Earthquake Response Analysis Of Cooling Tower Structure Considering The Effect Of Traveling Wave

Ordinary buildings in seismic response analysis,the method be used commonly was to consider the foundation as a rigid body,and the actual seismic wave transmission to the time difference problem was often be ignored,the method which was used to put the exactly same excitation to each bearing point,but the cooling tower is a big span,takong degree structure,adopting the assumption of rigid foundation is not reasonable enough.In recent years,with the increase of national electricity demand,as an important cooling device of the cooling thermal power plant,the size and dimension of cooling tower are also increasing,most of the mega structures have been reached the height over 200m,reached above 180m in diameter,most of them was located in the hinterland of the north-south where with the high risk of seismic and complex site condition,in this case,it is very necessary that the soil-structure interaction and multipoint excitation input mode to be considered.Around these problems,the finite element numerical simulation analysis method was adopted in this paper,the viscoelastic artificial boundary of ground motion input by equivalent load method was established,and studies the traveling wave effect,soil-structure interaction,multi-support excitation and other problems of large cooling tower structure.The main contents and results are as follows:.1)The influence of foundation stiffness change on the dynamic characteristics of cooling tower structure is studied.With the background on the project example established rigid foundation model and soil-structure model under the II condition of site,pick the first 500 vibration modes,observe the law of the change.The results show that the natural vibration frequency distribution of cooling tower structure is very dense,with low natural frequency and long period.The number of overall vibration modes is small and they appear late.The soil-structure interaction model is basically consistent with the rigid foundation model.However,the natural vibration frequency is smaller,the natural vibration period is longer,and the whole vibration pattern appears earlier.2)By comparing the seismic response differences of 8 degrees on rigid foundation model and the model considering traveling wave effect under rarely earthquake and frequently earthquake,found that the maximum level values always appear on the top of the pillar in two conditions,the response amplitude increases gradually along the height on the pillars,decrease gradually along the height on tower drum,in the model with uniform excitation,the ring amplitude change of tower drum is small,present the overall characteristics of translation,compared with the rigid model,after be affected by the traveling wave effect,the horizontal earthquake effect decreases with the decrease of the apparent wave velocity,and the vertical seismic action increases with the decrease of the apparent wave velocity,when the apparent wave velocity increases,the foundation to achieve a certain rigidity,the ground motion input under multi-point excitation is not different from the result of rigid uniform excitation.3)Analysis of the cooling tower structure under rigid foundation,traveling wave effect and soil-structure dynamic interaction with traveling wave effect,found that after the soil-structure interaction be considered,the response amplitude in the part of the tower drum will decrease with height increase firstly then increase with height increase,it suggest that this interaction has the amplification effect on the top of the tower,so when considering soil-structure interaction,located at the top of the structure of the weak positions.4)Compared with the characteristics of rigid uniform excitation model that with little change in amplitude in the circumferential direction,the fluctuation amplitude in the circumferential direction is more obvious when the traveling wave effect is taken into account.When the soil-junction dynamic interaction is taken into account,the fluctuation becomes gentle and the overall dynamic response decreases significantly.After considering the elastic function of soil,the structure response is far less than the rigid model,slightly less than the model only considering traveling wave effect,shows that the more rigid of foundation soil,the greater the earthquake effect,the elastic soil as vibration isolation at the bottom of the structure,greatly weakened the seismic response,due to the obvious respense difference between rigid foundation model and soil-structure model,the large span structure like cooling tower,should not ignore the soil-structure dynamic interaction.