histories of concrete, thereby greatly facilitates the computer analyses of timedependent effects on concrete structures. The multilayer viscoelastic creep model is completely general in the sense that it is capable to reproduce any creep function by expressing the function in the form of Dirichlet series, i.e. a series of real exponentials. Herein, reference has been made to the Model Code 1990 [3] in the valuation of the model parameters. Excellent agreement is achieved between the Model Code 1990 and the proposed creep model. To demonstrate the general applicability of the proposed model, numerical examples on restrained concrete prism and concrete podium structure are presented. The authors advocate the use of the multilayer viscoelastic model in timedependent analyses for construction projects. References
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