The design of semi-continuous composite beam systems requires that the rotation capacity of the joint regions exceed that required in those regions necessary for the degree of redistribution of moments assumed in the design to be safely accommodated. Concern has previously been expressed that some combinations of connection detail and adjacent composite beam properties might not provide sufficient rotation capacity. One hitherto relatively unexplored possibility to improve the situation is to use the concept of partial shear connection.
This paper considers the effects of partial shear connection (employing the concepts of partial interaction) on the required and the available rotations of semi-continuous composite beam systems. Partial shear connection can be considered to occur in two distinctly different regions in a semi-continuous composite beam, these being characterised by sagging and hogging bending zones. Generally, the effects of partial interaction, which is increased by the use of partial shear connection, will result in reduced strength and stiffness and potentially enhanced ductility of the overall system. It is the perceived increased ductility of these systems which may be considered to alter the demands for rotations at the joints, resulting from the reduced curvatures within the span. Furthermore, the use of partial interaction within the hogging moment regions potentially increases the available rotation capacities of the joint regions. This study provides a method to evaluate the effects of partial shear connection on both the strength and ductility of beams in both the sagging and hogging bending zones. The method is validated against existing independent and original experimental results for sagging and hogging bending zones. A parametric study is conducted herein on unpropped composite beam systems with composite slabs spanning between secondary beams and supported by primary beams to elucidate the effects of various influential parameters. It is found that partial shear connection has the effect of increasing both the available and the required rotations. Furthermore, these two competing parameters reach parity in a design sense when the spans exceed 14m. For design cases which may require larger spans it is generally required that more localised issues are considered to try and satisfy this ductility limit state. Some suggestions are given for this in the paper. Recommendations suitable for design and more general conclusions are then provided which provide the basis for safer and more economic designs.
B. Uy, BE, PhD, CEng, CPEng, MIEAust, MASCE, MIStructE, MICE
University of Wollongong, Wollongong, Australia
D. A. Nethercot, BSc (Eng), PhD, DSc, FREng, FIStructE, FICE, FCGI
Imperial College London, UK