Twisting About Constrained Line Of Parallel Purlins Interbraced By Sagrods Under Wind Uplift

Cold-formed channel and Z-section purlins are widely used in light gage steel roof systems,and in such parallel purlin systems,purlins are connected with each other by sagrods.Considering the elasticity of sagrods and the longitudinal offsets between two adjacent sagrods,forces in sagrods will produce distortional deformation in purlin webs,which lead to remarkable reduction in the effective stiffness of the sagrods.In this paper,simply supported purlins interbraced by one or two lines of sagrods in a parallel purlin system under wind uplift are analyzed,including theoretical process and FE analysis.And the effects of the offset and the local deformation on the effectiveness of sagrods are analyzed.The main contents include following sections:(1)Analytical model of line of parallel purlins without local deformation and sagrod offset is raiseed.Theoretical solution obtained in this model and FE analytical results are compared.(2)Based on the results of the ideal model,analysis of line of parallel purlins considering local deformation and sagrod offset is conducted,where local flexural stiffness is introduced.(3)Utilizing the relationship of deformation in sagrods and purlins,tensile forces in sagrods and lateral displacement of each purlins are obtained.(4)The coefficient of tensions in sagrods is raised to describe the relationship of purlins in one parallel system,leading to deep perception on effectiveness of sagrods.(5)Based on previous research,parallel purlins with two lines of sagrods or with torsional restraints in upper flanges are analyzed,including theoretical research and FE analysis.(6)Methods on reinforcement of purlin webs are proposed,and FE analysis is conducted to research the local stiffness of purlin webs with steel pads.