PEELING-OFF PHENOMENON IN FRP STRENGTHENED CONCRETE BEAMS DUE TO THERMAL RESIDUAL STRESS

Peeling-off phenomena in FRP strengthened concrete beams are investigated in this paper. Based on the beam theory and the fracture mechanics, a new theoretical model is proposed to analyze the peeling-off behavior near FRP-concrete interfaces, which is governed by residual thermal stresses. Numerical examples are presented to provide a clear insight into the failure mechanism. Some suggestions are provided for the optimal design of FRP strengthened structures.

Assessment of Long-Time Behavior for Bridge Girders Retrofitted with Fiber Reinforced Polymer

Maintaining both the safety and serviceability of deteriorating highway bridge networks necessitates suitable BMS （bridge maintenance system） tools that can maximize cost effectiveness. Numerous experiments have been conducted to detect the long-term mechanical properties of the epoxy resin materials used in FRP （fiber reinforced polymers） strengthening and maintenance technique. Experiments were used to develop a short-term test and construct a model that can reliably predict the long-term behavior of epoxy resin. Furthermore, FEA （finite element analysis） models were developed, using the ANSYS software, to simulate three unstrengthened and FRP strengthened prestressed concrete girder bridges of different configurations. Models simulate the original and aged properties of construction and retrofitting materials under the application of AASHTO （American Association of State Highway and Transportation Officials） fatigue truck and a site-specific fatigue truck in different scenarios. These models were used to develop the bridge performance chart for the capacity of the bridge, with and without strengthening interventions, as a BMS tool. The results show an immediate significant improvement in the concrete tensile stress with the intervention of FRP strengthening.

Performance of insulated FRP-strengthened concrete flexural members under fire conditions

This paper presents the results of fire resistance tests on carbon fiber-reinforced polymer(CFRP)strengthened concrete flexural members,i.e.,T-beams and slabs.The strengthened members were protected with fire insulation and tested under the combined effects of thermal and structural loading.The variables considered in the tests include the applied load level,extent of strengthening,and thickness of the fire insulation applied to the beams and slabs.Furthermore,a previously developed numerical model was validated against the data generated from the fire tests;subsequently,it was utilized to undertake a case study.Results from fire tests and numerical studies indicate that owing to the protection provided by the fire insulation,the insulated CFRP-strengthened beams and slabs can withstand four and three hours of standard fire exposure,respectively,under service load conditions.The insulation layer impedes the temperature rise in the member;therefore,the CFRP-concrete composite action remains active for a longer duration and the steel reinforcement temperature remains below 400°C,which in turn enhances the capacity of the beams and slabs.