Equivalent static wind loads of large cooling towers based on weighted combinations of time-variant internal forces

The equivalent static wind load（ESWL）is a quasi-static equivalent load model for dynamic wind loads and structural inertia forces，covering the envelope values of structural dynamic responses，which belongs to a simplified analysis of load effects inthe structural design. In the wind-resistant design of large-span spatial structures，the selection of equivalent criteria and load pattern recognitions are the key steps to transform complicated dynamic loads into quasi-static ones. At present，there are a series of criteria adopted to evaluate this equivalent mode. However，ESWLs based on different criteria generally turns out to be divergent and no universal，reasonable and comprehensive ESWL evaluation standard heretofore has been widely accepted. To reflect the comprehensive influence of different internal force responses on structural safety under the action of wind，a novel evaluation criteri on is therefore proposed，which further develops the existing criteria from the load or structural response to weighted combinations of internal forces. For reinforced concrete structures，the weighted internal force combination can be embodied by reinforcement ratio with a clear physical meaning and engineering application feasibility. A large cooling tower was selected to perform case studies.The time-variant wind pressure measured in wind tunnel tests was applied to the FE model. The transient dynamic analysis was conducted to calculate the time histories of wind-induced dynamic responses and to get the corresponding dynamic reinforcement ratios based on the weighted combinations of time-variant internal forces. Furthermore，the safety redundancy of traditional ESWLs defined in the present code could be evaluated on the level of single internal force and reinforcement ratio，respectively. Finally，the ESWLs based on the equivalent target of reinforcement envelope and the weighted combinations of multiple internal forces was derived，revealing rationality and convenience of the proposed algorithm.