Experimental Study On Active Reinforcement Of Concrete Cylinder By Shape Memory Alloy

Since the 1950 s,reinforced concrete have been widely used in bridge projects in China because of the strong durability and good fire performance.However,bridges will continue to age by the passage of service time and the influence of the environment,even they had better material selection,reasonable design,and guaranteed construction quality.Which causes a variety of problems such as reveal of reinforcement,pockmarks of the concrete,detachment of the surface layer,and so on,may cause hidden dangers in the safety performance of the structure.Especially in the earthquake,the piers once damage occurs can cause serious economic losses and even serious life safety threat.Reinforced concrete bridge pier,as a kind of ductile member,can counteract seismic energy by bending deformation of the plastic hinge region.Therefore,it's more and more important to reinforce the existing reinforced concrete bridge piers.Above-mentioned,this thesis proposes a method of strengthening concrete piers with NiTiNb shape memory alloys,provide active force by winding SMA wire around the plastic hinge region of the piers.The main works of this thesis are listed below:(1)Based on references at home and abroad,summarize the common damage forms and existing reinforcement methods of bridge piers,and the research status of shape memory alloys in Civil Engineering application.(2)Preparation for the reinforcement test: testing the mechanical properties of NiTiNb shape memory alloy,to find out the maximum stress of the material by changing the prestressing force length and the heat stimulating temperature.(3)The constitutive relation of the new shape memory alloy wire is introduced in detail,and its mechanical properties and phase transformation conditions under different phase transformations are explained.Combined with the research status at home and abroad and the elastic-plastic model of materials,the theoretical calculation of RC Columns Strengthened with ring shape memory alloy is given.(4)The pseudo-static test of the concrete pier column was performed with the winding pitch,winding height,incentive or not,excitation of the NiTiNb alloy wire as the variables.The design process of the entire test was described in detail.The hysteresis curve,skeleton curve,residual displacement,strength degradation,stiffness attenuation,cumulative energy consumption and other performance indicators have been analyzed and compared.