Strain-Rate Effect in Rapid Triaxial Loading of Concrete

by Zdeněk P. Bažant, (F.ASCE), Prof. of Civ. Engrg. and Dir.; Center for Concrete and Geomaterials, Northwestern Univ., Evanston, Ill. 60201,
Byung H. Oh, Grad. Research Asst.; Northwestern Univ., Evanston, Ill. 60201,

Serial Information: Journal of the Engineering Mechanics Division, 1982, Vol. 108, Issue 5, Pg. 764-782

Document Type: Journal Paper


Presented is a generalization of time-independent nonlinear triaxial constitutive relations for concrete to model short-time viscoelastic effects. The effect of strain-rate magnitude upon the initial elastic modulus, the peak stress, and the sharpness of the stress peak is taken into account. To obtain a model that also exhibits short-time rapid creep and stress relaxation, the incrementally linear constitutive law fully characterized by tangential moduli is replaced by a nonlinear first-order differential equation in stress, strain, stress rate and strain rate. This requires introduction of the (apparent) instantaneous modulus, the relaxation time and retardation time. The irreversibility at unloading, caused by the short-time viscoelastic mffects, is also analyzed. The model allows more realistic dynamic finite element analysis of concrete structures.

Subject Headings: Stress strain relations | Triaxial loads | Strain rates | Load factors | Concrete | Constitutive relations | Viscoelasticity | Relaxation (mechanics)

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