If you live in an area affected by earthquakes, you likely have some knowledge about the structural damage to buildings that can happen from a natural disaster. When earthquakes occur, some buildings must be retrofitted with components that strengthen their foundations against future destruction. This process is called seismic retrofitting. Here are a few facts to know about seismic retrofitting and the foundation repair needed for buildings devastated by earthquakes.
1) Some buildings need retrofitting more than others.
The biggest foundational problems are usually seen in "soft-story" buildings. A building is classified as soft-story if it has more than one floor over a ground level that is "70% as stiff as the floor immediately above it, or less than 80% as stiff as the average stiffness of the three floors above it." This is generally a building with a parking garage or several retail businesses on the lower level. Since this soft story has a weak and open-front wall line, this type of building is particularly prone to earthquake damage. In the event of an earthquake, a soft-story building is more likely to collapse if it is not properly reinforced.
2) It's the law.
In certain locations where seismic activity is more prevalent, government ordinances have strict guidelines about what buildings must be retrofitted. In Los Angeles, California, for example, there are specific ordinances that outline a mandatory retrofit program. Buildings that were built under code standards prior to 1978 with open ground floor space and two or more wood-frame stories fall under these ordinances. These unprotected buildings are required by law to receive seismic retrofitting to reduce their vulnerability to structural inadequacy. Once a property owner receives an order to comply, there are definitive time limits that must be met to have the retrofitting fully completed.
3) The process depends on the building.
Seismic retrofitting is accomplished by adding elements to a building's foundation to ensure that the building is still upright following an earthquake. However, the actual process and implementation are different for each building. Structural and building materials, degree of wear and tear, and geographical zoning laws all vary per building. Contractors and their engineers must, therefore, consider many factors when designing the precise retrofitting techniques to use when repairing the foundation of any given building. The engineer assigned to the project can implement a variety of options, including adding new anchor walls, strengthening existing walls, or putting a steel frame into the soft spots of the building. Whatever choice is ultimately selected, the International Code Council Guidelines for the Seismic Retrofit of Existing Buildings mandates that the retrofitting repairs deliver no less than 80% strength of the weak level above the soft story.
Whether mandatory by law or just preventative, seismic retrofitting services can help to safeguard a vulnerable building in an earthquake hot zone from damage. Soft-story buildings are especially vulnerable and benefit greatly from the foundational repair and reinforcement that seismic retrofitting can provide.
For more information, contact a seismic retrofitting service.Share