Research On Self-repairing Performance Of Prestressed SMA Intelligent Concrete Beam

The shape memory alloy(SMA)is a kind of new material which possesses the functions of perception and drive.It has been gradually utilized in structural control,test and reinforcing because of its characters of shape memory,super elasticity,large driven force emerging with the restricted recovery,high sensitivity of the resistance to strain and high damping.Until now,significant outcomes has been derived after sorts of investigations in the dampers and concrete intelligent structure made by SMA material.However,the impact of SMA concrete structure on the aspects of test and reinforcement needs deeper investigation and the mechanical behavior of the structure is not precise after the reinforcement.In this paper,the two characters of the SMA that shape memory and large driven force emerging with the restricted recovery had been utilized to exert the pretension on the Ni-Ti shaped memory alloy which works as the pre-stressed tendon in the reinforced concrete beam and the SMA unbonded pre-stressing concrete beam.Exerting load on the bending part of the SMA concrete beam with different pre-stress values,then repeat the process after the reinforcement,after that the repaired beam was loaded again.The theory derivation had been conducted based on the experiment.The main works are as follows.(1)The experiment is investigation in the physical mechanical behavior of the SMA silk.To ensure the better characteristic of the material under the suitable temperature,the phase transition temperature of the SMA silk was adjusted through the thermal treatment.The melting curve of the SMA after the thermal treatment can be obtained by the DSC method in order to get SMA silk temperature data to ensure the phase transition temperature.The heating temperature of the SMA can be determined by taking the phase transition moving forward into consideration in the process of the repairing.The monotonic tensile test of the SMA had been conducted under the normal temperature,it shows that recoverable deformation of the SMA silk meets the requirements of the crack repairing.The anchoring force test of the anchorage was conducted to ensure the reliability of the anchoring.(2)The experiment is investigation in the self-repairing behavior of the SMA pre-stressing smart concrete beam.The mechanical property of the experimental beam is tested by two point symmetrical loading method.It can be concluded the cracking load of the beam that increases along with the pretension of the SMA silk augmenting.Compared beam without pretension,the crack load of experimental beam with 9%pretension is 2.19 times.Furthermore,the beam can recover through the electric heating.And result displays if the general strain is lower than the maximum recoverable strain of the SMA,the cracks can recover completely.(3)The experiment is investigation in the second loading mechanical behavior of the SMA pre-stressing smart concrete beam.When the repaired beam was loaded again,the results show that the bearing capacity of the specimen decreases and when the unrecoverable deformation occurs,the excellent pretension value for the crack recovery is 6%-8%and when the crack recovery is 7%,the pretension is best for 80.6%,which is 2.74 times of the beam without pretension.(4)The paper made theoretical analysis of the self-repair behavior of the pre-stressing SMA concrete beam.The theoretical formula can be derived based on constitutive relation of SMA and it provides a method to calculate the pretension value related to the maximum recovery stress occurring of the SMA.The more strain of SMA wire is more than the maximum recoverable,the recovery of the cracks is worse.The validity of the formula can be verified through comparison with the experimental results.It also can be concluded through the comparison that by calculating the pretension of SMA silk under the load effect,the optimal initial pretension for the best crack recovery can be found.