Research Progress on Creep Response of FRP-strengthened Reinforced Concrete Beams
YAO Weilai1, JIANG Shiyong1,2, CAI Tao1, GONG Hongwei1, TAO Shuai3
1 Department of Military Facility, Army Logistics University of PLA, Chongqing 401331 2 School of Civil Engineering, Chongqing Jiaotong University, Chongqing 400074 3 Unit 72695 of PLA, Qingdao 266103
Abstract: Due to the excellent performance of fiber-reinforced polymers (FRP) and ease of application, the techniques of strengthening concrete structures by externally bonding FRP had been widely applied in actual projects (e.g., structural modification, repairing, reinforcement and seismic retrofit), since the end of the last century. FRP presents low density, well corrosion-resistant and high strength. Recently, FRP has been more generally used since the material compensate is further declined. It should be noted that the service time of building structures is long. After strengthening, the strengthened structures still suffer sustained loads for long-period of time. However, so far, the long-term performance of strengthened structures under sustained load has not been fully explored. The practical strengthening designs do not consider the creep effects. To the actual fact that the strengthening techniques of bonding FRP externally have been already widely used, it is needed to further investigate the creep response of FRP-strengthened concrete structures. Under sustained load, the long-term deformation of FRP-strengthened structure increases with time, along with complicated stress redistribution occurs in structure. These phenomena are basically caused by the creep behaviors of materials. Researches on the time-dependent properties of concrete had been carried out long before. Up to now, there is relatively adequate understan-ding for the shrinkage and uniaxial compressive creep of concrete, and some generally accepted models worldwide are recommended to theoretically describe such behavior. Researches show epoxy resin, which is used as adhesive to bond FRP on concrete exhibits evident creep performance. Higher environmental temperature and relative humidity increase the creep deformation of adhesive, which may even induce creep fracture. Experimental researches and numerical studies have demonstrated that the viscous flow of epoxy leads to obvious relaxation of interfacial stress. The CFRP and GFRP used for structural strengthening present ignorable creep performance, which has been validated by tests. For the increasing of deformation of FRP-strengthened concrete structure under sustained load, the increasing rate is high in the earlier stage, but gradually reduces in the later stage, which is basically in consistent with the creep law of concrete and epoxy resin. Strengthening has evident effect on reducing the instantaneous deformation, whereas, its effect on reducing the long-term deformation is comparatively not pronounced. The believed reason is that the shear creep of adhesive relieves the stress in FRP, which degrades the strengthening effects and causes additional deformation. Based on cross section analysis, the long-term performance of FRP-strengthened concrete beams can be theoretically investigated, however, the shear creep of adhesive cannot be properly taken into account. Reasonable discussion on the time-dependent behavior of FRP-strengthened structures fundamentally dependents on the adequate understan-ding of the creep response of materials. Thus, this paper first review the research progress on the creep behaviors of concrete, epoxy adhesive and FRP. It is noteworthy that in actual engineering projects, the sustained load for structure is service load. Under such level of load, the stress in steel is lower than the yield strength, which can be considered as linear elastic materials, hence the creep of steel can be reasonably neglected. Therefore, this paper no longer addresses the creep behavior of steel. Afterwards, the recent study progress on the time-dependent response of FRP-strengthened concrete beam is reviewed in the aspects of experimental study and theoretical analysis. The reviewed experimental studies cover the methods, phenomena and conclusions of long-term test. The reviewed theoretical analyses mainly include the methods for calculating the long-term deformation. Finally, the problems of existed studies are concluded, and the suggestions for further researches are presented.
姚未来,江世永,蔡涛,龚宏伟,陶帅. 粘贴纤维增强复合材料加固混凝土梁的蠕变特性研究进展[J]. 材料导报, 2019, 33(17): 2890-2901.
YAO Weilai, JIANG Shiyong, CAI Tao, GONG Hongwei, TAO Shuai. Research Progress on Creep Response of FRP-strengthened Reinforced Concrete Beams. Materials Reports, 2019, 33(17): 2890-2901.
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2019, Vol. 33 
