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CROSS Safety Report

Corrosion causes collapse of steel floodlight mast at football club

Report ID: 683 Published: 1 April 2018 Region: CROSS-UK

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Overview

This is an alert that was issued by a local authority responsible for enforcing the Safety of Sports Grounds Act after a floodlighting mast collapsed at a football club's ground.

Key Learning Outcomes

For asset owners and operators of floodlights:

  • Inspection and maintenance regimes for floodlighting masts should include a risk assessment for internal corrosion of steel tubes

  • A check for internal corrosion should be carried out by a suitably qualified person where internal corrosion has been assessed as a significant risk

  • Inspection and maintenance regimes should include a check for cracking around any openings in tubular steel masts

  • Assessment of the structural adequacy of the floodlighting masts should include an assessment of the adequacy of any strengthening around openings in tubular masts

Full Report

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This is an alert that was issued by a local authority responsible for enforcing the Safety of Sports Grounds Act with the full co-operation of the football club concerned, after a floodlighting mast collapsed at their ground (Figure 1). The mast consisted of a single column fabricated from five lengths of steel tube which successively reduced in diameter. The mast had an opening with a detachable cover just above ground level. The mast was believed to be of a bespoke design and installed in 1969. The mast had been painted externally but had no protective coating internally.

Image
Figure 1: bottom of mast after removal

Factors contributing to collapse

Investigations have highlighted the following factors which contributed to the collapse:

  • Moisture was able to enter the inside of the mast through corroded and unsealed brackets supporting the floodlight lamps

  • Moisture was able to enter the inside of the mast through gaps between the detachable cover and the tubular section

  • Drainage holes at the bottom of the mast had become blocked allowing water to gather in the bottom of the mast

  • In addition to losing water by evaporation, water is likely to have been able to escape when it reached the level of the opening. This led to the internal face of the column corroding below the level of the opening leading to a significant reduction in the thickness of the steel tube.

  • A horizontal crack had developed in a corner at the top of the opening and it is possible that a similar crack had developed at the bottom of the opening (Figure 2)

  • Strengthening plates around the opening appear not to have been long enough to transfer load back into the body of the mast

Image
Figure 2: Upper part of service door opening (note crack at the top right of the opening)

Advice to other clubs

An inspection of other columns after their removal also revealed extensive corrosion below the level of the door openings. Advice from the reporter to other clubs is as follows:

  • Your maintenance regime for floodlighting masts at your ground should include a risk assessment for internal corrosion of steel tubes

  • A check for internal corrosion should be carried out by a suitably qualified person where internal corrosion has been assessed as a significant risk

  • Your maintenance regime should include a check for cracking around any openings in tubular steel masts

  • Your assessment of the structural adequacy of the floodlighting masts at your ground should include an assessment of the adequacy of any strengthening around openings in tubular masts

Expert Panel Comments

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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.

This is a good example of the type of report CROSS continues to benefit from. Points to note are:

  • Lighting columns are often made of thin steel so the percentage loss of material due to minor corrosion may be significant in its effect on strength

  • The full stress demand will only occur in very high winds, or if resonance occurs. Consequently, the effects of weakening may not be noticed until it is too late i.e. with the risk of a mast failing suddenly

  • Wherever they are located, falling masts may injure but masts located in crowded places (like stadia) may be deemed to present a higher risk of injury consequence

In this case, the crack and its location are suspicious. Lighting columns have been known to oscillate and thence fail by fatigue. The risk of fatigue is enhanced by higher stress ranges consequent on thinning sections; by corrosion (giving stress concentrations) and at corners (again for stress concentrations). This crack is in a corner. Hence the advice to look for cracks in corners is very sound, not least as in this location, crack propagation rate is likely to accelerate with increasing crack length.

There have also been experiences of failures of tubes just below ground level, so there should be means to inspect the internal face when designing for the future. Also, steel will not corrode without oxygen so maintenance should include effective sealing of holes provided for fixings and the original drain holes provided for in galvanising processes.

There have also been experiences of failures of tubes just below ground level, so there should be means to inspect the internal face when designing for the future

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