| The main contribution of this investigation is the establishment of efficient and practical nonlinear dynamic computational procedures for steel framed structures subjected to complex cyclic loading. The beam-column elements are modeled by a novel concentrated plasticity formulation. This model describes effectively the hysteretic behavior of members subjected to relatively stable cyclic loads such as developed by an earthquake. The elasto-plastic stiffness matrix of the element is derived in a concise form using force-space concentrated plasticity assumptions. Three kinematic hardening rules are implemented, including bilinear strain hardening, a nested-surfaces approach, and a more gradual plastification and hardening modeled by a bounding-surface concept.;A major part of the thesis deals with the implementation concepts of the models in an interactive-adaptive three-dimensional, full nonlinear analysis program. The computational environment includes vector-refresh graphics displays and a 32-bit, virtual-memory minicomputer. The graphics capability of the system facilitates data input, definition of the analysis parameters, description of the behavior of the structure, display of the yield surface motion, monitoring of different variations of the variables, and comparison of different analyses.;The advantages of the formulation, together with the preferred bounding-surface hardening model, are the following: (1) realistic representation of the hysteretic behavior of the element; (2) modeling of semi-rigid connections; (3) approximate modeling of residual stresses; (4) simulation of the effects of overal member curvature on the concentrated plastic zones at the member ends; (5) the need for only a few hardening model parameters; (6) possible extension to accommodate viscoplastic behavior for high strain-rate problems; (7) a closed-form strain-hardening stiffness matrix for beam elements which reduces to the elastic-perfectly plastic matrix as a special case; (8) modeling for geometric nonlinearities via the use of a geometric stiffness matrix and an Updated Lagrangian formulation; and (9) efficient evaluation of the ductility factors of the structural elements based on the total rotation of the end of the member. |
