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CROSS Safety Report

Change in use results in masonry wall failure

Report ID: 884 Published: 6 April 2023 Region: CROSS-UK


Overview

A room with walls of traditional cavity and single skin masonry was lined with plywood and used for storage of wood chips. No thought was given to the lateral pressure on the walls which eventually failed.

Key Learning Outcomes

For owners, asset managers and all built environment professionals:

  • Be careful when converting parts of a building from one use to another as different loading conditions may apply
  • It is good practice to also consult with building control prior to making alterations as approval may be required by them

  • Be aware that any retained material creates lateral loads to walls
  • Advice should be sought from a suitably competent engineer with the relevant experience prior to any alterations being made

Full Report

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An oil tank room had been converted to a woodchip store in a public building. The room was of traditional cavity and single skin masonry construction with high level ribbon windows. The conversion was undertaken by lining the walls and windows with plywood, with no apparent structural thought for the new imposed retaining loads from the woodchips on the cavity walls, says a reporter.

Notwithstanding what was clearly an unsuitable design for retaining walls, the structure stood for around a decade until a water leak in a tank room over increased the retained weight loading, possibly with associated expansion forces, to cause an outward rotation failure of the masonry wall. The failure was apparently arrested by an external post preventing complete failure of the structure.

The reporter says that the underlying cause was clear - an inappropriate change in use of the building which failed to appreciate the new retaining loads. They say that it is unlikely that a structural engineer was consulted at the point of the change in use of the building.

Expert Panel Comments

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An Expert Panel 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-US Expert Panel page.

There is a common perception that masonry walls must be 'strong', including against lateral loads. They may not be. Mostly they only achieve reasonable lateral strength if they are preloaded with a heavy roof or equivalent.

Furthermore, their potential mode of failure under lateral loads is complete collapse rather than controlled displacement. Hence any masonry wall acting as a retaining wall needs proper structural design by a suitably qualified and experienced engineer.  

CROSS has received a large number of reports on masonry failures. You can search for safety information on masonry failures on the CROSS website.

 

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