CROSS Safety Report
Very slender props
This report is over 2 years old
A reporter noticed prop that did not have ties installed while carrying out a site inspection.
Key Learning Outcomes
For construction professionals:
It is good practice to carry out a risk assessment and method statement (RAMS) for all construction activities. This can ensure the sequencing of work activities are properly considered and planned.
For civil and structural design engineers:
Speak to the contractor about your proposed construction methodology, highlighting any particular areas of risk or uncertainty that they should be aware of
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An unusual house was designed by a firm of avant guarde architects and its form required some interesting structural engineering solutions. Most of the structure was timber framed but part of the roof was held up by steel beams supported by two very slender (50x50mm) rectangular hollow section (RHS) posts which carried on down through a third storey loft and then through two floor levels to a concrete foundation – a total height of about 10m.
The contractor erected the timber frame around the edge of the building and the internal steelwork. Floor and roof joists were put in place and preparations were made for cladding the roof with tiles. At this stage an engineer saw that the props were continuous through the two floors with no ties or bracing and hence had unacceptably high slenderness ratios.
The consulting engineer’s drawings showed ties, but their importance had not been appreciated by the builder who intended to install them as the floors were being finished. Once the contractor’s attention was drawn to the importance of the ties they were installed. Had this not been done before the roof tiles were added the additional loads on the props could have caused them to fail.
The consulting engineer’s drawings showed ties, but their importance had not been appreciated by the builder who intended to install them as the floors were being finished
Expert Panel Comments
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Unusual structures, whatever their size, need vigilance and frequent site inspections can be very important. These should be by the designer and by the local authority or approved inspector. A review of the drawings to together with local knowledge about the capability of the builder should form the basis of an informal risk assessment.
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