ENDURANCE TIME METHOD IN THE LINEAR SEISMIC ANALYSIS OF HYPERBOLIC COOLING TOWER SHELL STRUCTURES

Endurance Time (ET) method is a response history based analysis method that can predict seismic responses of structures at different excitation levels in each response history analysis. This method of seismic analysis uses specific intensifying acceleration functions for seismic assessment. One of the potential applications of the ET method is in the seismic analysis of shell structures. In this paper, a procedure for linear seismic analysis of hyperbolic cooling tower shell structures is proposed. For this purpose two cooling tower shells finite element models are selected and these structures are analyzed under three ET acceleration functions in one direction and results are compared to time history analysis considering seven ground motions. Also the results of ET method are compared to response spectrum analysis method. Results show that ET method predicts the linear seismic performance of hyperbolic cooling tower shell structures with acceptable precision and significant reduction in time of analysis is achieved but this method sometimes cannot predict von-Mises stresses of near base elements of shells as well as other elements. Furthermore it is shown that stress distributions resulted from ETA and THA procedures have good consistency. Also it is concluded that scattering of results of three ET analyses is very low and one analysis can be used instead of three. The comparison between THA and RSM results show that response spectrum method is a conservative method that sometimes has problem evaluating bending stresses of hyperbolic cooling tower shell structures