Safety Assessment Of Existing Structures Based On Proof Load Method

The statistics and calculation to existing structures' resistance is an important part in reliability analysis specially safety analysis to existing structures.At the present time, the analysis to resistance basically belongs to indirect calculation methods.This method is influenced by many factors like calculation mode,sample space and so on.Then the precision of its calculation results is limited.As a direct calculation method,proof load method has advantages over indirect calculation methods in theory,so the purpose of this thesis is to utilize the information from proof load directly to analyse and calculate the resistance of structures,search the applications of proof load method in safety assessment of existing structures.In this paper,the basic principle of proof load method is introduced and the ultimate principle of distinguishing the validity of proof load method is discussed.On this foundation,the applied range of proof load method in safety assessment of structures is discussed:Through the survey of proof load's validity in the two-dimensional space of standard normal distribution,the essential that proof load method can have effect on structure reliability is analysed.Based on the results of numerical calculation combining with theoretical analysis,the factors that affect the validity of assured proof load and the rules of the validity's changing are discussed. Accordingly,the confine that proof load method can be applied is obtained.Based on the assured proof load method,the proof load method is extended and the universal definition of broad proof load method is given.By the survey of stochastic proof load's effect in the three-dimensional space of standard normal distribution,the validity of stochastic proof load is discussed.The method based on the probability that the proof load could be exceeded is expatiated and the limit proof load needed to acquire different safety class is calculated based on the principle that different safety class of structures are divided in the national standard of reliability evaluation to civil architecture.Then,the method based on the distributing of resistance after suffering proof load is expatiated.Through example calculation and theoretic analysis,the advantages,disadvantages and applied ranges of the two methods is pointed out.Finally,the attenuation of structure resistance is considered in.The time-influence that proof load has on structure resistance in different degenerate models is discussed. According deducing and theoretic analysis,the law that the area proof load cuts off in the tail of resistance's probability density does not change along with time and the attenuation of resistance.These lay the root for extending the method of safety assessment based on proof load to be a more extensive method of safety assessment that's based on loading history.