Research On Deformation Monitoring And Moving Load Identification Of Box Girder Bridges Based On Distributed Strain

With the box girder bridges being widely used on the highways and railways,engineers who work in engineering field pay more and more attention to security situation of these bridges.It is necessary to monitor health status of the bridges accurately and manage operating conditions of the bridges scientifically because of that they are related to the safety of the people’s life and property,the healthy development of the social and economic directly.Deformation of bridges is an important index for monitoring the health status and there are many methods to measure it,but methods adapt to the bad environment in which bridges are across the valleys and rivers are absent.Weights of vehicles must be strictly controlled in the operation management of bridges because that overweight overrun vehicles not only damage structures of bridges but also form a threat to people’s personal and property security.This paper focuses on deformation monitoring of box girder bridges and weight identification of vehicles passing bridges.The main contents of the paper are following:Firstly,a deformation monitoring method based on improved conjugated beam method was put forward for box girder.In the process of box girder deformation monitoring,effecting of the shearing action and shear lag of the box girder should be both considered.So a formula by which the deformations of box girders can be calculate with distributed strain is deduced using Timoshenko beam shear theory.Then the formula would be correct by the shear lag.Numerical example indicates that formula deduced is applicable to deformation measurement of box girders.Secondly,a method on moving load identification of bridge is put forward for weighing the weights of vehicles passing the bridges,which is based on the theory of influence line.When it works,strain-times curves would be draw with the date from the distributed strain sensors on the bridges.Then the speeds of vehicles can be identified by combining strain-times curves of two sensors.Integral areas of strain-times curves are calculated,which are used to identify weights Of vehicles.Numerical example indicates that the weights of vehicles can be identified accurately when the speeds are known and when speeds are unknown,it can also be effective.Thirdly,model test of a box girder was done to validate the formula derived from the theory.The test results showed that deformation monitoring method based on the distributed strain could measure the deformation of box girder accurately.That the ratio of shear displacement in the monitoring results was consistent with the results from theoretical derivation and numerical example analysis was found by comparing bending deflection and shear deflection of the monitoring results.The test results also showed that vehicle weighing method based on the theory cf the influence line weighed weight of vehicles passing the bridges accurately.Weighing method proposed in this paper worked without that the speeds of vehicles were unknown Relative error of test result on vehicle weighing can be controlled within 5%.