Masonry Structures

Many of America´s older buildings were built with unreinforced masonry (URM). These buildings are extremely vulnerable to quake-induced failures because of the nature of the material and the manner in which they were constructed. The inability of URM to stand up to seismic stresses stems from the fact that masonry is a brittle material. When a building is subjected to lateral accelerations caused by a quake, large forces are put on structural members of the buildings. Unlike buildings made of ductile materials like steel or timber which are able to deform to these forces, masonry can only deform to a very small degree unharmed. If too large a force is imposed upon these buildings, the masonry will crack and fail. The 4 most common areas of danger are:

1. In-Plane Failure
2. Out-of-Plane Failure
3. Anchorage Failure
4. Diaphragm Failure