Cracks in steel structures

Under overload, the mode of failure in any steel structure should ideally be ductile not brittle; the possibility of cracking in steelwork should thus be actively guarded against. Historically, steel cracking has caused some spectacular failures. Steel can fracture rapidly at low temperature and can crack during welding, in fatigue or as a result of stress corrosion. Certain fabrication processes such as welding, flame cutting and punching exacerbate the risks, especially if the steel is ‘thick’. Galvanising can also be a risk factor. Design engineers should understand potential cracking mechanisms and risk factors to minimise the likelihood of in-service failure. This paper discusses the historical background of cracking, explains causes and suggests avoidance measures.