Damage identification of supporting structures with a moving sensory system

© 2017 Elsevier Ltd An innovative approach to identify local anomalies in a structural beam bridge with an instrumented vehicle moving as a sensory system across the bridge. Accelerations at both the axle and vehicle body are measured from which vehicle-bridge interaction force on the structure is determined. Local anomalies of the structure are estimated from this interaction force with the Newton's iterative method basing on the homotopy continuation method. Numerical results with the vehicle moving over simply supported or continuous beams show that the acceleration responses from the vehicle or the bridge structure are less sensitive to the local damages than the interaction force between the wheel and the structure. Effects of different movement patterns and moving speed of the vehicle are investigated, and the effect of measurement noise on the identified results is discussed. A heavier or slower vehicle has been shown to be less sensitive to measurement noise giving more accurate results

Comparison of methods for solving vibration response of Plate Girder Bridge

2004-2005 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Temperature-based stiffness identification of que-Ti’s in a historic Tibetan timber building

© 2017 Taylor & Francis Group, London. Que-Ti, like the corbel brackets connecting beam and column in modern structures, is an important component in typical Tibetan historic timber buildings. It transfers shear, compression and bending moment by slippage and deformation of components as well as limited joint rotation. A rigorous analytical model of Que-Ti is needed for predicting the behaviour of a timber structure under load. However, few researches have been done with this model, particularly on the parameters describing the performances of this joint under load. The equivalent stiffness of a Que-Ti connection in its operating state is determined by using ambient temperature variations as a forcing function in the complete input(temperature)-output(local mechanical strains) relationship when it is incorporated in a finite element model of the structure. The identification is done iteratively via correlating the calculated strain responses with measured data

A layered beam element for modeling de-bonding of steel bars in concrete and its detection using static measurements

Copyright © 2018 John Wiley & Sons, Ltd. In the formulation of finite elements, the variation of elemental internal forces and displacements are interpolated. The force interpolation functions are known to reproduce the variations of forces better than the interpolation functions on the displacements. Layered section beam model is not as complicated as the fiber model, and yet, it is much more accurate than ordinary beam model. The force-based finite element is revisited in this paper with its application in the numerical studies of a damage detection strategy for a reinforced concrete beam under static load. Two kinds of damages are studied including the cracking or other local damage of the concrete and the bonding between the concrete and the steel bar. Both kinds of damages in an element can be detected separately or in combinations with the proposed strategy. The force-based layered finite element is shown to be a practical, accurate, and efficient representation of the bonding damage of steel bars in concrete structures

Identification of Railway Ballasted Track Systems from Dynamic Responses of In-Service Trains

© 2018 American Society of Civil Engineers. Railway track is one of the most important parts of the railway system, and monitoring its condition is essential to ensure the safety of trains and reduce maintenance cost. An adaptive regularization approach is adopted in this paper to identify the parameters of a railway ballasted track system (substructure) from dynamic measurements on in-service vehicles. The vehicle-track interaction system is modeled as a discrete spring-mass model on a Winkler elastic foundation. Damage is defined as the stiffness reduction of the track due to foundation settlement, loosening in the rail fastener, and lack of compaction of the ballast. Accelerometers are installed on the underframe of the train to capture the dynamic responses from which the interaction forces between the vehicle and the railway track are determined. The damage of the railway track can be detected via changes in the interaction force. Numerical results show that the proposed approach can identify all stiffness parameters successfully at a low moving speed and at a high sampling rate when measurement noise is involved

Crack identification of functionally graded beams using continuous wavelet transform

