Analytical studies of the behaviour of semi-rigid non-sway frames with tubular columns
This thesis reports the research investigation on the behaviour of non-sway frames with SHS columns taking into consideration the influence of semi-rigid flowdrill connections. The aim of the studies was to investigate the behaviour of the non-sway frames in the elastic and inelastic ranges, the acceptability of the flowdrill connections for low-rise non-sway frames and to develop a simplified semi-rigid design that is suitable for daily design routine. The analytical studies were conducted using an existing finite element program which was modified to work with frames employing tubular columns. The program is able to simulate the response in the elastic and inelastic ranges taking into account the semi-rigid connections, the geometrical and material nonlinearities and the development of spread yield. The program has been validated against the experimental results and can reasonably predict the true frame behaviour. The results of the parametric studies show several important observations;one of which is the phenomenon of moment shedding. This phenomenon causes the relaxation of the detrimental moment at the column top end which in turn causes the moment redistribution to the neighbouring members. Eventually, the detrimental column moment diminishes and sometimes acts as restraining moments. As a consequence, at ultimate load, the columns behave in the general form of axially loaded compression members and the beams as simply supported with a certain degree of end restraint. Knowing that restrained beam-columns can be treated as axially loaded, extensive parametric studies on different frame configurations were conducted to determine the ultimate strength of beam-columns. The studies were conducted on low rise multi-storey non-sway frames. The principal parameters varied are the column slenderness, connection types and the magnitude of beam loads. The values of ultimate strength of restrained beam-columns are compared directly against the strength of pin ended columns as specified by the BS 5950 and EC3 codes. The results show that in many cases, the ultimate strength of restrained beam-columns are in excess to the strength of axially loaded pin ended column as specified by BS 5950 and EC3. Based on the results of the parametric studies, a simplified design for simple, semi-rigid and rigid frames is developed. The columns are designed as axially loaded compression members without any consideration of eccentricity or partial fixity moments. The beams for simple construction are designed as simply supported with pin ends; whereas, the beams for semi-rigid and rigid construction are designed as simply supported with a certain amount of end restraint moment to take into account the effect of semi-rigid and rigid connections. The design of strength for beams and columns can be carried out individually and is not dependent on the stiffnesses of the M-0 of the connections, beams and columns. Finally, general conclusions and recommendations for further work are also included.