13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- loading. Qi proposed the application of full-bore wall imaging technology to detect damage of the pile foundation in service, and achieved very good detection accuracy[13]. But the piles will produce some damage when the cores of piles are drilling. In order to weaken the flat-slab superstructure on the foundation pile test signal, Zhang et al. [14] used wavelet analysis method to eliminate the interference signal, and the applied wavelet analysis technology to detect the high-pile integrity. In summary, scientists at home and abroad have done a series of studies on the pile injury, and they have achieved a certain amount of research. However, the in-service structure damage identification of pile foundation is only in the exploratory stage, a lot of work needs to be further in-depth research if the methods would be used in engineering practice. Especially for the small initial crack damage detection of pile foundation, it need more theoretically further analysis and further explore in practice. This article established a recognition method of small injury on the pile positioning and degree. The method take full use the advantage of the natural frequency on the integrity of the damage to determine, the sensitivity of the element modal strain energy method on small injuries, the efficient local analysis capabilities of time domain wavelet analysis. Finally, the engineering application examples are used to verify the accuracy and efficiency of the damage identification method for the piles in service. 2. Basic theory 2.1. Structural vibration eigenvalue equation with fracture damage The general performance of the structure fracture damage is that the local stiffness of the structure reduced, and it has nothing to do with the quality of the structure. Therefore, according to the perturbation theory, the structural vibration injury eigenvalue equation is as follows[15]: ) 0 ) )]( ) ( [( +Δ = +Δ − +Δ i i i i M K K φ φ λ λ (1) Where, ∑ ∑ = = Δ = Δ =− n j j j n j j K K K 1 1 α （ 1 0≤ ≤ jα ） (2) i T i i i Kφ φ ω λΔ =Δ = Δ 2 (3) M K, represent the mass matrix and stiffness matrix of the structure respectively; iφ represents the th i order modal vector of the structure; iλ represents the eigenvalue of th i modal of the vibration system, 2 2 (2 ) f i i π ω λ = = ; KΔ represents Changes of structural stiffness; jα represents th j element damage factor of the structure; j K represents structural stiffness matrix of the th j element before damage; n represents the total number of elements of the structure. Expand the Eq.(1) and finish structural vibration eigenvalue equation, the Eq.(1) of the structure can be expressed as: 0 + Δ Δ + Δ = Δ + i T i i i T i i T i i i T i K K K K φ φδφ φφφδφ φ (4) Where, i i i λ λ δ / =−Δ is structure Eigenvalue change rate, it is used to determine sensitivity of the th i modal structural damage detection for the structure; therefore, it is called modal damage sensitivity factor. 2.2. Structural damage identification equation
RkJQdWJsaXNoZXIy MjM0NDE=