Two-Level Load Bearing Capacity Design And Optimization By Analysis For Transmission Tower

Transmission tower is an important structure in power networks, and its load bearing safety and economic performance is closely related to the operation safety and social influence of electric power system. Therefore, it is an important research work with social and economic significance to provide a design and optimization method of load bearing capacity for transmission tower. Based on the elastic modulus reduction method (EMRM), this thesis carried out the following research work focused on the two-level load bearing capacity design and optimization by analysis for transmission tower:(1) The homogeneous generalized yield function (HGYF) for commonly used thin-walled components of transmission tower was established. For angle steel and circular tube section, the homogeneous generalized yield function was established with regression analysis and least square method. The highest power was determined with error analysis, which gave the theoretical foundations for introducing the generalized yield function into elastic modulus adjustment method.(2) The EMRM for limit analysis of transmission tower was established. The element bearing ratio (EBR) of components was defined with the HGYF for angle steel and circular tube section. The dynamic adjustment threshold for elastic modulus was established in terms of uniformity of EBR (UEBR), and the adjustment strategy of elastic modulus was proposed in terms of deformation energy conservation principle. The EMRM for limit load analysis of transmission tower was proposed, which can overcome the problems such as poor calculation precision and stability caused by not meeting the proportional conditions.(3) Two-level load bearing capacity analysis and design method was proposed. Component bearing ratio (CBR) was defined with EBR, criterion for high and low stressed components was determined according to the iterative process of CBR, and the component and global safety factors were determined by means of EBRs obtained from the first and last iteration. The section strength of high stressed components was determined in direct proportion to the safety factor according to the preset global safety factor, which meets the requirements for bearing capacity and safety of transmission tower satisfied at both global and component level. Then it provides a good approach for quantitative design of global bearing capacity of transmission tower.(4) Two-level load bearing capacity optimization method was proposed. Two-level bearing capacity safety of transmission tower was taken as the main constraints, with uniformity of bearing capacity, or maximum of UEBR as optimization target. In terms of the inverse proportion between section strength of components and CBR, the optimization adjustment strategy for section strength of low stressed components was established, then two-level optimization method for transmission tower was proposed. Accordingly a structural design scheme can be achieved safely and economically. The optimization method not only can solve the problem of load bearing optimization design for overall structure, but also can integrate with traditional structure design method.