FLEXURAL BEHAVIOR OF FIRE-DAMAGED REINFORCED CONCRETE SLABS REPAIRED WITH NEAR-SURFACE MOUNTED (NSM) CARBON FIBER REINFORCED POLYMER (CFRP) RODS

Abstract

After exposure to fire, the decrease in load capacity of reinforced concrete (RC) structure will take place and may lead to a damage. However, the fire-damaged concrete member still can be reused if an effective rehabilitation method is applied. Many researches have proposed a lot of techniques on repairing fire-deteriorated structures. Among them, the experimental studies using Fiber Reinforced Polymer (FRP) materials have become popular in recent years due to its high advantage. An important point in this field is the requirement for a FRP system that could restore and enhance the serviceability of weakened structure with only a small change in comparison with its initial size. Moreover, it is also necessary to consider a repairing design in order to protect the FRP system from external agents during service process after the rehabilitation. This research aims to carry out a method to repair flexural reinforced concrete members after exposure to fire based on near-surface mounted (NSM) technique with the application of carbon fiber reinforced polymer (CFRP) rods and repairing material. The purpose is in order to propose a repairing design that could be possible to rehabilitate fire-damaged flexural concrete members by using FRP materials without changing original size of structure. In this study, a series of slabs were conducted to evaluate the flexural behavior of structures after exposure to fire as well as strengthened specimens. The arrangement or the location of CFRP bars was the main factor that had been considered to evaluate the effectiveness of this method. Besides, the direct bond test on C-shaped concrete block specimens was carried out to investigate the bond behavior between CFRP rods and concrete-repairing material substrate in three different embedding positions of FRP bars. Based on the experimental data, it is clear to conclude that the strengthened slabs not only improved endurance limits but also improved load-carrying capacities and stiffness values as compared to control specimen and fire-damaged slab. Especially, based on the results from slab strengthened with CFRP rods embedded in repairing material overlay, it could be considered that this is the most effective method among the proposed techniques in this study. In addition, a numerical simulation was conducted by using 3D nonlinear finite element software ABAQUS in order to develop a model for simulating the flexural behavior of fire-deteriorated slabs strengthening with the proposed method. Based on the comparison with experimental results, the model is possible to predict the load-deflection relation of RC slabs before and after exposure to fire. This numerical simulation is also capable to predict the behavior of strengthened slabs mentioned in experiment. Furthermore, a parametric study was carried out to determine the influence of changing the length of CFRP bars and evaluate the effect as a partially-bonded system could be applied.