| Cold-formed steel(CFS)structure is a type of structure system that combines cold-formed steel members with lightweight surface panels as the supporting and maintenance structure.Because the application range of conventional CFS structure is mostly low-rise buildings,the author’s group proposes a new type of CFS wall sheathed with steel sheets for the base layer combined with gypsum wallboards for the face layer to extend the CFS structure to multi-story buildings.The new type of CFS wall with good fireproof property has higher shear capacity and better seismic performance than the conventional CFS wall.The shear behavior of CFS walls hinges considerably on the screw connections,which are the important components of CFS walls.In view of this,this paper presented the experimental and numerical investigation on self-drilled screw connections of CFS wall sheathed with steel sheets for the base layer combined with gypsum wallboards for the face layer,and conducted the simulator investigation of the walls’shear capacities based on the test data of connections.The content and conclusions of this paper are stated as follows:(1)In order to investigate the influence of end distance of screw,edge distance of screw,diameter of screw,thickness of boards,space of screw and thickness of studs on shear behavior for connections,75 self-drilled screw connections were tested under monotonic loading and low-frequency cyclic loading.Failure modes and load displacement curves of all specimens were obtained.The following conclusions can be drawn.The failure mode of the connections is mainly the ductile damage caused by bearing of wallboards on the hole surface and tearing of steel sheets while a few specimens occur with brittle failure caused by screw shear.When the end distance and edge distance of screws exceed 15 mm and the spacing of screws exceeds 100 mm,the increase of their values have no obvious influence on the shear capacities of the connections.The increase of thickness of gypsum board can not improve the shear resistance of connections.The increase of thickness of steel sheets and studs in a certain range can significantly increase the shear capacities of self-drilled screw connections.The increase of diameter of screw can effectively improve the shear capacities of self-drilled screw connections.(2)The numerical simulation on shear capacities of 10 self-drilled screw connections was carried out by ABAQUS to obtain the failure modes and load displacement curves of specimens,which were compared with the test results of the self-drilled screw connections.The results show that there are two kinds of failure modes obtained from finite element simulation of connections,which are tilting and pulling out of screws and screw shear.Except for a few specimens,the failure modes obtained from simulation are basically consistent with the experimental results.The load displacement curves obtained from simulation are similar to the test curves in shape and the error in peak loads between simulation and test is small,which indicates the validity and reliability of the numerical simulation method.(3)The numerical simulation on shear capacities of 7 pieces of full-scale wall specimens was conducted by OpenSees to obtain load displacement curves of specimens,which were compared with the test results of walls.The results show that Pinching4 material constitutive model can reflect availably the hysteresis characteristics of self-drilled screw connections.The load displacement curves of the finite element models of walls,which are in good agreement with the test results,can reflect the ’pinch and slide’ effect and the stiffness degradation in hysteresis curves of composite walls under cyclic loading.The validity of the numerical simulation method is demonstrated.(4)Through the finite element models of the walls,the effect of different factors on the shear capacities of the walls was compared.The results show that the shear capacities could be improved effectively by raising the thickness of steel sheets and studs or reducing aspect ratios of walls for CFS walls sheathed with steel sheets combined with gypsum wallboards.By adding gypsum board outside the walls sheathed with steel sheets,the shear capacities of the walls can also be significantly improved. |
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