Shear Behavior Of Connections In Metal Skin Diaphragm

With the development of steel structures, metal skin diaphragm structure has been widely used in civil engineering. And the structure styles are becoming more and more diverse. The metal sheeting is connected with the main structure by connections. The in-plane stiffness of metal sheeting takes the effect of skin diaphragm into effects. Furthermore, the in-plane stress state of metal skin diaphragm induce that the connections mainly bear the shear load. Then, based on conclusion of achievements of former researchers, the dissertation mainly studied the shear behavior of connections in metal skin diaphragm. Because of the variety of connections in skin diaphragm, the dissertation, through careful comparison and selection, finally chooses two types of connection, self-tapping screw connection and resistance spot weld connection, as study objects for finite element method analyzing. The major work contains the following:1. Set up 3-D solid models to simulate the connections. For self-tapping screw connection, material nonlinear and contact nonlinear effects are included in the analysis. For resistance spot weld connection, residual stress is calculated first; then the finite element analysis including material nonlinearity and contact nonlinearity is carried out.2. Obtain the failure modes of both types of connections by analyzing a large number of examples. For self-tapping screw connection, there are three failure modes:①The hole in the thinner plate is elongated and the slippage between the two plates is more serious (often found in connection between a thin and a thick plate) .②The screw is wry, the side of plate is tilting, and the edge of hole is squished (often found in connection between two thin plates) .③The screw becomes obviously lean, the side of plate becomes tilting, and the screw is pulled out because of the broken screw thread (often found in connection between two thick plates). For resistance spot weld connection, there are also three failure modes.①The thinner plate is tore without obvious displacement or deformation in the model (often found in connection between a thin plate and a thick one) .②The steel plate fails because of bending. The edge of the nugget fails because of tension and shearing. And the deformation of the model is extremely severe (often found in connection between two thin plates).③The nugget fails because of shearing with crimple of the back edge and obvious displacement (often found in connection between two thick plates).3. According to two types of connections, load-deflection curves(P—Δcurves) with different thickness plates and different diameters nuggets are obtained respectively. And the curves show that most models present ductile failure, and the connection strength and stiffness increase with the thickness of the plates and the diameter of the connection.4. According to the regularity of the connection strength and stiffness curves, using least square method and based on the original empirical formulas, this dissertation proposes formulas for calculating connection strength and stiffness. The formulas have a guarantee ratio up to 95 percent, and thus can be directly used in practical engineer design. Furthermore, these formulas have uniform formats despite of thickness differences in connection, which strongly embodies rationality and continuity. In this dissertation, there are 5 formulas for self-tapping screw connection and resistance spot weld connection. Compared with foreign empirical ones, formulas from the dissertation gain finite element results that are much closer to the test data. And it can also reflect some regularity that they are unable to.