Thermal And Structural Analysis Of Steel Structure With Concrete Slabs In Fire

With features of lightweight, high-strength, convenient adjustment and short construction period, the steel structure and composite structure are widely used in practical construction. But these structures are very sensitive to fire. Special concern should be gave to their fire resistance. Considering the problem of fire resistance of steel structure with concrete slabs, some efficient and reliable numerical methods are presented from the following aspects and applied to the fire resistance analysis of practical structures.1. Concrete floor is commonly used in engineering structure. In order to calculate the temperature field in the floor, the temperature gradient in the plane and along the direction of thickness should be considered. And a kind of temperature element is presented here by considering its temperature gradient along thickness. With this element, the floor is decomposed in the plane, and the temperature distribution was assumed linear along the direction of thickness. Considering the assumption that the temperature difference(measure in K) are far less than the mean temperature(measure in K), the mean temperature and temperature difference are decoupled in process of deducing the heat conduction equation. So that the temperature field can be calculated by the following two steps: (1) solving nonlinear ordinary differential equations of average temperature; (2) solving the nonlinear ordinary differential equations of difference temperature based on knowing the average temperature of every time step. Two degrees of freedom are employed for node of element: average temperature and difference temperature. The numerical examples show that the present element can be calculated fastly and effectively.2. The equivalent force caused by temperature field of plate are presented in structural analysis. The thermal flexure are caused by difference temperature along plate thickness. Numerical examples prove the accuracy of thermal flexure calculation.3. Based on the method above, the finite element programs are applied to calculate the transient temperature field, elastic thermal deformation and elastic heat stress of steel structure with concrete slabs in fire, and applied in calculation of structural fire resistance. The effect of whole structure which influence the fire resistance performance of the structure are discussed in numerical examples.