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Reducing derailments of freight trains is of utter importance for improving railway transportation since derailments lead to large service disruption, economic losses and risk related to transporte...

From an aerodynamic point of view, very large observation wheels are complex structures. Several parts are slender with bluff cross sections, and therefore wind–structure interaction effects can in...

IABSE Task Group 3.1 has the mandate to define reference results for the validation of methodologies and programs used to study both stability and buffeting responses of long-span bridges. These to...

Smart monitoring systems are currently gaining more attention and are being employed in several technological areas. These devices are particularly appreciated in the structural field, where the collected data are used with purposes of real time alarm generation and remaining fatigue life estimation. Furthermore, monitoring systems allow one to take advantage of predictive maintenance logics that are nowadays essential tools for mechanical and civil structures. In this context, a smart wireless node has been designed and developed. The sensor node main tasks are to carry out accelerometric measurements, to process data on-board, and to send wirelessly synthetic information. A deep analysis of the design stage is carried out, both in terms of hardware and software development. A key role is played by energy harvesting integrated in the device, which represents a peculiar feature and it is thanks to this solution and to the adoption of low power components that the node is essentially autonomous from an energy point of view. Some prototypes have been assembled and tested in a laboratory in order to check the design features. Finally, a field test on a real structure under extreme weather conditions has been performed in order to assess the accuracy and reliability of the sensors.

The paper presents a modal model to describe the interaction between a 4-conductor bundle and wind. A finite-element model of the bundle is used to perform a linear analysis, to extract mode shapes and natural frequencies of the system. The motion of the expanded bundle is then described through mode coordinates representing the first horizontal, vertical and torsional modes. Wind tunnel tests were performed adding templates over the cables to mimic the presence of ice over the same conductor bundle; tests allowed to characterize the aerodynamic coefficients of the entire bundle and provided data for the model validation. The model was then applied to a case study to predict the maximum oscillations produced by iced conductor galloping. Time-domain simulations were used for the purpose, together with an alternative approach named energy method; this last directly estimates the amplitude of limit cycles avoiding the integration of the equations of motion and can be much more useful from the engineering point of view.

This paper presents the ongoing benchmark results of IABSE Task Group 3.1. The task of this working group is to create benchmark results for the validation of methodologies and software programs developed to assess the stability and the buffeting response of long span bridges. Indeed, accurate estimations of structural stability and response to strong winds are critical for the successful design of long-span bridges. While the first results of the benchmark, dealing with a section approach, have been already published, in this paper the ongoing activity and results of the task group are presented. The topic of these results is the numerical response of a full-bridge model under the actions of a multi-correlated wind field both in terms of aeroelastic stability and buffeting response.

IABSE Task Group 3.1 has the mandate to define reference results for the validation of methodologies and programs used to study both stability and buffeting responses of long-span bridges. To this ...

This paper is part of a series of publications aimed at the divulgation of the results of the 3-step benchmark proposed by the IABSE Task Group 3.1 to define reference results for the validation of the software that simulate the aeroelastic stability and the response to the turbulent wind of super-long span bridges. Step 1 is a numerical comparison of different numerical models both a sectional model (Step 1.1) and a full bridge (Step 1.2) are studied. Step 2 will be the comparison of predicted results and experimental tests in wind tunnel. Step 3 will be a comparison against full scale measurements.The results of Step 1.1 related to the response of a sectional model were presented to the last IABSE Symposium in Nantes 2018. In this paper, the results of Step 1.2 related to the response long-span full bridge are presented in this paper both in terms of aeroelastic stability and buffeting response, comparing the results coming from several TG members.

The non-linear aerodynamic effects on a bridge deck section are both experimentally and numerically investigated using a new time-domain numerical model based on the combination of a non-linear corrected quasi-steady theory and a rheological approach. The model is developed to reproduce the response of a bridge to turbulent wind taking into account the non-linearities of the aerodynamic forces induced by the fluctuation of the angle of attack. The methodology introduces rheologic mechanical model to reproduce the dependence of aerodynamic forces on the reduced velocity. Through a one-shot integration the single numerical model is able to describe the static response, the low-frequency response and the high-frequency response of the bridge to turbulent wind. Finally, the numerical model is validated against aeroelastic wind tunnel tests performed by means of an active turbulence generator acting on a deck sectional model suspended on springs.

For new transmission line design, it is important to know how much additional damping is needed to control aeolian vibration within safe levels. To this purpose, various researchers have developed computation methods—based on the energy balance principle (EBP)—to predict the aeolian vibration level of a conductor plus damper. This paper evaluates the computation methods, through direct comparison among them and with experimental results, with the final aim of defining the uncertainty of the considered methodology.

The specific power input imparted by the blowing wind to an oscillating circular cylinder is a key topic in calculating aeolian vibrations of overhead transmission lines using the energy balance principle, i.e. the most common methodology used to design new lines and to dimension fittings and damping devices. The specific power input as function of the vibration amplitude was measured, during the last decades, by different research groups using different models. The obtained curves show a large dispersion of the results increasing the uncertainties in determining the vibration amplitudes. Aim of this paper is to describe the results obtained during experimental campaigns carried out at Politecnico di Milano Wind Tunnel using both flexible and rigid sectional model and to highlight the differences among the two cases in terms of vortex induced vibrations with particular reference to specific power input.

