Retrofitting of R/C structures on gravity columns using inverted-Y steel bracings.

摘要

It is common practice in Puerto Rico to build elevated reinforced concrete frame and shear wall structures in hillsides and hilly terrains by supporting them on gravity columns. Recent studies have indicated the vulnerability of these structures to seismic events, especially when the loading is amplified to account for the site topography. It is an objective of this research to examine the use of inverted-Y steel bracing system as a retrofitting measure. The system performance is evaluated against shear wall retrofits which is the only option currently used in the Island. The building prototypes are retrofitted and numerically analyzed in order to develop design guidelines. The size and placement of retrofits were found to be a function of geometric and topographic properties such as the building footprints, column heights, number of bays, and whether or not the earthquake is amplified. The inverted-Y retrofit is proven to be the more cost effective of the two options and is recommended as such. Details on the acceptable retrofitting configurations are provided as well as the built-up sections that may be used for shear links in an inverted-Y system. In the aftermath of an earthquake, it is only the shear links that will most likely need replacing. Easy reparability is an added cost benefit of these systems over the shear wall retrofits.