Implementation of Lumped Plasticity Models and Developments in an Object Oriented Nonlinear Finite Element Code.

摘要

Numerical simulation tools capable of modeling nonlinear material and geometric behavior are important to structural engineers concerned with approximating the strength and deformation capacity of a structure. While structures are typically designed to behave linear elastic when subjected to building code design loads, exceedance of the linear elastic range is often an important consideration, especially with regards to structural response during hazard level events (i.e. earthquakes, hurricanes, floods), where collapse prevention is the primary goal. This thesis addresses developments made to Mercury, a nonlinear finite element program developed in MATLAB for numerical simulation and in C++ for real time hybrid simulation. Developments include the addition of three new constitutive models to extend Mercury's lumped plasticity modeling capabilities, a constitutive driver tool for testing and implementing Mercury constitutive models, and Mercury pre and post-processing tools.;Mercury has been developed as a tool for transient analysis of distributed plasticity models, offering accurate nonlinear results on the material level, element level, and structural level. When only structural level response is desired (collapse prevention), obtaining material level results leads to unnecessarily lengthy computational time. To address this issue in Mercury, lumped plasticity capabilities are developed by implementing two lumped plasticity flexural response constitutive models and a column shear failure constitutive model. The models are chosen for implementation to address two critical issues evident in structural testing: column shear failure and strength and stiffness degradation under reverse cyclic loading. These tools make it possible to model post-peak behavior, capture strength and stiffness degradation, and predict global collapse.;During the implementation process, a need was identified to create a simple program, separate from Mercury, to simplify the process of implementing a new constitutive model. A constitutive driver tool with a graphical user interface is developed to address this issue, providing benefits for Mercury development and classroom learning.;A Mercury pre and post-processor graphical user interface is also implemented. The developed tool is a standalone application which allows Mercury users to visualize numerical models for verification and view analysis results without the need to transfer information. Mercury analysis may also be run from within the application. All necessary pre-process, analysis, and post-process procedures are, therefore, combined into the program, collectively referred to as Mercury++.