This paper presents a procedure to calculate the characteristic value of braking forces of road bridges using monitored data and stochastic simulation. In the model, the braking force is a random variable characterized by a probability distribution. In addition to the properties of the bridge such as length, number of lanes, as well as stiffness and damping in longitudinal direction, the model also takes into account all essential stochastic variables that characterize a braking process. That is the composition of the traffic as a temporal sequence of vehicles, the weight of heavy vehicles according to vehicle type, the individual reaction time of the respective vehicle driver, the individual deceleration of each vehicle involved in the braking process and the probability of the occurrence of a braking process. All model parameters of these variables were characterized with traffic data monitored on Swiss motorways (automatic vehicle counting and weigh-in-motion stations) and data from naturalistic driving studies. Parameter studies with the simulation model show that the braking force strongly depends on the bridge length, the fundamental frequency of the bridge in longitudinal direction, the spontaneous clustering behavior of heavy vehicles, the frequency of hard braking events, and the return period. Since the return period is explicitly included in the model as a parameter, the model can be used for both the design of new and the assessment of existing bridges.

Twenty years ago, in 2003, a European project was started to increase the sustainability of existing railway bridges. This paper summarises what was achieved and looks ahead. Nine Working Packages were organized: (1) Background material; (2) Guidance by stakeholders; (3) Condition Assessment and Inspection Guidelines; (4) Loads, Capacity and Resistance Guidelines; (5) Monitoring Guidelines; (6) Repair and Strengthening Guidelines; (7) Demonstration with Field testing of Bridges; (8) Demonstration on Monitoring on Bridges; and (9) Training and Dissemination Some of the main results (from 4 Guidelines and 47 Background documents) are highlighted and some experiences, conclusions and thoughts about the future are given. Hidden strengths and weaknesses are discussed, analyses and codes for assessment can be improved, new monitoring and strengthening methods are available and life length can be prolonged.

This paper reports about tests that were carried out on the motorway bridge “Viaduc de Matran” in Switzerland. The 115 m long, three span bridge was equipped with reinforced elastomer bearings, which dominated the longitudinal stiffness and damping. A series of tests with hard braking trucks were performed that incrementally exceeded the design load for braking forces. Displacements and accelerations of the bridge in longitudinal, transversal and vertical directions were recorded. The trucks were equipped with accelerometers and a GPS-antenna to record the deceleration during the braking event and the position of the vehicle. Time synchronization between the independent measurement systems was achieved via GPS time stamps. The tests on the bridge show that the bridge behaved non-linearly and much more rigid than was to be expected based on the properties of the bearings. In addition, the bridge behaved significantly different in the two loading directions. Furthermore, no coupling between longitudinal and bending or torsional vibrations was observed. The jerk of the braking vehicle shortly before the stop induced significant bending vibrations. The observed dynamic behaviour of the bridge confirms that a single-mass oscillator is an appropriate model assumption for describing the behaviour of a bridge during a hard braking event.

Event-driven monitoring policies enable to significantly reduce the power consumption of wireless sensor networks by reducing the recording period to those time intervals that provide valuable data. The resulting longer operation lifetime increase discloses fields of application that require long monitoring periods. This paper presents a structural monitoring system that uses specialized sentinel nodes for detecting possibly heavy road vehicles and for alarming monitoring nodes, which are specialized on strain sensing. Heavy vehicles are identified by estimating nearly in real time height and length of vehicles of a traffic flow by processing data recorded from low-cost ultrasonic and magnetic displacement sensors. Field tests demonstrated that while height detection is very reliable, length detection is too imprecise to discriminate with high success rates between trucks and delivery vans.

The dynamic analysis of a pneumatic beam structure, termed the Tensairity girder, is experimentally, numerically, and analytically studied. The structural concept of Tensairity relies on the combination of an airbeam with conventional struts, which leads in a light-weight structure of significant load-bearing capacity. By focusing on the analysis of the dynamic response of this structure, the objective of this work is to determine the pressure-dependent modal characteristics of the pneumatic beam and to couple these with the associated material properties. Based on the results of a modal identification procedure, relying on hammer and white noise excitation tests, a finite-element (FE) model is updated to reflect the actual system response. This procedure reveals the membrane's shear modulus as the material property that more heavily relies upon the pressure level of the Tensairity girder. The experimental and numerical investigations indicate that the dynamic behavior of the beam can be expressed as a superposition of pressure dependent and pressure independent modes. The obtained insight allows for a better exploitation of the Tensairity in a new range of applications involving dynamic loading. (C) 2016 American Society of Civil Engineers.

