Performance-based design criteria were developed and used to guide the seismic retrofit of a twelve story residential tower building that was constructed circa 1976. The tower structure consists of 5-inch thick precast post-tensioned concrete floor and roof slabs supported by interior and perimeter precast concrete wall panels. The precast wall panels are joined together by dowels set in grouted joints, and were intended to behave seismically as monolithic shear walls. The building is supported on piles with a system of concrete grade beams and pile caps. A seismic performance evaluation was conducted based on ASCE 41-06 with a target structural performance level of Life Safety (S-3) for a reduced-level design basis earthquake with the intent of meeting the requirements of the U.S. Department of Housing and Urban Development -Multifamily Accelerated Processing (HUD-MAP) Guide. A primary deficiency revealed by the seismic evaluation was that the grouted joints between the wall panels were not adequate to develop the necessary shear transfer for monolithic shear-wall behavior. However, the configuration of the wall jamb reinforcing and the existing shallow grade beams between foundation piles cannot accommodate the seismic demands if these panels resist seismic lateral forces independently. A retrofit scheme was developed utilizing Fiber Reinforced Polymer (FRP) materials to enhance the shear transfer capacity between precast wall panels, with virtually no change in member size. This type of strengthening maintained the dimensions of doorways, hallways and other critical areas and so was much better able to maintain the functionality of spaces than more traditional methods. The construction duration is minimized by this method and it is less intrusive to implement compared to conventional strengthening involving steel plate jackets or shotcrete construction. Because of these features this retrofit scheme was desired by the owner and contractor.
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