Two Level Bearing Capacity Optimization Design Research For Truss And Frame

In order to save the cost on engineering structure, optimization design can be performed under the requirements of security through proper use of material. At present, traditional optimization design methods usually aim to provide a scheme by using elastic analyses under the design load. But, these optimization design methods cannot be employed to guarantee the global safety of structures in their elastic-plastic state under severe load and ultimate load conditions. Combined with the full stress criterion method, this thesis provides a two level bearing capacity optimization design method for truss and frame. The main contents are as follows:(1)An optimization design method for truss was presented, which can ensure the safeties of the component level and the global level. The elastic modulus reduction method (EMRM) was introduced to analyze the ultimate bearing capacity of structure. Based on the bearing ratio of components, a recognition criterion for highly and lowly stressed components was presented. The sectional strength of highly stressed components was determined in direct proportion to the safety factor. Then, the two level bearing capacity design method was proposed systematically. With the well distributed bearing as optimization criterion, a sectional strength adjustment strategy for lowly stressed components was proposed further to realize the optimization design for truss.(2)An optimization design method for frame was also given, which can ensure the safety of the component level and the global level. In view of the bearing characteristics under the combination of internal force of frame, the homogeneous generalized yield function was used. A recognition criterion for highly and lowly stressed components and the sectional strength adjustment strategies for highly stressed components and lowly stressed components are presented. Then, the two level bearing capacity optimization design method was proposed systematically. At the same time, an inversion method for calculating sectional geometric parameters for rectangular section and I-shaped section were presented.(3)The influence factors on the proposed optimization design method for truss and frame were analyzed, including the convergence tolerance of the EMRM, the strength adjustment enhancement coefficient and the convergence tolerance of optimization. And then, recommendations for magnitude value of these three parameters are suggested.