Sensors, which collect data for further information processing, are core component of any viable structural health monitoring system. Continuous on-line structural health monitoring can be achieved through the use of advanced sensors developed for real-time structural health monitoring applications. To overcome the problems associated with traditional piezoelectric ceramics, a polymer-based piezoelectric paint material has been developed and recently used for sensors. The piezoelectric paint is composed of tiny piezoelectric particles mixed within polymer matrix and therefore belongs to "0-3" piezoelectric composite. Because of the electro-mechanical coupling properties of piezoelectric paint, the dynamic responses of host structures can be monitored by measuring the output voltage signals from the piezoelectric paint sensor. Piezoelectric paint sensors hold a great potential for dynamic strain sensing applications due to the ease with which their mechanical properties can be adjusted, low fabrication cost, ease of implementation, and conformability to curved surface Additionally, a novel surface crack detection technique has been conceived and validated experimentally, in which cracks of the host structure is detected by observing the measured signals from an piezoelectric paint sensor with multi-electrode configuration. This paper presents this piezoelectric paint-based crack monitoring method as well as validation test data. The piezoelectric paint sensor is ideal for surface crack detection in locations with complex geometry, such as welded joints, which conventional sensors are ill equipped to do.
The development of the transportation industry has led to an increasing number of overloaded vehicles, which reduces the service life of asphalt pavements. Currently, the traditional vehicle weighing method not only involves heavy equipment but also has a low weighing efficiency. To deal with the defects in the existing vehicle weighing system, this paper developed a road-embedded piezoresistive sensor based on self-sensing nanocomposites. The sensor developed in this paper adopts an integrated casting and encapsulation technology, in which an epoxy resin/MWCNT nanocomposite is used for the functional phase, and an epoxy resin/anhydride curing system is used for the high-temperature resistant encapsulation phase. The compressive stress-resistance response characteristics of the sensor were investigated by calibration experiments with an indoor universal testing machine. In addition, the sensors were embedded in the compacted asphalt concrete to validate the applicability to the harsh environment and back-calculate the dynamic vehicle loads on the rutting slab. The results show that the response relationship between the sensor resistance signal and the load is in accordance with the GaussAmp formula. The developed sensor not only survives effectively in asphalt concrete but also enables dynamic weighing of the vehicle loads. Consequently, this study provides a new pathway to develop high-performance weigh-in-motion pavement sensors.
Fatigue-induced cracking is a common failure mode in many steel bridges reaching their original design life. These aging bridge structures have experienced increasing traffic volume and weight, deteriorating components, as well as a large number of stress cycles. This paper presents a case study of fatigue assessment of an interstate highway steel bridge through real time monitoring under traffic. The bridge is a single-span, composite steel I-girder structure with K-type cross frame diaphragms. The study also included numerical analysis using 3D global finite element models. Based on the simulated traffic flow, statistical dynamic responses such as displacements and stress of bridge girders were studied for the cause of fatigue cracks that occurred in some cross frame connections. Meanwhile, long-term field monitoring has also been conducted. Furthermore, the influence of connection plate configuration and bracing system configuration was discussed using a series of controlled finite element tests. Based on the information from field tests, simulated numerical analytical results were verified. Thus, the performance of highway bridges under truck load can be predicted in a more realistic way to estimate the fatigue performance of highway bridges.
This paper presents a special type of bracing element termed self-centering friction damping brace (SFDB) for use in seismic-resistant concentrically braced frame (CBF) systems. The SFDB is a passive energy dissipation device with its core recentering component made of stranded superelastic Nitinol wires while enhanced energy dissipation mechanism of the SFDB is achieved through friction. Compared with conventional braces for steel frame buildings, SFDB has a few desirable performance characteristics such as minimized residual drifts of the CBF system and its ability to withstand several design level earthquakes without the need for replacement. The mechanical configuration of the SFDB is first described. A comparative study of SFDB frame and buckling restrained braced (BRB) frame was carried out, which is based on nonlinear dynamic analysis of two prototype CBF buildings—a three- and a six-story steel frame. Two suites of earthquake ground motions, which represent the frequent and design basis earthquakes for Los Angeles, were considered in the nonlinear time-history analysis. The results of the nonlinear time-history and pushover analysis show that the SFDB frame can achieve a seismic response level comparable to that of the BRB frame while having significantly reduced residual drifts. The SFDB thus has a potential to establish a new type of CBF system with self-centering capability.
