Study On The Safety Factor Of Static Wind-uplifted Resistance Tests For Standing Seam Mental Roof System

Because the metal standing seam roof system has good performance in water waterproofness,anti-corrosion properties,and aesthetics,it is used widely in practical engineering.But wind uplift failure of claddings usually occurs.At present,static wind uplift experiments can obtain the ultimate bearing capacity of the metal standing seam roof system under uniformly distributed load.The actual wind loads distribute complexly and change transiently,the difference between actual wind loads and uniform distributed loads using in the tests is remarkable.So ultimate wind load bearing capacity is not exactly the same as the real situation.At the moment,such studies are few.The contents and conclusions of this paper are as follows:(1)The codes about the wind uplift experiments of many countries are compared to study,there are mainly two kinds of ways: fluctuating wind uplift experiment and static wind uplift experiment.The purpose,process and structural security check calculation of two experiments are compared and analyzed.The purpose of fluctuating wind uplift experiment is to ascertain the anti-fatigue performance of the roofing system,change the actual wind load into the cyclic load,and consider the variation of actual wind loads of the metal roofing system.The purpose of the static wind uplift experiment is to determine the ultimate bearing capacity of the roof system and simplify the actual wind load into a uniformly distributed load without considering the distribution characteristics of actual wind loads.Static wind uplift resistance specification and related research do not clearly describe how to solve the problem above,only the safety factor between ultimate bear capacity and standard wind loads value is given by the experiment.Specifications are discussed and analyzed,and the problem of safety factor in the specification is summarized.The effects of the different distribution characteristics of wind load should be considered.(2)The finite element calculation model of metal standing seam roof system is built to study the impact of load level,unload and load,durable load,and short-term load on roof system and bear capacity.Result shows that the roof system bear capacity estimation is more precise when load level became smaller.Unload and sustained load have little impact on roof system bear capacity.Based on above results,the load pattern of the finite element calculation model is set as linear load.(3)The response characteristics of the metal roof system at different positions of the flat roof are studied to ascertain the bear capacity of the roof system under static wind uplift uniformly distributed load and actual wind load time history of each region by finite element analysis.The conversion relationship between the ultimate wind bearing capacity of the roof system under uniform load and real wind loads is established.The factors and calculation formula of wind uplift resistance value K which should be considered in the wind-uplifted resistance tests safety factor are given.(4)According to the static wind-uplifted resistance tests safety factor express formula given by this paper,the influence of roof system supports spacing,wind loads landform type and roof slope on K value is studied.The K value of each area roof system declines as the pedestal spacing increases.The K value of width edge area and corner area declines as the geomorphic roughness increases.The K value of length edge area and middle area increases as the geomorphic roughness increases.The K value of length edge area and corner area increases as the roof slope increases.The K value of width edge area and middle area declines as the roof slope increases.The K value obtained from the static wind-uplifted resistance tests safety factor formula proposed in this paper is less than the empirical coefficient 2 specified in the code.It is conservative to check the calculation through the specification.