Skip to main content

CROSS Safety Report

Telecommunications towers and resin anchors

Report ID: 315 Published: 1 April 2013 Region: CROSS-UK

This report is over 2 years old

Please be aware that it might contain information that is no longer up to date. We keep all reports available for historic reference and as learning aids.

Overview

A correspondent shares their concerns following the collapse of a telecommunications tower.

Key Learning Outcomes

For the construction team and design engineers:

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

  • Manufacturer’s requirements and guidance for the installation and storage of fixings should be followed

  • Consider having representatives of the manufacturer attending site to train operatives on best practices. They can help 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

Find out more about the Full Report

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others. If you would like to know more, please visit the reporting to CROSS-UK page.

A telecommunications tower, held down by resin anchors which apparently passed pull-out tests of 125kN (although it is not known how these were carried out), failed six years later with little resistance in light winds, says a correspondent.

The collapsed tower was a replacement, and the original tower was half the height of the replacement. The engineers of the original tower had gone to great lengths to ensure that there was no chance of a failure at the steel to concrete interface at the base.

Although the prime cause of the collapse was poor workmanship, the correspondent have several concerns:

  • There is a growing tendency for towers and elements to be held down or secured by resin anchors and risks may not have been adequately considered

  • Stability should, in the opinion of the correspondent, never rely on just a chemical bond without assessment of the risks

  • No data appears to be available on pull out tests carried out after a few years

  • The companies who provide the anchors may not have been informed of failures

  • Resin anchors could be used in high-risk environments such as for towers positioned beside railway tracks

  • Pull-out tests at the time of construction might not be relevant after a few years, particularly if water can penetrate and freeze

  • There will be a need for continued and regular testing and replacement of anchors that rely on non-mechanical bonds

  • Some of these anchors do not allow for testing and replacement of critical bolts at the superstructure/substructure interface because of levelling nuts below the base plate

The correspondent concludes by saying that they has reservations about the long-term behaviour of resins for exterior use.

Expert Panel Comments

Find out more about the Expert Panels

Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

Designers of safety-critical elements have to avoid the possibility of failure wherever reasonably practicable. This is particularly so in cases such as this when the long term behaviour may be affected by a harsh environment and the quality of workmanship which is critical in post-drilled fixings. Anchor failures of various kinds have been reported including those in the spate of ceiling collapses sent to CROSS and in some serious collapses of tunnel linings.

This is particularly so in cases such as this when the long term behaviour may be affected by a harsh environment and the quality of workmanship which is critical in post-drilled fixings.

There is also an issue with the use of resin anchors to hold down structures such as freestanding towers which are predominantly subject to fluctuating wind load. It arises when the hole is completely filled with resin and the bolt is bonded along its full length. In such a situation, there may be strain incompatibility at the point where the resin and bolt meet. Over time, under fluctuating load, the bond between bolt and resin may have a tendency to weaken. This is in addition to the valid concerns raised by the reporter.

There is a case for assembling a database of resin anchor performance both short and long term and for developing more guidance on best practice which will need to include installation and testing. CROSS would therefore be interested to hear about other cases, particularly where there have been unexpected or premature failures.

Share your knowledge

Your report will make a difference. It will help to create positive change and improve safety.

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others.