Structural Safety Assessment And Design Optimization Based On Redundancy

The traditional structural design is based on the strength of the components.It aims to checking whether the design of the sectional dimensions of the components can meet the specified requirements under the limit state and normal use limit state.However,as the number of years increases,the changing environment,the aging of materials and the appearance of unexpected loads,the stability and safety of the structure will decline.The structure is likely to have collapsed directly when damage occurs since designers did not take the impact of component damage on the structural collapse into account at the initial design stage.Therefore,the traditional structural design based on component strength often leads to lower redundancy of the structure.It is necessary to consider redundancy theory in structural optimization design.The advantage of structural optimization design considering redundancy theory is that it can quantitatively control the “degree” of its performance of using the structure.Excessive redundancy feature design can fully guarantee the safety performance of the structure,but it will certainly result in the waste of structural performance and economic.Too few redundant structural designs do not guarantee the stability and safety of the structure under unintended loads.Redundancy can reflect the collapse resistance of the structure.The paper uses the redundancy theory to evaluate the structural stability and safety of the three-span continuous and two-girder bridge,bridge pier model,simple steel truss bridge model and three-tier three-by-three framework model.It can show the key components,vulnerable components,damage paths,and redundancy values of the structure in the collapse from the evaluation results.And we feedback these assessment results to the optimal design of the structure.The main optimization methods used are changing the size of the components,changing the parameters of the materials,and adding additional redundant components.Finally,the rationality and effectiveness of the optimization are verified by simulation and other theoretical analysis.The main research completed and results are as follows:(1)The thesis summarizes the research and application status of redundancy theory in civil engineering structure at home and abroad.(2)The redundancy indicators of previous studies are verified and analyzed by using the redundancy evaluation of the finite element model of a three-span continuous double-girder bridge.The relationship between the stress of the main beam and the allowable stress when the bridge collapses is obtained.We also see the stress development trend and deformation trend of the main beam under the limit state.(3)A redundancy demand value based on capability spectrum was proposed.Through a bridgepier model,pushover analysis was carried out to obtain the capability curves of different pier heights of the model.And it combined with the seismic demand spectrum to find performance points.Redundancy demands are evaluated at different heights of the model.The relationship between redundancy and pier height is drawn.(4)A redundancy index based on structural performance parameters was proposed and a structural redundancy damage curve was established.It established a simple steel truss bridge model.The key components,vulnerable components and damage paths in the model are obtained by selecting the stress safety factor and displacement to evaluate their redundancy.The original model was optimized of size parameters based on the redundancy damage curve of key components in the model.The degree of allowable damage of the optimized components has been improved,and the initial redundancy has also increased.(5)A sensitivity-based redundancy calculation formula is established for the characteristics of the frame structure.The sensitivity-based redundancy evaluation was performed on the three-tier three-span frame structure,and the redundancy distribution of the entire frame model was obtained.Two optimization schemes are proposed According to the redundancy distribution diagram of beams and columns,and the optimized redundancy distribution is more even.The rationality of the optimization scheme was verified from the overall structure through the elasto-plastic analysis of the original model and the optimized model.