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

The bridge engineering as the key to road plays an important role in transportation system. Whether the bridge can work properly or not directly affects the use of road. Because of the limitation of construction and the overloaded vehicles, all bridges have different degree damage. It plays an important role for the normal use of roads whether we can timely find the position and degree of the bridge damage.On the based of the previous methods of damage detection, this paper put forward that difference of deflection influence line is taken as the signature for damage detection. Using this method can detection the damage only use one displacement sensor. Firstly, 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 field 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. The difference of deflection reaches the maximum value when the move load located at the damage field, and the maximum value is related to the damage degree. It shows that this method achieves good recognition effects for single damage position and degree.Because the difference of deflection and the position of the move load has a cubic relationship when the move load located at the damage field 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 the Curvature of deflection influence line. This method not only can detect the single damaged, but also detect multiple damaged.The above methods can detect the damage on the premise of knowing the deflection influence line of undamaged beam. But in the practical application of damage detection, the deflection influence line can't be measured. Because the practical damage position and degree of the bridge are not symmetric, a method using the Curvature of deflection influence line under symmetrically loading is advanced. Using the three above mentioned methods, a simply support beam was numerical simulated and tested. The result of numerical simulation and testing shows that the three above mentioned methods have good effect for damage detection of simply beam.