Structural Durability & Health Monitoring

Features for Early Detection of Defects and Assessment of Structures

2022-08-29T09:54:31+08:00

Damage detection is of great importance in mechanical and structural engineering. One of the critical problems in damage detection is determining indices sensitive to structural damage and the insensitivity to environmental variations. Current damage indices focus on dynamic structural characteristics such as natural frequencies, mode shapes, and frequency responses. This study aims to develop a technique based on energy Curvature Difference and power spectrum density to diagnose damage in the structure. The proposed technique is based on various damage indices to assess the bridge condition, such as energy curvature, tracking energy, and frequency over time using wavelet packet energy. In addition to the correlation-based index, load distribution factor, and neural axis shift. In order to further show the feasibility and validity of the proposed technique for damage identification, experimental data from abridge are used. The results show that the proposed technique is sensitive to damage. The proposed approach can effectively identify structural damage in mechanical and civil structures.

Determination of Reflected Temperature in Active Thermography Measurements for Corrosion Quantification of Reinforced Concrete Elements

2022-06-23T06:05:47+08:00

Reflected temperature (T_refl) is one of the noise parameters in thermography test. The results of the study will be used as a reference for testing reinforced concrete corrosion by thermography method. This paper sums up of the determining analysis of the measuring location of T_refl using a thermocouple during the thermography tests. Laboratory temperature distribution testing methods, value analysis and location T_refl are explained in this paper. The heat source is used as two halogen lamps of 500 watts each fitted at a distance of 30-50 cm. Noises appearing during testing of thermography are corrected with the point of measuring T_refl. The results of thermogram correction of corroded concrete surfaces using T_refl values are also displayed in this paper. The concrete surface temperature results of quantitative image processing method are compared to the experimental test results. The results showed good accuracy, which was seen from most errors <3% and the maximum error is < 5%. The end of paper, explained of application T_refl value to the corroded reinforced concrete thermogram.

Effect of Freeze-thaw Cycles on Chloride Transportation in Concrete: Prediction Model and Experiment

2022-07-11T08:04:08+08:00

In this paper, a model is developed to analyze the transportation of chloride ions into concrete damaged by freeze-thaw cycles. In this model, the damage levels vary according to concrete cover depth and freeze-thaw cycles, which are considered as two main influencing coefficients. Three types of concrete, including ordinary Portland concrete (OPC), polypropylene fiber concrete (PFC), and steel fiber concrete (SFC), were prepared and immersed in NaCl solution for 120 days after 10, 25, and 50 freeze-thaw cycles. Dynamic elastic modulus was measured to determine the damage coefficient of concrete. The results showed that the relative dynamic modulus of elasticity of concrete specimen decreases with the freeze-thaw cycle, and the chloride diffusion coefficient of concrete specimen increases with frost degradation degree. Samples containing steel and polypropylene fibers were more resistant to cyclic water freezing than the controlled concrete without fibers. A model considering the damage in response to freezing-thawing cycle and concrete depth is available to predict the variation of free chloride concentration in different depths. The calculated value agreed well with the test results. The new damage-induced diffusion model can help compensate for the lack of research on the effect of freeze-thaw cycles on chloride diffusion.

Numerical study on the mechanisms of blast-induced damage with the guiding effect of water jet slotting

2022-07-20T02:41:46+08:00

Damage is the important characterization of rock fracture. It is of great significance to study the damage evolution mechanism of rock blasting under the guiding effect of water jet slot for revealing the mechanism of controlled blasting with water jet assistance. In this paper, the rock - like material was choose as research object, and the experiment was conducted to calibrated the numerical model. Then, the numerical simulation model was established by FEM software ANSYS/LS-DYNA, and the blast-induced damage mechanism under the guiding effect of water jet slot was analyzed according to blasting theory. The result indicates that explosive energy gathers in the direction of slot under the guiding effect of water jet slot, which let rock mass in the direction of slot easier to damage, and accordingly reducing the damage of the retained rock mass. Meanwhile, the rock mass in the middle of the connection line between the two holes is more likely to be damaged under the combined effect of the stress concentration effect of explosion stress wave and the guiding effect of the water jet slot on the detonation gas, and the blasting damage zone similar to the shape of “gourd” is formed. In addition, the influence of water jet slot on the blast-induced damage is different in different stages of blasting process.

