A big problem involves homes built before 1979 with a handful of steps above the ground, where in between the floor of the house and the concrete slab foundation is a crawl space a few feet tall.
The heavy house rests atop a flimsy wood-frame perimeter that is not bolted to the concrete foundation. So when an earthquake hits and the concrete foundation moves, the wooden part of the house snaps off — possibly falling into the backyard or through the neighbor’s fence.
In an earthquake, what happens is that the house can either topple or slide off of the foundation,” said Janiele Maffei, a structural engineer and executive director of the California Residential Mitigation Program. “Essentially, it’s like you’re trying to pull the rug out from underneath the house.
No building has a perfect structural soundness. With all structures erected on the ground, there is always that vulnerability for them to be moved laterally through earthquakes. When there’s seismic activity that shakes every object on land, the resilience of such structures decline and thus need to be restored or repaired.
The solution to this is not to destroy the entire building. It is not also recommended to just let it pass only because there is no visible sign of damage. Instead, what engineers do with this problem is to do seismic retrofitting.
Seismic retrofitting is done to keep structures from being displaced from its concrete foundation, which makes the building less prone to structural damage whenever earthquakes hit. It essentially provides existing buildings the resistance to seismic activity, which includes strengthening weak connections found in roof to wall connections, continuity ties, shear walls and the roof diaphragm.
Like in any engineering solution, safety and security are the primary reasons why structures need to be retrofitted seismically. The core of applying this to structures is to protect the people, machinery, and inventory. Other than that, it also allows the marketability of a building to go higher.
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Posted on Tuesday, August 20th, 2019.