Multi-storey car parks are a common feature in the UK's towns and cities. In the past they tended to be utilitarian structures, designed to be functional, perhaps without an appreciation of the perceptions of the users.
More recently, designers have recognised the need to improve safety and security by providing long clear span by removing the columns from the parking spaces. This has led to a series of solutions using spans of up to 16m.
The structural frame for a car park has to perform well in a number of different areas. The following list gives an indication of the many benefits of using concrete for a car park structure.
The durability of the structural frame is an important aspect of car park design. A well-detailed concrete car park, correctly specified using BS 8500 should achieve a design of 50 years (or more if required). BS 8500 is the British Standard for specifying concrete and is based on the state of the art knowledge of concrete performance in a number of different exposure conditions.
Vibration of the floor plate can be a concern in the performance of a car park. Concrete structures generally have more mass compared to other materials and are therefore less prone to footfall-induced vibration.
Inherent fire resistance means concrete structures generally do not require additional fire protection. This removes time, cost, use of a separate trade and ongoing maintenance to applied fire protection.
Concrete is a robust material that can withstand the wear and tear from normal use with minimal or no damage.
Fair-faced or visual concrete can be both aesthetically pleasing and durable, ensuring car parks keep looking good with little maintenance.
The current trend is for clear spans of up to 16m, these give an open feeling and reduce the risk of damage to vehicles and columns because of columns placed between spaces. There are three widely-used concrete floor solutions to meet this requirement, and can all be used with either precast or in-situ concrete columns.
Double-tee floor units are ribbed precast prestressed concrete units. They can be procured in a variety of depths from 300mm to 800mm and even beyond but the most common unit is 600mm deep as this conveniently carries car park loading up to 16m. The top flange is usually 50mm or 60mm deep and the ribs taper from a minimum of 140mm at the base, widening upwards towards the underside of the top flange, the taper of 1 in 20 each side allowing for easy lifting out of a fixed mould. Double-tee floor units are produced in standard widths of 2,400mm. More information on double-tee floor units is in the publication Offsite Concrete Construction.
For spans up to 16m a post-tensioned band beam offers an economic solution. Band beams are shallow, wide beams that minimise the overall structural depth. The pre-stressing maximises the performance of the concrete and controls deflection. Typically the beam depth is 550 to 600mm deep. Further information on post-tensioning can be found in the publication Post-tensioned Concrete Floors.
Hollowcore slabs derive their name from the voids or cores which run through the unit, which reduce the self-weight of the slabs, maximising structural efficiency. Units are generally available in standard 1,200mm widths and for up to 16m span a 400mm deep unit is appropriate. More information on hollowcore slabs is in the publication Offsite Concrete Construction.