Composite beams - Shear connection part 2

1. INTRODUCTION

This lecture describes the design of partial shear connection in composite beams. In general, 'full shear connection' is defined as the least number of connectors for a given beam, loading, and design method, such that the bending resistance of the beam would not be increased if more connectors were provided; otherwise, the shear connection is partial. In practice, partial shear connection is often used in multi-storey, multi-bay buildings for the following reasons:

• to save costs - design may be governed by serviceability requirements or other criteria (architectural aspects, ease of construction) and not by ultimate flexural resistance
• to enable the use of a wider connector spacing and a corresponding reduction of transverse reinforcement in the slab
• to coordinate with the floor system used, e.g. with precast floor slabs, or when the slab is cast on profiled steel sheeting with corrugations transverse to the axis of the steel beam

Accurate models dealing with partial connection are difficult to develop [1, 2]. Therefore, the main objective in this lecture is to present and explain simplified design methods, which are appropriate if an idealisation of the connectors' behaviour with regard to their deformation capacity in slip is accepted. So, in conformity with the classification adopted in Eurocode 4 [3], a clear distinction is made here between ductile and non-ductile connectors. The case of absolutely rigid non-ductile shear connectors is addressed briefly in Section 3. The best solution, in this case, is to design the shear connection by a simple and safe process based on an elastic analysis of the beam, which does not raise theoretical difficulties.

The lecture is devoted principally to the case of ductile shear connectors in simply supported beams. As explained in Section 4, the concept of partial shear connection is relatively easy to apply to simply supported beams because plastic theory may be used for determining the resistance of cross-sections. This ease of application is because, according to the definitions given in the Single span composite beams lecture, critical cross-sections in sagging bending are often in Class 1 (even with thin webs) or at worst in Class 2 (if the plastic neutral axis lies in the steel web). Attention is also drawn to restrictions on the use of partial shear connection, e.g. at ultimate limit state for very long spans and also at serviceability limit state because of amplification of deflections due to bending.