Experimental Study on the Degradation of Bonding Behavior between Reinforcing Bars and Concrete after Corrosion and Fatigue Damage

2021-11-10T23:49:41+08:00

In marine environments, the durability of reinforced concrete structures such as bridges, which suffer from the coupled effects of corrosion and fatigue damage, is significantly reduced. Fatigue loading can result in severe deterioration of the bonds between reinforcing steel bars and the surrounding concrete, particularly when reinforcing bars are corroded. Uniaxial tension testing was conducted under static loading and fatigue loading conditions to investigate the bonding characteristics between corroded reinforcing bars and concrete. An electrolyte corrosion technique was used to accelerate steel corrosion. The results show that the bond strength was reduced under fatigue loading, although the concrete did not crack. Therefore, fatigue loading has negative effects on the bond strength between corroded steel bars and concrete. The effects of corrosion cracking on bond strength become more pronounced after corrosion cracking appears along the main reinforcing bars. When the average width of cracking along main reinforcing bars exceeds 3 mm, the bonding properties deteriorate rapidly based on the effects of corrosion cracking, whereas fatigue loading exhibits no additional effects on bond strength.

Reliability Prediction and Remaining Useful Life Prediction for the Rolling Bearing Based on Optimized Neural Network

2023-04-11T14:52:47+08:00

In this paper, an optimized long short-term memory (LSTM) network is proposed for the reliability prediction and remaining useful life (RUL) prediction of the rolling bearings based on an improved whale optimized algorithm (IWOA). The multi-domain features are extracted to construct the feature dataset as the single domain features are difficult to characterize the performance degeneration of the rolling bearing. Kernel principle component analysis is given to reduce the dimensionality of the features to provide covariates for reliability assessment. A weibull distribution proportional hazards model (WPHM) is given for the reliability assessment of rolling bearing, and a beluga whale optimization (BWO) algorithm is combined with maximum likelihood estimation (MLE) for improving the estimation accuracy of the model parameters of the WPHM that provides the data basis for reliability prediction. Considering the possible gradient explosion by training of the rolling bearing lifetime data and the difficulties in selecting the key network parameters, an optimized LSTM network, namely, IWOA-LSTM network is proposed. As IWOA better jumping out the local optimization, the fitting accuracy and the prediction accuracy of the network is correspondingly improved. Experiment results show that, compared with the whale optimization algorithm-based long short-term memory (WOA-LSTM) network, not only the reliability prediction accuracy, but also the RUL prediction accuracy of the rolling bearing are improved by the proposed IWOA-LSTM network.

Design of Wireless Self-powered Intelligent Spindle Vibration Sensor System

2022-08-07T18:18:26+08:00

In recent years, the industrial field of high-end equipment is widely used, the accuracy requirements are increasing year by year, But it is easy to produce loss and failure in application, any slight wear may have a great impact on the processing quality of high-end equipment, so it is necessary to carry out state monitoring and fault diagnosis of equipment. But at present, most of mechanical equipment condition monitoring equipment has the problems of large volume, Low accuracy and low energy utilization. In this paper, a wireless self-powered intelligent spindle vibration acceleration sensor system based on piezoelectric energy acquisition is proposed. On the one hand, the energy management module is used to collect the mechanical energy in the environment, and the piezoelectric vibration energy is converted into electrical energy for the subsequent circuit, and the lithium battery is used to supplement the power supply. Meanwhile, the energy storage circuit is monitored in real time. On the other hand, the three-axis acceleration sensor module is used to collect, analyze, filter and other signal processing steps of vibration signal in the environment, and the signal is sent to the upper computer for real-time monitoring by wireless transmission. Write and debug system software through KEIL 5 platform. Based on the spindle of the machine tool, the piezoelectric vibration sensor is small in volume, high in speed monitoring, high in energy utilization, high in accuracy and easy to install.

Fault diagnosis of rotor winding inter-turn short circuit in excitation system based on interval observer

2022-07-18T02:48:22+08:00

Aiming at the fact that there are too many parameters and strong electromagnetic coupling effect in the excitation system, an interval observer based on current residual is designed to diagnose the inter-turn short circuit fault of the rotor winding. Firstly, the mechanism of the inter-turn short circuit of the rotor winding in the excitation system is modeled, and electromagnetic decoupling and system simplification are carried out through Park Transform. An interval observer is designed based on the current residual in the two-phase coordinate system, and the sensitive and stable conditions of the observer is preset. The fault diagnosis process based on the interval observer is formulated, and the observer gain matrix is convexly optimized by linear matrix inequality. The numerical simulation and experimental results show that the inter-turn short circuit fault is hardly detected directly through the current signal when there are less short circuit turns, but the fault is quickly and accurately diagnosed through the interval observer in the residuals. Compared with the traditional fault diagnosis method based on excitation current, the diagnosis speed and accuracy are greatly improved, and the probability of misdiagnosis also decreases. This method provides a theoretical basis for weak fault identification of excitation systems and is of great significance for the operation and maintenance of excitation systems.

