Quick Search

793 Street sign collapse causes fatality

Report ID: 793

Published: Newsletter No 52 - October 2018

Report Overview

This report highlights the potential dangers of street signs on fixed vertical supports subject to wind loading.

Report Content

This report highlights the potential dangers of street signs on fixed vertical supports subject to wind loading and draws attention to a possible failure mechanism in welded section support posts with defective joints.

The findings arise out of an investigation following the death of a pedestrian who was walking past a sign that failed during high winds in 2015.

The sign was located adjacent to a public footpath and highway. The support was a single steel hollow square section post measuring 130mm by 130mm at the base, tapering to 62mm by 62mm at the top. The post was 4,460mm in height and a steel rectangular plate had been welded in place on top. A plastic box section sign measuring 1,200mm wide by 1,800mm high was attached to another steel plate, which was then bolted to the rectangular support plate.

The support post had been formed with sections of steel U-channel which had been butt welded end to end to create the full length of the post. The square section was formed with longitudinal welds between the two full length channels. The transverse butt welds to each U-channel were offset so that no full cross section transverse weld occurred in the post.

The post had been embedded approximately 600mm into the ground and into a concrete foundation. The 1,200mm by 1,800mm box sign had been in place for two months, replacing a sign that had measured 1,009mm wide by 725mm high. The age of the post is not known.

The incident occurred during a named storm force event. During the event, a gust wind speed was measured at 68mph some 17miles away from the sign. The exact speed at the sign location is not known. On the morning of the incident, a pedestrian was walking past the sign when the support post broke apart, striking and fatally injuring passer-by.

A metallurgical examination was carried out on the support post which had fractured approximately 2,600mm above ground level at one of the transverse weld sections. The transverse butt weld at the fracture location exhibited regions of incomplete weld penetration through the post wall and internal corrosion.

A fatigue crack was present in the full-length U-channel adjacent to the butt weld and had initiated at the unfused edge of the transversely welded channel. The unfused areas would have raised the local stresses in the post, reducing resistance to fatigue crack initiation, propagation and an increased susceptibility to failure.

Whilst the larger sign would have increased the forces acting upon the post and were a contributory factor in the post failure, calculations indicate that the support post would not have structurally failed had it been free from defects.

Whilst it is acknowledged that the incomplete weld and internal corrosion may not have been obvious as part of a routine inspection, this shouldn’t detract from the importance placed on the inspection and maintenance of all assets, including those that are ubiquitous and seemingly low risk. This tragic event also highlights the need to properly assess the condition and suitability of elements that may be affected when alterations are made.

Comments

A fatality that occurred because of faults in a mundane piece of street furniture and should not have happened.

In the same category are garden walls that fall on children and signs above shops that fall on pedestrians. These are not the result of deliberate acts but of the importance of structural matters not being understood.

Those responsible for the procurement of signs, posts, advertisement hoardings, lamp posts and other ancillaries to our streets must be aware that they are dealing with potentially life-threatening issues and act accordingly.

Specifications must be of a high enough standard to give confidence that the components in question will give long, reliable, and safe service. The same standards must be followed through for construction, inspection, and maintenance.

 

CROSS depends on you for reports - if you have experienced a safety issue that you can share with CROSS, please Submit a CROSS Report

If you have any comments regarding this CROSS report, please Submit Feedback

View other CROSS reports published in Newsletter No. 52

Images

Failed support post



Email Updates

How to Report

Online submission:
Submit by post: