| Highway traffic is the lifeline of transportation system,and bridge is the key to the highway traffic,so the health of bridge is the premise to ensure the normal operation of transportation system.However,various bridge cracks may occur owing to a range of causes,including the rapid increase of traffic volume,overweight vehicles,environmental factors,congenital deficient of design and construction.Therefore,it is of great significance and value to study crack detection of bridge and ensure the normal operation of bridge.Crack detection theory is an essential part of bridge health monitoring system,and the traditional crack detection method generally need complicated calculation or complex signal transformation,in general only long span bridge possess health monitoring system.But now China is entering the era that maintenance and repair bridge are replacing construction.Small and medium span bridge occupy a significant proportion in bridge maintained,and those bridges need to be detected,repaired and reinforced,so it has practical significance to study the crack detection method for small and medium span bridges.The generalized local information entropy of mechanical damage index is introduced into the field of bridge crack detection,and the index is extended to the application of static.In order to make the results more intuitive,the data processing method is further improved.The index has the advantages that the theory is simple,concept is clear,undamage data of structure and finite element simulation is needless.Therefore the generalized local information entropy damage index solves the problems of traditional crack detection method,that computing process is complicated,undamage data of structure is difficult to obtain,and crack detection accuracy is strongly affected by precision of finite element simulation.The numerical model of reinforced concrete beam is simulated by Midas/Civil and data of mode shape and deflection is obtained,and then generalized local information entropy is established by the data.In this paper,when establish generalized local information entropy damage index by data of mode shape,reinforced concrete simply supported beam and three span continuous beam are analyzed and the index is established by the data of first mode shape and second mode shape.When establish generalized local information entropy damage index by data of deflection,only reinforced concrete simply supported beam is analyzed and the index is established by the data of deflection.In order to facilitate the subsequent experimental verification,four sets of deflection data sampling points are analyzed.The effect of generalized local information entropy on crack localization,crack quantification and noise immunity are studied.Reinforced concrete beam with single crack and multi-point cracks are analyzed in crack location.The crack degree was only qualitatively analyzed.In the aspect of noise immunity,the single crack and multi-point cracks under two kinds of noise levels are analyzed.The numerical simulation results show that in the reinforced concrete simply supported beam and three span continuous beam the generalized local entropy based on shape can locate crack,the generalized local entropy based on first mode shape can quantify crack degree,the generalized local entropy based on second mode shape has better noise immunity ability.the generalized local entropy based on deflection can locate crack,quantify crack degree and has better noise immunity ability in reinforced concrete beam at the appropriate number of deflection data sampling points.The generalized local entropy practicability needs further experimental verification.The damage identification method based on generalized local information entropy has advantages compared with the traditional damage index.Therefore the index is expected to provide a new method for crack detection of small and medium span bridges and provides a new idea for crack detection in monitoring system of long span bridge. |
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