Research On Shear Performance Of Strengthed Self-drillng Screw Connections And Axial Load Capacity Of Cold-formed Steel Framing Walls

The failure modes of the cold-formed steel composite wall under horizontal load are mainly characterized by the failure of connection screw between the wall panel and the column as well as the slippingoccurred at joint seam region on the wall panel.When a slipping failure occurred atthe connection seam region on the wall panel or the connection screw is destroyed,the supporting function of the wall panel on the columnwould not be exploitedfully,whichsubsequently result in the complete loss of the bearing capacity of the wall panel.Under vertical loading,thecold-formed steel composite wall plays a role as a constraint supportfor restricting the in-plane overall buckling of the column,where,thereby,the failure mode of the cold-formed steel composite wall under such a loading conditionwill be characterized by the local buckling at end of the column.In conclusion,screw connection plays an important role in the mechanical performance of the cold-formed steel composite wall.This paper proposesa method for strengthening the mechanical performance of the screw connection with the use of the thin steel strips.A series of researches on the axial compression behavior of the cold-formed steel composite wall are conducted.The main contents of the research are summarizedas follows:(1)in this paper,the constraint supports of the wall panel onthe column is modeled as equivalent spring constraints along the three directions,i.e.the in-plane spring constraint,theout-planespring constraint and the torsional spring constraint.Corresponding equivalent analysis models for these spring restraint stiffness in three directions are proposed.Analytical formulae for calculating the constraint stiffness of the equivalent spring are derived.(2)in order to verify the validity of the equivalent spring constraint stiffness analysis model proposed in this paper and study the effects of different factors,including the panel materials(plasterboard and OSB plate),the thickness of plate,the diameter of self tapping screws,the thickness of reinforced steel strip and the thickness of the column,on the bearing capacity and shear stiffness of the screw connection specimens,monotonic axial tension tests were conducted on designed 27 specimens.Theoretical and experimental studies on the shear stiffness and bearing capacity of the shear joint are carried out.The research results show that the shear stiffness and bearing capacity of the screw connection are positively related to the thickness of the panel,the diameter of the self tapping screw,the thickness of the steel strip and the thickness of the column.The shear connection stiffness and bearing capacity of the panels for OSB plate connections are larger than those of the wall panels for gypsum board connection specimens,respectively.(3)in order to verify the stiffness analysis model proposed in this paper,the mechanical parameters of the material used are calibrated.Meanwhile,the stiffness of plasterboard and OSB plate is calculated by ABAQUS finite element software.The results obtained from numerical analysis were compared with theresultsobtained fromthe theoretical calculation,which verified the stiffness analysis model in the paper.(4)Axial compression testswere was conducted on three full-scale cold-formed steel composite walls,including the wall of screw hole without steel strip reinforced wall,1.2mm-thick steel strip reinforced screw hole wall and 1.5mm-thick steel band reinforced screw hole wall.The failure process of the panelwall was observed in the test.It is found that the failures of the wall arecharacterized by the buckling waveforms occurred on the webs of the column.Then a local buckling failure occurred at the end of the column.Finally,the test results were analyzed.The results showed that the axial load bearing capacity of the screw holes reinforced with 1.2mm and 1.5mm thick steel strips is 8.57% and 17.85% higher than that of the screw holes without steel straps respectively;the axial compression of the wall after the screw holes are strengthened.The stiffness basically has no effect.