Study On Wind-induced Reponse Of Large Cooling Tower Consideing Soil-pile-structure Interaction

Large cooling towers,usually served as cooling equipments in power stations,are typical thin-wall reinforced concrete structures.With the rapid development of national economy in recent years,a large number of cooling towers with higher heights and greater diameters are being built.Those cooling towers have large sizes but extremely thin shells,which make them both sensitive and vulnerable to the wind loads.Besides,when wind flows across cooling tower,there are significant differences between the flow fields on the top and bottom of the tower and that on the middle part of the tower due to the three-dimensional flow effect.Therefore,the three-dimensional flow effect of cooling tower is studied through wind tunnel test in this paper.A finite element model of cooling tower based on rigid foundation was built and an integrated finite element model of cooling tower considering tower shell,herringbone column,circular foundation and pile was established.Comparisons between these two models on self-vibration characteristics,wind-induced responses and local stability coefficients were studied.Besides,by using integrated finite element model,the comparisons between wind-induced responses and local stability coefficients of the cooling tower under wind loads obtained from the codes and the wind tunnel test were made.Furthermore,finite element contact analytical models of single pile and slab-pile group were built in order to calculate the horizontal pile group efficiency coefficients.An integrated finite element model of cooling tower considering horizontal pile group efficiency coefficients was established,which can provide theoretical proofs for engineering applications.Main contents of the paper and some conclusions are listed as follows.(a)Three-dimensional flow effect of cooling tower was analyzed.Wind pressure distribution of an isolated cooling tower was obtained based on wind tunnel test.Comparison between the wind pressure distribution coefficients derived from Chinese,British and Germany codes and the wind tunnel test was made.The wind pressure distribution of cooling tower caused by three-dimensional flow effect was analyzed.(b)A pile-soil interaction finite element model based on the foundation reaction force method was built.The soil horizontal resisting force-displacement curve was obtained based on the calculation method of horizontal pile-soil action,which is recommended by codes.And a spring-beam element model depicting the relationships between pile-soil reaction force and displacements at each depth was established by applying the COMBIN spring element.The responses of a single pile under typical load conditions were calculated and compared with the results from the FB-pier software.Comparison shows that the p-y curve method fits best with the single pile responses.(c)Numerical simulation of the integrative finite element model of the cooling tower was carried out.A finite element model of the cooling tower based on rigid foundation was established,and the wind-induced responses and local stability analysis under the wind loads obtained from wind tunnel test was conducted.A soil-foundation-superstructure integral calculating model was established through connecting superstructure and infrastructure by employing the spring-beam single pile model.Comparisons were made between the mechanical characteristics of solid foundation model and the integral model.The wind-induced responses and local stability coefficients of the tower under the wind loads obtained from the codes and the test are also compared.(d)Numerical simulation of the cooling tower finite element model based on contact analysis was carried out.A single pile-soil contact finite elment model was established and the ultimate horizontal bearing capacities of the single pile under different pile diameters,pile lengths,cohesions,soil stiffness and internal friction angles were analyzed.The base slab-pile group contact finite elment model was established based on the cooling tower circular foundation truncation model and the horizontal pile group efficiency coefficients under different pile space conditions were analyzed.(e)A pile-soil interaction finite element model based on horizontal pile group efficiency coefficients was built.The differences of vibration characteristics and wind-induced responses of cooling tower after considering horizontal pile group efficiency coefficients were analyzed.The wind-induced responses of cooling tower under different pile space were analyzed and results shows that four times of pile diameters is the most reasonable pile distance for pile arrangement.