CROSS Safety Report
Serious injury from free standing wall collapse
This report is over 2 years old
A 100mm wide brick masonry wall in a garden collapsed seriously injuring one person.
Key Learning Outcomes
For civil and structural design engineers:
Careful consideration is required for the design of cantilevered masonry walls, particularly in the temporary stage because there is no redundancy and relatively small loads at the tip can precipitate failure
Consider what reasonably foreseeable loads could be applied beyond the code minimum values on elements such as freestanding walls
For homeowners and construction professionals:
Be aware that masonry walls should be designed and assessed by a suitably qualified and experienced engineer
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A reporter wants to raise important structural points about free standing walls especially those that are planned and built by untrained people. They say that in the back garden of a house stood a 100 mm brick wall, built of Flettons in cement mortar, about 2.5m long, and just under 1.0m high. There was a patio behind it about 200mm high, and in front of it grass. It was therefore nominally retaining some ground, certainly enough for it to have plenty of water going into the bottom two or three courses.
It had no restraint, neither by a cross wall at either end, nor were there any piers. It was some years old. Examination of photographs (the wall has disappeared) indicates that there was a certain amount of damp at the base, and it seems likely to the reporter that there would have been minor thermal and moisture movements here, and possibly freeze/thaw effects, which caused the lowest exposed mortar course just above the grass to lose its bond.
Late one evening, says the reporter, three young people returned home. Two sat on chairs on the patio, a young lady perched herself on the wall. It rocked, she fell backwards, and the wall came down as a single piece of brickwork weighing the best part of half a tonne, on top of her. Apart from bruising and laceration, her neck was broken in two places. Amazingly, and according to the medical experts as a result of outstandingly good emergency treatment coupled with outstanding long term care, she has only limited disablement. The reporter believes that simple guidance should be more readily available to builders and the public.
Expert Panel Comments
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As well as this report to CROSS there have been many articles in the press about injuries and fatalities from free standing wall collapses. Several years ago, there was lengthy correspondence on the subject in the Journal of the Institution of Structural Engineers. In Northern Ireland there are moves to introduce regulations covering new construction while in Scotland there have been regulations covering walls more than 1.2m high for some years. It is widely known that free standing walls are often poorly constructed and not adequately maintained. CROSS hopes to discuss this with the Sustainable Buildings Division of Communities and Local Government.
As is the case with shear failures in concrete discussed above, failure in free standing walls occurs with little or no warning and because they are cantilevers collapse is inevitable. The main design document for brick and blockwork walling is the British Standard BS 5628, Code of Practice for the use of masonry: Part 1 Structural use of unreinforced masonry, and Part 3 Materials and components, design and workmanship.
There is also the emerging Eurocode BS EN 1996 on masonry. Other guidance documents available which give advice:
Design of Free Standing Walls - Brick Development Association
Reinforced Brickwork Freestanding Boundary Wall - Brick Development Association
Building brick or blockwork freestanding walls - Building Research Establishment, Good Building Guide - GBG 14
Surveying brick or blockwork freestanding walls - Building Research Establishment GBG 13
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