Most Unfavorable Response Analysis And Safety Assessment For Drum Type Transmission Tower Under Wind-earthquake Combination Action

Transmission tower is an important engineering facility in the power system.It is vulnerable to damage or even collapse under the action of natural disasters such as wind or earthquake disaster,resulting in huge economic losses and serious social impact.Therefore,it is particularly important to ensure the safety of transmission tower in its life cycle.So far,the research on the mechanical performance of transmission tower mainly considers the influence of single load conditions such as pure wind or earthquake,but less attention is paid to the safety problems which are caused by wind-earthquake combination action in practical engineering.For this reason,the thesis paper presents a research of the most unfavorable response analysis and safety assessment method for drum type transmission tower under wind-earthquake combination action,and the main contents are as follows:(1)Results of different dynamic calculation models for drum type transmission tower are compared and the spatial beam-rigid model is suggested to be used.Firstly,the spatial rigid model and spatial beam-rigid model are established,and the influence laws of the dynamic characteristics between two calculation models are compared based on modal analysis.Then dynamic responses under severe earthquake between two calculation models are studied based on time history analysis.Thus,the spatial beam-rigid model for drum type transmission tower is recommended based on the response results and its security.(2)The modal contribution factors are adopted to weigh the relative participation of each mode,and the spatial Pushover analysis method for drum type transmission tower considering the influence of higher modes is proposed.Based on modal decomposition principle and elastic assumptions,spatial modal lateral forces are established through the modal contribution coefficients which are taken as a measure of mode participation.Equivalent modal vectors are introduced to consider higher modes in the process of capacity spectrum conversion process.The envelope value of calculation is adopted as seismic response of the transmission tower,and the influence of higher modes on the seismic performance of transmission tower is analyzed in order to further carry out performance analysis for drum type transmission towers under wind-earthquake combination action.(3)The most unfavorable response analysis method for drum type transmission tower under wind-earthquake combination action is established when considering the change of wind-earthquake combined angle.Based on the modal contribution coefficients,the calculation formulas of equivalent coefficient are further revised.And the target displacement is determined to analyze the mechanical behavior of drum transmission tower.Thus,the influence of wind-earthquake combined angle on the structural response is summarized and the most unfavorable response and load condition of drum transmission tower are determined.(4)Considering the randomness of material properties,the safety assessment under wind-earthquake combination action of drum type transmission tower is carried out.The displacement on the top of transmission tower is taken as the performance level of quantitative indicator.And the randomness of material properties is simulated by latin hypercube sampling method,and the structural capability curves under different material properties are constructed.Combined with the average of performance indexes on the capability curves which is corresponding to different structural failure states,the quantitative index limits and performance targets of the performance level of the transmission tower are defined.Then the safe state of the drum transmission tower under different wind-earthquake combination action is evaluated,then the weak parts of the structure are pointed out and maintenance suggestions are put forward.