Research On The Self-tapping Screw-fastened Cold-formed Thin-wall Steel Connection Behavior Based On Purlin Reinforcement

At present,cold-formed thin-walled steel buildings represented by light steel industry buildings have been widely used in industrial building systems,among which purlins,as a typical cold-formed thin-walled steel component,play an important role in the roof system of related buildings.However,with the application of solar photovoltaic panels on roofs and frequent natural disasters in recent years,the purlins of old factory buildings generally cannot meet the requirements of existing codes,and the purlins often have insufficient bearing capacity during modeling calculations.Therefore,this paper focus on the reinforcement of cold-formed thin-walled Z-purlins.The reinforcement method of applying steel plates on the lower flange of the purlins,which are fixed by self-tapping screws is adopted.Based on the actual engineering requirements,this paper takes the additional steel plate reinforcement method for the lower flange of the cold-formed thin-walled Z-purlin as a foothold,and carries out the corresponding material properties test,the cold-formed thin-walled steel plate single self-tapping screw connection shear performance test,Cold-formed thin-walled steel plate self-tapping screw group connection shear force transmission test,and introduced the cold-formed thin-walled Z-purlin reinforcement test plan and carried out corresponding numerical simulation research.The shear performance test of 48 cold-formed thin-walled steel screw connection test pieces was carried out,taking into account the influence of self-tapping screw material,diameter,ratio of different steel plate thickness,end distance and other factors on the shear capacity.Comparing the actual applicability of the calculation formula for the shear capacity of self-tapping screws in the domestic,American AISI standards and European standards,it is found that the design value of the shear capacity of self-tapping screws of the European standard<that of the domestic standard<the design value of the North American standard;In addition,in the future revision of the specification,it is recommended to appropriately reduce the design value of the shear capacity of the self-tapping screw when the thickness ratio of the connecting steel plate=1 and the thickness of the steel plate ≥2mm;Finally,according to theoretical analysis,the limit state prediction model of the single self-tapping screw connecting the cold-formed thin-walled steel plate is proposed.Subsequently,the shear force transmission performance tests of 46 cold-formed thin-walled steel screw joints were carried out.The shear force transmission was compared and analyzed according to the number of screws,the length of the reinforcement zone,the thickness of the steel plate and other factors,the results of which could provide suggestions for the reinforcement method of Z type cold-formed thin-walled purlins.It is recommended by the results to use carbon steel,self-tapping screws with a diameter of 4.8mm,which are widely used in the market and have good mechanical properties,arranged in a single row(the lower flange of the purlin is the reinforcement area,and the aspect ratio is considered to exceed the recommended limit),the thickness of the reinforcement plate to comprehensive consideration with the increase of the ratio of the original steel plate thickness and need cross section area of the situation,The optimal choice is that the thickness of the reinforced steel plate is the same as the thickness of the component to be strengthened.The number and spacing of screws should be considered comprehensively.Finally,this paper introduces the purlin reinforcement test scheme and conducts a finite element numerical simulation study before and after the purlin reinforcement.Based on the previous research results,the flexural bearing capacity of the reinforced purlin can be increased by 21.788% compared with the original purlin.