Appraising factors of safety in existing engineered structures – new technical guidance published

The guide and its methodology are published when there is a growing awareness in the built environment of the importance of structural assessments on existing buildings, either as part of a safety check or to justify adaption.

While there is a wide range of existing literature about how to assess existing structures, IStructE realised there was a lack of consistent approaches and terminologies, both of which this guide addresses.

Authored by Andrew Smith and Danny Kalokoti, both structural engineers at Arup, Appraising factors of safety in existing engineered structures provides a clear three-step method to undertake such important assessment projects.

Patrick Hayes, Technical Director at IStructE and one of the guide’s contributors says: “This is a timely publication, especially given the Building Safety Act’s focus on structural safety, and the growing need to extend the life of existing structures, instead of demolishing, so that embodied carbon emissions can be minimised.”

The assessment method’s development focused on six clear principles: safety, simplicity, consistency, rigour, applicability and objectivity. The resulting approach assesses what safety factors are acceptable when evaluating existing structures with a clear process to:

1. Refine the calculations.

2. Reduce partial safety factors to account for greater certainty of loading and strength compared to design situations.

3. Consider the severity of overutilisation.

Patrick Hayes concludes: “This clear, three step methodology aims to help engineers assess ‘factors of safety’ and determine acceptability based on established risk criteria. The aim is to avoid unnecessary strengthening or demolition, while also enabling the engineer to identify at-risk structures.”