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CROSS Safety Report

Structural steel - reinforced concrete interface

Report ID: 19 Published: 1 March 2006 Region: CROSS-UK

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Overview

A reporter describes how the substructure of a building was constructed out of position to the extent that the steel frame could not be erected to tolerance and could not be connected to the holding down bolts.

Key Learning Outcomes

For clients and construction professionals:

  • The need for collaboration over boundaries should be recognised where multiple parties are involved

  • The transfer and coordination of relevant information is important to overcome interface issues as demonstrated in this report

  • Quality control and competent supervision on site can help to ensure that the structure is built in accordance with the design

Full Report

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The reporter describes circumstances on site where organisations had different priorities. A client demanding instant progress, a main contractor with an inexperienced site manager, a steelwork contractor responsible for fabrication only and a steelwork erection subcontractor. There was a reinforced concrete substructure with conventional holding down bolts for a steel frame.

The substructure had been constructed out of position to the extent that the steel frame could not be erected to tolerance and could not be connected to the holding down bolts. The solution adopted was for the bolts to be burned off at foundation level and for the steel frame to be erected in true position without any bolts. The modification was completed by placing the burned off portions of the holding bolts complete with nuts in the base plate holes and disguising the assembly so that it looked to be normal.

The holding down bolts were required in order to sustain considerable uplift forces. Had the deception not been discovered by someone with sufficient knowledge to understand the potential implications of the loss of the anchoring forces a structural failure would have been a serious possibility and thus this incident constitutes a near miss.

Expert Panel Comments

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This is an extreme case but there is evidence that concrete/steel interface problems are not uncommon. Again, specific examples are sought so that any trends can be determined and recommendations for improvements can then be made.

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