The comparative costs of retrofitting existing structures in order to make them more earthquake resistant are generally greater than for new construction. In many cases this may not be economically feasible. While it may not be politically feasible to \f2mandate retrofitting of all susceptible buildings, e.g., unreinforced masonry apartments, building owners should be encouraged to do so when possible. This is especially important for critical facilities such as hospitals and emergency response facilities.
The magnitude of this task is illustrated by inventories in the St. Louis area. A tabulation of structures in the area critical to post-earthquake recovery included 15 at airports, 42 at ambulance stations, 160 at fire stations, 33 at hospitals and 97 at police stations. Within the City of St. Louis, there were about 98,000 residential structures of which 62,000 are single-family, 20,000 were two-family and 16,000 were three or more family. Of these structures 75 percent are unreinforced masonry and 25 percent are frame construction.
Similar inventories are not available for the rest of the area of concern, but it has been suggested that an estimate of the total number of structures in a region may be obtained by multiplying the population by a factor of 0.35 or 0.40.
Development of a strategy for retrofitting existing structures warrants careful study. For example, mandating retrofitting of unreinforced masonry residential structures could result in the abandonment of many such structures because economics might not justify the expenditure. This could create hardships for low-income residents and contribute to the blighting of neighborhoods. On the other hand, incentives such as tax and insurance reductions, may be attractive inducements. The appropriate organization to develop a plan to develop an effective strategy should be identified.
The first priority should be given to retrofitting critical facilities that will be essential for post-earthquake recovery. Hospitals, fire stations, police stations and other critical facilities should be encouraged to assess the vulnerability of their structures and develop a plan for retrofitting them. FEMA 273 contains provisions for retrofitting existing structures. An inventory of critical buildings should be undertaken in eastern Missouri, especially in southeastern Missouri. The condition of these structures should be initially assessed using the Rapid Visual Screening of Buildings for potential seismic hazards (ATC-21). Assessment of the vulnerability of critical buildings should also take into account the soil conditions.
Elementary and secondary schools, colleges and universities should be encouraged to assess their vulnerability and to retrofit seriously deficient structures. Architects, engineers and building officials should be trained in the methods for cost-effective seismic upgrades of existing buildings.
Each critical facility should be required to submit a "report of vulnerability" to its governing authority. This report would assess the most vulnerable elements of their structures, i.e., those which when damaged would render their facilities unusable or unable to carry out their essential functions. With this information, a prioritized plan can be developed with cost estimates and a schedule for upgrading. The seismic upgrading requirements for critical facilities should be used by building owners in their capital improvement plans. Tax and insurance incentives should also be considered to encourage retrofitting of essential facilities.