Non-ductile concrete buildings are structures that contain brittle concrete elements (columns, beams, walls, and connections) that tend to perform poorly during earthquakes due to the limited amount of provided reinforcing steel.

An unreinforced masonry (URM) building is a building made of brick, hollow concrete blocks, stone, or other masonry with no steel reinforcing bars embedded in it, making it susceptible to severe damage and collapse during an earthquake.

During the 1994 Northridge Earthquake in the Los Angeles area, many steel moment-resisting frame structures experienced unexpected brittle damage to their beam-to-column connections.