An Earthquake Retrofit provides existing structures with more resistance to seismic activity due to earthquakes. In buildings, this process typically includes strengthening weak connections found in roof to wall connections, continuity ties, shear walls and the roof diaphragm.
In the past, building codes were less stringent compared to today’s standards, thus it is a good idea to inspect buildings constructed prior to 1998, as they were built prior to current structural codes/requirements (1997 UBC).
Numerous types of structures may benefit from an earthquake retrofit, including various building structures, bridges, dams, etc…This article emphasizes building structures only, including the following:
Concrete Tilt-Up & Reinforced Masonry (CMU) – An earthquake retrofit for these types of building generally includes adding roof to wall anchors, and continuity ties throughout the building. Sometimes due to the size and shape of the building, steel brace frames are added to the structure. The concrete tilt-up walls used in many commercial properties are very heavy and when they move in an earthquake, they exert a great deal of force. The main purpose of an earthquake retrofit for these buildings is to keep the roof from pulling apart, especially at the perimeter.
Un-reinforced Masonry (URM) – An earthquake retrofit for this type of building typically requires adding roof to wall connections, continuity ties, and usually requires new plywood overlay at the roof. Usually there are too many openings or a large open storefront window, where it’s common to either fill in the smaller openings or install a moment frame to handle the shear loads. Some URM’s require a fix for their height over thickness of the wall. These walls can be strengthened with tube steel, gunite or epoxy fiber wrapping.
Concrete Buildings 2+ stories – These buildings exert a great deal of force, due to the weight of the buildings. An earthquake retrofit to these types of buildings typically includes a combination of concrete shear walls, gunite, column fiber wrapping, steel collectors, and many other types of strengthening systems. The concept is the same as far as strengthening connections and adding shear strength.
Soft Story Conditions or Tuck Under Apartment Buildings – These buildings have an open first floor (such as ground level parking or subterranean parking) and 2nd floor above (living or business quarters). These buildings perform poorly in an earthquake due to the shear or overturning that can occur. Strengthening these buildings usually includes adding a steel moment frame, concrete footing and drag lines to keep the 1st floor from rotating and collapsing. For apartments, shear walls are commonly added to the existing walls on the interior areas of the parking stalls.
Earthquake retrofitting is done for a variety of reasons, the most common being to ensure the safety and security of a building’s employees, machinery and inventory.
SIX MORE REASONS FOR AN EARTHQUAKE RETROFIT
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