Study On Measuring The Existing Stress Of Concrete Beam Based On Fiber Bragg Grating Sensor

With the rapid development of bridge industry in the past years,nowadays the focus of China's bridge industry is gradually transiting from the infrastructure to the detection and maintenance.The existing stress of bridge structure is an important basis for evaluating the state of bridge service and providing the scheme of maintenance.However,due to the large deviation of theoretical analysis and the poor precision measuring instruments and other reasons,there is no effective method to measure this hot issue of the existing stress in the industry.In order to find an accurate method for measuring the existing stress of bridge structures,to establish a basis for the accurate assessment of structural service,this paper makes research base on the stress releasing principle and the fiber bragg grating(FBG)technology to study the measure system and the testing method of the ring core slot method through theoretical analysis and model test.What is more,this paper also considers factors such as measured parameters and measurement errors and so on.The specific research contents are as follows.(1)This paper finds the measuring formula of uniaxial stress and biaxial stress after making a study of the ring-core method.It also analyzes the influence of the original stress state during the grooving process basing on the Saint-Venant's principle.Then the test model was established by ANSYS software to simulate the process of measuring the existing stress by ring-core method.And the simulating results find the relevant measuring parameters such as the depth of stress release,which lay the foundation for further experimental research.(2)This paper makes a study to the ring-core method system,including strain testing systems,drilling and grooving system and core-like concrete test system.That is to say,this paper studies the fiber bragg grating strain sensor which is suitable for ring-core method so that ensure the sensor has a good strain transfer efficiency;the development of continuous and stable slotting of the core equipment;the method that tests concrete strength and elastic modulus by ring groove and core sampling integrated test to eliminate the measurement error.(3)There is an experimental study on the internal beam of annular groove.In the study,three identical test beams were cast in the same period,which makes a comparison of the sensing accuracy between the resistance-strain sensor and strain sensors;studies the sensing accuracy under the state of axial compression and eccentric compression.All test results above shows that it is more accurate to make a measurement to ring-core method that base on fiber bragg grating sensing.(4)The main influence factors in the measurement of the ring-core method are water,temperature and the characteristics of concrete materials.The purpose of this study is to improve the measurement accuracy further so that the method can be applied as soon as possible to the actual engineering effective measurement.