| Optimum structural design has always been an intellectually challenging and practically important area of research interest. Today, it is more feasible to make the optimization procedures an integral part of the design process as analysis techniques advance. In the field of plastic analysis and design, it has been many years since the first linear programming formulation of the optimum rigid-plastic design was presented for two dimensional steel frame structure. That formulation, however, lacked many considerations for proper practical application.; For example, the plastic moment capacity is reduced by the presence of axial force with a magnitude above certain value. That is why the simple plastic theory should not be used for the design of high rise buildings. Most of the optimum rigid-plastic design methods developed are, therefore, limited to low rise structures.; As a second example why the rigid-plastic design method is not used in high rise slender structures is the inability to take into consideration the P-{dollar}Delta{dollar} effect in determining the failure mechanisms.; Although substantial improvements have been made to the original optimum rigid-plastic design method, specialized knowledge is still required for complicated structures in terms of data preparations and knowledge in releasing structures.; In this study, a reduced stiffness approach is adopted to develop an efficient optimum elastic-plastic design method for two dimensional steel structure. An mathematical programming formulation is derived to include the axial force effect on moment carrying capacity, multiple loading cases and the P-{dollar}Delta{dollar} effect.; After reviewing the static and mechanism approaches used in the classical plastic analysis and their applications to optimum rigid-plastic design, this dissertation introduces the reduced stiffness approach and presents a method of applying the reduced stiffness approach to the optimum elastic-plastic design. The strain-hardening effect is next included in the formulation. A computer program is developed based on this formulation. A number of design examples are given to demonstrate the versatility of the formulation and the usage of the computer program. |
