Applied Mechanics and Materials Vols. 578-579

Abstract: A type of frictional sensor which can be applied to measure the frictional force between soil and underground structure is invented. The key part of the senor is an elastic beam which has very small axial deformation under axial force but has much larger transverse deformation under same transverse forces, and the frictional force is calculated from the beam deflection. The advantage of the sensor is that it can be easily produced and it has very clear mechanical response under frictional force. Numerical analysis and experiments show that the frictional sensor is stable with high resolution. Moreover, it is almost not influenced by soil pressure normal to the soil-structure interface.

Abstract: Level test method is widely used to detect concrete crack depth. Accuracy of the methods is determined by measurement of concrete velocity and transit time. Some proposals are presented to improve accuracy of the test in terms of on-site testing methods as well as crack direction besides judgment of initial wave and role of steel reinforcement nearby. It proves well by way of project example.

Abstract: In this paper, we introduce a set of techniques for time series analysis based on principal component analysis (PCA). Firstly, the autoregressive (AR) model is established using acceleration response data, and the root mean squared error (RMSE) of AR model is calculated based on PCA. Then a new damage sensitive feature (DSF) based on the AR coefficients is presented. To test the efficacy of the damage detection and localization methodologies, the algorithm has been tested on the analytical and experimental results of a three-story frame structure model of the Los Alamos National Laboratory. The result of the damage detection indicates that the algorithm is able to identify and localize minor to severe damage as defined for the structure. It shows that the suggested method can lead to less amount of computing time, high suitability and identification accuracy.

Abstract: Structural crack damage will degrade its carrying capacity, and affect the security of the structure. Thus early detection of crack damage is a guarantee of the structure safety. Cracks can change the vibration characteristics of the structure, therefore we proposed a method of identifying the crack damage based on the vibration modal. Take both ends fixed beam as an example, through establish the finite element models of crack-free beam and the crack beam with different location and different depth, we calculate the displacement modal parameters of beam before and after the damage, analyze the variation law of displacement modal horizontal component of change and displacement modal Axial displacement difference rate of change varies with crack depth and location, results show that the variation of displacement modal horizontal component and the change rate of displacement modal Axial displacement difference along crack direction are sensitive to cracks location and depth, these can be used as a basis for identification of beam’s crack damage.

Abstract: In order to identify structural damage locations and extent, a method based on ridge estimation and modal strain energy is presented in this paper. First, structural modal strain energy is given and a modal strain energy sensitivity damage equation is obtained. Then, considering the TikhonovTT regularization theoryTT, a ridge estimation method is proposed to solve the damage equation and ridge parameter of the method is optimized. Simulation results demonstrate that the proposed damage detection method based on ridge estimation and modal strain energy can identify structural damage locations and extent with good accuracy.

Abstract: Starting with damage identification index method on the basis of the curvature mode, the first-order curvature mode ratio is proposed, and then it is made a numerical simulation analysis for a single span simple beam bridge with ANSYS. The identification of structure damage degree under the damage on the single position is studied. The fitted polynomial based on the derivation of the first-order curvature mode ratio can estimate the damage degree; it has a good reference value for the damage detection of structures in practical engineering.

Abstract: The FBG sensors of measuring stress and strain on the surface of concrete are mainly based on substrate encapsulation in engineering. Since the substrate encapsulation FBG sensor has a multilayer structure, there is certain consumption when the stress is transferred from the surface of concrete to optical fiber, which leads to difference between measured value and actual value. This paper analyzes the influencing factors of strain transfer rate by the method of theoretical calculation and finite element analysis. The formula of strain transfer is thereby obtained.

Abstract: Aiming at the defect happened in existing bridges, a side-excitation way is adopted. Here, the mutual interfere phenomenon between transverse-and longitudinal-wave will appear, which certainly will be influence the reflection the information from fault position. Meanwhile, considering the responses of displacement are too lower, the velocities are used as test data so as to reduce the influence of noise. In the paper, the eigencurves with significant distinctions is suggested, the feasibility of the proposed method is demonstrated by a concrete item.

Abstract: Aiming at the defect happened in existing bridges, a side-excitation way is adopted. Here, the mutual interfere phenomenon between P-wave and S-wave will appear, which certainly will be influence the reflection of the information from fault position. In the paper, considering that the multi-resolution and local features within time-frequency of signal can be appeared by wavelet transform, a defect diagnosing method which utilize eigencurves of acceleration responses is presented, a group typical eigencurves which fit for reinforced concrete piles are given.

Abstract: Displacement is a good descriptor of the structural behavior and safety status. However, measuring displacement of structures under dynamic excitations is still a challenging task. Videogrammetry shows great potential for dynamic displacement measurement, benefiting from its non-contact and long-distance characteristics. Nevertheless, its all-weather performance has to be fully evaluated before gaining wide applications. This study therefore carried out an investigation into the environmental effects of the all-weather videogrammetry for structural dynamic displacement monitoring. First, long-term outdoor dynamic displacement monitoring tests were carried out. Virtual structural displacement was generated by a motion simulation device and monitored by a commercialized industrial digital camera. The adaptive filter was then employed to filter out noises, which had the primary input of the major displacement component and the reference input of the minor displacement component. The results show that the adaptive filter is well capable of filtering out noises and the measurement accuracy of videogrammetry is significantly enhanced.