Structural health monitoring (SHM) of wind turbines has been applied in the wind energy industry to obtain their real-time vibration parameters and to ensure their optimum performance. For SHM, the accuracy of its results and the efficiency of its measurement methodology and data processing algorithm are the two major concerns. Selection of proper measurement parameters could improve such accuracy and efficiency. The Stochastic Subspace Identification (SSI) is a widely used data processing algorithm for SHM. This research discussed the accuracy and efficiency of SHM using SSI method to identify vibration parameters of on-line wind turbine towers. Proper measurement parameters, such as optimum measurement duration, are recommended.
KEYWORDS: Bridges, Iron, System identification, Sensor networks, Data analysis, Sensors, Finite element methods, Optical inspection, Wind measurement, Data processing, Manufacturing
The U.S. transportation infrastructure has many wrought iron truss bridges that are more than a century old and still remain in use. Understanding the structural properties and identifying the health conditions of these historical bridges are essential to deciding the maintenance or rebuild plan of the bridges. This research involved an on-site full-scale system identification test case study on the historical Old Alton Bridge (a wrought iron truss bridge built in 1884 in Denton, Texas) using a wireless sensor network. The study results demonstrate a practical and convenient experimental system identification method for historical bridge structures. The method includes the basic steps of the in-situ experiment and in-house data analysis. Various excitation methods are studied for field testing, including ambient vibration by wind load, forced vibration by human jumping load, and forced vibration by human pulling load. Structural responses of the bridge under these different excitation approaches were analyzed and compared with numerical analysis results.
Due to the urbanization in China, some building construction sites are planned on areas above abandoned underground mines, which pose a concern for the stability of these sites and a critical need for the use of reliable site investigations. The array-based surface wave method has the potential for conducting large-scale field surveys at areas above underground mines. However, the dense deployment of conventional geophones requires heavy digital cables. On the other hand, the bulky and expensive standard stand-alone seismometers limit the number of stations for the array-based surface wave measurements. Therefore, this study developed a low-cost cableless geophone system for the array-based surface wave survey. A field case study using this novel cableless geophone system was conducted at an abandoned underground mine site in China to validate its functionality.
Bolted connections are widely employed in facility structures, such as light masts, transmission poles, and wind turbine towers. The complex connection behavior plays a significant role in the overall dynamic characteristics of a structure. A finite element (FE) modeling study of a bolt-connected square tubular steel beam is presented in this paper. Modal testing was performed in a controlled laboratory condition to validate the FE model, developed for the bolted beam. Two laser Doppler vibrometers were used simultaneously to measure structural vibration. A simplified joint model was proposed to further save computation time for structures with bolted connections. This study is an on-going effort to marshal knowledge associated with detecting damage on facility structures with bolted connections.
Performing full-scale structural testing is an important methodology for researchers and engineers in civil engineering
industry. To conduct a full-scale structural testing, sensors are used for data acquisitions. Based upon their data
communication strategies, sensors used for civil-structure testing could be divided into traditional wired sensors and
wireless sensors. Compared to wired sensors, sensors that employ the wireless communication technology can
potentially reduce implementation time and expenses, thus facilitating deployment of a dense network of sensors for
structural health monitoring (SHM). This paper experimentally evaluates the advantages and disadvantages of wireless
sensors versus wired sensors. Accelerometers are selected for case studies since they are one of the most widely used
sensors in civil structure testing, primarily in system identification and SHM. Three different accelerometers studied in
this paper include the piezoelectric wired accelerometer, the force balance tri-axial accelerometers, and the wireless
smart sensing network sensor board based on the MEMS technology. These sensors were compared during a series of
tests, which include free vibration testing of a laboratory scale steel frame, field ambient vibration testing of a building
connection bridge, and full scale field monitoring of a 65-m high wind turbine tower vibration. The complete testing
procedure (instruments deployment, data acquisition, and data processing) shows the advantages and disadvantages of different types of sensors. It is expected that the results of this study can help structural researchers and engineers get familiar with the wired and wireless sensing technologies and select the most effective testing instruments.
Spun-cast concrete poles have been increasingly used in power line support in U.S. during the past decade. Dynamic
behaviors of these pole structures are critical design considerations due to the wind and conductor effects. However, free
vibration of pole structures has rarely been studied and existing design guidelines do not provide clear information
associated with pole natural frequencies. To build-up knowledge in pole vibration, analyses of concrete poles of various
sizes and classes were performed numerically. The finite element models were verified with experimental modal data
from several poles. Based on the study, empirical relations between geometric parameters and pole natural frequencies
were developed, which are very basic information for health monitoring of power lines.
A new skewed two span continuous steel girder bridge was constructed and opened to traffic recently. This bridge uses
high performance steel (HPS 100W) in the flanges of the negative moment region over the intermediate pier. For
construction verification and long-term structural health monitoring purposes, a finite element (FE) model was
developed for the bridge superstructure. Various field tests were performed to verify the model: 1) LiDAR scan, 2) static
truck load tests, and 3) Laser doppler vibrometer testing. LiDAR scanner was introduced to gain geometrical information
of the bridge in the real world. It was also used to measure girder deflections during load tests. The fundamental
frequency of the bridge vibration was obtained by using a Laser doppler vibrometer. Both dynamic and static
measurements are then used to update the FE model. This valid bridge superstructure FE model was provided to local
DOT bridge engineers with the completion of this study.
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