Experimental Study On Fatigue Behavior Of RC Beams Strengthened With High Performance Ferrocement Laminate

High Performance Ferrocement Laminate (HPFL) is a new type of inorganic material with series of advantages, such as high strength, small shrinkage, and good bonding properties with concrete. Concrete components strengthened with HPFL have an effective increase in carrying capacity, stiffness, ductility and crack resistance. Previous studies mainly concentrated in the static performance and very little information exists regarding the fatigue behavior of reinforced concrete beams strengthened with HPFL. This thesis presents the results of an investigation into the fatigue performance of RC beams retrofitted with HPFL.(1) A control specimen and four strengthened beams were tested under a higher fatigue loading. The results indicated that fatigue failure of the RC beams started with steel rupturing on the bottom followed by concrete crushed in case of overloading. The fatigue life of strengthened beams could be extended significantly compared with the control beam. The deflections, the spacing and the number of the cracks were decreased obviously. The strain of concrete and steels had also greatly reduced.(2) Fatigue experiments of four beams strengthened with HPFL were conducted under a normal level cyclic loading. All of the four beams did not fail after 2 million cycles. This proves that HPFL can be applied to the repairing of reinforced concrete beams subjected to fatigue loading. The experimental results also showed that the failure mode of the specimen without shear dowels was debonding between the interface of HPFL and concrete in the following static test. However, debonding of HPFL was not observed in the other three retrofit specimens. Thus, it is very effective to avoid debonding between the interface of HPFL and concrete by planting shear pins at the end of beams.(3) Theoretical analysis on strengthening of RC beams using HPFL under fatigue loading was carried out. The formula for fatigue stress calculation was put forward by transformed section method, in which changes of concrete fatigue deformation modulus with cycles was considered. The fatigue life can be predicted by using the steel S-N curves obtained from the experimental results. The formula for stiffness calculation was presented by reduction coefficient method, which indicated a good agreement between theoretical values and experimental results.