Resumen de Bond behavior of nsm frp strips in concrete under sustained loading
The Near-Surface Mounted (NSM) FRP strengthening technique, in which FRP reinforcement is bonded into grooves cut in the concrete cover, has been recently introduced in many projects and has attracted the researchers' attention due to several advantages it provides over the traditional plate bonding (Externally Bonded [EB]) technique with FRP. This interest is justified by the fact that in FRP strengthening of RC structures a proper bond between FRP reinforcement and concrete is a fundamental requirement to ensure the composite action development between both materials and to allow the stress transfer between them during the loading process. Therefore, bond has a major influence on the load carrying capacity as well as on the failure mode of the strengthened member.
This work has the aim of contributing to a better knowledge, as well as providing reliable data of the long-term bond behavior of the NSM FRP reinforcement systems. To this end, a study on the time-dependent bond-slip response of the NSM Carbon FRP (CFRP) strips in concrete when subjected to sustained loading and different environmental conditions has been performed.
In this study, two experimental campaigns have been carried out. In the first campaign, four test series have been performed to investigate the tensile creep behavior of epoxy adhesive specimens when subjected to different levels of sustained loading and different temperature and humidity conditions. In the second campaign, the long-term bond behavior, in terms of bond strength and bond-slip response, of NSM CFRP strips in concrete has been investigated, both analytically and experimentally, to further extend the knowledge in this particular research domain. In this respect, five series of single shear pull out concrete blocks strengthened with NSM CFRP strips subjected to sustained loading have been tested. Different sustained load levels, bonded lengths, groove widths, temperature and humidity levels have been considered. The experimental long-term results of both campaigns have been reported and discussed. In addition, a simplified methodology to analytically simulate the time-dependent bond-slip response of NSM CFRP strips in concrete has been presented. The experimental data have been compared to predictions obtained with the proposed methodology.
