Reasearch On Operation Status Evaluation Of Concrete Box Girder Bridge Based On Temperature Effect

There are a large number of concrete box girder bridges in our country.As one of the main loads of the bridge,the temperature load can not be ignored,so it is of great significance to study the temperature effect on the structure.At present,the research on temperature effect is mainly focused on the accurate distribution of temperature field in the bridge,the accurate calculation of structural response and the elimination of temperature effect in the state evaluation,which lacks the research on mining the physical characteristics of the structure based on the temperature response law.In this paper,based on the engineering background of the martyr River Bridge of Jiangsu Coastal Expressway(Yancheng Nantong section),the structural state characteristics are revealed based on the temperature effect.The principle and law of the temperature delay effect of the concrete box girder bridge are mainly studied.Furthermore,the ideal and universal temperature time delay elimination method is proposed,and the damage is numerically modeled based on the temperature effect data Finally,an evaluation system of operation state of concrete box girder bridge based on temperature delay effect is proposed.The main work and achievements of this paper are as follows:(1)Based on the measured temperature and response data,the law and principle of temperature delay effect of concrete box girder bridge are studied.According to the characteristics of the measured temperature time-delay curve image,it classifies it and explores the law of the temperature time-delay image.In this paper,the principle of time lag is studied from two aspects of space and time.Time action and space action are the two most important factors that affect the time lag effect of concrete box girder bridge.Time action is the essential reason for the time lag effect.Time action is reflected in the rate of temperature time curve change.Space action can not independently lead to the time lag phenomenon.The results show that there is no temperature gradient distribution,and the temperature response is linear.At the same time,the spatial effect of the structure can not be ignored.The influence of transverse temperature gradient on time-delay curve is greater than that of vertical temperature gradient.(2)Two time delay elimination methods based on temperature effect data are proposed.According to the law that the slope differenceΔK,intercept differenceΔB and the first derivative of temperature time history function have normal distribution((dT)/(dt))~2,the curve pinch method is proposed.The curve pinching method can effectively eliminate the time delay and improve the correlation between temperature and strain.In addition,image recognition and python programming language technology are used to construct similarity index based on time-delay image features,and determine the translation time of temperature-induced strain curve,so that the relationship between temperature and temperature-induced strain is more linear.Furthermore,based on a large number of measured data,the linear relationship between the strain and temperature of the structure after eliminating the time-delay phenomenon is verified,which conforms to the mechanical principle.The stable temperature response relationship shows the reliability of the time delay elimination method and provides a basis for further state evaluation based on temperature effect.This paper compares all kinds of time delay elimination and summarizes its applicability.(3)The damage assessment of the bridge is based on the temperature effect.Through numerical simulation,the time delay law of temperature action of damaged structure is explored.The results show that roof is more sensitive to damage than floor.The influence of local damage on the time-delay curve of the section near the damage is more significant,but the difference will decrease with the increase of the longitudinal bridge distance.When the damage degree is different,the time-delay curve image has certain difference.The time-delay damage index is constructed.The relative and absolute values of strain Euclidean distance and the damage degree indexγcan reflect the damage degree of the structure to some extent.The time-delay elimination method of Python image recognition is used to build the operation state evaluation system of concrete box girder bridge based on the temperature time-delay effect.The results show that the relationship between temperature and strain is linear at the far end of the damage,but not at the near end.The slope k of temperature strain line after damage is larger than that without damage.The real-time evaluation system is mainly composed of four parts:data collection and processing,structural damage determination,local damage location and damage degree evaluation.The validity of the method is verified by an example.