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WATCH YOUR STEPS!

Updated: Sep 21, 2023

FAILURE OF CANTILEVERED STONE STAIRCASE – CROSS REPORT 1147


DURING THE RENOVATION OF A STATELY HOME, A ‘CANTILEVER’ STAIRCASE FROM THE EARLY 1800S PARTIALLY COLLAPSED UNDER THE PEDESTRIAN LOADING BREAKING THROUGH A FLIGHT OF STAIRS BELOW AND SENDING A SITE WORKER TO HOSPITAL WITH SERIOUS INJURIES.




WHO/WHERE/WHAT

Cantilever staircases, or as I like to call them "clever stone staircases" in historical contexts, were commonly employed in stone construction and should not be confused with their modern-day counterparts. Unlike modern cantilever steps which rely solely on bending and shear actions at the wall face, clever stone staircases utilize a combination of torsional restraints at the wall sides and normal force translation of each step to the ground or through a horizontal thrust into the encapsulating walls (arch action). Additionally, the stiffening effects of the balustrades are often incorporated for added support.

The effectiveness of such staircases is reliant upon the integrity of their construction, ensuring that all forces are transferred to their intended locations. Any excessive material movement, be it due to creep, fatigue, or loosening of support rigidity or cross-section, may lead to staircase collapse, as can impact or excessive point loading.


WHY?

The report attributes several factors to the building's failure, including its partially derelict state which enabled moisture-induced movement and stresses. Additionally, the introduction of replaceable nosing reduced the cross-section of the triangle step by 40-50mm. The failure occurred at the transition point between the reduced and normal cross-section, further contributing to the failure.


HOW TO AVOID

Undertaking work on old buildings poses a range of challenges, particularly as potentially dangerous and concealed defects may exist, particularly in those that have been left unoccupied for extended periods. A comprehensive investigation into the quality of the fabric and structures is crucial to any such endeavour, despite the difficulties that may arise in identifying hidden defects. Not only is this essential for safe work execution, but it is also necessary for future use of the building. It is my recommendation that, in circumstances where buildings are being repurposed, a load testing of critical elements, such as staircases, should be given due consideration.


LESSONS LEARNED

Always tread carefully in old buildings, list out the possible failures and critical hidden defects and act on this before you start.


Ask yourself the question. Is chancing it worth a broken limb or a loss of life?

Also, ask your boss if he did the assessment and what are the conclusions and if you think he is chancing it with your health and life, whatever it may be, do not do it, it is not worth it.


That is it for today, folks. Have a safe week ahead of you and remember you are responsible for yourself and others!


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