Plastic analysis of steel frame with rigid and semi rigid connection

Fully plastic condition is defined as one at which a sufficient number of plastic hinges are formed to transform the structure into a mechanism,then the structure is geometrically unstable. On the other hand the actual behavior of beam to column connections in steel frames is seldom fully rigid or fully pinned. But in actual, the connection is behaved most likely between these two conditions. The connection is called semi-rigid. This paper presents rigid and semi rigid steel frame under nonlinear plastic analysis. One of the important issues in the study of steel frames is to find the ultimate load due to lateral load and besides a suitable formulation for semi-rigid connections. This study is focused on plastic analysis of steel frame structure in three steps. Firstly, elastic analysis of rigid frame based on the stiffness method was developed using software called MATLAB to simulate the behaviour of steel frame under rigid connection. The most important thing in this step was to reach a fully plastic condition with increasing the applied load until yielding occure according to yield locus. Secondly plastic analysis of steel frame under rigid connection and then semi rigid connections considerations. From the result of this study, it is found that by increasing the applied lateral load in elastic step we can find the ultimate load to reach to plastic condition. This is based on yield locus diagram. In addition this study clearly shows the comparison of displacement between rigid and semi rigid connection