Performance-based Seismic Fragility Analysis And Design Of Transmission Tower

Transmission tower is an important structure in lifeline engineering of overhead transmission.It would probably creative electric power engineering safety accident and negative social economic influence,if transmission tower suffered serious damage in earthquakes.So far,transmission tower seismic evaluation and design based on conventional seismic analysis method,can't satisfy different design demands for different important transmission towers,and the method is too simply.Therefore,the thesis presents a study of seismic fragility analysis and seismic design based on performance for transmission tower structures.The main content includes:(1)A pushover analysis method for transmission tower was presented.The influence on pushover analysis by Seismic lateral load patterns was studied and slection principle of lateral load patterns was recommended.An improved modal combination method was developed.The results of roof displacement,drift ratio and main member stress,etc.of transmission tower structure calculated by nonlinearstatic elastic-plastic analysis and nonlinear dynamic analysis were compared.The new method proved reliable lays the foundation for seismic fragility analysis and seismic design based on performance of transmission tower.(2)Performance-based seismic fragility analysis method for transmission tower was presented.Comparing pros and cons of different indexes,roof displacement of tower was selected as the performance indexes of transmission tower.Four-level classification standard of seismic damage was presented and different levels of quantitative index was determined relative with calculation the responses of transmission displacement and coderequirement.The seismic fragility curves for transmission tower was obtained by utilizing incremental dynamic analysis(IDA),which helped analyze probability of every damage level affected by different intensity earthquakes.(3)An improved modal lateral force combination capacity spectrum method used in performance and fragility analysis for transmission tower was presented.To consider the effect of high-order,this paper combines two high orders,and calculates equivalent modal,equivalent lateral force.Using the equivalent modal participating mass ratio,calculating process between Vb-ur cures and Sa-Sd cures is elaborated precisely.This method can evaluate how the high-order impact on performance and fragility analysis for transmission tower,which determines a good foundation on seismic performance and design for transmission tower.(4)Performance-based seismic design method for transmission tower was established.Roof displacement of tower was selected as the performance index of transmission tower,and four-level classification of performance,three-level Seismic fornications were divided,which were used to determined performance objectives.An improved capacity spectrum method of transmission tower was established based on conventional pushover analysis by utilizing improved modal combination method.According to seismic design demand for different performance objectives,a displacement-based seismic design method for transmission tower was established and then applied to the performance-based seismic design of typical cup type and drum type transmission tower.