Ultimate Wind Load And Failure Mechanism Of RC Cooling Towers Considering Material Nonlinearity

Reinforced concrete hyperbolic cooling tower is a kind of high-rise spatial thinwall structures,which is controlled by wind load.Previous studies were focused on the wind-induced behavior,including wind pressure distribution,wind vibration effect,group tower interference effect,and buckling behavior.There are few studies concentrated on ultimate load considering the material nonlinearity.In this paper,a hyperbolic cooling tower was taken as an example.The shell was modeled by layered shell element.The nonlinear stress-strain relation in compression,tensile cracking,and tension stiffening in concrete were modeled by concrete smeared crack model.And geometrical nonlinearity was also taken into account.Nonlinear behavior of the shell from virgin state to failure was analyzed,and ultimate load and failure mechanism were also examined.Main work is as follows:(1)Linear models of the cooling tower were built by ABAQUS,and then internal forces of the shell under gravity,winter load,summer load,and wind load were obtained individually and compared separately with those got from ANSYS.It is shown that results got from ABAQUS models,consisted of several elements,whole and half structure,are agreed well with those got from ANSYS,which demonstrates the correctness of built models and clarifies modelling method for subsequent nonlinear analysis.And features of internal forces of the shell under four kinds of load are understood.There are mainly double axial pressure forces under gravity,and double moments under winter and summer load,and meridian axial forces under wind load,where circumferential forces are not negligible.(2)On the basis of introduction to concrete smeared crack model and reinforcement bilinear model,two classical plate structures,the Mc Neice and Jain plates,and the Port Gibson cooling tower,were taken as examples to demonstrate the validity of nonlinear material model and computing method.It is shown that concrete smeared crack model can reproduce the experimental results of two plates,where the key lies in tension stiffening parameter.The nonlinear results of Port Gibson cooling tower got from present paper are agreed well with those got from existing research.Therefore,the validity of nonlinear material models and computing method used by present paper have been demonstrated.(3)Nonlinear finite element model of the cooling tower was built,and then ultimate wind load and failure mechanism of the shell under the combination of gravity and wind load and the combination of gravity,winter load and wind load,were analyzed.It is shown that crack and ultimate load factors under gravity and wind load are 1.384 and 2.007,respectively,and the cooling tower is failed by the successive cracking of concrete in windward and yielding of meridian steel in throat region.When winter load is considered,double moments caused by it makes shell crack earlier,where crack load factor is 1.0.However,the failure of the structure,at the ultimate load factor of 1.842,is still controlled by wind load.(4)Effects of six calculating parameters on ultimate wind load of the cooling tower were analyzed,including mesh size,element type,number of layers,shear retention model,tension stiffening parameter,and geometrical nonlinearity.It is shown that these six calculating parameters all have no effect on crack load,but it is different for ultimate load.Number of layers has little effect on ultimate load.While the others all have some effect on ultimate load,among which tension stiffening is the most influential parameter,and greater tension stiffening parameter will increase ultimate load.(5)Effects of five kinds of structural parameters on ultimate wind load of the cooling tower were analyzed,including concrete tensile strength,cover thickness,shell thickness,reinforcement ratio,and stiffening ring.It is shown that concrete tensile strength has great effect on crack load and ultimate load,both of them nearly decreases linearly with the reduction of tensile strength.Cover thickness has no effect on crack load,and little effect on ultimate load.Reinforcement ratio has little effect on crack load,but great effect on ultimate load,which nearly increases linearly with the increase of reinforcement ratio.The variation of shell thickness will significantly influence crack and ultimate load simultaneously,and they nearly vary linearly with the shell thickness.Stiffening ring has small effect on crack and ultimate load,and its main function is remarkably restraining structural deformation.