Cephalopods (octopus, squid and cuttlefish) are some of the most intriguing molluscs, and they represent economically important commercial marine species for fisheries. Previous studies have shown that cephalopods are sensitive to underwater particle motion, especially at low frequencies in the order of 10 Hz. The present paper deals with quantitative modeling of the statocyst system in three cephalopod species: Octopus vulgaris, Sepia officinalis and Loligo vulgaris. The octopus's macula/statolith organ was modeled as a 2nd-order dynamic oscillator using parameter values estimated from scanning electron micrograph images. The modeling results agree reasonably well with experimental data (acceleration threshold) in the three cephalopod species. Insights made from quantitative modeling and simulating the particle motion sensing mechanism of cephalopods elucidated their underwater particle motion detection capabilities. Sensitivity to emerging environmental issues, such as low frequency noise caused by near-shore wind farms and increasing levels of carbon dioxide in the ocean, and sensitivity to sounds produced by impending landslides were investigated in octopus using the model.
Existing research in the seismic response of wind turbine tubular towers subjected to long-period ground motions is lacking, especially when soil-structure interaction (SSI) is considered.This paper discusses the seismic performance of typical pitch-controlled 1.25MW wind turbine systems, with particular focus on the influences of SSI effect and ground-motion characteristics.Modal analysis and resonance analysis are carried out first, ensuring that resonance does not occur when the tower is in operation.Two long-period waves and a bedrock wave are selected from the worldwide earthquake record database, followed by detailed dynamic time history analysis.The results indicate that the maximum displacement, acceleration, stress level and internal force responses of the tower subjected to the long-period ground motions are significantly larger than the corresponding values induced by the bedrock wave.Some responses can be further amplified due to the SSI effect, and this highlights the importance of incorporating the SSI effect into seismic design of wind turbine towers, especially for those located in soft soil regions.Furthermore, neglecting the vertical seismic action could lead to unsafe design.Other important issues, including the risk of pounding, stress concentration near the door regions, spindle shear fracture, and foundation failure, are also discussed, and summarized as references or comments for design and analysis of such structures.
This paper presents an experimental study on the seismic performance of underwater bridge columns retrofitted with the combination of prestressed precast concrete panels (PPCP) and embedded fiber-reinforced polymer (FRP) reinforcements (PPCP-FRP). A newly developed retrofitting method with PPCP-FRP and the corresponding retrofitting processes were conceived based on the specific demands for underwater bridge columns. Traditional steel strands were placed outside the PPCP to connect the panels in a ring configuration and offset premature failure of the panels during an earthquake. Due to the potentially corrosive environment, the steel strands were designed to be easily replaced underwater, and the FRP reinforcement was set inside the PPCP to ensure a long-term service. A total of six 1/4-scale circular bridge column specimens were fabricated. Five specimens were strengthened either with different strengthened lengths of PPCP-FRP or with different types and reinforcement ratios of longitudinal FRP bars, and the remaining specimen was used as the control specimen. The retrofitting procedure of the PPCP-FRP method was verified as viable and efficient through experimentation. All column specimens were tested under reversed cyclic lateral loading along with a constant axial load. The load capacity, stiffness, ductility, and energy-dissipation capacity of the columns were significantly improved through strengthening. In addition, a more uniformly distributed column curvature and a reduced residual displacement were obtained for the strengthened columns, indicating enhanced repairability. A sufficient strengthening length and FRP reinforcements with a lower elastic modulus and higher ultimate strain are recommended during the retrofitting design with PPCP-FRP.
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