With the rapid growth of urban population, many footbridges have been used for improving the efficiency of transport. However, the construction process of the traditional footbridge is complex, especially for the urban concentrated area, which may involve massive demolition and renovation of the underground pipeline. Usually, it will involve the high cost and long construction period. Herein, the piers and foundations are essential for the construction of the footbridge. Moreover, the conventional pier requires extensive on-site implementations (e.g. casting-on-site, traffic restriction, demolition of underground infrastructure, etc.) Therefore, this study proposes to a novel modularized design of the pier for the aluminum alloy footbridge to avoid the demolition of the underground facility. For rapid installation of each member, each member was designed as the modular: RC shear walls as main bearing element, steel diagonal bracing and capping beams. With the connection of whole grouted sleeves and built-in bolt, all the members can be easily assembled. And also, all the components can be manufactured in the factory and delivered to the construction field conveniently because of the proposed modular design. Though checking computing of each member of modularized design was conducted analytically, the mechanical and seismic performance were evaluated and analyzed by the scaled experiment. The pseudo-static test was carried out. The seismic performance indicators such as the hysteresis curve, skeleton curve, energy dissipation curve and stiffness degradation curve were obtained; additionally, the damage mode was observed. The experimental results show that the novel modularized design of the pier for the aluminum alloy footbridge has good seismic performance. The proposed design can provide the promising option for the construction of footbridge especially in the urban concentrated area.
For the purpose of lightweight and long span, the structural solution using cable is proposed, especially for the bridges and roofs design. Herein, one of the key members is the anchor cable, which plays decisive role in the cable structure. But the prestressed anchor cable is vulnerable to corrosion and fatigue damage due to various environmental activities. Failure due to accumulative defects or broken wires is inevitable, which seriously effects on the status of the cable-structure system. Therefore, it is essential to propose an efficient method which can realize the real-time evaluation and monitoring of the health status of the prestressed anchor cable. In this paper, the acoustic emission (AE) technique was proposed to quantify the damage progress in the prestressed anchor cable. In order to verify the proposed AE-based method, three prestressed anchor cables with different prescribed defects were tested to failure under the fatigue tensile. Different depths of scratches were preset at different positions of the steel wires in the cables. Aiming to the bundle of the anchor cable, the conventional 1-D AE localization and zonal localization method were combined to localize the micro-crack and rupture of cable. The relationship between AE signal signature and damage was established. The acoustic emission signatures were identified and characterized: (i) friction between cables; (ii) plastic deformation of cable; (iii) rupture. With the localization of AE and typical AE signature, the failure progress can be described. The massive AE signals of plastic deformation can provide the precursor of the cable rupture. AE shows good potential for predicting the healthy status of the prestressed anchor cable.
With the development of prefabricated building (PB), the connection quality problems among the prefabricated components may cause negative effect on the safety of the entire PB, and severe defects in the connection may lead to catastrophic accidents. Herein, the half-grouted sleeve connection is one of the most commonly used connection in PB While, the grouting process has to be completed on site; so, internal defects are unavoidable. Currently, there are few effective and easy-used inspection methods which can be used in field and realize the real-time monitoring. Therefore, this study proposes to use the acoustic emission (AE) method to monitor the damage progress of sleeves with different defect rates under monotonic tensile tension. Different defect levels were artificially introduced in the sample. Two different failure modes were identified by AE, and the AE signatures are different. The proposed method provides a feasible nondestructive method for prediction of damage in half-grouted sleeve in the early stage.
Pipelines are an important type of transportation and are often buried underground, making regular maintenance and inspection challenging, especially for pipelines without network maps. Ultrasonic testing (UT) is a commonly used non-destructive method to assess surface or subsurface defects in pipeline. In this study, we proposed to correlate the UT signals with the geometric and spatial features to reconstruct the network of pipeline. The feasibility of the proposed method has been discussed numerically. Two key geometric features (pipe length and connections) were investigated to explore the correlation between ultrasonic guided wave features and different length and node conditions. This study used principal component analysis to select the characteristics, and integrated the backpropagation neural networks (BPNN) and radial basis function neural networks (RBFNN) to process the signals to establish the relationship between UT signal and spatial features. The results of the study show that BPNN performs better in pipeline length and connection type recognition, with an average coefficient of determination of 0.96 for recognizing the length and an average correct rate of 91.9% for recognizing the connection type. A comprehensive comparison of the two intelligent algorithms reveals that the BPNN performs well in improving the prediction of pipeline complexity, which significantly enhances the detection of geometric and spatial features of pipelines.
The conventional method for one-dimensional acoustic emission (AE) source localization relies on two sensors to calculate the time-of-flight (TOF) and subsequently determine the source location given the wave speed. However, this method encounters inaccuracies when applied to dispersive mediums. To address this challenge, we suggest a novel method for single-sensor source localization. This method leverages multi-frequency Micro-Electro-Mechanical Systems (MEMS) equipped with sixteen resonators, each tuned to a specific frequency within the 100 kHz to 700 kHz range. By employing the wavelet transformation technique, we can determine the arrival times of these sixteen unique frequencies. By incorporating these arrival times with the dispersion curve, obtained from numerical simulation, it becomes possible to pinpoint the acoustic emission source location using just one AE sensor. Initial experimental validation conducted on a steel plate demonstrated the method's validity, achieving approximately 90% accuracy in source localization. This technique not only streamlines the process by eliminating the need for multiple sensors but also provides reliable source localization results in dispersive mediums.
