3D Stiffness and Strength Degradation Models for Seismic Progressive Collapse Analysis of Reinforced Concrete Structures – Formulations and Implementations Framework

The principal objective of this research is to develop a comprehensive model for seismic response analysis of reinforced concrete structures subjected to multi-component seismic loading that captures the behaviours of members in new structures designed as ductile as well as non-ductile members in existing older deficient structures. The focus is on the formulation of a beam-column element using the concentrated plasticity approach and the development of a framework for the implementations of the new model using object oriented design concepts. The key modeling capabilities considered in this study include: capturing axial force-bending moment interactions; simulating post-yield hardening response; detecting brittle or limited ductility types of failure in shear; capturing degradation of shear strength in the plastic hinge zone with increased displacement ductility; simulating softening in the post-shear failure response; capturing stiffness degradation and cyclic strength deterioration under repeated load reversals; tracking the progression and accumulation of damage and its effects on stiffness and strength degradation.The element formulation employs yield and shear-failure surfaces as well as evolution models for the generalized plastic hinges at the element ends. The degradation of shear strength in the plastic hinge region with increasing flexural displacement ductility demand is captured by using ductility-related shear limit surface associated with the evolution model. The cyclic behaviour modeling is based on the incorporation of damage models in the beam-column element formulation to track the progression of damage and its effects on the gradual deterioration in stiffness and loss of strength. A consistent generalized approach for state determination is developed using event-based strategy.In the development of the object oriented implementation framework, the individual components of the proposed inelastic concentrated-plasticity model are identified and the functionalities of each component are defined. The interface and the interactions between the abstract base classes - beam-column element, yield surface, shear failure surface, evolution model, shear limit surface, cyclic model, cyclic control, damage model, and damage progression classes - are established based on the required functionalities. The hierarchal structure of the proposed classes and the independent implementations of the main components are designed to provide a comprehensive and flexible design that allows extensibility.