Fatigue Calculation Model Of Screw Joints Used In Light-weight Steel Roof And Its Application In Post-disaster Assessment

The roofing system in the form of self-tapping screws has a wide range of applications in light steel structures.Due to its light metal structure and high flexibility,the metal roofing is very sensitive to wind loads.Many windstorm investigations show that wind-induced static and wind-induced fatigue damage can occur under the action of strong winds,which leads to the failure of the roofing system and causes great economic losses.Therefore,in the post-disaster performance evaluation,while analyzing the static wind resistance performance,the weakening effect of wind-induced fatigue damage on the bearing capacity of the self-tapping nail node can not be ignored.Therefore,the establishment of self-tapping nail node bearing capacity degradation model caused by typhoon fatigue,and its application to post-disaster state assessment is a key scientific issue in self-tapping nail node wind resistance research.In this paper,the self-tapping screws of light steel roofing are taken as the research object.The static performance test of the fatigue-damaged joints is carried out,and the degradation law of the bearing capacity with fatigue load is obtained.Through the improved simulated typhoon method,the typhoon load model under different wind speeds is simulated by using the wind pressure coefficient time history data,and the bearing capacity degradation law of the self-tapping nail node is combined to obtain the bearing capacity degradation model under the typhoon.On this basis,the wind-resistance performance evaluation of self-tapping screws based on probability is carried out,and the time-varying reliability index and service life of self-tapping screws in coastal cities are analyzed and predicted.The main research contents of this paper are as follows:Firstly,this paper reviews the research status of static wind resistance and fatigue wind resistance performance for light steel roof self-tapping screws.It summarizes the post-disaster state assessment methods of light steel roofing system and summarizes the current needs to be solved.Secondly,the self-tapping nail node subjected to fatigue damage is taken as the test object,and the static test is carried out.On the one hand,by observing the relationship between the bearing capacity of the damaged joint and the cyclic load,the degeneration relationship between the bearing capacity of the self-tapping nail node and the cyclic load is obtained.On the other hand,through the force displacement curve and the strain displacement curve of the joint,the static failure process after the damage of the joint is studied,and the fatigue limit is judged;Then,based on the improved simulated typhoon method,the MATLAB software is used to analyze the rain flow through the wind pressure coefficient time history data,and the wind pressure coefficient matrix is obtained.Then the modified typhoon mathematical model is used to obtain the load matrix of the typhoon at different extreme wind speeds.After demonstrating the main concentrated area of the number of cycles in the load matrix,the fatigue characteristics of the self-tapping nail node can be reasonably combined,and the linear cumulative damage criterion is used to obtain the damage time history of the self-tapping node after different extreme wind speed typhoons;Finally,for the self-tapping screw node of light steel roof,this paper uses Monte Carlo simulation method to evaluate the wind resistance performance of self-tapping node based on probability.Among them,the typhoon wind speed and the number of typhoon occurrences are subject to probability distribution.In the evaluation of the performance degradation of the typhoon on the self-tapping nail node,based on the above research,the wind-induced self-tapping nail node fatigue damage model and the wind-induced self-tapping nail node resistance degradation model are obtained.The essence of both is caused by fatigue.Among them,the wind-induced node resistance degradation model is obtained by fitting the typhoon load model under different extreme wind speeds and the bearing capacity of the joint with the degradation law of the cyclic load.Finally,based on the typhoon probability parameters of each coastal city,the typhoon load model is obtained.Under the condition of considering the fatigue limit,the time-varying reliability index of the self-tapping nail nodes in each coastal city is calculated and analyzed.And by selecting the norms of China and the United States,it predicts the service life of self-tapping nodes in various cities.