Design And Optimization Of Flat Anchor For Shape Memory Alloy Wires

Crack is one of the most common diseases of reinforced concrete bridges.Cracks will affect the durability,safety and aesthetics of the structure.In view of the problem of concrete cracking damage,there are many active and passive reinforcement methods,such as prestressed steel strand reinforcement method,affixed steel plate reinforcement method,increasing section reinforcement method,etc.,but these reinforcement methods still have some limitations.With the research and application of smart materials in various fields,the active reinforcement of concrete structures using Shape Memory Alloy(SMA)with high strength smart materials has attracted more and more scholars' attention.This method mainly utilizes the unique shape memory property of SMA,and the reinforcement process does not need mechanical tensioning.Among them,the active reinforcement method of embedding SMA wire into the concrete protective layer and generating prestress through thermal excitation is a research hotspot.Aiming at the problems such as high strength,smooth surface,difficult welding,poor bonding performance between SMA wire and concrete,and prone to slip failure,this paper proposes a new flat anchor for clamping SMA wire,and studies its anchoring performance and design optimization:(1)In order to study the anchoring performance between flat anchor and SMA wire,the anchoring system composed of flat anchor and SMA wire was pull-out tested.The results show that the flat anchor can provide enough anchoring force and will not be deformed or damaged during normal use.The finite element numerical simulation method was used to analyze the mechanical characteristics and anchoring performance of the flat anchor,and the results were compared with the test results.The results verified the correctness of the finite element analysis.In addition,from the results of numerical simulation,the most vulnerable failure location of the modified flat anchor is obtained,which provides a basis for the design optimization of the flat anchor.(2)In view of the bond problem of the three-phase two interfaces of "SMA wire-cement mortar-concrete",the flat anchor and SMA wire were embedded into the cement mortar test block,and the bond performance of flat anchor-SMA wire and cement mortar was studied through the drawing test.The results show that the cement mortar has a strong binding force with the flat anchor,which can avoid the slip failure of the flat anchor in the concrete protective layer.Then the finite element numerical simulation method is used to analyze the stress process of the above tests,and the finite element results are in good agreement with the test results.In addition,the stress distribution and diffusion trend of the specimen can be obtained from the results of numerical simulation analysis,and the contact surface between the flat anchor and cement mortar begins to show a fan-shaped diffusion.(3)The influences of the number of screws,screw spacing,screw insertion depth(screw fastening force)and other factors on the anchoring performance of the flat anchor were discussed.The design of the flat anchor was optimized from these three aspects,and the calculation formula of anchoring force was obtained.The results show that the number of screws has a great effect on the anchoring force of flat anchor,which shows a positive linear correlation.Screw depth(screw fastening force)is positively correlated with anchor force of flat anchor,but too high will cause damage to SMA wire.In this paper,the anchoring problems of reinforced concrete beams strengthened by SMA wire are systematically studied,and the proposed flat anchor is further designed and optimized,which provides some references for the anchoring problems of SMA wire in practical application.