The FEMA P-807 Guidelines for Seismic Retrofit of Weak-Story Wood-framed Buildings are cost-effective retrofit procedures for a vulnerable class of buildings with a history of poor performance in earthquakes in the United States.
The Guidelines’ cost-effective retrofit solutions limit work to the ground story. The Relative Strength Method optimizes the expected seismic performance by increasing the strength and ductility of the ground story without over-strengthening. Extensive modeling, using a broad scope incremental dynamic analysis (IDA), examines a population of around six hundred (600) simple surrogate structures. The population was created from permutations of five normalized parameters: ground story strength, upper structure strength, ground to upper story strength ratio, ductility and torsional imbalance.
The procedure itself is straightforward and prescriptive. The engineer needs only to characterize the subject building (i.e. determine the strength, weight, and other relevant parameters) to calculate if and what kind of retrofit is required.