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Structural elements of car parks are susceptible to movement both during and after construction. With careful design, appropriate joints can be provided to accommodate such movement and to suit the structural design. Car parks can suffer from premature deterioration if the sealants break down, for example under traffic loading, allowing water and salts to get into the joints.
The exposed nature of car park structures produces a greater design temperature range than in other building structures. Joints must also take account of the potential for differential movements between the relatively flexible car park deck and the stiff zones created by ramps and access shafts. Typical mastic joint fillers can accommodate around 20% strain, so a mastic-filled joint would typically need to be five times as wide as the predicted movement. Elastomeric joint fillers are generally regarded as more effective for joints with large predicted movements. Their additional cost must be balanced against potentially expensive remedial work in the event of joint sealant failure.
See separate entry Cracking and associated sub-entries for guidance on various causes of cracking, which can lead to premature deterioration of structural elements. Structural design should also be aimed at controlling such cracking, mainly resulting from differential strains due, for example, to restrained movements at the interface between pours or between precast and in-situ concrete.
Further information on movements and cracking in car parks and other concrete structures may be found in Concrete Society Technical Report 67, Movement, cracking and restraint in concrete structures.
Acknowledgement: The Institution of Structural Engineers
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