Speed Measurement Feasibility by Eddy Current Effect in the High-speed MFL Testing

2022-12-30T14:06:07+08:00

It is known that eddy current effect has a great influence on magnetic flux leakage testing (MFL). Usually, contact-type encoder wheels are used to measure MFL testing speed to evaluate the effect and further compensate testing signals. This speed measurement method is complicated, and inevitable abrasion and occasional slippage will reduce the measurement accuracy. In order to solve this problem, based on eddy current effect due to the relative movement, a speed measurement method is proposed, which is contactless and simple. In the high-speed MFL testing, eddy current induced in the specimen will cause an obvious modification to the applied field. This modified field, which is measured by hall sensor, can be utilized to reflect the moving speed. Firstly, the measurement principle is illustrated based on Faraday's law. Then, dynamic finite element simulations are conducted to investigate the modified magnetic field distribution. Finally, laboratory experiments are performed to validate the feasibility of the proposed method. The results show that Bmx(r2) has a linear relation with moving speed, which could be used as an alternative measurement parameter.

Experimental Investigation of Performance Characteristics of PZT-5A with application to Fault Diagnosis using EMI-based Structural Health Monitoring

2022-05-23T09:17:58+08:00

In the last few decades, techniques to harvest energy and empower low voltage electronic devices have received remarkable attention. Most of the methods based on the piezoelectric effect to harvest the energy from ambient vibrations have been revolutionized. There is a lack of experiment-based investigation which includes the microstructure analysis and crystal morphology of these energy harvesting materials. Moreover, the impact of variable mechanical and thermal load conditions has rarely been studied in the previous literature to utilize the effectiveness of these materials in different practical applications such as energy harvesting, structural health monitoring (SHM), etc. In the proposed research work, scanning electron microscope (SEM) and energy dispersive x-ray (EDX) analysis are performed to examine the inside crystal morphology of PZT-5A and ensure the quality of the piezoelectric ceramic. Further, the performance of piezoelectric vibration-based energy harvester has been investigated in the second phase of current research work under the variable mechanical and thermal load conditions through a regular series of experiments. It has been found that the output voltage of piezoelectric sensors increases by increasing the vibrating load, while a decreasing trend in output voltage is noticed by increasing the applied temperature, resistance and frequency. In the third phase, a measurement setup is developed in the laboratory to further investigate the effectiveness of PZT-5A in the practical application such as electromechanical impedance (EMI) based structural health monitoring under the controlled heating environment. Therefore, the current research work not only evaluates the performance of PZT sensors under the variable operating conditions but also encourages developing a temperature compensation approach in EMI-based SHM to exclude one of the major reasons of false fault diagnosis.

Research on Breeze Vibration Law and Modal Identification Method of Conductor Considering Anti-vibration Hammer Damage

2022-10-14T09:45:53+08:00

Although the anti-vibration hammer can effectively suppress the transmission line conductor vibration, prolonged vibration will lead to anti-vibration hammer damage. This causes a change in the dynamic response law of the conductor. Based on the conductor vibration experiments to analyze the impact of the anti-vibration hammer on the vibration characteristics, as well as the modal analysis of the hammer head damage and position changes under multiple faults. Analyze the change law of the modal natural frequency under each kind of fault, and propose an anti-vibration hammer damage online monitoring technology. The results show that when the hammer is damaged, it can effectively increase the vibration acceleration value and vibration intensity of the conductor. The modal natural frequencies of each order increased. The absolute change of the modal natural frequency ranges from 0.15 Hz to 6.49 Hz. The 1st order modal natural frequency increases from 8.18 Hz to 16.62 Hz as the anti-vibration hammer slips more and more away from the contact terminal due to looseness. Therefore, it is possible to monitor the changes in the state of the anti-vibration hammer structure by monitoring the modal natural frequency of the conductor in engineering applications.

Finite Element Model Updating for Structural Health Monitoring

2020-05-21T08:22:20+08:00

This paper provides a model updating approach to detect, locate, and characterize damage in structural and mechanical systems by examining changes in measured vibration responses. Research in vibration-based damage identification has been rapidly expanding over the last few decades. The basic idea behind this technology is that modal parameters (notably frequencies, mode shapes, and modal damping) are functions of the physical properties of the structure (mass, damping, and stiffness). Therefore, changes in the physical properties will cause changes in the modal properties which could be obtained by structural health monitoring (SHM). Updating is a process fraught with numerical difficulties. These arise from inaccuracy in the model and imprecision and lack of information in the measurements, mainly taken place in joints and critical points. The motivation for the development of this technology is presented, methods are categorized according to various criteria such as the level of damage detection provided from vibration testing, natural frequency and mode shape readings are then obtained by using modal analysis techniques, which are used for updating structural parameters of the associated finite element model. The experimental studies for the laboratory tested bridge model show that the proposed model updating using ME’scope technique can provide reasonable model updating results.

