Bridges

Ductile behaviour of steel is an important characteristic that underpins structural steel design approach. Ductility of steel enables it to undergo plastic deformation under overload conditions which serves as a warning sign indicating that the structure is in distress. This allows the caretaker of an asset to adopt appropriate measures to manage the risk of ultimate structural failure. Structural steel, used extensively in different types of road and rail structures including bridges, has high ductility under designated testing temperature. However, when it is exposed to lower temperatures e.g. zero or below, its ductility reduces dramatically and it behaves like conventional ceramics, failing in brittle fracture. When there exists a flaw in any part of an element of a steel bridge, the risk of brittle failure increases. The major concern with brittle fracture of steel is that it does not provide any warning sign and results in catastrophic failure of the structure. Non-ductile behaviour of steel due to low temperature has resulted in several brittle failures in the past. To minimize this risk, steel with high toughness should be used. Exposure to low temperature is not the only cause of brittle failure. When carbon steel is worked on e.g., welded during fabrication, it develops hardened zones around the weld, called heat affected zone, that may also result in brittle behaviour of steel.

This paper describes ductile and non-ductile or brittle behaviour of steel and provides examples of brittle failure that led to failure of storage tanks, ships, pressure vessels and bridges. It also provides information regarding measures that can be adopted to help minimize the brittle fracture of steel and, thus, minimize the associated risks.