Experimental Investigation On Flexural Behavior Of RC Beam Strengthened With Superelastic SMA And Engineered Cementitious Composites Materials

With the degeneration of the material performance and change of the load condition,existing building structures probably cannot meet the safety requirement of the current codes.Therefore,it is necessary to reinforce and retrofit the existing building structures.The traditionalmethods,such as pasting FRP,enlarging RC section andpacking steel plate,and so on,due todurability,usability or otherproblems,can not make the structures realize the high performance.Recently,the occurrence and development of smart materials and high performance fiber reinforced cement-based composite materials provide a new strategy for the reinforcementtechnology of the existing buildingstructures.Shape Memory Alloys(SMA)are a kind of functional materials,characterized by significant shape memory effect(SME)and superelasticity(SE),and their recoverable strainsis up to 6%-8%.These unique properties enable SMA to be widely utilizedin the area of structural vibrationcontrol.Engineered cementitious composites(ECC)are a kind of high performancefiber reinforced cementitious composites with.When the fiber volume fraction is 2%,the ultimate tensile strain of ECC can reach 3%~6%.ECC has high ductility and self-controlled crack capacity,andits ductility is much better than ordinary concrete.Therefore,the utilization of in reinforcement of RC structures can fully develop the high performances of the SMA and ECC can significantlyenhance the re-centering,energy-dissipation and deformation capacities,achieving the high-performance of the building structure.In this paper,the flexuralbehaviors of reinforced concrete beams strengthened by SMA/ECC were studied.The main contents are as follows:(1)Experimental investigations on the mechanical properties of SMA bar of diameter 5.5mm were carried out considering the effect of heat treatment process,strain amplitude,strain cycle times on the mechanical properties of SMA bar,proving bases for the experimental investigation of beam strengthened.(2)Four specimens were made,and the effects of different materials on the seismic behavior of reinforced RC beams were considered: RC,SMA-RC,SMA-ECC,and RC-ECC.The specimens were subjected to three dividing point loading,and the loading mode was repeated loading and unloading cycle until the specimen was damaged.(3)The load displacement hysteresis curve,skeleton curve,and other important analysis of mechanical properties are completed by the crack width,number,midspan deflection,steel strain,and other test date.And the flexural behavior of RC beams strengthened with SMA/ECC composites was studied.(4)Based on the bending bearing capacity calculation formula of RC beam recommended in thecurrent concrete code,considering the tensile capacity provided by ECC,and then deduce the simple calculating formula of bearing capacity of strengthened reinforced concrete beams by ECC.According to the calculation formula,the calculated values were compared with the experimental values,and the results verifiedits applicability.Experimental results show that SMA,instead of ordinary reinforcing bar,can improve the recovery of the specimen,andECCreplacing the ordinary concrete,can significantly improve the ductility of the specimen with multiple cracks and the seismic performance of RC structure members.