Glauco Feltrin

Long-term monitoring of cable stays with a wireless sensor network

Wireless sensor networks (WSNs) are a promising technology that could induce a significant innovation in the field of structural monitoring. The main advantages of WSNs are fast deployment, little interference and self-organisation. However, since WSN are battery powered, the power management of the sensor nodes significantly influences the operation method and the overall data management process. Since data communication is the most energy-consuming task, a significant data reduction has to be attained in the sensor nodes to achieve system lifetimes that are useful for real life applications. This paper discusses several basic aspects of data processing and data management for long-term monitoring with WSNs. It presents a specific monitoring system and illustrates a long-term field test performed with this system on a bridge. The test results demonstrate that in-network data reduction is a very promising but challenging approach, since it has to be implemented with very limited computational and memory resources.

Cycle energy control of magnetorheological dampers on cables

The dissipated cycle energy of magnetorheological (MR) dampers operated at constant current results from controllable hysteretic damping and from almost current independent, small viscous damping. Thus, the emulation of Coulomb friction and linear viscous damping necessitates current modulation during one vibration cycle and therefore current drivers. To avoid this drawback, a cycle energy control (CEC) approach is presented which controls the hysteretic MR damper part such that the total MR damper energy equals the energy of optimal linear viscous damping by constant current during one cycle. The excited higher modes due to the hysteretic damping part are partially damped by the MR damper viscous part. Simulations show that CEC copes better with damper force dynamics and constraints than emulated linear viscous damping due to the slow control force dynamics of CEC which are given by cable amplitude dynamics. It is demonstrated that CEC of MR dampers with viscosity of approximately 4.65% of the optimal modal viscosity performs better than optimal linear viscous damping. The reason is that this damper viscosity represents an optimal compromise between maximum energy spillover to higher modes due to the controllable hysteretic part which produces more cable damping and maximum viscous damping of these higher modes. Damping tests on a cable with an MR damper validate the CEC approach.

Assessment of European railway bridges for future traffic demands and longer lives – EC project “Sustainable Bridges”

A European Integrated Research Project has recently been started within the 6th Framework Program of the European Commission. The project aims at improved methods for the upgrading of existing railway bridges within the European railway network. The main objectives of the project are to increase the transport capacity by allowing higher axle loads and by increasing the maximum speeds. Other objectives are to increase the residual lifetime of existing bridges and to enhance management, strengthening and repair systems. The overall goal is to enable the delivery of improved capacity without compromising the safety and economy of the working railway. A consortium consisting of railway bridge owners, consultants, contractors, research institutes and universities will carry out the project, having a gross budget of more than 10 million Euros. Funding from the European Commission covers a major portion of the four-year project costs.

Stress recovery behaviour of an Fe-Mn-Si-Cr-Ni-VC shape memory alloy used for prestressing

This paper describes the stress recovery behaviour of an Fe‐17Mn‐5Si‐10Cr‐4Ni‐1(V, C) (mass%) shape memory alloy used for prestressing of civil structures. The prestressing due to the shape memory effect was simulated by a series of tests with pre-straining of the material followed by heating and cooling back at constant strain. Different pre-strain and heating conditions were examined. Moreover, the response due to additional mechanical and thermal cyclic loading has been investigated. These results were used to predict the partial prestress loss in a structure due to variable loading during operation. Finally, a heating test at constant strain was performed after the cyclic loading to check the possibility of reactivating the prestress lost during an exceptionally high load. (Some figures may appear in colour only in the online journal)

Adaptive Tuned Mass Damper based on Pre-stressable Leaf-springs

Lightweight bridges exhibit a high live load to dead load ratio. Thus, their resonance frequencies depend on the current loading state and can vary in quite a broad range. This behavior is a real challenge in vibration mitigation of such structures controlled by tuned mass dampers (TMDs), since the performance of single passive TMDs degrades significantly if the resonance frequency of a structure differs even slightly from design frequency. This study proposes an adaptive TMD, which continuously adapts its natural frequency to the current resonance frequency of the structure. The concept is based on pre-stressable leaf-springs that are controlled by piezoceramic stack actuators. Experiments performed on a first prototype show that the TMD is continuously tunable in a broad frequency range.

