Car park and deck structures

Durability is what really separates car park design from ordinary structures. Cars carry in rain, road salt and de-icing chemicals, and the decks are subjected to wetting, drying and freezing, so chloride attack on reinforcement is the main enemy. We design the concrete to the exposure classes of BS EN 1206 and BS EN 1992, with adequate cover, low-permeability concrete and, where the deck is exposed, a waterproofing or deck coating system to keep water and chloride out of the structure.

The detailing has to shed water and cope with movement. We fall the decks to drainage, detail movement joints that stay watertight, and protect the tops of columns and the joints where water collects. For steel-framed decks we specify corrosion protection suited to the exposure, and we design for the maintenance and inspection the structure will need over its life, because a car park that cannot be inspected and repaired will not reach its design life.

Car parks have their own fire regime. Open-sided car parks with enough natural ventilation are treated more favourably in the fire strategy than closed decks, which affects the fire protection the structure needs, so we coordinate the structural design with the ventilation and fire engineering from the outset. The frame is designed for the required fire resistance while taking credit for ventilation where the codes allow it.

Foundations carry the accumulated deck loads and the wind on what is often a tall, open structure. We design piled or spread foundations for the column loads and the overturning that wind produces on an open frame, and where the car park is below ground or partly buried we design the retaining walls and the basement box for ground and water pressure. The whole substructure is tied into the stability system that keeps the open decks standing in a storm.