Dynamic effects in progressive failure of structures

This paper considers the behaviour of loaded structures when a member (or members) breaks prematurely. This behaviour consists of a transient vibration of the remaining damaged structure as it moves towards a new state of equilibrium. Static calculations may predict that the structure, with the failed members omitted, is capable of safely bearing the external loading. This static approach to the load-bearing capacity of the damaged structure is implicit in many design codes for redundant, damage-tolerant, structures. But it is shown here that transient overloads induced by the sudden fracture of a member may cause progressive fracture of other elements before a new equilibrium state is reached. Sometimes the cascade of fractures arrests; sometimes catastrophic failure of the whole structure occurs. Experiments with a redundant radially-tied (spoked-wheel) structure confirm the prediction that there are structures which are statically safe, but which are dynamically unsafe. In spite of the simplistic nature of these experiments they shed light on several aspects of dynamic failure which will be important for real engineering structures.