© 2018 Elsevier Ltd This paper proposes a new damage index for the crack identification of beams made of functionally graded materials (FGMs) by using the wavelet analysis. The damage index is defined based on the position of the wavelet coefficient modulus maxima in the scale space. The crack is assumed to be an open edge crack and is modeled by a massless rotational spring. It is assumed that the material properties follow exponential distributions along the beam thickness direction. The Timoshenko beam theory is employed to derive the governing equations which are solved analytically to obtain the frequency and mode shape of cracked FGM beams. Then, we apply the continuous wavelet transform (CWT) to the mode shapes of the cracked FGM beams. The locations of the cracks are determined from the sudden changes in the spatial variation of the damage index. An intensity factor, which relates to the size of the crack and the coefficient of the wavelet transform, is employed to estimate the crack depth. The effects of the crack size, the crack location and the Young's modulus ratio on the crack depth detection are investigated

Green tea polyphenols ameliorate non-alcoholic fatty liver disease through upregulating AMPK activation in high fat fed Zucker fatty rats

© The Author(s) 2017. Published by Baishideng Publishing Group Inc. All rights reserved. To investigate protective effects and molecular mechanisms of green tea polyphenols (GTP) on nonalcoholic fatty liver disease (NAFLD) in Zucker fatty (ZF) rats. METHODS Male ZF rats were fed a high-fat diet (HFD) for 2 wk then treated with GTP (200 mg/kg) or saline (5 mL/kg) for 8 wk, with Zucker lean rat as their control. At the end of experiment, serum and liver tissue were collected for measurement of metabolic parameters, alanine aminotransferase (ALT) and aspartate aminotransferase (AST), inflammatory cytokines and hepatic triglyceride and liver histology. Immunoblotting was used to detect phosphorylation of AMP-activated protein kinase (AMPK) acetyl-CoA carboxylase (ACC), and sterol regulatory element-binding protein 1c (SREBP1c). RESULTS Genetically obese ZF rats on a HFD presented with metabolic features of hepatic pathological changes comparable to human with NAFLD. GTP intervention decreased weight gain (10.1%, P = 0.052) and significantly lowered visceral fat (31.0%, P < 0.01). Compared with ZF-controls, GTP treatment significantly reduced fasting serum insulin, glucose and lipids levels. Reduction in serum ALT and AST levels (both P < 0.01) were observed in GTP-treated ZF rats. GTP treatment also attenuated the elevated TNFα and IL-6 in the circulation. The increased hepatic TG accumulation and cytoplasmic lipid droplet were attenuated by GTP treatment, associated with significantly increased expression of AMPK-Thr172 (P < 0.05) and phosphorylated ACC and SREBP1c (both P < 0.05), indicating diminished hepatic lipogenesis and triglycerides out flux from liver in GTP treated rats. CONCLUSION The protective effects of GTP against HFD-induced NAFLD in genetically obese ZF rats are positively correlated to reduction in hepatic lipogenesis through upregulating the AMPK pathway

Bridge Operational Modal Identification Using Sparse Blind Source Separation

© 2020, Springer Nature Singapore Pte Ltd. The bridge infrastructures are subjected to continuous degradation due to ageing, environmental and excess loading. Monitoring of these structures is a key part of any maintenance strategy as it can give early warning if a bridge is becoming unsafe. Most of the current approaches are using direct measurements that the sensors are installed at different specific locations on the bridge to capture the dynamic characteristics of the structure under random input, such as wind loads, traffic loads and ground motions. Based on the assumption on the white noise characteristics of the random input, structural properties of the bridge could be extracted from the vibration responses only. However, the bridge is subjected to non-stationary traffic loads, and the frequency characteristics of vibrations are varied. Especially for short-span bridges, the non-stationary traffic excitation is significant and most of the existing output-only structural identification methods could not be used to assess the bridge condition. This study proposes a blind source separation (BSS) method using short time Fourier transform (STFT) for the analysis of non-stationary measurements in time frequency (TF) domain. The proposed method is capable of source component separation from response measurement for underdetermined problems when the number of independent measurements (sensors) is less than that of source component. The proposed method is applied to a cable-stayed bridge in the field for the operational modal identification under different traffic conditions

Moving loads identification on slab-on-girder bridge by use of state variables

2005-2006 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe