Multi-storey car parks

Car parks are usually large-span structures subjected to frequent load changes as well as the effects of long-term creep, deflection and temperature movements. Failure to make sufficient provision for movement will lead to cracking and disruption of joints, which, if severe enough, can damage waterproof coverings and lead to water ingress.

Joints through decks are particularly troublesome and often badly maintained. It is not unusual to find accumulations of short-life materials and various inadequate attempts to seal a joint, usually leading to failure and at worst the entrapment of reservoirs of water, which gradually leeches out.

Movement joint designs are many and varied, ranging from simple membrane types (EPDM for example) or more sophisticated bolted joints. These systems can be effective but rely on correct installation and sealing. Often the holding down bolts perforate the waterproof membrane and give rise to leakage problems. To prevent water from penetrating the joint it may be preferable to contrive a raised joint to minimise the flow of water over it. Such a detail would of course only apply if adequate drainage can be provided elsewhere.

The detailing of reinforcement at the joint between a column and a flat slab is difficult to engineer but is also critical in terms of performance and the avoidance of problems of progressive collapse. In 1972 and again in 1984 design codes were modified to improve shear reinforcement around column heads. However, these changes in code would obviously not apply to structures constructed during the 1960s where design was often carried out to CP114, CP115, CP110 and BS 449 - all of which were found to be inadequate for the task. For this reason particular regard should be given to any signs of cracking around column head positions.

Joints at bearing positions are notoriously troublesome. Above, the bearing of a trimmer beam supporting a double tee deck has failed as a result of water ingress and corrosion of reinforcement.

Water ingress above this beam/column connection has lead to corrosion of reinforcement and spalling of the bearing and reduced support.

The end of a double tee beam shows a halved joint at its bearing end. However, due to movements in the structure the original bearing was compromised and an additional steel beam has been retrofitted in order to provide adequate support.

Worrying amount of slippage in beam bearing, coupled with shear cracking.