CROSS Safety Report
Safety issues with composite metal deck floors
This report is over 2 years old
A contractor had a near miss when pouring a concrete slab with permanent formwork.
Key Learning Outcomes
For civil and structural design engineers:
Be aware that the deflection of permanent formwork under the self weight of the concrete needs to be properly considered
If there are any uncertainties seek advice from the permanent formwork manufacturer
It should be clearly stated on the drawings if temporary propping is required and whether slabs are to be laid to level or to a constant thickness
Helpful guidance can be found in the Steel Construction Institute (SCI) publication P300
For construction professionals:
If you are unsure of the deflection allowances or propping requirements of permanent formwork, seek clarification from the design engineer
For permanent formwork suppliers:
The deflection of permanent formwork should be taken into account when specifying the sheeting
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A reporter had an enquiry from a contractor who had a near miss: they were building a structure with 8-10m span beams supporting a large slab on metal decking and using laser levelling as the concrete was being poured.
Works stopped on site
The slab kept taking more concrete to bring it up to level and the site engineer became concerned when the structure began to make creaking and banging noises. They stopped placing concrete and phoned the design engineers and asked them whether they wanted the slab placed to constant level or constant thickness.
They took time to think about it and then phoned back to say ‘you’d better place it to constant thickness’. The slab was safely cast - but the contractor had a problem because its surface was up to 80mm out of level, which was well outside specification.
Industry wide problem
The reporter then made enquiries and spoke to various people in the industry who confirmed that there is a problem. However, because of the fragmented nature of the industry with design and build contracts and reliance on performance specifications, everyone felt that it was a problem they could not solve on their own.
It was obvious, said the reporter, that unless there is a concerted campaign for an industry wide solution, nothing is going to change until there is a disaster. It would be very helpful if CROSS could take up the issue and support the proposal as nothing is going to happen unless a lot of people across the industry can be made aware of the problem and persuaded to make solving it a priority.
There is a paper in Concrete (September 2011) entitled 'Floor slabs, lasers and levels' which discusses problems which have developed from changes in the methods of constructing and levelling in situ concrete slabs, particularly composite slabs on metal decking.
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