CROSS Safety Report
Thermal effects on long span concrete car park beams
This report is over 2 years old
A reporter describes how long span precast hollow core units in a car park started to bow upwards due to thermal effects.
Key Learning Outcomes
For civil and structural design engineers:
Take account of the durability requirements of car parks and the thermal effects on exposed structural members
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While in the Gulf a CROSS correspondent received a report from an engineer in his company who had visited a car park built with a system using long span precast hollow core units. The pattern of cracking in the supporting beams showed that solar radiation was causing the units to bow upwards with the rotation at the ends forcing the supporting reinforced concrete L-beams to crack through friction at the bearing - contact was concrete-to-concrete with no provision for movement. The structure was three years old and had progressively worsened during each summer.
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The effect is acknowledged in some countries where it is referred to as ‘sun camber’. In principle the movement from solar radiation needs to be allowed for, or provision made in the detailing to prevent relative movement at the connections. The Concrete Centre’s Hybrid guide includes references and details. As with all building and design activities the best results are not just purely a matter of stress calculation. It is fundamental that there is an appreciation of material behaviour and of probable deformations with appropriate measures being taken to accommodate predicted movements.
In 2006 New Civil Engineer published an article describing problems with a car park in the UK where solar radiation effects were apparently blamed for widespread concrete cracking and spalling. At the time the Standing Committee on Structural Safety (SCOSS) called for the reasons for the structural failure to be made public, but this has not yet come about.