Form of construction - car parks
The structural form of a multi-storey car park will be heavily influenced by the design geometry adopted.
Concrete car parks may be assembled from precast units or cast in-situ. In-situ concrete structures may be cast on a wide variety of proprietary formwork and falsework systems; proprietary lift-slab methods avoid the need for formwork for some types of car park.
The use of lightweight-aggregate concrete can also be considered. In car parks, the weight of the concrete slab usually exceeds the live load, and a 25% reduction of this weight is significant, both in the slab and in its effect on column and foundation loads. Lightweight concrete also offers better fire performance. This must be set against the disadvantages: a smaller permitted span/depth ratio, additional shear reinforcement in the slab, and in composite beams a slightly reduced effective breadth of flange and an increased number of shear connectors.
Car parks in composite construction generally comprise a framework of steel beams and columns supporting concrete floor slabs. The latter usually combine in composite structural action with the steel beams in one or both directions and can be wholly cast in-situ or precast with in-situ joints and topping. Some of the advantage in speed of erection afforded by prefabrication may be lost if wholly in-situ construction is adopted for floor slabs.