Influence Of Temperature And Load On The Smart Aggregate Based Health Monitoring System Of Concrete Structures

Concrete structure is one of the main buil ding structures we apply today.It is of great significance to improve the health-monitoring system of concrete structure.PZT has been widely employed in structural health monitoring system featured by its sound piezoelectric effect,high sensitivity,goo d repeatability and low cost.Smart Aggregate(SA)can be applied in monitoring damage cracks,concrete filled steel tube and structure impact loads in laboratory situation.The actual projects are often under complex temperatures and load conditions.Temperatures and loads need to be taken consideration for the promotion of in-situ monitoring system.In this thesis,the performances of bare SA under different temperatures and loads were experimentally studied first.After that,the performances of structure health monitoring system of concrete structure based on SA under different temperatures and loads were also been researched through experiments.The specific research contents are as follows.In order to clarify the influence of temperatures on the SA base d structural health monitoring system,the temperatures effect on bare SA’s driving performance and sensing performance were studied first.Then,this thesis would study the propagation performance of stress wave pro duced by SAs in concrete specimens under changing temperature.Tests results show that the effect of temperatures on SA performance and stress wave propagation in concrete is obvious and the effect seem to be more drastic on the health-monitoring system.In general,the lower the stress wave frequency,the more s ensitive to the temperature.Higher frequencies and lower frequencies signal amplitude show opposite trends in temperature variation.In order to explore the influence of load on the SA based structural health monitoring system,the author researched performance of bare SAs sensing and driving properties first.Then the SA pairs were casted into the concrete to build a health-monitoring system,and the propagation properties of stress wave in concrete under single cycle load,equal magnitude cyclic loading and increasing magnitude cyclic loading were studied in the experiment.Results show that SA can work effectively under the stress below 65 MPa.The longitudinal microcracks can affect the results of stress wave signals in different direction of concrete.There is an extension and generation of microdefects in concrete though the long duration load and cyclic load are in the elastic stage.Stress wave signals can reflect the four stages of microstructure development,stress memory effect and progressive damage effect of concrete.Based on the finite element software Comsol Multiphysics,the three dimensions models of SA and concrete were set up to simulate the temperature and load effects on SA and the stress wave propagation in concrete.Results show that the mode of vibration and internal stress of SA are remarkably affected by temperature.The effects of temperatures an d loads on SA based on finite element method were similar to the results from the experiment.The stress wave attenuation and velocity are proportional to the Young’s modulus and the stress wave frequency.