Analysis Of Mechanical Performance Of Concrete And Dynamic Characteristics Of Concrete Supported Beams Under Influence Of Temperature And Research On Damage Identification Method

With the rapid development of Chinese national economy and transportation,bridge construction has also developed vigorously and has played an important role in Chinese infrastructure construction.However,during the long-term use of the bridge structure,it will inevitably be affected by vehicle loads and impacts,human factors and natural disasters,which will cause the bearing capacity of the bridge to decline,structural damage,and even collapse.It endangers human survival and health.A large number studies of domestic and foreign experts and scholars have shown that the ambient temperature will cause significant changes in the dynamic characteristics of the bridge structure,and often mask the impact of the damage on the dynamic characteristics of the structure.Therefore,how to effectively eliminate the influence of the ambient temperature on the dynamic characteristics of structure and carry out structural damage identification is particularly important.Our study was founded by the National Natural Science Foundation Project “Research on modal parameter identification and damage detection of bridge structure considering temperature effect”.In this paper,through the experimental monitoring of the simply-supported reinforced concrete beam,the temperature field distribution of the simply-supported concrete beam with time and temperature is studied.Combining experiments with theory,the influence mechanism of the temperature on the modal frequency of the simply supported beam is discussed.Finally,through the method of probability statistics,the damage identification of concrete simply supported beam is realized.The main research content of this paper is as follows:1.This article introduced the concept of ultrasonic testing and ultrasonic basic parameters,and conducted experimental research on concrete specimens that reached the specified control temperature,and analyzed the influence of temperature changes on the ultrasonic parameters of the concrete.2.The change law of mechanical properties of concrete with temperature was studied,and the effect of temperature change on the dynamic and static modulus of elasticity and axial compressive strength of concrete was tested.Also,axes compressive strength and the dynamic and static elastic modulus were calculated by data fitting.as functions of temperature.3.The outdoor modal test of concrete simply-supported beams was conducted to study and analyze the changes of the internal temperature field of the test beams with the ambient temperature.The relationship between the first four order frequencies of test beams and the internal temperature distribution of the concrete was obtained.The theory and the test were combined to analyze the influence mechanism of temperature on modal frequency of simply supported beam.4.A probabilistic statistical method combining uncertain frequency and modal shape data was proposed.It was used to identify structural damage by comparing the measured vibration data before and after damage.It was assumed that the measured vibration data and the influence of uncertainty in the finite element model include normal distributed random noise.The perturbation method was used to calculate the mean and covariance of structural stiffness parameters.The probability of damage existence in the structural component was defined to identify the damage.