Research on Non-Contact and Non-Fixed Cable Force Measurement Based on Smartphone

Stay cable is the major load-carrying element in cable-stayed bridges. The process of monitoring cable forces would be beneficial to ensure the safety of bridges. The conventional sensor-based approaches to measure stay cable forces is complicated in operation, time-consuming and relatively expensive. In order to confront these disadvantages, a lightweight measurement method using smartphone imagery was proposed in this paper. The video data acquisition process was first standardized by using a pre-designed target. Then, a novel algorithm to extract the vibration displacement of stay cables under complex condition was developed. An automatic correction algorithm was provided to further improve the displacement results. On top of that, a smartphone-based software for determining cable forces was developed and tested on a real-life bridge. The results showed a maximum error of 1.99% compared with the cable force obtained by using a dynamic tester. The developed software is proven to be feasible in real-life projects and can achieve high accuracy in cable force determination. At the same time, the proposed method does not require a fixed camera for measurement and is not limited by personnel experience and measurement time, facilitating real-time monitoring of multiple projects, multiple cable surfaces and multiple personnel in a visual vibration environment.

Suspender Replacement Method for Long-Span Concrete-Filled Steel Tubular Arch Bridges and Cable Force Measurement Based on Frequency Method

The suspenders on the sides of an arch bridge are highly vulnerable to damage caused by traffic load and environmental corrosion. To accurately estimate the cable force of suspenders, herein, we analyse the influencing factors through a suspender tension test based on the principle of suspender vibration. The frequency of each suspender of the bridge is evaluated using the frequency method. By combining the cable force data measured directly and the measured suspender frequency, the formulas for calculating the cable forces of long and short suspenders are fitted, and a reasonable estimation method for the calculated length of short suspenders is provided. The formulas are verified through application to a CFST arch bridge. Results indicate that the proposed formula effectively considers the influence of the sleeve on the overall calculated length of the suspender. The formula calculates the suspender cable force with higher accuracy, proving its suitability for engineering use.

Cable Force Measurement Technology and Engineering Application

With the continuous development of prestressing technology, cables have been widely used in structural engineering. A special concern in practical engineering is selecting the appropriate cable force measurement technology. This paper analyzes and introduces the principle of cable force measurement technology commonly used in current engineering from three aspects, namely, strain, vibration and wave fluctuation, and force balance. Combined with an actual project, the selection and arrangement of measuring points in the cable pre-tension measurement and other issues are discussed. The engineering example shows that the cable force measurement method based on FBG sensor presented in this paper can capture the action of each construction tensioning operations in real time and accurately. Monitoring the tension of the structure in real time is convenient for engineers and technician. The process is suitable for cable force monitoring during the construction tensioning stage. Furthermore, the EM sensor has good stability and durability and is suitable for long-term cable force monitoring.

Feasibility Study for Vision-Based Cable Force Measurement Using Smartphone

An accurate cable force measurement is one of very important practical problems during construction period as well as during service period of cable stayed bridge. In the recent years, with the advances in smartphone technologies, it is possible to rapidly evaluate structural health status and postevent damage using ubiquitous smartphones. In this paper, a novel vision-based cable force measurement method using smartphone camera is proposed for the first time, which enable to estimate cable force by recognizing cable vibration using smartphone camera, and then cable model test is carried out to verify the feasibility of the proposed method. The comparison test between the smartphone application Orion-CC measuring cable force from smartphone built-in accelerometer and the proposed method is conducted on a laboratory scale cable model with different sampling rates. In the proposed method, the vibration responses of cable are obtained by monitoring displacements of a preprinted black circular target attached on the cable model using smartphone camera. The test results showed satisfactory agreements between two methods in both frequency domain and cable force value, demonstrating the feasibility of the proposed cable force measurement method and its advantages such as convenience, ease of operation, and speediness.

The Research on Cable Force Measurement Based on Degenerated Element with Frequency Method

At present, among the methods of cable force measurement, the frequency method is applied extensively for its mature theory and rapid and repeated operation procedure. Based on the theory of frequency method measurement, it generally uses the numerical method with beam element to analysis the parameters of cables under the given conditions. However, the conventional beam element is not able to simulate the bending stiffness in beams section. Therefore, it turns to degenerated beam element to simulate cables and the results agree well with the results based on beam element and formulas calculation, and it provides theoretical basis for the later cable force testing system.