Semi rigid connections and their influence on steel column behaviour
A review of the development of the analysis of frames with semi-rigid end restraint is given, including the treatment of frame stability and effective lengths. The available experimental data relating to the moment versus in-plane rotational behaviour of practical beam- to-column connections, as used in steel frames, has also been reviewed. This data is found to be a non- linear function of connection deformation. Methods of mathematically modelling connection data have been reviewed and an improved representation based on the use of cubic B-spline curve fitting techniques is proposed. An analytical procedure has been developed to investigate the influence of realistic end restraint on the strength and behaviour of "real" steel columns. A FORTRAN finite element computer program, which includes the effects of initial out-of-straightness, spread of yield and internal residual stresses is outlined. This is based on an incremental approach, with Newton Raphson equilibrium iterations, to follow the load-deflection behaviour up to the maximum load level. The validity of the procedure is verified by comparison with available experimental data for an end restrained column test. A parametric study was carried out to assess the behaviour of columns with semi-rigid end restraint. The important pararReters relating to the connection, the column section and the geometrical imperfections were studied. It was found that an increase in connection stiffness produces a corresponding reduction in column deflections and an increase in maximum load capacity, except in those cases where the column is so stocky that it can attain its full squash load. Effective length factors calculated from these results indicate the column design economies th at would be possible if the actual end restraint conditions were properly accounted for.