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CROSS Safety Report

Failure of epoxy fixings due to high temperature

Report ID: 244 Published: 1 October 2011 Region: CROSS-UK

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Overview

Two mobile phone towers erected on the roofs of nearby buildings collapsed when the epoxy anchors pulled out of the drilled holes.

Key Learning Outcomes

For construction professionals:

  • Connections can often be the weak link in structures and attention to detail is required

  • Manufacturers requirements and guidance for the installation and storage of fixings and resins should be followed

  • Consider having representatives of the manufacturer attending site to train operatives on best practices. This can help to raise industry standards.

  • Where fixings are key components and part of the quality assurance procedure consider carrying out site testing to ensure their strength capacity

Full Report

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Two mobile phone towers were erected on the roofs of two nearby buildings using drilled epoxy anchors into the roof slabs. During a storm of moderate intensity, both towers collapsed; the failure mechanism being the pull out of the anchors from the drilled holes. The recorded wind speed was below the design wind speed for the site (a built-up area) and there were no other structural failures in the vicinity.

On examination, it was identified that the epoxy grout used had a limiting temperature of application of 35 degrees. Although the temperature at the time of construction was marginally below this, the capsules had been left out on the roof for the best part of a day in the direct sunlight on the black tarmac covered roof. The grout had therefore been subjected to conditions that were well outside its operating limits.

The corrective action identified after the failure was to monitor and control the temperature of all chemical fixings, with recognition that ambient shade temperature and exposed surface temperatures on site can be vastly different. The product labelling was not particularly clear on this, although with hindsight, the failure could easily have been avoided through better preparation of method statements and a focus on environmental effects at the time of construction.

Expert Panel Comments

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The reporter succinctly summarises the situation and the required actions. The strength of epoxies is generally related to temperature. Engineers know about the fatal consequences of the Boston Big-Dig when epoxy fixing failures led to fatalities and massive civil claims. The Standing Committee on Structural Safety (SCOSS) has issued an Alert on The Selection and Installation of Construction Fixings.

The construction industry uses some sophisticated materials and compliance with manufacturer’s instruction is always essential, not least as otherwise the supplier’s liability will be invalidated. Detailed advice on fixings generally can be obtained from the Construction Fixings Association.

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