The proposed investigation uses experimental and analytical methods to evaluate the effects of temperature and sustained loading on reinforced concrete structures strengthened with externally bonded fiber reinforced polymers. It includes the individual components of the strengthening system and the concrete/epoxy interface, and uses this information to model the long-term structural performance of strengthened systems. The robustness of the proposed numerical analysis procedures stems from the innovative use of fracture and damage mechanics approaches to characterize the individual materials and interfacial properties of strengthened systems. Therefore, the analysis will be capable of predicting the behavior of strengthened structures of any scale.
Upon successful completion of the project, the research and engineering communities will have a better understanding of the dual mechanisms of time dependent deformation and degradation of adhesion in the strengthened system and how these mechanisms affect the remaining structural strength and safety. The investigators have detailed plans for integrating their activities and findings into the profession, in their university teaching, and in outreach programs targeting underrepresented groups. Thus, the research will contribute: (i) new experimental data on the effects of time and temperature on strengthened system performance; (ii) a new modeling approach for overall structural performance based on material and interfacial properties; and (iii) knowledge dissemination and human resource development for the benefit of the research community, practicing engineers, and students.
The overall goal of this project is to evaluate the effects of temperature and sustained loading on reinforced concrete structures strengthened with externally bonded FRP sheets. These temperature and sustained loading effects were also investigated for the individual components of the strengthening system (concrete substrate, epoxy, and FRP sheet) and the concrete/epoxy interface. The knowledge gained from the experimental characterization of these components was used to model the strengthening response of concrete specimens externally bonded with FRP sheets. Our research revealed the presence of a strong nonlinearity between the time-dependent bond behavior and the level of sustained loading applied to the strengthening system; this finding supports the need to consider the interaction of creep and damage in modeling the concrete/epoxy bond performance. A comprehensive database on creep, glass transition, physical aging, and degree of cure characteristics for one epoxy system aged under various conditions and times was developed in this investigation. This data was used to prove that experimentally observed changes in the glass transition temperature and creep response are due to physical aging rather than chemical aging (post-curing) at service temperatures of interest. Nonlinear finite element models of concrete/FRP pull-off specimens were developed using as input the quasi-static and creep test data for the epoxy, concrete, and concrete/epoxy interface. These FEA models incorporate damage and time dependent deformation and are able to capture not only the creep deformation during sustained loading but also the change in residual strength of the pull-off specimens.
