BEHAVIOUR OF BOX-COLUMN TO I-BEAM CONNECTIONS

Abstract

A significant portion of the construction cost of an average steel building goes into the fabrication and erection of the structural system. Thus, any saving in these can reduce the cost of construction considerably. One of the main areas of potential cost saving is in the fabrication and erection of beam-to-column connections which is inherent in every building. Due to the repetitive nature of these connections, even a minor material or labour saving in one connection is compounded throughout the entire building, giving rise to substantial cost savings. The traditional way of stiffening the I-beam to box-column connection is to weld an internal plate in the column. However, this is a complex and hence expensive process. It is the objective of this study to find a simpler method of stiffening the connection. This can be achieved by stiffening the connection externally with suitable stiffeners. The finite element method has been used in a preliminary study to investigate the effect of different types of external stiffeners on the behaviour of connections. The stiffeners considered include triangular plates, angle and T-sections of which the T-section was found to be the most efficient form. The initial stiffness provided by the T-stiffener has been found to be as good or even better when compared to the internal stiffener which is traditionally used. A total of fifteen full-scale 2-way connection specimens have been tested to failure in the laboratory. The specimens were stiffened either internally by diaphragm plates or externally by angle or T-sections. To investigate the behaviour of connections subjected to reverse loading, seven of the specimens were subjected to cyclic loading. The rest were loaded with monotonically increasing load. A detailed investigation into the load-deflection behaviour, the moment-rotation (M- ?) relationship and the normal stress distribution at the connections have been carried out. The results have been found to compare well with those obtained from the nonlinear finite element analysis. In order to make the design of the connection stiffened externally by T-sections more accessible to the practising engineer, a simple design procedure is proposed, both for the 2-way and 4-way connections. This design procedure has been verified by a series of nonlinear finite element analyses on connections comprising of beam and column sizes from a wide range. The connections have been shown to satisfy the basic design criteria for a moment connection ie, stiffness, strength and ductility. A curve-fitting method has been used to obtain the moment-rotation relationship of the connections designed. Two sets of standardised M- ? functions have been obtained, one for the 2-way connection and one for the 4-way connection. The functions are expressed in terms of the geometrical properties of the connection. To verify the design procedure and the moment-rotation relationship proposed, four full-size 4-way connection specimens have been designed and tested to failure. The experimental results have shown that the specimens satisfy the basic requirements for a good moment connection as well as verifying the moment-rotation relationship proposed.