Safety Assessment Program Evaluator Student Manual

CA Emergency Mgmt. Agency Safety Assessment Program Evaluator Manual April 2011Photo courtesy Global Emergency ManagementFigure 3-19 – Collapsed house with failing upper room, 1992 Big Bear EarthquakeThe 1992 Big Bear Earthquake caused the cripple wall failure of this newer home, whichillustrates that not all cripple wall failures occur in older homes. The home is a two storystructure, with a part of the second story supported by wood posts. The failure of the cripplestuds caused the structure to shift to the right, moving off the foundation. The upper room abovethe carport has been shifted down by the cripple wall failure and is in danger of collapsing.In Figure 3-18, it is clear why the cripple wall failed. The T1011 siding that was nailed to thecripple wall studs was not nailed properly, with nails closely spaced at the siding edges. Thiswould have allowed proper transfer of lateral forces from the structure to the sill plate at thefoundation. Instead, it simply pulled out. Also, the metal straps that were used to anchor the sillplate were not properly installed. Instead of coming up both sides of the sill plate and nailingacross the top, these straps as installed do not prevent the sill plate from tipping.Figure 3-19 shows the room over the carport leaning against the rest of the house. The bracingwas installed in a hopeful manner by either a contractor or the owner. It may help somewhatwith keeping the support posts from kicking out due to gravity loads, but does not help muchwith lateral loads from aftershocks or wind. The brace on the lower left is attached to a verticalsupport that is not designed for lateral loads, which the brace on the lower right is attached to thehouse, which now is not attached to the foundation.99