Retrofitting Gravity Load Designed R.C Frames Using FRP

Abstract

Many existing worldwide Reinforced Concrete (RC) structures, such as non-ductile RC frames, were designed for gravity loads only during the 1950s through 1970s or earlier. Due to variations in the identification of seismic active zones by national codes, such structures may not satisfy the current design requirements, especially when lying in a recently identified seismic active zone. This is because such structures, as a result of poorer reinforcement detailing, may generally do not possess the adequate ductility and strength needed to withstand an expected earthquake. Consequently, older RC frames may undergo substantial damage during earthquakes. One of the main damage aspects in such case is clear cracks around and within the beam-column connections. This is the case where the failure of beam-column joints is governed by bond and shear failure mechanisms which are usually brittle. This may be attributed to inadequate shear reinforcement in the beam-column joints region., This paper presents the first results of an experimental campaign performed – at the Laboratory of Materials & Structures of the Arab Academy And Technology (EGYPT) – with the aim to investigate the seismic performance of RC beam-columns joints strengthened with FRP. The experimental program includes testing specimens realized to be representative of existing exterior beam-column subassemblies with inadequate seismic details. A technical solution was selected in order to improve the joint seismic behaviour, and the performance of the proposed strengthening system is investigated in this paper. To this aim, two as built beam-column joints have been tested, one strengthened specimen and a reference unstrengthened one. Test results provide useful information for the adopted strengthening systems in terms of strength, ductility and energy dissipation capacity. Results indicate that the proposed strengthening technique was successful in adding up to 50% of the beam column joint capacity. The results are encaging to apply this technique on existing gravity load designed buildings.