An Application of Frp System for the Flexural Seismic Retrofit of Reinforced Concrete Beams

Abstract eng:
The design and construction of structural retrofit on concrete reinforced elements is an applied engineering field that is growing and developing new techniques. Among the modern techniques of structural strength, we have the use of externally bonded systems, like the FRP systems. This new technique of retrofit concrete reinforced structures is highly regarded and accepted around the world due to its light weight, high resistance and anticorrosive properties. The FRP system has a linear elastic behavior of stress-strain to the ultimate failure without any ductility. This characteristic suggests a serious limitation on its applicability to seismic-resistant structures, where it is expected that the seismic energy is dissipated by the inelasticity of materials. Beams externally strengthened with FRP have a more fragile behavior than a respective beam without an external FRP system. The ductility of a concrete reinforced beam externally strengthened with an FRP system is limited by the amount of steel reinforcement and the FRP system used, this can lead to different failures modes, some could be ductile and others more fragile. The present study shows the feasibility of the use of FRP systems in strengthened concrete reinforced elements by bending in seismic resistant applications, from the analysis of the ductility feature derived from moment-curvature curve. The main objectives of this study were: to identify characteristics of an FRP system for external retrofit and to identify which features from the beam impact in the seismic-resistant behavior. Another objective was to propose a practical approach to estimate the beam capacity to reach an acceptable ductile failure mode when a beam was externally strengthened with a specific FRP system; experimental tests were carried out on full-scale prototypes of reinforced concrete beams in order to corroborate the results. The experimental tests were carried out using 6 reinforced concrete beam prototypes, built to full-scale. The beams had a rectangular cross section of 200 x 400 mm2, with a total span of 2700 mm. The beams were reinforced internally with longitudinal bars of steel reinforcement quality ASTM A615 grade 60; the amounts provided were 0.86%, 1.42% and 2.53%. The specific concrete resistance reached f' c = 32 MPa. The external FRP for strengthening were formed by laminated layers of 200 mm wide by 1 mm thick and extended along the tensile zone to a length of 2300 mm. The tests took place in the Structures Laboratory of the Centro Peruano Japonés de Investigaciones Sísmicas y de Mitigación de Desastres (CISMID) of the Universidad Nacional de Ingeniería. These tests were by pure bending and allowed calculating the experimental ductility under pseudostatic conditions, and permitted us to corroborate the analytical results. The study concludes that there are limited ranges of strengthening with an FRP system, which allow the development of an acceptable ductility for a specified concrete reinforced beam (3 to 5), and indicates how to estimate this range. Additionally this study looks to propitiate the investigation of FRP for seismic applications on strengthened concrete reinforced beams by bending.

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