Performance-Based Seismic Retrofit Strategy for Existing Reinforced Concrete Frame Systems Using Fiber-Reinforced Polymer Composites

TLDR

The study evaluates the feasibility and efficiency of externally bonded fiber‑reinforced polymer composites for retrofitting existing reinforced concrete frame systems designed before modern seismic codes, using analytical and experimental investigations on beam‑column joint subassemblies and full frame systems. A multilevel retrofit strategy based on a hierarchy of strength considerations and capacity‑demand M‑N performance curves, coupled with an analytical procedure predicting enhanced nonlinear panel‑zone behavior from CFRP laminates, guides the design of the retrofit. Quasi‑static tests on beam‑column subassemblies and three‑storey, three‑bay frames confirm that the retrofit solution is viable and reliable, and that the analytical predictions accurately capture the sequence of events.

Abstract

The feasibility and efficiency of a seismic retrofit intervention using externally bonded fiber-reinforced polymer composites on existing reinforced concrete frame systems, designed prior to the introduction of modern standard seismic design code provisions in the mid-1970s, are herein presented, based on analytical and experimental investigations on beam-column joint subassemblies and frame systems. A multilevel retrofit strategy, following hierarchy of strength considerations, is adopted to achieve the desired performance. The expected sequence of events is visualized through capacity-demand curves within M-N performance domains. An analytical procedure able to predict the enhanced nonlinear behavior of the panel zone region, due to the application of CFRP laminates, in terms of shear strength (principal stresses) versus shear deformation, has been developed and is herein proposed as a fundamental step for the definition of a proper retrofit solution. The experimental results from quasi-static tests on beam-column subassemblies, either interior and exterior, and on three-storey three-bay frame systems in their as-built and CFRP retrofitted configurations, provided very satisfactory confirmation of the viability and reliability of the adopted retrofit solution as well as of the proposed analytical procedure to predict the actual sequence of events.