Another important factor that has played a role in creating safer buildings is our choice of structural materials. Wood, steel, aluminum, and concrete are characterized by a degree of plasticity. They do not fail suddenly, but exhibit obvious deformation before they reach their ultimate limits. We do not use glass or ceramics, even though both are quite strong, because they also are brittle, and they fail without warning. This is not to say that there are no problems.
Many structural failures occur during construction or during repair of an existing building.
But because the buildings are not occupied at the time, the degree of damage and injury is limited. A case involving a crane in Milwaukee is an example. In this case, a crane failed while lifting an enormous piece of roof truss into place. Completion will be delayed a year or more. While these are not inconsequential damages, they would pale in comparison to those that would have resulted from the same piece of roof falling on an occupied building.