Built according to good practices, concrete homes can be among the safest and most durable types of structures during an earthquake.
Homes built with reinforced concrete walls have a record of surviving earthquakes intact, structurally sound and largely unblemished.
In reinforced concrete construction, the combination of concrete and steel provides the three most important properties for earthquake resistance: stiffness, strength, and ductility.
Scientists study damage from earthquakes to determine what types of buildings best withstand seismic forces. Modern earthquake-resistant design relies on several recent studies:
|1989||Loma Prieta||7.1||University of California, Berkeley|
|1994||Northridge||6.8||NAHB Research Center
National Institute of Standards and Technology
Studies of earthquake damage consistently show well-anchored shear walls are the key to earthquake resistance in low-rise buildings.
Optimal design conditions include shear walls that extend the entire height and located on all four sides of a building. Long walls are stronger than short walls, and solid walls are better than ones with a lot of openings for windows and doors. These elements are designed to survive severe sideways (in-plane) forces, called racking and shear, without being damaged or bent far out of position. Shear walls also must be well anchored to the foundation structure to work effectively. Properly installed steel reinforcing bars extend across the joint between the walls and the foundation to provide secure anchorage to the foundation.
Most of these buildings were 3 to 4 stories tall with a parking garage or a living area with many large windows on the ground level. The columns may have been strong enough to hold up the structure, but did not provide an adequate amount of racking resistance during a seismic event. When the earthquake shook the building side-to-side, the upper stories sometimes tipped over to one side. Whether built of wood, steel, or concrete—they all suffered damage.
Masonry or concrete walls not reinforced with steel bars were not ductile enough to be effective shear walls. And if there is no steel connecting them to their foundation, the joint between walls and foundation can be a weak point.
Studies have shown that properly designed reinforced concrete walls offer greater earthquake resistance than other types of construction.