Investigation Of Joint Behavior Of Steel Structure In Fire

In the designation of multi-storey steel framed buildings at elevated temperature, choosing good joint is very important. Now, the study of the semi-rigid connections is in the beginning in our country. End-plate joint is the most common form of semi-rigid connection. But the designation of steel construction has many disadvantages. (i) Most research works on steel construction are done by experiments. But the experiments are expensive and they are limited by the samples and the conditions of experiment. Different values of the same parameter or the influence of different parameters could not be studied. (ii) The end-plate connection consists of bolts, endplate, column flange etc. It takes on non-linear characteristic. The current regular doesn't take into account of this problem and adopts the formula of full-welded connection to calculate the semi-rigid connection. Obviously, it is not according to the engineering. (iii) The code of steel construction designation in our country prescribes that in analysis of inner force, the moment-rotation relationship curves of connection must be determined. It definitely indicates that the influence of semi-rigid connection must be considered in analysis of steel frame constructions, but it doesn't define how to determine the moment-rotation relationship curves. In order to solve these problems, the following research work was done:Parametric analysis on the behavior of flush end plate connections in fire were discussed using ANSYS. The model took into account of the assemblies of components and various parameters which affected the stability of complete structure and failure mode of connections. It was found that the thickness of end plate had large effect on the initial stiffness of connection. The load ratios affected the rotation of connection greatly. The stiffeners that were mounted in compression zone can decrease the plastic strain of joints and improve the stability of column, which ensured the stability of the steel frames.A lot of research work was carried out to study the behavior of flush end-plate connection and extended end-plate connections and many groups of moment-rotation relationship curves on these two connections are obtained. But for flexible end-plate connection, the main characteristic of a flexible endplate is that the response has two stages. The center of rotation has been changed resulting in an enhanced stiffness and capacity. Due to lack of elevated temperature experimental data, only the first stage is accounted for in the model. The response of the second stage and the moment-rotation curve of whole course are presented using"component method"and"three-fold-line model"in this paper. In addition, the two-stage moment-rotation relationship curves at elevated temperature are introduced using"retain factor"in EC3, which lays a theoretical basis and analysis method of the study of flexible end-plate connection in fire.