The current provisions for the braking force in the Eurocodes are much more demanding than previously enforced national codes from most European countries. Hence, safety assessments of existing bridges may show a lack of compliance with the new safety requirements of current maintenance codes, making the relevant authorities responsible for their strengthening. The current load model for the braking force was derived from a deterministic evaluation of traffic configurations with characteristics that do not correspond with actual traffic measurements. This procedure differs from models describing vertical traffic loads, where the effects of traffic were analysed within a probabilistic framework in compliance with the partial safety factor design method. This paper investigates the advantages, limitations and hypotheses of a probabilistic model for the braking force when compared with deterministic models. Original results for the characteristic value of the braking force on road bridges are presented, which consider a realistic time-history of bridge crossing vehicles generated by a traffic microsimulation tool with input data from a Swiss Weigh-In-Motion station. The results are compared with the braking force of the Eurocodes, highlighting the role of the probability of braking and the influence of the dynamic characteristics of bridges on the characteristic value of the braking force.

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.

Due to the increasing traffic volume on the European railway network, the remaining fatigue life of existing steel bridges is a major concern. Several investigations demonstrated that supplementing the assessment with monitoring data enables to achieve more reliable remaining fatigue life estimations. In this paper, an event-driven monitoring system based on a wireless sensor network that consists of two functionally different components was designed and tested. Sentinel nodes, which were mounted on the track, were used for detecting approaching trains and alerting with alarm messages the monitoring nodes. These nodes, which were mounted on the bridge, started strain sensing and data recording after receiving the alarm message and went back to a power saving mode upon completion. An embedded data processing algorithm transformed the recorded raw data into a much smaller data set representing strain cycles. A test deployment on a railway bridge demonstrated that train detection and alarming was fast and reliable. The combination of event-driven monitoring and embedded data processing allowed to extend the battery lifetime of monitoring nodes to several months.

A probabilistic approach is necessary to estimate the magnitude of the braking force that compares in terms of return period with the vertical traffic loads present in bridge design codes. A data set from a Danish Field Operational Test served as support to identify hard braking episodes and to compute travelled distances by road hierarchy. The rate of braking events per vehicle travelled distance is used as estimate of the braking probability. Concurrently a structural model was developed for stochastic analysis of the dynamic response of bridges to braking events from realistic traffic configurations. This paper presents results for extreme braking forces on bridges with site-specific traffic data and within a probabilistic framework. Such evaluation is economically advantageous when compared to the application of structural codes, while still meeting the reliability targets they impose.

A 3-storey residential building with OSB-sheathed light-frame timber walls and timber-concrete composite slabs was subjected to dynamic excitation in two different stages of construction. The experiments consisted of measurements of the accelerations resulting from forced horizontal vibrations which were excited by means of a hydraulic actuator shaking a mass of 940 kg. The exciter was positioned on the second floor of the building and rigidly anchored in the slab. It excited the building in its two main directions to vibrations with frequencies within a range of 0.2–14 Hz. Natural frequencies, modal damping ratios and mode shapes of the building were estimated using accelerations of the building measured in the four external corners of each upper floor. For increasing displacement amplitude (1/8000 mm → 0.7 mm) the natural frequencies decreased moderately (−15 %) whereas the modal damping ratios increased markedly (+100 %). Modal damping ratios computed using ambient vibration data were generally smaller than modal damping ratios obtained from forced vibration tests, which suggests that modal damping for the levels of vibration in interest in design might be significantly underestimated if based on results from ambient vibration tests. However, the mode shapes computed using ambient vibration data turned out to be reliable. The differences in dynamic properties assessed in the different stages of construction were much smaller than expected. Compared to the natural frequencies estimated by the designer by applying a simple single degree of freedom model, the measured natural frequencies were considerably higher. This may be attributed to the impact of non-structural internal walls and walls with openings not accounted for in the designer’s model.

