In light of the seismic retrofitting ordinance implemented by the City of Los Angeles, many building owners are looking for commercial retrofitting agencies to make their buildings earthquake resistant. Many techniques are used by the retrofitting companies in Los Angeles, and here, we discuss one of the retrofitting methods named Cripple Wall Bracing.
Most of the Los Angeles houses have a short wood-framed wall. This wall can be anywhere from a few inches to many feet high, running up from the top of the foundation to the bottom of the main floor. In construction terminology, this wall is referred to as the ‘cripple wall’, and the collapse of cripple wall is one of the main reasons of earthquake related fatalities.
Cripple wall collapse can lead to dropping of main wall to the ground. Also, the house will slant to the side of foundation, as the cripple wall will roll out. This is why bracing and stiffening of the cripple wall is an important step in earthquake retrofitting.
Cripple wall bracing is achieved by attaching structural grade plywood to the wall to offer necessary strength to it at times of earthquake activities. In engineering terms, the cripple wall will become a ‘shear wall’ after reinforcing it with structural grade plywood.
The plywood running along the sidewalls will brace the house in front-back direction and that running along the front and back walls will brace it in side-to-side direction. To have the best seismic protection, it is very important to brace all the sides of the house.
It is not necessary to brace the complete length of cripple walls, and it can be undesirable to do so, as over bracing can lead to wastage of money and manpower. In addition to that, many engineers think that it is more necessary to maintain some ductility in sub areas.
Lastly, following the principle that a chain is only as strong as its weakest link, it is necessary to complete the connection from foundation through the walls to the overhead floor framing. This will facilitate good load transfer at times of earthquake. Get in touch with our experts to learn more on earthquake retrofitting of cripple wall in a commercial or residential building.
Posted on Friday, January 26th, 2018.