The Total Hip Replacement (THR) is a procedure involved removing the damaged bone and cartilage and replacing with prosthetic components, which is one of the most common and successful surgeries. However, clinic examination and medical imaging methods are the main and only efforts to evaluate the status of THR, which is time-consuming and costly. Therefore, to develop a rapid and real-time evaluation of THR is meaningful and promising. Acoustic Emission (AE) is a non-invasive and Non-Destructive Evaluation (NDE) method, which is also accurate, reliable and real-time. The use of AE to assess damage after THR can be feasible. Firstly, using silicone material to simulate in the hip in the axial and radial force, ultrasonic wave propagation characteristics in silicone to do exploratory tests. Secondly, this study proposed to introduce the AE to evaluate the status of prosthetic components. The feasibility of adapting AE has been discussed based on numerical model. As the first step, the behavior of elastic wave propagation is the main concern. A model of the bio-layer between the in-vitro sensor and the hip was built through COMSOL Multiphysics. The parametric study was conducted with consideration of the influence of frequencies of elastic wave, human action and bio-layer thickness on AE signal propagation. The results show the attenuation of the AE signal with the increase of frequency, the AE source position and the change of bio-layer thickness. The study can provide the basic understanding of elastic wave propagation due to different human action and status of the prosthetic components, which is beneficial for further design of in-vitro device in addition to the clinic examination.
Bridge pier is the key components for transferring loads between the bridge and foundation. Its status significantly impacts on the safety of the entire bridge. While the sudden external force (e.g. vehicle collision, explosion, earthquake etc.) could cause catastrophic properties loss and casualties. Therefore, many anti-collision implementations are used in the bridge pier. The rigid protections and soft buffer structures, which are the conventional anti-collision methods. The former cannot lower the damage to vehicle and passengers, and the latter is capable of withstanding the minor or moderate vehicle collision only. In order to overcome the shortcomings of the conventional anti-collision method, tensegrity as a prestressed tensioned structure is proposed to be integrated with the bridge pier as a shielding component. The integrated tensegrity can absorb impact energy of the vehicle-pier-collision through large deformation or localized damage to protect the core pier. Therefore, this paper proposed a detailed anti-collision design with integration of tensegrity for the bridge pier. Additionally, the assessments of its statics and dynamics are given. Furthermore, the anti-collision effect has been illustrated, numerically. The process of the vehicle-pier-collision in three different velocities were simulated by ANSYS/LS-DYNA; the energy absorption is analyzed. The relationship between deformation state and absorbed energy was also obtained. Therefore, the feasibility of the proposed design has been fully explained. It provides an option for the anti-collision design in the bridge pier.
Acoustic Emission (AE) source localization is an effective technique to monitor the invisible damage in structures. However, when multiple damage mechanisms coincide, a single AE hit may summate multiple AE events. Concrete structures, especially 3D geometries such as slabs, may have multiple crack initiations simultaneously, which influence the arrival time accuracy. The source localization is highly affected by the selected arrival time picking method. Most commercial data acquisition systems use a threshold-based method to extract the arrival time. Due to the occurrence of multiple cracks simultaneously and the influence of system noises, signal with low signal-to-noise ratios or the continuation of a prior event in the pre-trigger regime are more likely to have more significant errors. This paper implements the conventional threshold-based method, floating threshold-based method and Akaike’s Information Criteria (AIC) method. In addition, the wavelet transformation technique was applied to the waveform to decompose the complex multi-frequency signal into a family of single-frequency wavelets. Damage-related wavelet was selected based on the wavelet coefficients in the wavelet spectrogram. This paper compares these two methods' results using raw and decomposed signals. Efficiency of the results were verified by conducting the source localization algorithm. The source localization results illustrated that the accuracy of the damage localization is significantly improved by adapting the wavelet transformation on threshold-based since the arrival time was picked more accurate.
We demonstrate the enhancement of contact nonlinear ultrasonic testing by implementing the 1-D phononic crystal layers. Nonlinear ultrasonic testing (NLUT) can detect sub-wavelength defects in concrete using the second harmonic generation method (SHG). SHG method is based on the generation of the second harmonic signal in solids when the first harmonic wave interacts with defects. Due to the inherent heterogeneous characteristic of concrete, the typical ultrasonic frequency for NLUT in concrete is 50 - 100 kHz. Frequency higher than 100 kHz may introduce high nonlinearity due to the multiple scattering in concrete, which would mask defect-related nonlinearity to be detected by NLUT. A 1-D phononic crystal is placed between the sensor and concrete surface to enhance the signal quality to block the signal beyond 100 kHz exhibited from instrumentation and couplant. The 1-D phononic crystal structure consists of a periodical arrangement of composite layers that can tune the band gap 100 kHz-200 kHz. The binary composite system configuration using the mixture of steel and aluminum is numerically studied. The periodic array exhibiting a band gap near 100kHz-200kHz is selected for experimental validation. The sensitivity of NLUT is improved by detecting the sub-wavelength inclusion in concrete. The results demonstrated that the nonlinearity due to defects becomes more apparent by removing the instrumentation-induced nonlinearity in concrete.
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