effects of temperature and sustained loading on the response of FRP-strengthened concrete elements
Open Access
- Author:
- Jeong, Yoseok
- Graduate Program:
- Civil Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 04, 2014
- Committee Members:
- Dr Maria Lopez De Murphy, Dissertation Advisor/Co-Advisor
Dr Maria Lopez De Murphy, Committee Chair/Co-Chair
Charles E Bakis, Committee Member
Farshad Rajabipour, Committee Member
Gordon Patrick Warn, Committee Member
Ivica Smid, Committee Member - Keywords:
- FRP
epoxy
creep
temperature
sustained loading
fracture energy - Abstract:
- Fiber reinforced polymer (FRP) repair systems for concrete structures have been widely used in civil infrastructure. Concrete-epoxy interfaces (CEI) are formed during the installation of externally bonded FRP systems to concrete structures. Research on their short-term behavior under aggressive environmental conditions has been conducted extensively in the past. Nevertheless, long-term performance and durability issues of these strengthening systems still remain largely uncertain. Thus, it is critical to study the effects of sustained load and temperature on the time-dependent deformation of the concrete-epoxy interface along with the residual strength of the FRP-strengthened concrete element. Single-lap shear and three-point bending test specimens were used to evaluate temperature effect and the time-dependent behavior during sustained loading below and at ultimate strength after the sustained loading period. The test results demonstrated the effects of temperature and sustained loading on creep behavior and on the remaining strength (the fracture energy) after creep duration. The creep responses of single-lap shear and three-point bending test specimens depend on the creep response of the epoxy. The effect of sustained loading on the remaining strength is positive for the single-lap shear specimens. However, this positive effect decreases as the creep duration increases. On the other hand, for the three-point bending test specimens, the sustained loading effect is negative on the remaining strength because presence of sustained loading leads to a weakening in the bond strength in the concrete-epoxy interface, which is evidenced by the fracture surface analysis of tested three-point bending specimens. Results of a numerical study of the single-lap shear specimens are also presented. Numerical models used the viscoelastic model for the creep tests and a plastic damage model for the bond tests. Results were compared with the available experimental results. The results show good correlations between the analysis and tests. It is proven that the creep behavior of the single-lap shear specimen is mainly governed by the creep characteristics of the epoxy. The numerical results also suggest that the redistributing of the interfacial bond stress can lead to an increase in the remaining strength of the single-lap shear specimens. A parametric study is carried out in order to investigate the various factors affecting creep behaviors and bond behaviors of single-lap shear specimens. Elevated temperatures and increased epoxy thicknesses lead to an increase in the remaining strength of the single-lap shear specimens due to stress redistribution occurring during the sustained loading period.