Cycling through the city this week I came across a construction project near London Bridge:
The project utilises composite decking, probably one of the two most popular methods of construction for medium rise buildings (along with flat span reinforced concrete). In composite construction, steel beams and reinforced concrete floor slabs are connected, (using profiled decking and welded studs) which transfer the shear between them and allow them to act as one composite unit. Thus a higher proportion of the concrete floor slab at the top of the beam can be under compression and a shallower section can be used.
Another feature of the building which can commonly be seen is cellular beams, i.e. steel beams with openings in the web. This is mainly so services can easily be channeled around the building where required. The various advantages of this design are evident; the decking, as well as providing permanent formwork for the concrete flooring can be used as a safe platform during construction, and technical guidance is produced by the decking manufacturers, which can be a great aid at the design stage.
So as this is a pretty vital bit of structural design for an engineer to get their head around, I thought I would have a go at broadly designing one of the sections to ULS, albeit with a few caveats and assumptions:
So there’s the initial sizing of the beam. There’s still far more to be done of course, as the web openings will complicate matters. Vierendeel bending (that is, a complex hybrid of shear, axial and bending interaction at the corners of the openings) must be accounted for, as well as the usual checks of deflection and vibration to SLS.
Structuralism 