| It is widely used for metal roof system in the roof structure of various large-span buildings due to its advantages of light weight,large span,and wide appearance adaptability.However,their performance is greatly affected by wind loads.Under severe wind conditions,accidents of metal roofs being lifted by the wind occur from time to time.According to incomplete statistics,the direct or indirect economic losses caused by wind-uplift damage of metal roofs can reach hundreds of millions of yuan each year.As wind uplift accidents have attracted more and more attention,countries with frequent hurricanes such as Canada,Europe,Australia,Japan,and the United States have formulated different test methods and compiled relevant test methods based on wind load codes and wind tunnel test results in different regions.Test specifications,but there are little test methods based on domestic specifications and test results in China,and there is a large gap in test methods between national specifications.The same test piece may get a variety of different wind resistance levels by using different test methods.Therefore,it is of practical significance to conduct in-depth research on various test methods.In order to understand the applicable scope and rationality of each method further,this paper compares the parameters of each test method.Through numerical simulation analysis,the influence of each parameter on the analysis result is discussed separately,with emphasis on the test method proposed in the Canadian standard.Based on the results of the existing long-span roof wind tunnel pressure test results,the dynamic loading sequence statistics are developed,and finally a dynamic loading sequence suitable for the wind resistance test of the large-span metal roof system is proposed.The main research contents are as follows:(1)Based on numerical simulation methods,this paper compares the size of the specimens,load levels,compression methods,pressure rise time,holding time,and pressure starting points in the wind-lifting tests by comparing with domestic and foreign standards for wind-lifting tests and summarizing the differences in test methods,finally reaches the conclusion that the biggest influence of parameters on the analysis results is the compression method.Compared with static loading,dynamic loading can increase the vertical displacement in mid-span and maximum stress by 80% and 15%,respectively.(2)With reference to the method of dynamic wind load sequence generated in Canadian code,the wind pressure time history of flat roof wind tunnel pressure test is calculated,filtered,counted,sorted,classified and finally converted into a practical dynamic loading sequence in wind uplift test combined with rain flow counting method.This paper compares the influence of roof partition,wind direction angle,span-to-height ratio,wind speed,landform and other factors on the statistical value of wind load sequence,and finally reaches the conclusion that the statistical value of the loading sequence of I partition located at the front edge of the wind is more susceptible to the influence of different factors,but that in the V district in the middle of the roof is relatively stable,and has more cycle numbers in Group1 in contrast.(3)Comparing the statistical value of the loading sequence between flat roofs and cylindrical roofs,it is found that the distribution of each roof presents different symmetry characteristics,and the V zone in the middle of the cylindrical roof has more cycle numbers,and the method to design dynamic wind uplift test in Canadian standard is also introduced.By integrating the maximum and minimum of the statistical value of the wind load sequence of the partition I of different conditions,an A-level dynamic loading sequence is proposed,which can be used to test the safety of the metal roof under the design wind load.Based on that,the B,C,D,E-level loading sequence that can be used to determine the wind resistance capacity is proposed. |
PDF Full Text Request