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CROSS Safety Report

Inadequate foundation reinforcement

Report ID: 112 Published: 1 October 2008 Region: CROSS-UK

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Overview

Subcontractors carrying out the ground works for a multi-storey development failed to provide sufficient continuity reinforcement in the ground beams.

Key Learning Outcomes

For the construction team:

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

For civil and structural design engineers:

  • If possible, attend site and inspect the installation of critical structural elements such as foundations

  • If you are unable to attend site, ask the contractor for site photos of the installation of these critical structural elements

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Subcontractors carrying out the ground works for a multi-storey development failed to provide sufficient continuity reinforcement in the ground beams. In an attempt to provide continuity, the steelwork was repositioned with the result that all reinforcement from a corner of the building was removed (highlighted in Figure 1). The local authority building control officer twice advised the sub contractors that this was unsatisfactory, but they claimed that the consulting engineer had considered the work acceptable. Regardless of this statement the work was not approved.

Image
Figure 1: missing reinforcement in ground beam

The reporter advises that this is not an isolated case because on many sites there is little or no involvement of the design engineer to ensure that his details are being followed on site. Traditional checks on construction standards from clerk of works and site resident engineers are now rare because clerk of works are not generally employed and the site engineers knowledge usually relates to setting out only.

A reputable design team and main contractor were carrying out this development but the lack of basic knowledge of the ground workers would have gone unchecked if it had not been for the local authority inspection. There is, considers the reporter, a concern about the lack of site involvement by design engineers in respect of critical areas of construction. Reliance is placed on sub contractors but their lack of knowledge creates risk of fundamental errors in the construction process.

Expert Panel Comments

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Unless adequate supervision is provided on site, problems will eventually result. This separation of design from construction is a potentially dangerous trend. It is common practice in the UK for reinforcement to be detailed by the contractor. In such a situation the design engineer would check that the reinforcement placement drawings met the design intent.

It would appear that no such placement drawings were approved or if they were the steel fixing details were not followed. Whilst the involvement of the original designer in site inspections provides the best check of design intent, there appears to have been failures in good practice prior to the start of works on site.

Even for relatively trivial details checks should be in place. Design briefs often exclude any site involvement by designers whose activities are restricted to monitoring. However the key lesson here is that there must be competent structural engineers on site either from the design side or from the contractor to prevent failures.

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