Object oriented development of strength and stiffness degrading models for reinforced concrete structures.

摘要

The aim of this research is to develop structural simulation models that can capture the strength and stiffness degradation of reinforced concrete frames up to collapse under earthquake-induced motions. The key modeling aspects of the element formulations include: (1) rigorous modeling of large deformation response, (2) flexural yielding and inelastic axial force-moment interaction (3) degradation of the element stiffness under cyclic loading and (4) axial force-moment-shear interaction for shear critical reinforced concrete columns.; Beam-column models are developed and implemented in an object-oriented analysis framework called OpenSees (Open System for Earthquake Engineering Simulation). The large deformation element formulations employ an updated Lagrangian approach. Inelastic models are based on stress resultant plasticity to simulate inelastic hardening/softening response under combined axial loads and bending. A two surface evolution model is proposed for combined non-uniform expansion/contraction and kinematic motion of the yield surface. The yield surface can be used to simulate inelastic section response at integration points along a beam-column element (distributed plasticity) or inelastic hinging at the ends of a beam-column element (concentrated plasticity). In the concentrated plasticity approach, the element between the hinges is quasi-elastic, in which hysteretic models are developed to model the cyclic degradation. This concentrated plasticity model is extended to simulate shear critical column behavior, including shear strength degradation and failure, axial-shear force interaction, and pinched cyclic response.; Implementation of the models in OpenSees is planned and structured using object oriented programming concepts. Individual components of the inelastic modeling problem are identified and the interactions between the governing classes are established. The models are implemented in a hierarchal structure, which provides a modular and extensible software design.; The accuracy and the capabilities of the proposed models are verified by comparing the analytical results with the experimental data. The models developed as part of this research provide ideal tools for conducting extensive application studies. An extensible framework is provided to facilitate tool development for nonlinear/inelastic analysis.