Silos: Evolution by Failure

The last twenty years have seen the development of structural codes based on partial safety factors and load resistance factor design (LRFD). Such codes consider the theoretical probability of failure, assuming statistically well-behaved distributions of loads and resistance. There have been very few structural collapses of bridges and buildings against which these theoretical models can be calibrated. Silo failures, because of their high frequency, provide a good yardstick for evaluating safety concepts. The patterns of silo features clearly demonstrate the validity of the partial factor approach. Many failures arise from factors that are not properly considered in structural standards. Despite the high structural reliability achieved in initial design, structures often are not achieving the lifetime performance owners require as deterioration erodes the margins of safety.