Durability of Concrete Beams Reinforced with Fiber Reinforced Polymers

Open Access
Author:
Artun, Kivanc
Graduate Program:
Civil Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
September 17, 2012
Committee Members:
  • Associate Professor Of Civil Engineering Dr Maria Lopez De Murpy, Thesis Advisor
Keywords:
  • durability
  • FRP
  • debonding
  • DIC
Abstract:
Externally bonded Fiber Reinforced Polymer Composites (FRP) are widely used for repair and strengthening of concrete members. Despite the widespread use of this technique there is still insufficient knowledge about the long-term durability of FRP systems externally bonded to concrete. FRP bonded concrete members can be exposed to various environmental effects during the lifetime of the structures, as this system is applied for both indoor and outdoor members in buildings and bridges. To ensure the safety of these structures during their service life, durability of the FRP material under such weathering conditions and service loading should be understood. In this study, long term durability of Glass and Carbon FRP reinforced, pre-cracked concrete beams without steel reinforcement under sustained loading is investigated. The flexural test results of seventeen beams, which were casted and reinforced with FRP in 2005 are used. Eight of these beams were tested within eight months after the manufacturing date without any weathering or sustained loading exposure by Whitaker (2007). Nine of them were exposed to indoor and outdoor conditions in State College/PA under sustained loading for 72 months, and tested in 2011. During the tests, in addition to deflection and crack opening measurements, 2D Digital Image Correlation (DIC) was used to obtain full field strain and slip distributions. The long term performance of the beams is evaluated by comparing the flexural test results of these unconditioned and 72 months conditioned beams. Externally bonded FRP sheets and plates introduce failure modes such as debonding and FRP rupture. Therefore, in addition to the ultimate strength, deflections and strain distributions, the failure modes, and interfacial bond strength between the FRP and the concrete are also compared. In this study, it is observed that; direct exposure to outdoor conditioning causes reduction in the ultimate capacity of FRP reinforced concrete beams. Moreover, the first debonding of the conditioned beams occurred with the tensile rupture of the concrete; also, the moment capacity at the initiation of debonding showed an increasing trend with the increase of the tensile strength of the concrete beams. The furthest debonding propagation before the failure is observed for the outdoor conditioned CFRP and GFRP beams, whose FRP reinforced side is directly exposed to outdoor conditioning. In terms of local behavior, fracture toughness is obtained by a fracture mechanics analysis in which a local non-linear shear stress-slip model is assumed and its parameters are obtained by curve-fitting to experimental slip versus position data. According to the analysis results, the lowest fracture energies are observed for the indoor CFRP beam which had the largest sustained moment with 47% of the ultimate, during conditioning. For this beam; increasing local fracture energy further away from the pre-crack and especially from the active region of the FRP during sustained loading, resulted in no reduction of the ultimate moment capacity. Among the beams that have the same level of sustained moment, the beams, FRP reinforced sides of which were directly exposed to outdoor conditioning have the lowest fracture energies. In eight out of nine beams local fracture energy increases further away from the pre-crack, the location, where the affect of conditioning and sustained loading is assumed to be the most severe. Also, the 2D DIC Method, which is more practical compared to the 3D DIC, is found to be a successful method to obtain full-field strain and slip distributions of the FRP sheets that are externally bonded to concrete members, under flexural loading, unless there is a movement of the FRP strip relative to the concrete.