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

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 stresses͒ 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 quasistatic 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.

Strengthening and rehabilitation of RC beam–column joints using carbon‐FRP jacketing and epoxy resin injection

“…The gravity (dead and live) loads acting on the beam might represent a substantial portion of the negative yield moment of the beam at the column interface [23]. Consequently they can possibly affect ductility curvatures, rotation capacity, failure modes etc.…”

“…These analytical models for the evaluation of shear strength do not take into account the variation of axial load during the test. Pampanin et al [23] adopted the simplified version of that of Antonopoulos and Triantafilou [22] with a few simple modifications in order to account for the variation of the axial load on the joint region in the evaluation of shear strength. The present study has experimental orientation and the design approach adopted for the examined specimens is the simplified and easy-to-apply approach by Tsonos and Stylianidis [19] and Gergely et al [18].…”

“…Typical strength degradation models in terms of principal tensile stress versus shear deformation are available in the literature (e.g. Pampanin et al [23], Priestley [24]). These models can be adopted to define limit states in a joint panel zone subjected to shear and axial load.…”

Development and validation of a metallic haunch seismic retrofit solution for existing under-designed RC frame buildings

“…As part of an extensive recent experimental and analytical research program on the seismic vulnerability of existing reinforced concrete frame buildings designed for gravity loads only, as typically 15 found in Mediterranean countries before the introduction of seismic-oriented codes in the mid1970s, a series of quasi-static cyclic tests on 2 3 scaled beam-column joint subassemblies (interior 17 and exterior) as well as on two three-storey three-bay frame systems, prior to and after retrofit using FRP solutions, have been carried out at the University of Pavia [6,7,11,12]. These tests 19 confirmed and further highlighted the vulnerability of the panel zone region.…”

“…According 9 to a multi-level retrofit strategy approach [12,24], two levels of retrofits can be adopted when considering the global response of the frame: (i) a complete retrofit would consist of a full 11 upgrade by protecting all joint panel zones and developing plastic hinges in beams while columns are protected according to capacity design principles, and (ii) a partial retrofit would consist of 13 protecting exterior joints (which are the most vulnerable), forming plastic hinges in beams framing into exterior columns, while allowing for column hinging and minor joint cracking in interior 15 joints due to their more stable behaviour with hardening after first cracking.…”