Failure of cast iron beams
Many buildings utilising cast iron (CI) continue to give good service with adequate reliability when used in a risk assessed manner and current best practice documents. As is normal with this type of beam, there is rarely any apparent warning of imminent collapse.
Certain combinations of actions may lead to an unsafe situation that should be investigated by a competent structural engineer. These situations include:
- Additional loading on a CI beam, typically arising from further deadweight added since original completion. The unregulated increase of load on a structure should always be a matter of concern.
- Long-standing ingress of water leading to corrosion, deterioration of the concrete infill, and loss of any composite action. Extended basements or roof garden arrangements are particularly prone to this action.
- The beams working at high levels of stress as originally installed. This is more likely in a domestic structure where the beam may have been sized by rule of thumb.
Professionals working in this field, or with clients responsible for property of this type and era, should be aware of these issues and be ready to advise the relevant parties of the need for a structural risk assessment if the identified conditions exist.
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