Probabilistic anomaly trend detection for cable-supported bridges using confidence interval estimation

To rate uncertainties within anomaly detection course for large span cable-supported bridges, a probabilistic approach is developed based on confidence interval estimation of extreme value analytics. First, raw signals from structural health monitoring system are pre-processed, including missing data imputation using moving time window mean imputation approach and thermal response separation through multi-resolution wavelet-based method. Then, an energy index is extracted from time domain signals to enhance robust of detection performance. A resampling-based method, namely the bootstrap, is adopted herein for confidence interval estimation. Four confidence levels are defined for the anomaly trend detection in this study, namely 95%, 80%, 50%, and 20%. Finally, the effectiveness of the proposed anomaly trend detection methodology is validated by using in-situ cable force measurements from the Nanjing Dashengguan Yangtze River Bridge. As a result, the four-level anomaly detection triggers are determined by using the confidence interval estimation based on cable force measurements in 2007, which are 58,671, 48,862, 42,499 and 39,035, respectively. Subsequently, three cases are presented, which are spike detection, overloading vehicle detection and snow disaster detection. Through the spike detection, it is verified that energy index is capable to tolerate signal spikes. Three overloading events are simulated to conduct overloading vehicle detections. As a result, the three overloading events are detected successfully associated with different confidences. Snow disaster is detected with a more than 80% confidence based on the field measurements during the snow storm time window.

Cable Force Determination Using Phase-Based Video Motion Magnification and Digital Image Correlation

The mode shape-aided method provides a simple and effective way for cable force determination, which, however, requires accurate parameter identification of the cable structure. This paper proposes a phase-based video motion magnification to process the image sequences of a cable. Digital image correlations were engaged to measure the dynamic displacement–time history, through tracking the surface characteristic features of the cable. Thereafter, a frequency–domain decomposition technique was applied to extract the natural frequency and mode shape of the cable from the displacement–time history measurements. The identified cable mode shapes, along with a tensioned pinned-pinned cable model, were used to estimate the cable force. The accuracy of the proposed methodology was subsequently verified through laboratory testing on an inclined cable model and field testing on a typical hanger cable of a real-world arch bridge. Overall, the study results indicated that the proposed methodology could expediently and cost-effectively estimate the tension forces of a cable with reasonably acceptable identification accuracy.

Mechanical Behavior of a Multisegmented Tower Anchorage Structure with an Exposed Steel Anchor Box

A tower anchorage structure with an exposed steel anchor box is commonly used for cable-stayed bridges. Many researchers have conducted studies on this structure by considering a single segment. However, in practical engineering, the stress of multisegmented tower anchorage structure is not completely similar to that of single segment, and the forces between segments affect each other. Hence, in this study, the mechanical behavior of a multisegment anchorage structure with an exposed steel anchor box was investigated via finite element analysis. Furthermore, the load transfer path and stress distribution characteristics of the structure were investigated. The results indicate that the horizontal component of the cable force is borne by the side plate of the steel anchor box, the diaphragm, and the side wall of the concrete tower column, while the vertical component is transmitted by the steel anchor box and concrete tower column. Under the action of this cable force, the horizontal component of the cable force borne by the middle segment increases, while the components at the two end segments decrease. The vertical force is greater on the lower tower segments. The stress levels on the side plate and on the diaphragm of the steel anchor box in the middle section are high. Under the cable force load, the frame formed by the end plate and side plate of the steel anchor box expands outward. The end plate is mainly under a tensile load, and the tensile stress level on the lower section exceeds that on the upper section. A high-stress area for the concrete tower is observed in the steel-concrete joint. The stud group of the anchorage structure is subjected to horizontal and vertical shear forces, and no “saddle-shaped” distribution of the stud shear is found. An optimal arrangement method for the stud group was proposed to optimize its mechanical performance.

Optimization and Control of a Planar Three Degrees of Freedom Manipulator with Cable Actuation

The paper analyzes a planar three degrees of freedom manipulator with cable actuation. Such a system can be understood as a special type of hybrid parallel kinematic mechanism composed of the rigid serial chain and the additional auxiliary cable system. The advantage of the auxiliary cable mechanism is the ability to reconfigure the whole system. The fulfillment of sufficient prestressing is the constraint of the optimization process. Computed Torque Control with a cable force distribution algorithm is implemented. The control algorithm performance is examined on different trajectories, including non-smooth motion requests, and its robustness is tested by randomly generated errors of the model parameters in regulators. The results demonstrate that the optimized structure is capable of controlling the manipulator motion and keeping the cable prestressing within the given limits.

