Probabilistic Evaluation Method Of Wind Resistant Ultimate Bearing Capacity Of Rigid Structures Based On Static Shakedown Theory

The light steel portal frame structure has been widely used in industrial and civil buildings.When subjected to strong wind load,the structure is vulnerable to damage,resulting in large economic losses.At present,the research on wind resistance mainly focuses on the elastic wind resistance design of structures under 50 years return period wind load,without paying attention to the elastic-plastic ultimate wind resistance performance of structures under rare strong wind(return period is much longer than 50years).The common incremental dynamic analysis method is too inefficient to determine the ultimate wind bearing capacity,and the calculation time is too long.To solve these problems,combined with the randomness and incomplete correlation of wind load distribution,this thesis proposes a probability analysis method of ultimate bearing capacity of rigid structures based on the static shakedown theory,which can significantly improve the calculation efficiency.Taking the calculation of portal frame as an example,the specific calculation process is expounded.The main contents and conclusions are as follows:(1)This thesis discusses the shakedown theory,and clarifies the calculation method of structural ultimate bearing capacity based on shakedown theory.The plastic strain energy and calculation non convergence are determined as the basis of the structural shakedown judgment.In order to verify the applicability of this method,this method is used to calculate the ultimate bearing capacity of the portal frame under concentrated force.To verify the characteristics that the structural stability is independent of the loading path,the loading waveform,the number of cycles,the initial loading value and the loading process are studied.(2)Aiming at the problems of the randomness and incomplete correlation of the wind load distribution,based on the classical shakedown theorem,this thesis proposes a probabilistic evaluation method of wind bearing capacity of rigid structure considering randomness of wind load and incomplete correlation of distribution mode.Multiple groups of wind load time-history samples are generated by random simulation.Through elastic time-history analysis of multiple samples,multiple most unfavorable wind load distribution modes corresponding to the key response of the structure are obtained.Then the static shakedown theory is used to calculate the wind resistance ultimate bearing capacity of the structure under each most unfavorable load distribution mode.The probability distribution of wind resistance ultimate bearing capacity of the structure is obtained by statistical analysis of multi sample results.Compared with incremental dynamic analysis method,this method has higher accuracy and higher efficiency.Finally,taking the portal frame as an example,the specific calculation process of this method is described.(3)In order to obtain the average value of the wind resistance ultimate bearing capacity of the structure quickly,the load response correlation coefficient is used to get the most unfavorable load distribution mode of the maximum probability corresponding to the maximum response at the key position of the structure.This load distribution mode is the average distribution mode of all possible most unfavorable distribution forms.This load distribution model is used to calculate the stability of the structure,and the average value of the ultimate bearing capacity of the structure under wind load is obtained.Taking the portal frame structure as an example,the most unfavorable load distribution mode is determined according to the load-response correlation method.The ultimate bearing capacity calculated by shakedown theorem is in good agreement with the average value of wind resistance ultimate bearing capacity calculated by multi sample method.