Study On Creep Damage Characteristics Of Concrete Based On Nonlinear Ultrasonic Technique

Under long-term continuous load,concrete material and structure will be subject to creep.When the level of continuous load is high,creep will show certain non-linear.The analysis of cause whose nonlinear creep and creep failure occur in concrete,is the basis of long-term performance evaluation.In this paper,the damage evolution characteristics of concrete in creep process were measured by nonlinear ultrasonic method.And the interaction law between damage and creep was revealed.It could provide some experimental and theoretical basis for the research of concrete creep damage and the analysis and design of concrete structures in real working environment.It could also provide some reference for accurately evaluating the safety and durability of concrete structures.The specific research content and results of this paper were as follows:(1)The nonlinear ultrasonic testing system for concrete was established.The experimental parameters of concrete were optimized,and the feasibility of the system was verified by tests of different moisture content and high temperature damage of concrete.The results showed that the nonlinear coefficient decreased with the increase of water content.Especially for the small high temperature damage and the ultrasonic wave velocity,the nonlinear ultrasonic method could be used as a supplement to representing the high temperature damage of concrete.(2)Through concrete creep tests under different sustained loads,and by measuring ultrasonic wave velocity and ultrasonic nonlinear coefficient in creep process,the law of concrete deformation and damage increasing with the increase of duration was obtained.The first stage of concrete creep deformation was the stage of rapid increase of deformation and damage.At this stage,the concrete changed from elastic deformation to creep deformation.The second stage was the stable development and slow growth of deformation and damage.At the same time,the relationship between creep deformation of concrete and ultrasonic nonlinearity coefficient was established through nonlinear ultrasonic test and creep test.(3)Combined with all the experimental data,the influence of damage on creep deformation of concrete was revealed.And the mechanism of material damage caused by non-linear creep of concrete was discussed.The mechanism of nonlinear creep and creep failure caused by the coupling of creep and damage of concrete was analyzed.And the calculation method of nonlinear creep of concrete was proposed...