Seismic Retrofit of Real Beam-Column Joints Using Fiber-Reinforced Cement Composites

Abstract

This paper studies the seismic behavior of old-style reinforced concrete beam-column joints and the effectiveness of an innovative application of fiber-reinforced concrete (FRC) as a seismic strengthening solution. Two real joint subassemblies were extracted from an existing building damaged and demolished after the L’Aquila 29 earthquake and tested in the laboratory. The joints exhibited poor-quality concrete and reinforcement details typical of old design practice, which are very difficult to reproduce in laboratory simulations. The joint tested in the as-built configuration shows brittle failure with joint diagonal cracking, as commonly observed in the aftermath of recent devastating earthquakes. The FRC thin jacketing prevents the joint panel shear failure, promoting a more favorable beam yielding. This results in a significant increase of the shear strength (until 5%) and energy dissipation (85%). The strengthening phases and the details of the proposed strengthening layout are described. The as-built and strengthened specimens are compared in terms of global and local behavior. Strain measurements on the FRC jacketing are also discussed as an effective design parameter.