Limit Analysis And Two-level Load Bearing Capacity Design And Optimization For Bridge Structure

Highway transportation network is the basis of national economic development.Bridge is the extremely important part of transport system.However,bridge collapse accident has occurred many times by insufficient of ultimate bearing capacity.This thesis carried out the following research work focused on the limit analysis and two-level load bearing capacity design and optimization for bridge structure:(1)The homogeneous generalized yield functions(HGYFs)are presented for commonly-used sections in bridge structures.The box section,I-shaped section,thin-walled circular section,rectangular section and solid circular section are among the most commonly-used sections in bridge structures,considering the global and local features of GYF,the selection principle of points for HGYF regression analysis and the power for a HGYF then be determined,and then HGYFs of the commonly-used sections are provided.which overcome the problem of variation of limit load result with different initial load induced by GYF.(2)The proposed elastic modulus reduction method(EMRM)can provide a promising and stability result for limit analysis of the bridge structures.The HGYFs are presented for five types of commonly used sections based on regression analysis.The element bearing ratio(EBR),the reference EBR and the uniformity of EBR for commonly used sections are defined on the basis of the HGYFs,the strategy of elastic modulus adjustment is proposed for the damage evolution of bridge structure based on deformation energy conservation principle,then the limit load of truss bridge,through arch bridges and concrete filled steel tube bridge are analysed.Numerical examples show that the HGYF-based EMRM is an accurate and efficient calculation method for the limit load analysis of bridge structures.(3)The two-level load bearing capacity design and optimization for bridge structure was presented.Safety factors of the two-level load bearing capacity are determined;the design and adjustment formula of the sectional strength is given.The relationship between the component bearing capacity and the ultimate bearing capacity is established based on the definition of the component bearing capacity ratio.Then,the goals for the quantitatively design of structural ultimate bearing capacity are achieved by adjusting the section strength of the component.The two-level load bearing capacity optimization was presented as the uniformity of element bearing ratio is the largest for optimization target and two level load Bearing safety for constraint condition.This optimization method can correctly identify the low load bearing component considering the redistribution of internal forces.(4)Comparative analysis of two-level load bearing capacity design and current structure design method showed that this proposed approach can design the component load bearing in the first step and the structural ultimate bearing capacity at the end of the iteration step.The high and low load bearing components are identified based on iterative process of analysis.This approach is a uniform and coherent design method based on the requirements two level load bearing safety and overcome the shortcomings of current structural design method in the quantitatively design of structural ultimate bearing capacity.