Vibration Analysis Of The Structure With Multiple Cracks

For reinforced concrete structures, the existence of the partial discontinuous cracks are inevitable, with the role of alternating stress and the time of growth, this crack will continue the expansion until the structure of fracture. Currently, the analysis of the most scholars on the dynamic characteristics of cracked structure is limited to within the linear range, so the model and conclusions have different degrees of limitations. With dynamic loads, collision is generated between in the two crack surfaces, which makes that nonlinear characteristics is exist in dynamic characteristics, and that is the theoretical foundation of the bridge damage detection, so the geometrically nonlinear dynamic characteristics analysis of the structure is very reasonable and necessary. The paper uses a standard cantilever beam as an example, proposes a new method of calculating the structural natural frequency, and thus does geometric nonlinear analysis of structure with multiple cracks. Based on simulating the crack surface into three-dimensional non-thickness Goodman unit, the article uses transient dynamic analysis in the ANSYS finite element analysis to calculate inversely natural frequency of the structure and defines the concept of resonance domain and the resonance amplitude to reflect the effect on structure dynamic characteristics caused by craek surface collision."The paper investigates the crack structure dynamic characteristics and variation under the action of the harmonic, identifies the master cracks, and provides an effective way for bridge inspection.(1) The paper studied the geometric nonlinear dynamic characteristics of a crack beam using two model which are reduction modulus model and the direct establishment cracks model respectively. The article discusses the first order natural frequency variation of the structure with different crack location and depth, and analyzes with the experimental data, and thus obtains that the two methods have some limitations.(2) The paper studied the geometric nonlinear dynamic characteristics of a crack beam using contact surface simulation crack model. Studies show that there is a good agree with the experimental data, and the proposed method in the paper is reasonable(3) Geometrically nonlinear analysis of Single, two and three cracks beam were done respectively using the proposed method, and the results reflect the effect on structure natural frequency caused by the different crack location and depth. Changes of the resonance domain quantify the impact on the dynamic characteristics caused by crack surface collisions.(4) By using transient dynamic analysis, the time displacement curves of multi-crack structure are given, and show that:There are key parts in the structure; in a multi-crack case there is the master crack, and that what continues to crack is the first master crack.