Steel Buildings in Europe

Part 4: Detailed Design 4 – 31 be used to calculate the resistance of members in compression, bending, tension and combined bending and compression, as well as the resistance of webs and the shear resistance of cross sections. Design software is increasingly available for the design of both restrained and unrestrained beams and should generally be adopted for commercial design. 5.2.3 Downstand composite beams Downstand composite beams are used as:  Secondary beams, to provide direct support to composite floor slabs, with shear connectors to ensure overall composite action.  Primary beams, to support the secondary beams and transmit their loads to the columns. Shear connectors are used to ensure overall composite action. For simplicity in construction, it is strongly recommended that composite beams are designed to be unpropped for the construction condition. Verification for this condition needs to be carried out in accordance with Section 5.2.2 of this guide before proceeding with the composite condition for the completed structure. Before proceeding with the composite checks, it is necessary to determine the approach to shear connection (this may well have been considered initially during the conceptual design stage). Two approaches are possible: Full interaction Sufficient shear connection is provided to develop the full plastic resistance of the composite section. This approach simplifies the design approach and maximises the stiffness of the composite beam. However, if the beam is larger than is required for the ultimate limit state of the completed structure, significantly more shear connectors may be required than would be necessary for basic strength. There is clearly a cost implication for these additional shear connectors, particularly for longer span primary beams. It may also be difficult, or impossible, to fit sufficient shear connectors onto the top flange. Figure 5.5 presents the detailed design process for full shear connection for secondary beams (primary beams are likely to be designed for partial interaction). This simplified approach is restricted to Class 1 or 2 sections; this is unlikely to be restrictive in practice.