Fatigue performance analysis and evaluation for the steel box girder based on structural health monitoring system

2020-05-21T08:22:21+08:00

The finite element model of Taizhou Yangtze River Bridge is established the finite element method(FEM). Based on the vehicle load survey, the Monte Carlo method is applied to simulate the traffic load flow, and the overall dynamic response analysis is carried out. Taking the bending moment of the main beam as the control index, the fatigue sensitive section of the steel box girder is studied. Based on the strain time history data of steel box girder recorded by the health monitoring system, the true stress response of steel box girder under vehicle load is extracted. Taking the cumulative fatigue damage increment as the evaluation index, the fatigue sensitive section of the steel box girders is studied and the results is compared with the results using FEM. The results indicates that the box girder section near the middle tower, especially the first section of the left and right sides of the middle tower, has the most obvious dynamic response, which is the key section for the fatigue analysis.

Mechanical Experimental Study On Tensile Bolted Connections Of Cross-laminated Timber

2020-05-21T08:22:21+08:00

In order to explore a kind of high-strength, earthquake-resistant, economical and suitable connection, 4 groups of cross-laminated timber wall-to-floor and wall-to-wall bolted connections were tested under monotonic and cyclic loading. The deformation characteristics and failure modes of the cross-laminated timber wall-to-floor and wall-to-wall bolted connections were exploited. Load-slip curves, bearing capacity, yielding point, stiffness and ductility of each group of specimens were analyzed. The test results indicate that the loading process of cross-laminated timber bolted connections under tension can be categorized as five stages, namely the elastic stage, the slip stage, the embedding stage, the yielding stage and the ultimate stage. The ultimate tensile capacity of cross-laminated timber bolted wall-to-floor connections is 2.67 times that of the wall-to-wall bolted connections. Compared with cross-laminated timber self-tapping screwed connections, the ultimate tensile capacity of the cross-laminated timber wall-to-floor bolted connections is 2.70 times that of the self-tapping screwed connections, and the ultimate tensile capacity of the cross-laminated timber wall-to-wall bolted connections is 3.83 times that of the self-tapping screwed connections. The cross-laminated timber bolted connections have larger yielding displacement and wider plastic range, and they are more energy dissipative and more ductile. Furthermore, the cost of the cross-laminated timber wall-to-floor bolted connections is 46% that of the self-tapping screwed connections, while the cost of cross-laminated wall-to-wall bolted connections is 53% that of the self-screwed connections.

Integrity analysis on existing crane runway girders with defects using constraint-based R6 criterion

2020-05-21T08:22:22+08:00

Abstract: In order to resolve the safety problem of the existing crane runway girders (CRGs) with defects, the constraint-based R6 criterion is proposed to assess their structural integrity. The existing steel CRGs with defects at the weld joint between the upper flange and web plate, are characterized to three-dimensional finite element models with a semi-ellipse surface crack. The R6 criterion has been modified by considering the constraint effect which is represented by T-stress. The analysis results illustrate that working condition of the cracked CRGs leads to high constraint level along the crack front. The crack aspect ratio (a/c) and runway eccentricity (e) have significant influence on the integrity of the cracked CRGs. The integrity assessment results using modified constraint-based R6 failure criterion enable to more effectively protect the cracked CRGs from brittle fracture failure.

Key Words: crane runway girder, finite element, crack, structural integrity, constraint-based R6 failure criterion

Research Advances on the Influence of Different Fibres on the Mechanical Properties of Recycled Concrete

2022-08-17T14:11:33+08:00

The application of recycled concrete for engineered projects not only protects the ecological environment but also improves the utilization rate of waste concrete to satisfy sustainable development requirements. However, the mechanical properties of recycled concrete are not as good as those of ordinary concrete. To improve the performance of recycled concrete and increase the popularity and application of recycled concrete in engineering fields, important research advances have been made in steel, synthetic, plant and mineral fibre materials. These advances are introduced from the perspective of improving the mechanical properties of recycled concrete. The results show that (1) steel fibres have a distinct reinforcing effect, and they improve the strength, toughness and elastic modulus of recycled concrete; (2) the addition of synthetic fibres can improve the tension, crack resistance and durability of concrete, but there is a size effect that needs to be further studied and elaborated; (3) vegetable fibre concrete is lightweight and environmentally friendly and provides high toughness and good thermal insulation, but the fibres corrode in alkaline environments; in addition, the plant fibres have a high water absorption capacity, which leads to wet expansion and dry shrinkage phenomena that need to be further studied; and (4) the cost of basalt fibre is relatively low, and a suitable basalt content can improve the mechanical properties of recycled concrete to a certain extent.