Keywords: elasto-plastic damage constitutive model, nonlinear analysis, damage evolution, short-pier shear wall, coupling beam, stress pattern, internal force redistribution, tensile damage, shear damage.

This paper presents a nonlinear analysis taking into account damage evolution to simulate a short-pier shear wall specimen with twin coupling beams. The numerical results obtained in this study mainly rest with three parts: the experiment of a new short-pier shear wall specimen with twin coupling beams, a novel damage energy release rate-based elasto-plastic damage constitutive model for concrete and the user-defined material subroutine(UMAT) provided by the engineering simulation program ABAQUS.

In virtue of the yielding of twin coupled beams earlier than the failure of the wall panels as well as the subsequent internal force redistribution, a short-pier shear wall specimen is designed as an energy dissipative structure superior to ordinary shear walls. Test observations during the whole loading process have verified its excellent ductility and energy dissipative capacity.

As a synthesis of the continuum damage mechanics and the plastic mechanics, a novel rate-independent elasto-plastic model for concrete is developed within the framework of classical continuum damage mechanics [1,2,3], whose basic principles can be summarized as:

1. A tensile damage variable and a shear damage variable leading to a fourth-order damage tensor are adopted to describe the degraded macro-mechanical properties of concrete materials.
2. By virtue of the decomposition of the effective stress tensor, the elastic free energy is obtained to define the elasto-plastic damage constitutive relation with internal variables, and thus the explicit expressions for the elasto-plastic free energy and the damage energy release rates are derived to establish the damage criteria.
3. In accordance with the normal rule, the evolution laws of damage variables and plastic strains are constructed respectively for the subsequent program implementation.

By means of the user-defined material subroutine(UMAT) supplied by ABAQUS in solving nonlinear problems [4], a numerical simulation of the short-pier shear wall specimen with twin coupling beams is implemented in this paper. A finite element model meshed by CPRS8R elements and a new convergence criterion named double control by load and displacement are adopted to obtain the macro and micro mechanical responses of the test specimen. By virtue of the stress patterns at typical levels of the free-end displacement, a series of distinctive structural responses are disclosed in a real and vivid way, namely homogeneous compression of the specimen, yielding of the coupled beams, internal force redistribution, root stress concentration and overall crushing of the wall panel at the compression side. Furthermore the corresponding tensile damage states and shear damage states in the course of damage evolution process are particularly reproduced to set up a brand-new nonlinear analytical mode from the constitutive model to the structural responses.

1

J.Y. Wu, J. Li and R. Faria, "An energy release rate-based plastic-damage model for concrete", International Journal of Solids and Structures, 43, 583-612, 2006. doi:10.1016/j.ijsolstr.2005.05.038

2

J. Li, "Research on the stochastic damage mechanics for concrete materials and structures", Journal of Tongji University (Natural Science Edition), 32(10), 1270-1277 (in Chinese), 2004.

3

J. Li and J.Y. Wu, "Energy-based CDM model for nonlinear analysis of confined concrete structures", Keynote in ISCC-2004 (No. Key-9), Changsha, China, 2004.

4

Documentation of ABAQUS version 6.4 (2004).

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