Study On Flexural Behavior Of Embedded SMA And CFRP Composite Strengthened RC Beams

The crack load and ultimate load of reinforced concrete beam（RC）will be improved after flexural reinforcement of reinforced concrete beam by carbon fiber reinforced polymer（CFRP）.Though the ultimate load of reinforced members is improved significantly,the utilization ratio of CFRP materials is low,and it is easy to peel off in RC beam reinforcement,and the effect of crack closure and crack load is not obvious.Using shape memory alloy（SMA）to prestress the RC beam and then paste the CFRP can effectively improve this problem.This paper uses NiTiNb-SMA,CFRP and SMA / CFRP to reinforce the beam,and carries out experimental research and theoretical calculation on the bending resistance of the strengthened beam,and compares the theoretical calculated value with the experimental value.The main contents and conclusions are as follows:（1）Study on annealing treatment and DSC test of NiTiNb-SMA wire.The annealing treatment can change the transformation temperature of the SMA and maintain a large permanent recovery force at room temperature.At the same time,the annealing treatment can improve the hysteresis width of the SMA and increase the stability of martensite.Reduce the phenomenon of martensite inverse transformation and effectively avoid stress relaxation.（2）NiTiNb-SMA wire tensile test and recovery force test study.SMA wire has undergone three stages: austenite deformation,martensite transformation and martensite deformation.To make the SMA prestress,stress induced martensitic transformation is needed at room temperature,that is,the SMA wire should be preformed.The maximum permanent recovery stress of 16% NiTiNb SMA wire is about 345 MPa when it is excited to 200℃ and then reduced to room temperature.（3）Study on the resilience of NiTiNb-SMA wires embedded in PCM.The results show that after designing a single side extruded Anchorage fixed SMA wire,the SMA wire can be embedded in the concrete beam by PCM filling,which can solve the problem of poor bond performance between the SMA wire and the concrete.The permanent recovery force can be produced when the wire is electrified.the permanent resilience produced by the SMA wire bonded with the PCM decreased by 10.6% compared to the unbonded wire.（4）Study on flexural behavior of concrete beams reinforced with embedded SMA wire and bonded CFRP.The RC beam bearing capacity of the three reinforcement methods is improved,but the effect of SMA/CFRP composite reinforcement is the most obvious.the cracking load of SMA reinforced beam,CFRP reinforced beam with end anchor and SMA-CFRP composite reinforced beam with end anchor increased29.6%,124.5%,148.6% compared with reference beam,while the ultimate load increased23.8%,130.7%,188.8% respectively.SMA reinforcement improves the cracking load and ductility,delays the cracking time of concrete,and effectively inhibits the development of main cracks.Compared with CFRP reinforcement,the main tensile stress of concrete is reduced by the introduction of prestress,which effectively reduces the number of oblique cracks and further improves the ductility.（5）Theoretical analysis.On the basis of the formula of flexural bearing capacity provided by the code,considering the prestress produced by the SMA,the calculation method of flexural bearing capacity of SMA/CFRP composite reinforcement RC beam is put forward,and the theoretical calculation value is in good agreement with the test value.