In this work, we investigate active flutter control of a bridge section model equipped with arrays of flaps. We consider three simple control algorithms based on an amplitude-gain and a phase-shift for actuating the flaps and stabilizing the section model. We have leveraged a linear analytical model of the structural and aeroelastic forces during flutter in order to find efficient control parameters. The proposed solution was validated with wind tunnel experiments, where all the algorithms showed capable of suppressing flutter, and the most efficient one was using all of the flaps on the deck.

Cross girders of a riveted steel frame bridge were monitored with a wireless sensor network. Since strain sensing is very expensive in terms of power consumption a novel signal conditioning hardware was developed that enabled to significantly reduce the power consumption. An embedded data processing algorithm transformed the recorded raw data into a sequence of maxima and minima representing the strain cycles thus reducing data communication and enabling an additional energy saving. By using a software based event triggering algorithm the embedded data processing was performed only for data acquired during train transits. Strain cycles of more than 900 trains were recorded. The quality of the recorded data was very good and demonstrated that WSNs can be a competitive alternative to conventional tethered monitoring systems for recording operational data for fatigue assessment of steel railway bridges.

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.

The monitoring of rigid structures of modal frequencies greater than 5 Hz and sub-mm displacement is mainly based so far on relative quantities from accelerometers, strain gauges, etc. Additionally, geodetic techniques such as GPS and robotic total stations (RTS) are constrained by their low accuracy (few mm) and their low sampling rates. In this study, the application of QDaedalus is presented, which constitutes a measuring system developed at the Geodesy and Geodynamics Lab, ETH Zurich and consists of a small CCD camera and total station, for the monitoring of the oscillations of a rigid structure. In collaboration with the Institute of Structural Engineering of ETH Zurich and EMPA, the QDaedalus system was used for monitoring of the sub-mm displacement of a rigid prototype beam and the estimation of its modal frequencies up to 30 Hz. The results of the QDaedalus data analysis were compared to those of accelerometers and proved to hold sufficient accuracy and suitably supplementing the existing monitoring techniques.

In this work we investigate the applicability of the wing-aileron-tab model for a bridge section model being actively controlled with leading and trailing edge flaps. The structural and aerodynamic model parameters have been extracted experimentally from a total of 140 wind tunnel experiments. Our in-house developed set-up has been employed for this purpose. Four different control strategies, with increasing complexity have been used for the parameter estimation. The first eight flutter derivatives have been obtained from step responses performed without control. The modified versions of these flutter derivatives have been estimated from step responses performed with three different types of active flap control, from which the leading edge and trailing edge flutter derivatives have been derived. The presented results are encouraging, however, further investigation is necessary in order to fully evaluate the wing-aileron-tab model’s applicability.

In this work, we investigate a model-based control for a flap system aiming at mitigating wind-induced vibrations of long-span bridges. Our contribution is threefold: first, we developed an integrated flap system able to control a bridge section model; second, we proposed a model able to properly capture the nonlinear interaction between wind and the structure; third, we optimized a linear control law for the flap position able to robustly cope with the nonlinear forces exerted on the flap. The model accuracy and the system performance were systematically validated by wind tunnel experiments.

Due to favourable mechanical and physical properties, and the potential to provide a resilient and low-carbon infrastructure, fibre-reinforced polymer (FRP) material has increasingly been used for construction of highway and pedestrian bridges. Relative low mass, low damping and low stiffness make these bridges sensitive to dynamic excitation, which may lead to discomfort of human occupants and larger dynamic amplification of stress and deformation than is encountered in structures made of traditional structural materials. Consequently, design might be governed by a vibration serviceability state. Lack of data on vibration performance of FRP structures and non-existence of a state-of-the-art vibration serviceability design guideline means that current practice is conservative, often meaning only short-span FRP bridge solutions are executed. To fully exploit the benefits of using FRP material and to extend its use beyond current practice requires a better understanding of dynamic behaviour.