Elasto-plastic large displacement analysis of planar frames with joint flexibility using the finite element method

When framed structures are subjected to static or dynamic loading, several geometric and material nonlinearities can be encountered in an earlier stage of loading. These nonlinearities include changes in geometry, material yielding and connection flexibility. For a realistic prediction of the nonlinear behavior of framed structures, members of framed structures such as beam-column and connection elements must be modeled as closely to reality as possible. This dissertation attempts to provide realistic and accurate analytical tools for predicting large displacements in the planar elasto-plastic frames analysis, including the effects of connection flexibility.; In lieu of distributed plasticity, concentrated plasticity has generally been employed to simulate inelastic behavior due to limitations in computer memory and speed, especially for large structures. However, recent advances in computer hardware as well as in computer software technology make distributed plasticity more attractive than before. Therefore, two new beam-column finite element models based on distributed plasticity including geometric nonlinearities are proposed. The first beam-column model uses the Timoshenko Beam assumption, while the second is based on the Bernoulli-Euler beam assumption. The formulated beam-column elements are tested using the rigid body motion test to determine if the stiffness matrices can be used for nonlinear analysis. Then the results obtained from the distributed plasticity method are compared to the results from the concentrated plasticity method.; The influences of connection flexibility on the behavior of framed structures are conventionally ignored in analysis. When they are taken into account, their effects are included in the analysis by modifying the element stiffness matrix of beam-columns. As a result, the beam-column element stiffness matrix is completely different from the matrices used in the conventional approach. As an alternative to revising the beam-column element stiffness, an independent finite size connection element is employed to describe the nonlinearities arising from the joints of framed structures. A solution strategy for nonlinear inelastic analysis, an incremental-iterative method based on the generalized displacement control method, is employed. The finite element formulations presented in this work have been implemented into a computer program named NPFrame++ which is based on the object-oriented paradigm and the C++ programming language.; Several example problems such as elastica, plastica, rigid and semi-rigid frame problems are solved by using NPFrame++. Results from the work presented have been compared with those obtained from a theoretical, an experimental and a commercial finite element computer program, namely ABAQUS. The examples illustrate the effectiveness of the beam-column and connection elements presented for nonlinear analysis.