Study On Damage Identification Of Urban Simply Supported Beam Bridge Based On The Deflection Influence Line

The healthy status of urban bridges as one of the vital parts of urban traffic structures is the premise of traffic and transportation system to operate normally.At present,with the growth of the bridge service time,some bridges appear damage for some reasons,such as environmental erosion,material aging,long term effect of load,fatigue effect and so on.This has affected the bridge structure normal use enormously.If there is any serious damage in bridge,people's lives and properties,social stability will be affected.Therefore,it is of great theoretical significance and engineering value to study the damage identification for urban bridges.Based on the current research status of structural damage identification,especially the damage identification based on the deflection influence line,this paper analyzes the existing problems in the current damage identification,and in view of the simply supported girder bridge,put forward that different of deflection influence line is taken as the signature for damage detection.The main works and results as follow:(1)This paper derived analytic formula of the difference of deflection influence line for simply support beam by using principle of virtual work.From the analytic formula we can find that the difference of deflection and the position of the move load have a cubic relationship when the move load located at the damage filed and the difference of deflection and the position of the move load has a linear relationship when the load located at the undamaged field.The difference of deflection reaches the maximum value when the move load located at the damage field,put forward a method of damage detection by using difference of deflection influence line.(2)According to the difference of deflection and the position of the move load has a cubic relationship when the move load located at the damaged filed and the difference of deflection and the position of the move load has a linear relationship when the move load located at the undamaged field,this paper put forward a method of damage detection by using second derivatives of difference of deflection influence line.(3)The results of time history analysis show that influence line of deflection difference presents a larger undulatory property and free vibration when the load moving speed is larger,damage can be identified.The influence line of deflection difference presents linear variation when the load moving speed less than 5Km/h,damage can be identified?(4)Numerical simulation and experimental results show that using the difference of deflection influence line has better recognition effect for single damage of simply supported beam,damage detection incompletely for multiple site damage.It has better recognition effect for single damage and multiple site damage of simply supported beam by using second derivatives of difference of deflection influence line.