Research On Flexural Behavior Of Seawater Sea-sand Concrete Beams Strengthened With Superelastic SMA Bars

As the country pays more and more attention to the development and construction of marine resources,and the deterioration of the ecological environment caused by the increasing demand for concrete year by year is becoming more and more serious,the application of seawater sea-sand concrete instead of ordinary concrete in practical engineering structures has broad prospects.However,the chloride ions in seawater and sea-sand will accelerate the corrosion of steel reinforcement inside the structure,which limits the use of seawater sea-sand concrete.In recent years,the rapid development of smart materials such as Shape Memory Alloys(SMA)provides a new idea for the design of seawater sea-sand concrete structures.In this paper,SMA is used instead of steel bars as the stress reinforcement,seawater sea-sand concrete is used instead of ordinary concrete.The experimental research on the mechanical properties of the material,the experimental research on flexural properties,numerical simulation and theoretical analysis of SMA strengthened seawater sea-sand concrete beams are carried out.The main research contents and conclusions are as follows:(1)The effects of strain amplitudes and cycle times on the mechanical properties of SMA after heat treatment were analyzed by uniaxial tensile tests.The results show that the increase of strain amplitude will significantly affect the mechanical properties of the material,and the increase of cycle times is conducive to stabilizing the mechanical properties of SMA.The seawater sea-sand concrete with two strength grades of C35 and C50 was prepared,and the compressive strength test proved that the standard value of the compressive strength of the test block met the standard strength requirements.(2)Three SMA reinforced seawater sea-sand concrete beams and one anti-corrosion reinforced seawater sea-sand concrete beam were designed and fabricated.And the flexural performance of the four specimens were studied through the cyclic-loading test,and the failure process,displacement ductility,stiffness degradation and self-centering capacity of each specimen was analyzed.The test results show that the crack recovery rate and ultimate displacement of SMA seawater sea-sand concrete beams are significantly larger than those of reinforced beams,showing superior self-centering ability and ductility;the increase of SMA reinforcement ratio and seawater sea-sand concrete strength can significantly improve the bearing capacity of beams;the self-centering effect of SMA reinforced beams with smaller diameters is better.(3)The finite element analysis model of SMA reinforced seawater sea-sand concrete beam was established,and the influence of SMA reinforcement ratio and seawater sea-sand concrete strength grade on the flexural performance of the beam was studied,and compared with the experimental results.The results show that the bearing capacity values obtained by the simulation have little difference with the test results,and the overall trend of the curves is consistent,which indicates the correctness of the model establishment.The increase of SMA reinforcement ratio can significantly improve the self-centering ability of the specimen;the improvement of the strength grade of seawater sea-sand concrete can improve the bearing capacity of the specimen.(4)The theoretical analysis of the flexural performance of SMA seawater sea sand concrete beams is carried out.Based on the constitutive model of SMA and seawater sea-sand concrete,the calculation method of cracking load,yield load and peak load of the SMA seawater sea-sand concrete beams are proposed,and the experimental values are compared with the experimental values.The results show that the results obtained by the calculation formula are in good agreement with the experimental values,which verifies the correctness of the theoretical calculation.