Safety Performance Analysis And Assessment Of Outer-Attached Construction Facilities Of Super High-Rise Buildings Under Extreme Tornado Environment

Tornado is a violently rotating column of air that is extend from the bottom of the cumulonimbus cloud to the ground.It has the characteristics of rapid occurrence,difficult monitoring and huge damage.Tornado disasters occur frequently in China,and most of them are concentrated in the eastern and southern coastal areas,which is consistent with the regional distribution of super high-rise buildings in China.Moreover,the long construction period of super high-rise buildings makes it easy to be attacked by tornadoes during the construction stage.In the process of construction,the wind load on the surface of the super high-rise building varies constantly with the construction progress.Meanwhile,the large-scale construction facilities attached to the outer surfaces of super high-rise structures,such as tower cranes and construction elevators,further increase the complexity of the wind field around buildings during construction period,which makes the safety performance of the outer-attached facilities more uncontrollable.Therefore,it is urgent to study the wind environment characteristics and wind-induced response mechanism of the construction facilities of super high-rise buildings under tornado environment.To ensure construction safety,the safety performance of the construction facilities should also be evaluated.Based on the numerical simulation technique of computational fluid dynamics(CFD),this paper conducts the wind environment characteristics simulation of super high-rise attachment system under tornado environment.And the wind-induced vibration response of attached facilities is analyzed based on the finite element method.Combined with the monitoring techniques,the safety performances of the construction facilities in tornadoes are evaluated,and the early warning to construction safety under extreme tornado environment is realized.The following tasks are mainly completed:(1)A CFD numerical modeling and simulation method for tornado environment of in-construction super high-rise main structure and attached facilities is proposed.The wind field numerical model is established based on the device used in the tornado wind tunnel test,and the reliability of the numerical simulation is verified by comparing with the radar measuring data.Considering the characteristics of configuration change of super high-rise building under construction,a sectionalized numerical model containing outer-attached tower crane and construction elevator is established.The results show that the hybrid meshing method with Interface treatment can ensure the mesh quality of complex geometric model,and the convergence of numerical simulation is improved effectively.(2)The wind environment characteristics of the in-construction super high-rise building and attached facilities under tornado environment are analyzed.In particular,the influences of the wind direction,wind velocity,structure height,slewing and elevation angle of tower crane lifting arm,and the enclosed form of elevator cages,on the wind field around the attachment system are studied.The results show that the distribution of wind pressure on the surface of the super high-rise main structure varies significantly in different construction stages under the tornado environment.The wind load shape factors of the curtain wall stage and leading core-tube stage are greater than the values suggested in the code.(3)The wind vibration response and wind-induced fragility analyses of the construction facilities attached to the super high-rise buildings under the action of tornado are investigated.According to the wind load shape factor,the fluctuating wind velocity time-history load is generated,and the nonlinear dynamic time-history response of tower crane and construction elevator is analyzed with the displacement time-history of main structure as the support excitation.The results show that the attachment support is the key component to determine the safety performance of the attached tower crane.The comfort requirements are difficult to meet for the construction elevator in the tornado environment.(4)A method of safety performance assessment and early warning of construction facilities attached to the super high-rise buildings under the action of tornado is proposed.Based on the fine wind environment monitoring technology of construction site,as well as the safety operation monitoring techniques of facilities,the safety performance assessment and early warning of outer-attached facilities are completed by combined with the wind-induced fragility analysis.The results show that the four-level safety early warning considering the limit of structure approaching collapse,i.e.,blue,yellow,orange,and red,can cover all the performance levels of attached construction facilities,so as to achieve risk detection and preventive measures.