Elastic stability of steel planar frames with semi rigid joints

In daily design routine, stability of columns is assessed by the effective length concept by using charts. It is assumed that the frame is either rigidly or pin connected. This procedure is very easy to handle. It has been found that the effective length obtained by such method at times differ significantly from solutions obtained by the exact methods. It is known that connections are neither true hinges or rigid. Hence such simplification can lead to either overestimating or underestimating the buckling load. In this research semi rigidity of connections have been incorporated in the members’ stiff nesses. With these stiff nesses normal structural analytical methods can be applied in stability analysis. Stiffness of connections have been expressed by connection factors. A parametric study has been carried out to assess the effect of the stiffness of connections. It has been found out that increasing the connection stiffness increases the the buckling load. Hence great economies can be achieved by considering the connections semi rigidity. The method to determine the effective lengths for braced and unbraced columns by using charts have been improved and semi rigidity of connections have been incorporated. The results obtained by this procedure were very close to the solutions obtained by exact methods. Hence this procedure can still be used as an accurate method for stability assessment.