Aspects of sway frame design and ductility of composite end plate connections

Abstract

This thesis reports work on two aspects of framed structures: part I is concerned with sway frames and part II with the ductility of composite flush end plate connections. Part I has investigated the effect of adopting standardised end plate connections as the method of providing the load path between the structural members of a steelwork sway frame. Practical low to medium rise multi-storey frame geometries have been designed in accordance with limit state principles in conjunction with the Wind-Moment Method. Each frame was analysed by undertaking a second-order elastic-plastic computer analysis to ascertain their structural performance, with particular emphasis directed towards problems associated with stability and sway deflections. The computer simulation necessitated the formulation of a prediction equation that modeled the initial stiffness characteristics of the standard connections. This model has been verified by comparison with full scale experimental test results, mainly taken from the literature. The investigation confirms that standardised end plate connections provide levels of stiffness and resistance which enable unbraced steel frames to be safely designed by the Wind-Moment method. There are however certain frame geometries where serviceability considerations dictate that stiffening to the frame would be necessary, if the standardised end plate connections were used. Part II has investigated the ductility of five major axis composite flush end plate connections that incorporate nominally identical amounts of reinforcement in conjunction with either 457 or 533 serial size Universal Beams. Other variable parameters include end plate thickness and horizontal spacing of the rebars. The work was undertaken experimentally and the results analysed in the context of connection performance. The results have shown that it will not prove difficult to ensure virtually rigid behaviour of the overall composite connection, despite the use of relatively thin end plates. Moreover, the experiments also show that the rotation capacity of composite connections in which 1% reinforcement is provided, would be sufficient to allow plastic methods of design to be used for composite beams with 457 serial size designations; however, ductility remains a problem when the depth of beam is further increased. To this end, an empirical model for assessment of ductility has been proposed, based on the observed deformation characteristics of the joint as a whole. This enables the total rotation capacity of one type of a composite connection to be determined when the failure occurs by fracture of the reinforcing bars