Strain Incremental Adjustment Method of Cable Force of Composite Saddle Anchor Span of Single-Tower Single-Span Ground-Anchored Suspension Bridge

To improve the efficiency of cable force adjustment of composite saddle anchor span of single-tower single-span ground-anchored suspension bridge, a strain incremental adjustment method is proposed. The analytical calculation model is established according to the relative spatial position of the cable strand and the saddle groove of the composite saddle, and the target cable force of the cable strands is calculated by the target position of the composite saddle in the cable-stayed bridge and construction phases. Considering the coupling relationship between the cable strand and the composite saddle, the calculation formula of the change in main span main cable force and anchor span cable force after the adjustment of a single cable strand is derived. Based on the condition of equilibrium of forces along the slip surface of the composite saddle, the slip amount of composite saddle after a round of cable strand adjustment is obtained, then the adjustment amount of actual construction of the cable strands is also obtained through the strain incremental adjustment method. With the help of a numerical simulation platform, the calculation program of the cable force adjustment of composite saddle anchor span is established by an iterative solution method. In this paper, taking the Jinsha River Bridge at Hutiao Gorge as a research object, the adjustment of cable force of composite saddle anchor span is analyzed and calculated. The research results indicate that the calculated cable force is obtained by the strain incremental adjustment method, and it is similar to the measured cable force. The cable strand adjustment and optimization method avoids excessive repeated stretching and relaxation of a single cable strand in the process of multiple rounds of cable strand adjustment and reduces the amount of construction adjustment. This method can effectively reduce the times of cable strand adjustment and improve the efficiency of adjusting the anchor span cable force.

Temporary Cable Force Monitoring Techniques During Bridge Construction-phase. The Tajo River Viaduct Experience

This article addresses the comparative analysis of current techniques for monitoring cable forces. Additionally, the experience of three cable force different monitoring techniques for strain control in bridge cables during the construction phase is included: a) installing load cells on the active anchorages of the cables, b) installing unidirectional strain gauges, and c) assessing the stress on cables by applying the vibrating wire technique through the installation of accelerometers. The main advantages and disadvantages of each technique analyzed are highlighted in the construction process context of the Tajo Viaduct, one of the most singular viaducts recently built in Spain.

“Relief-Retaining” Control Technology of Floor Heave in Mining Roadway with Soft Rock: A Case Study

The floor heave problem is one of the important factors affecting the stability and safety of surrounding rocks of roadways, especially in deep high-stress mining roadway with soft rock. The return airway of no. 130203 working face in Zaoquan Coal Mine of Ningdong Mining Area in Northwest China is the research object in this study. Firstly, an innovative “relief-retaining” control scheme of floor heave is proposed, which is the comprehensive measure of “cutting groove in floor + drilling for pressure relief at roadway side + setting retaining piles at the junction of roadway side and floor.” Then, the specific parameters suitable for floor heave control of no. 130203 return airway are determined using numerical simulation method. Finally, the yield monitoring results show that both the deformation of surrounding rocks and the cable force are significantly reduced. The roof falling capacity, floor heave displacement, and thickness increasing value of 0–2 m floor strata are 596 mm, 410 mm, and 82 mm, respectively, which are 43.67%, 67.49%, and 75.38% less than those of the control section. The maximum force of cables at roadway sides is 140.13 kN, about 32.54% less than that of the control section. The results verify the reliability of the proposed “relief-retaining” control scheme and can provide some reference for the floor heave control of similar roadways.

Self-Localization of Tethered Drones without a Cable Force Sensor in GPS-Denied Environments

This paper considers the self-localization of a tethered drone without using a cable-tension force sensor in GPS-denied environments. The original problem is converted to a state-estimation problem, where the cable-tension force and the three-dimensional position of the drone with respect to a ground platform are estimated using an extended Kalman filter (EKF). The proposed approach uses the data reported by the onboard electric motors (i.e., the pulse width modulation (PWM) signals), accelerometers, gyroscopes, and altimeter, embedded in the commercial-of-the-shelf (COTS) inertial measurement units (IMU). A system-identification experiment was conducted to determine the model that computes the drone thrust force using the PWM signals. The proposed approach was compared with an existing work that assumes known cable-tension force. Simulation results show that the proposed approach produces estimates with less than 0.3-m errors when the actual cable-tension force is greater than 1 N.