Analysis of moisture-induced stresses in an FRP composites reinforced masonry structure

It has been shown in many studies that fiber reinforced polymer (FRP) composite laminates can be used to effectively strengthen structures constructed by unreinforced masonry units. For practical application of this reinforcement method, the long-term interface bonding degradation due to moisture and temperature environmental effects needs to be addressed further. In this study, a finite-element modeling procedure for analyzing moisture-induced stresses in a multi-layered structure constructed with distinct permeable materials was developed. The modeling procedure was used to analyze moisture-induced stresses in a concrete block reinforced with a unidirectional glass–epoxy FRP composite laminate partially covering one lateral surface. The nonlinear humidity transport properties of both the concrete and FRP materials were taken into account in the analysis, and the convergence issue of the interfacial shear stress components associated with the free edge effect was addressed by the use of the submodeling technique. It was demonstrated that the moisture-induced stresses at the FRP–concrete interface critical to structural integrity could be determined for any time instant. The results showed that the interfacial stresses increased with the increase of the humidity diffusion time and monotonically approached the stress level at the steady-state condition of the humidity diffusion. It was also shown that the analysis by assuming constant humidity transport properties resulted in a significant underestimation on the maximum interfacial stresses. The current finite-element analysis procedure provides a general method for determining moisture-induced stresses in a multi-layered permeable structure. It can be used to aid with the design of FRP–masonry structures or other similar structures for minimizing interfacial stresses induced due to the mismatch of moisture swelling properties of the constituent materials.