Existing buildings which do not satisfy modern seismic design requirements may be strengthened by the addition of steel bracing or reinforced concrete shear walls. This strengthening, however, can transfer more loads to the foundation. This research will examine the seismic vulnerability of such structure-foundation systems. The study will review the major methods of strengthening and rehabilitating buildings for seismic loading. The demands of these rehabilitation methods on the foundation will be evaluated and typical deficiencies of commonly used foundation systems will be ascertained. A range of foundation rehabilitation schemes including: a) use of additional piles, b) provision of an additional footing around the perimeter of the building, c) reinforcement of existing footings and pile caps with additional concrete and steel, and d) improvement of structure-foundation connections will be considered. The improved connections may include mechanisms for safely transmitting short duration overloads to the soil or may allow temporary separation of parts of the structure from the foundation to prevent damage to critical elements. The study will involve analyses of a variety of structures and broad categories of foundation systems and soils. Several earthquake induced acceleration records will be used as base excitations for analysis and evaluation. The analytical studies will be correlated with past performance of buildings and foundations during earthquakes. The emphasis will be on developing guidelines and recommendations for selecting the foundation rehabilitation techniques for buildings of intermediate height (approximately 4 to 20 stories). The results will be summarized in a final report and professional publications.
