Wind-induced collapse mechanism and failure criteria of super-large cooling tower based on layered shell element model

Abstract

Many wind-induced collapse events of super-large cooling tower have been taken place in history. Existing norms are limited within local excessive strength or buckling failure of the tower body, but ignore the follow-up phenomena after the general continuous collapse caused by local damages. Hence, they are difficult to disclose the wind-induced collapse mechanism and failure mechanism of super-large cooling tower. A case study on the world highest (228 m) cooling tower under construction in Northwest China was carried out. Variations of multi-scale wall thickness and reinforcement ratio at different positions of the tower body were considered by the layered shell element modeling method. The wind loads on the cooling tower surface were acquired through a wind tunnel test of pressure measurement on the rigid body. Displacement and internal force responses of the tower body under typical wind speeds were analyzed by combining the incremental dynamic analysis (IDA), thus determining the critical wind speed. Three redistribution of internal forces mechanisms during collapse of tower body were extracted based on the stress variation indexes before and after the node failure. Moreover, the development paths of three collapse mechanisms among units with different thicknesses of the tower body were discussed. Finally, the wind-induced failure criteria of super-large cooling tower structure were proposed based on throat deformation of the tower body. Research results demonstrated that the layered shell element model could simulate the full process of collapse of super-large cooling tower effectively and a central damage area from the throat of windward side to the center of tower body was formed. Subsequently, a crack network was formed after diffusion of the damage area along the circumferential and meridian until the complete collapse. Three redistribution mechanisms of internal forces during the collapse of the super-large cooling tower were proposed, including the sliding surface mechanism, rotating hinge mechanism and slipping surface mechanism. The super-large cooling tower structure developed wind-induced failure and collapse when the deformation failure index is δ ≥ 1.5%. It is of great significance to the design and construction of super-large cooling towers.