Dynamic Response And Wind Vibration Control Of The Long-span Truss Structure Under Downburst

Downburst is an outburst strong wind spread from the center to periphery on or near the ground in thunderstorms,producing a transient strong wind and causing a high near-surface wind velocity,and results in a strong damage on structure.Long-span roof structures are sensitive to wind loads,and most of the long-span truss structures are within the height of the downburst damage.At present,the rules of our country are not given to the winds caused by extreme weather such as downburst and there are relatively few studies of the wind-induced dynamic responses of downburst at home and abroad.Hence,the paper adopted the theory formula to simulate the wind speed and made a detailed analysis on the wind-induced dynamic responses and the wind vibration control of the long-span truss structure under downburst.The main contents was as follows:(1)This paper selected a hybrid stochastic model to simulate the strong wind load of downburst.Wood's velocity profile for the vertical profile and Holmes' empirical model was utilized to generate the mean wind.The non-stationary fluctuation was generated by combined the stochastic process with the time-varying mean wind.The simulation methods of different stochastic processes was used to simulate the wind speed of the downburst on two structures.Considering the accuracy and efficiency,AR model was used to simulate the stochastic process of wind speed.Power spectrum estimation theory was used to evaluate whether wind speed simulation results are reasonable and through the comparisons of three kinds of power spectrum estimation method,the result shows that the maximum entropy method is more accurate.(2)In this paper,the influence of structural parameters and wind parameters on the wind-induced dynamic responses of two simplified models was studied as the long-span truss structures is complex.The parametric analysis results of a simply supported beam show that the stiffness,span,maximum wind speed radius and the velocity of storm moving have great influences on structural wind-induced response.This paper adopted the global wind-induced coefficient calculation method which is based on the envelope concept,where the global displacement wind-induced coefficient and the global load wind-induced coefficient under different parameters were studied respectively.The results show that adopting the structural global displacement wind-induced coefficient to calculate equivalent static wind load of downburst have a higheraccuracy for a simply supported beam.However,the result of the equivalent static load analysis of the arch beam is less than that of the time-domain analytical method.(3)For two kinds of plane trusses,a nonlinear dynamic analysis that accounts for both material and geometrical nonlinearities was carried out by the ANSYS finite element software.The results show that four web members of the truss near the windward side and two diagonal web members of arch truss near the windward side trend to yield.The residual deformation that should not be neglected generates in the structure after the storm,posing a threat to the safety.(4)For the status that plane truss had irreversible residual deformation after the storm,the wind vibration control analysis is carried out after replacing the web members whoses stress was larger with self-centering members.The results show that nodes' peak residual displacement of truss structure decreased 48.07%.Nodes' vertical peak residual displacement of arch truss decreased 84.57%and horizontal peak residual displacement decreased 86.85%.It can be seen that the residual deformation obviously decreased and the wind-induced dynamic responses reduced.A parametric analysis was conducted to analyze the influence of vibration performance with activation force,activation displacement and strength ratio of the self-centering members.The results indicate that increasing the activation force and can reduce the peak displacement.In general,the increase of activation force can reduce the peak residual displacement of the structure.However,when activation force is too large that the web members near self-centering members yield,the peak residual displacement of the structure increases.The peak displacement and residual displacement increased as the activation displacement increased.Incresing strength ratio improves the energy dissipation capacity of self-centering members,but it reduces the self-centering performance.(5)For a truss string structure in the practical engineering,an analysis of wind-induced dynamic responses was carried out under the downburst.The structure sustained a large wind pressure due to the large wind area,which eventually led to obvious plastic deformation of the structure.Vertical peak residual displacement is 0.83m and horizontal peak residual displacement is 0.26m,which means that the structure is not conducive to use.The analysis of wind-induced dynamic responses was carried out after four root self-centering members was added.The results show that vertical peak residual displacement is 0.26m,decreasing 68.16 percent and horizontal peak residual displacement is 0.089m,decreasing 65.77 percent.The use of self-centering members significantly minimizes the residual deformation of the truss string structure,improving the security.