Innovative Use of FRP in combination with structural steel shotcrete for retrofit of a non-ductile RC building: A Case Study

摘要

The Wharf-side building is a 100-year-old 6-story non-ductile reinforced concrete building with a subterranean parking level located adjacent to the Bay in San Francisco, California. Designed originally as a warehouse, the building currently primarily houses offices for high-value tenants. The building is approximately 100ft wide × 825ft long × 70ft tall above street level. After studying numerous seismic retrofit & vertical addition schemes over the past twenty years, the building ownership has chosen to implement a minimally invasive voluntary seismic retrofit scheme that will allow the building to be occupied during construction. The seismic retrofit project is currently under construction and is anticipated to be completed in 2021. The building owners are extremely sensitive to disturbances to their high-value tenants and have pushed the design team to come up with less noisy and less intrusive alternatives to conventional retrofit methods. This has resulted in a retrofit scheme that involves adding a new vertical lateral force resisting system (LFRS) built entirely outside the building and extensive use of FRP. on the inside, to tie the new LFRS to the existing building. The design team came up with an innovative way to transfer horizontal seismic shear between the existing building and the new exterior shotcrete walls using a precured FRP slab-wall shear-transfer-bracket system (CSS-STB), thereby significantly reducing epoxy rebar dowels between the shotcrete and the existing building. The CSS-STB bracket will also be used to transfer forces from exterior FRP collectors to the new shotcrete wall. Full-scale quasi-static testing was performed on the CSS-STB brackets in order to validate their use for this project. The testing demonstrated that such an FRP based system can be designed, manufactured and installed to achieve the desired shear transfer between the existing building and the new shotcrete walls, within which the CSS-STB will be encapsulated. This paper discusses the details of the testing as well as some of innovative ways in which FRP is proposed to be used in combination with structural steel & shotcrete on this project.