The catastrophic collapse of a building frame five years ago at a church in Ilford has led to the publication of new advice on how to improve a steel frame’s robustness.
The City Gates Church building frame dramatically collapsed in January 2012. Welded truss joints at hanger connections are believed to be the main cause of failure. No one was injured.
The collapse occurred during the construction of a 29m long, one storey deep, steel frame, spanning over the top of a an auditorium.
An alert from safety body Structural-Safety contains new advice to engineers about structural stability of steel frame buildings following an investigation of the incident. The investigation included some information included from a freedom of information request.
Investigators found that the shear capacity of gusset plates welded to SHS hangers had been reduced because bolt holes had been double drilled. They said that combined with the misalignment of welded joints and undersized welds, the structure was susceptible to slow plastic yielding followed by a brittle fracture in some of the thicker sections – particularly when it was carrying the weight of building materials.
As a result of the finding, Structural Safety is warning engineers to consider the possibility that a local failure could cause a disproportionate collapse. This scenario is possible at every stage of the construction process and is more likely when the structure has hangers.
The new advice says robustness is essential and horizontal and vertical ties should be properly connected. It lists a series of measures engineers can undertake to ensure robustness.
Structural-Safety works with the profession to collect data on safety and promote best-practice.