CROSS Safety Report
Misleading instructions for a structural component
A reporter confirms the difficulty encountered whilst endeavouring to ensure cast-in insulated connectors supporting a parapet wall and balustrade were properly fixed.
Key Learning Outcomes
For construction product manufacturers:
- Provide clear and unambiguous product instructions illustrated with diagrams as necessary
For structural and civil design engineers:
- Provide unambiguous construction information
For builders and contractors:
- Contractors may inadvertently be assuming design responsibility by modifying designs and construction information on site
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A reporter writes about the difficulty their firm encountered whilst ensuring that cast-in insulated connectors were properly fixed. A contractor was installing proprietary fixing components to connect a concrete parapet to a concrete slab. The parapet was relatively small with a balustrade proposed to be fixed to it. As such the connectors were intended to transfer shear and bending moment from the parapet back into the slab below.
The contractor tried to install the connectors following the manufacturer's instructions but found they didn't fit, and they chose to cut reinforcement protruding from the connectors to make them fit.
The reporter’s firm, as the engineering designer, was asked to review the situation. Upon finding the situation different from their expectation they queried it with the technical department of the product manufacturer. The manufacturer confirmed that the installation was incorrect and supplied a drawing showing the correct orientation of the connectors. A new batch of connectors was ordered. However, the new batch arrived with the same instructions as the first batch. The manufacturer's technical department was again consulted and confirmed that the instructions supplied with the connectors were incorrect. The reporter’s firm had further dialogue with the manufacturer and sorted out the installation requirements.
Questions were asked as to why incorrect installation instructions had been supplied twice. The manufacturer asserted that they were not to blame and that the error was caused by the contractor cutting the connectors. Clearly, the contractor should not have cut the connectors, but the reporter considered a contributing issue to be that the manufacturer's fixings instructions were not correct for the units supplied. In this instance, the problem was uncovered prior to the concrete elements being cast. However, incorrect fitting could have resulted in failure of the joint and collapse of the parapet.
incorrect fitting could have resulted in failure of the joint and collapse of the parapet
The reporter considered the contributing causes of the issue were:
- A lack of manufacturer's drawn details on how to install the connectors
- The drawings provided by the reporter’s firm showed the position and type of connectors but failed to confirm the orientation
- Incorrect manufacturer’s instructions supplied with the connectors
The reporter’s firm confirmed they reviewed their procedures and now indicate the way cast-in products of this nature are to be fixed/orientated.
Expert Panel Comments
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The reporter picks up on a number of the key issues. It should also be noted that the contractor by modifying the design, i.e., cutting off the reinforcement, is assuming design responsibility for the product. Whilst it is tempting to "adjust" things to get on with the job, contractors may be less willing to do this if they knew the consequences. Ultimately the lack of fit should have been referred back to the designer or manufacturer rather than attempting to ‘adjust’ the components.
It is pleasing that the reporter’s firm reviewed their procedures and now indicates how cast-in products are used. The connection of a parapet to a concrete slab is obviously critical (as a cantilever) and the detailing of concrete reinforcement should be undertaken to a standard such that the contractor is provided with unambiguous instructions. Drawings should be easy to understand and show how reinforcements mesh into one another. Where reinforcement is congested, or there are particularly complex connections, or for example, cast-in elements are required, then details should be sketched at a large size, even full-size, to confirm buildability. Details should take account of manufacturing and construction tolerances and specify which positions are essential and how suitable adjustments can be made – producing unambiguous construction information is all part of 'design'. Clash detection using BIM can be useful in such cases.
producing unambiguous construction information is all part of 'design'
Finally, it appears the manufacturer was less than appreciative of the feedback provided. Hopefully, this was an isolated case as considering feedback is an essential part of improvement for all people and organisations. Product instruction from manufacturers must be sufficient to ensure products will be used as intended by the design. Clearly, it would be folly not to ensure that instructions for products that are used multiple times are clear and unambiguous. Indeed repetitive issues with apparently minor components can be very serious as motor manufacturers find from time to time when large numbers of vehicles are recalled for retro-fitting.
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