Vibration monitoring of a footbridge with a wireless sensor network

Monitoring the vibration performance of structures for serviceability assessment purposes usually requires a deployment of several weeks or months to collect a dataset allowing a reliable assessment. Since for this type of medium term deployments installation costs are a key factor, wireless monitoring with its fast deployment has an advantage over wired monitoring systems. This paper describes a deployment of a wireless monitoring system on a timber footbridge. The goal of the monitoring was to provide information about vibration amplitudes during operation and to track changes of relevant natural frequencies with the temperature. Accelerations were permanently recorded and the acquired data was processed in the nodes to compute the envelope of the vibration amplitude and the dominant peaks of the Fourier spectrum. The wireless monitoring system that was deployed for one year provided accurate data matching the requirements of vibration performance assessments. The deployment demonstrated that a wireless sensor network is a technically feasible and economically effective mean to monitor the vibration performance of a structure.

Measured linear–quadratic–Gaussian controlled damping

This paper investigates experimentally the characteristics of LQG control for controlled vibration mitigation. The control algorithm is implemented in LabVIEW RT. The controller performance is measured at a test set-up consisting of a vibrating taut cable with MR damper. Measurements of the closed-loop system clearly point out that LQG control enables damping vibrations with respect to their intensity and frequency. When the cable is excited at constant frequency, the desired control force is dissipative and proportional to the vibration velocity at the damper position. Thus, for the system under consideration, LQG control ends up in the desired viscosity. With increasing frequency of the cable excitation, the desired viscosity decreases. The desired viscosities for the first four cable modes depend on the pole locations of the observer and regulator. The nearer they are located, the higher are the desired viscosities. Therefore, a design parameter describing precisely the distance between observer and regulator poles is introduced. Based on this design parameter, the paper proposes a systematic method of LQG controller design for practical applications.

Delamination detection in an I-section glass fiber reinforced plastic beam with an optical fiber-based stress wave method

An optical fiber-based technique for the detection of the delamination at the web/flange junction of an I-section glass fiber reinforced plastic beam is presented. A fiber optical interferometric sensor is adhered to the surface of the web to serve as a stress wave receiver, and a piezoelectric transmitter (PZT) is employed to produce a stress wave in the structure. Several methods are applied to detect the delamination, and summing the frequency spectra from multiple measurements is proved to be effective. From the frequency components of the sensor output corresponding to various positions of the PZT, the delamination location can be revealed. The feasibility of delamination detection with the proposed technique is demonstrated.

A novel bridge section model endowed with actively controlled flap arrays mitigating wind impact

In this work, we present the SmartBridge, a novel bridge section model equipped with actively controlled arrays of flaps aiming at mitigating wind-induced vibrations of long-span bridges. The active model, as well as its support structure, is described in detail and the key design choices are motivated. Finally, the capabilities of the system and the active control of the bridge section model with moving flaps was validated by wind tunnel experiments. In spite of the relative simplicity of a, manually tuned, control law, the results are encouraging and show a significant damping of the pitch vibration of the deck.

A Wireless Sensor Network with Enhanced Power Efficiency and Embedded Strain Cycle Identification for Fatigue Monitoring of Railway Bridges

Wireless sensor networks have been shown to be a cost-effective monitoring tool for many applications on civil structures. Strain cycle monitoring for fatigue life assessment of railway bridges, however, is still a challenge since it is data intensive and requires a reliable operation for several weeks or months. In addition, sensing with electrical resistance strain gauges is expensive in terms of energy consumption. The induced reduction of battery lifetime of sensor nodes increases the maintenance costs and reduces the competitiveness of wireless sensor networks. To overcome this drawback, a signal conditioning hardware was designed that is able to significantly reduce the energy consumption. Furthermore, the communication overhead is reduced to a sustainable level by using an embedded data processing algorithm that extracts the strain cycles from the raw data. Finally, a simple software triggering mechanism that identifies events enabled the discrimination of useful measurements from idle data, thus increasing the efficiency of data processing. The wireless monitoring system was tested on a railway bridge for two weeks. The monitoring system demonstrated a good reliability and provided high quality data.