Research Article Bond-Slip Models for FPR-Concrete Interfaces Subjected to Moisture Conditions Justin Shrestha, 1 Dawei Zhang, 2 and Tamon Ueda 3 1 Engineering Development Department, Takenaka Civil Engineering & Construction Co., Ltd., Shinsuna, Koto-ku, Tokyo 136-8570, Japan 2 Department of Civil Engineering, College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China 3 Division of Engineering and Policy for Sustainable Environment, Faculty of Engineering, Hokkaido University, Kita 13 Jo Nishi 8 Chome Kita-ku, Sapporo 060-8628, Japan Correspondence should be addressed to Dawei Zhang; dwzhang@zju.edu.cn Received 22 September 2016; Accepted 14 December 2016; Published 18 January 2017 Academic Editor: Baolin Wan Copyright © 2017 Justin Shrestha et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Environmental related durability issues have been of great concerns in the structures strengthened with the fber reinforced polymers (FRPs). In marine environment, moisture is one of the dominant factors that adversely afect the material properties and the bond interfaces. Several short-term and long-term laboratory experimental investigations have been conducted to study such behaviors but, still, there are insufcient constitutive bond models which could incorporate moisture exposure conditions. Tis paper proposed a very simple approach in determining the nonlinear bond-slip models for the FRP-concrete interface considering the efect of moisture conditions. Te proposed models are based on the strain results of the experimental investigation conducted by the authors using 6 diferent commercial FRP systems exposed to the moisture conditions for the maximum period of 18 months. Te exposure efect in the moisture conditions seems to have great dependency on the FRP system. Based on the contrasting diferences in the results under moisture conditions, separate bond-slip models have been proposed for the wet-layup FRP and prefabricated FRP systems. As for the verifcation of the proposed model under moisture conditions, predicted pull-out load was compared with the experimental pull-out load. Te results showed good agreement for all the FRP systems under investigation. 1. Introduction Te use of fber reinforced polymer (FRP) is extensive in strengthening and rehabilitation of infrastructures. However, there are great concerns regarding the environment-related durability problems. To precisely predict the service life of the strengthened/rehabilitated structures, it is necessary to take account of the environmental durability related deteriorations. In the marine environment, the moisture is considered as one of the dominant factors which could afect both the material and the bond properties of the FRP strengthened/rehabilitated concrete structures. Various existing design guidelines for FRP strengthening reinforced concrete members recommended deterioration coefcient for FRP materials to refect the efect of exposure environ- ment. Te coefcient was usually applied to the material properties of FRP itself, while the efect of environment on the bond-slip relation of FRP-concrete interfaces was not considered. Meanwhile, there are quite a number of studies trying to simulate the marine environmental conditions by altering the materials, immersion solutions, exposure durations, environmental conditions, testing methods, and so forth [1–5]. Among them, most of the studies have pointed out that the moisture conditions severely deteriorated bond interfaces between FRP and substrate concrete while the degree of efect varied. Generally, the moisture afects the interface between FRP and the concrete resulting in the reduction of the bond capacity. Such efects are usually refected by transition in failure mode from concrete cohe- sion to the mixed or adhesion failures [1]. Te extensive experimental investigation conducted by the authors found that the efect of moisture was largely dependent on the selection of the materials. Among 6 of the commercial FRP systems investigated for the maximum moisture immersion Hindawi International Journal of Polymer Science Volume 2017, Article ID 4031565, 14 pages https://doi.org/10.1155/2017/4031565