Nonlinear Finite Element Analysis Of Continuously Reinforced Concrete Beam Under Fire

Fire resistance of structures is an important and difficult problem in structural engineering. Fire resistance of reinforced concrete structures is better than other structures such as steel structures and wood structures, but it will become disabled under conflagration too. Because of the high cost of fire testing facilities and of the fire tests itself, it is becoming considerably important to use software of finite element analysis to model the thermal and structural response of individual members and structures in fire environments. In addition, advances in fire science and technology have fostered a movement in some industrialized countries developing performance-based fire safety design method. This transition toward performance-based method has made software of finite element analysis become a predominant tool for fire design and analysis. Without this kind of software, it is impractical to investigate the response of a large variety of structural elements under differing restraint, loading, and fire conditions.This dissertation comprises two parts. The first part, making use of the pre-investigators' conclusions, summarizes various parameter models of the pyrology and the dynam to both the concrete and the reinforced. It also summarizes various curves about the relation between the temperature and the time. Furthermore, it briefly introduces the equation of the heat exchange. The second part integrates the content of the first part to establish the temperature field finite element model of a two-dimensional section of the reinforced concrete component. And it has analyzed the influence of each kind of parameter model to the temperature field. It has also established a three-dimensional frame beam finite element model, to discuss the stress distribution and the distortion situation under different operating modes of the fire. The main results of this dissertation are as follows:(1)The temperature field of the section of the reinforced concrete component is very diffirent when it is loaded by diffirent calefactive temperature curve. When the component is loaded by the calefactive temperature curve of the parameter, In the temperature ascending phase, the temperature of the steel bar rises more quickly; When the temperature ascending phase ends, the interior of the section possibly exists at least two extremely district with high temperature.(2)When the temperature load of the section is different, the temperature distribution of the interior section is also different. And the temperature distribution always presents a descending trend along the surface on fire to the non-fire surface or the interior of the section; The section size has no effect to the steel bar's temperature; Under the same condition, it can reduce the temperature of the reinforced when the protecting thickness of the reinforced is increased, and it can also enhance the carrying capacity of the reinforced concrete component under high temperature.(3)The temperature of the inner section is sensitive to the change of the product between the density and the specific heat; The temperature of the point which is more far away from the on-fire surface, is more likely to be influenced by the change of the thermal conductivity.(4)When the structure load and the temperature load simultaneously load on the frame beam, the displacement isn't equal to the summation of the two load operated alone; When the structure load is small and the component is sufficiently burned, the temperature load is more influence to the steel bar's temperature than the structure load, and it possibility leads a non-tensile stress condition to the steel bar.(5)The displacement in the corner of the two on-fire surfaces which are near to each other is larger than the corner place of the surface which is the only one on-fire. At the bottom of the beam, two sides of which has been fixed, a displacement centralized region exists in the place which is 200mm near to the end of the beam.(6)The temperature load is same to the structure load, both of which have the problem of the most disadvantageous distributing on the frame continuously beam.