Research on bolt end plate welding of steel structure

Very few bolts or joint welds were damaged in the test. During the whole heating process, since the connection temperature is lower than the steel beam temperature (the bolt temperature is about 15% lower than the steel beam temperature when the steel beam reaches the limit state), the internal force of the test piece is redistributed, that is, the beam span is in the middle bend. The moment decreases and the negative bending moment increases at the joint, so the connection improves the fire resistance of the steel beam to a certain extent; when the average temperature at the joint reaches 400e600e, the joint rotation angle begins to increase rapidly; despite the stress of each test piece The level is different, but its deformation characteristics are very similar to those of the normal temperature test piece, that is, the steel column flange of the tension zone produces a large bending deformation, and the deformation of the end plate and the bolt is small; because the friction coefficient of the steel contact surface is at a high temperature The change is small, so the area under pressure on the pressed side can still withstand a certain shear force (although the bolt may be subjected to shear due to slippage). When the actual shear force used for the connection is not more than 50% of the normal temperature shear capacity, the bolt limit state is still a simple tension control, not a pull-shear combination force.

Theoretical studies For most structures, the thermo-structural coupling is small, and the deformation of the structure caused by high temperature generally does not lead to changes in thermal boundary conditions. Therefore, thermal reaction and structural reaction can be regarded as two independent processes. To analyze the calculations. Thermal analysis The temperature field calculation of a component under a given fire air temperature rise condition is based on the basic equation of heat conduction, and the finite difference method or the finite element method is often used for numerical solution. For components with relatively simple temperature field distribution, after some simplifying assumptions, the approximate solution can be obtained according to the lumped heat capacity method, and a practical formula for calculating the temperature of the component is established.

Ac = Kp / tp (32) where Ac is the corrected heat convection coefficient, Kp is the thermal conductivity of the fire protection material, and tp is the thickness of the fire protection material. The calculations show that the temperature calculated by the finite element is higher than the temperature calculated by the practical temperature calculation method of the EC3 component. Franssen believes that there are two main reasons for this difference: one is that the temperature of the adjacent component is higher, and there are some The heat is transferred to the connection node; the second is that the size and components of the connection component are not an order of magnitude, and the component temperature calculation method is not fully applicable to the calculation of the connection temperature.

The structural analysis has done a lot of research work on the finite element calculation of the connection fire resistance performance. The finite element model is as follows: All the plates are simulated by the 8-node shell element, and the bolts are simulated by one-dimensional rod element, and the connection is not considered. The contact problem in the middle; obviously, the model is relatively rough compared to the finite element analysis model commonly used at room temperature. Based on the analysis of the bending moment-rotation angle of the joint method at room temperature, the high-temperature material and temperature load of the steel were introduced, which was extended to analyze the whole process reaction calculation under the fire. The experimental and theoretical analysis of the mechanical properties of the connected tension zone and the compression zone under fire were carried out. China's research in this area has been carried out relatively late. Only Tongji University has done some theoretical research on high-temperature tension and shear high-strength bolting.

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