End plate connections and their influence on steel and composite structures
The structural members of steel frames are jointed by connections. These connections are neither rigid nor pinned but semi-rigid. The performance of steel structures is highly influenced by the behaviour of connections which is characterized by the moment-rotation curve. This thesis studies the effects of semi-rigid connections on steel and composite steel-concrete frames, in particular the behaviour and influence of end plate connections. The first part of the thesis concerns the performance of unbraced planar steel frames with semi-rigid joints. Several aspects are investigated, concerned mainly with the serviceability limit state. Using the definition given in Eurocode 3 for a rigid connection, it is suggested that the conventional limit for the sway angle should be relaxed by 10% when the rotational behaviour of the joints is included in the analysis. For frames designed by the wind-moment method, it is proposed that deflections based on the assumption of rigid joints should be increased by 50% to allow for the connection flexibility. An approximate method, in which the stiffness of beams are reduced to account for joint flexibility, was found to be sufficiently accurate if deflections based on semi-rigid behaviour were to be calculated. Finally, studies on the ultimate limit state show that the resistance of a joint has significant effect on the collapse load of a frame, compared to the more modest influence of joint flexibility. The second part of the thesis concerns the behaviour of composite connections in braced frames. This part consists of a concise collection of the available experimental data, a description of the test programme conducted by the author, a proposed method for prediction of connection stiffness and studies on redistribution of moments in composite beams. Eleven tests have been carried out on bare steel and composite end plate joints. Their moment-rotation behaviour is recorded and the influence of variables on the joint stiffness is pointed out. These variables are the amount of reinforcement in the concrete slab, the type of steelwork connection and the beam depth. Increase in the amount of reinforcement increases significantly the moment resistance of the composite joint but does not influence its initial stiffness. I % reinforcement with respect to the area of concrete slab is proposed to be used for an efficient design. The increase in the depth of steel section increases the moment resistance and stiffness of composite connection but reduces its rotation,capacity. The effect of semi-rigid composite connections on column stability is also studied and a value of 0.75 is proposed as the effective length factor for columns. The proposed method for prediction of connection behaviour is shown to be in satisfactory agreement with the test results. From the final studies in Part Two formulae are proposed for calculation of the required rotation capacity of composite connections.