Reliable transmission line design requires that vibration of the conductors due to wind is controlled below critical levels to avoid fatigue damage. Newly designed lines, lines that are being modified to carry higher current voltage and lines that are being assessed for life extension, all require vibration control for safe levels. Approaches available to guide this assessment process can be pragmatic, through design rules based on the past experience. Also, conditions can be assessed through measurement on existing lines, using special purpose measuring instruments. This chapter deals with an analytical approach which may be used to investigate alternatives in the design or redesign process. In particular, this chapter describes the energy balance principle (EBP) which is used to estimate an upper bound to the expected vibratory motions, gives examples of measured wind and conductor data used, and some comparisons with available field measurements.

The IABSE Task Group 10 (super-long span bridge aerodynamics) has the mandate to create a standard procedure for validation of methodology and software programs applied for stability and buffeting response analyses of super-long span bridges. Precise estimations of structural stability and response to strong winds are critical for the successful design of long-span bridges.Task Group 10 covers several important problems related to its mandate including: review and verification of methods developed and adopted by researchers and bridge designers; the definition of guidelines and sample tests for verification and calibration of analytical procedures; identification of fundamental problems of the computation methods; relevant input and output data.Since the beginning of its work, this working group has developed a 3-step benchmark, with multiple sub-steps of fundamental problems to resolve. The first step of this benchmark has been a numerical comparison of the results obtained using different models adopted across the workgroup members. Using the same inputs: flutter stability and the buffeting response of both a deck sectional model and a full bridge are studied. Step 2 will be the comparison of predicted results and experimental tests in wind tunnels, and Step 3 will be of validation against full scale measurements. In this paper, the results of Step 1 will be presented, highlighting critical issues and differences found during the comparison of results. The response of a 3-degrees of freedom bridge deck will be presented both in terms of aeroelastic stability and buffeting response. The results presented are intended to be a reference for the validation of methodologies and software programs that solve for wind response of bridges.

This chapter follows the two previous chapters on undamped single conductor and single conductor plus one damper. The purpose of this section is to evaluate the effectiveness of the technology based on the energy balance principle for the design and/or verification of the damping system of long, single conductor spans strung at relatively high tensile loads, such as crossings, which need more than one damper per span extremity to be effectively damped against aeolian vibration.

A large scale aeroelastic model of the Third Bosporus bridge deck was designed and built to measure the aeroelastic response under different incoming flow conditions and to validate numerical models for the buffeting response of Super-long Span Bridge. The 8 m long model, with a deck chord of 1.17m, can reproduce the multi-modal dynamic response of the deck in a range of reduced velocities V*=V/(fB) between 1 and 10. The model is intended to overcome the limitations on aerodynamic similarity of traditional small scale aeroelastic models (typically 1:200 – 1:400), for validation of numerical codes to study the aeroelastic and buffeting response of long span bridges. The model allows to contemporary measure the dynamic response and the aerodynamic forces acting on the deck using 2 instrumented sections equipped with pressure taps. In the present paper, a procedure to measure the flutter derivatives coefficients of the deck, at different reduced velocities, on the large scale aeroelastic model, using forced motion tests, is presented. The research is aimed at investigating the feasibility to measure the aerodynamic properties of the deck directly on the large scale aeroelastic model presenting aeroelastic coupling among vertical and torsional modes. These results will be used in the validation procedure of numerical codes relying on the aerodynamic coefficient data set coming from the rigid model.

The wind tunnel campaign was performed on two circular cylinders to investigate subspan oscillation, a typical phenomenon that affects high-voltage and ultra-high-voltage overhead transmission lines. In particular, aerodynamic forces were measured in static and in dynamic conditions. Dynamic conditions were realized by moving the cylinders along quasielliptical orbits as when subspan oscillation occurs. Tests were performed by changing the relative position between the two cylinders, the frequency and the amplitude of the motion, and the wind velocity, that is, the Reynolds number. Both smooth and rough cylinders were tested. The effects of all these parameters in the evaluation of the energy introduced or dissipated by the system have been highlighted, with special care for the Reynolds number effects.

One of the most common solutions adopted to reduce vibrations of skyscrapers due to wind or earthquake action is to add external damping devices to these structures, such as a TMD (Tuned Mass Damper) or TLCD (Tuned Liquid Column Damper). It is well known that a TLCD device introduces on the structure a nonlinear damping force whose effect decreases when the amplitude of its motion increases. The main objective of this paper is to describe a Hardware-in-the-Loop test able to validate the effectiveness of the TLCD by simulating the real behavior of a tower subjected to the combined action of wind and a TLCD, considering also the nonlinear effects associated with the damping device behavior. Within this test procedure a scaled TLCD physical model represents the hardware component while the building dynamics are reproduced using a numerical model based on a modal approach. Thanks to the Politecnico di Milano wind tunnel, wind forces acting on the building were calculated from the pressure distributions measured on a scale model. In addition, in the first part of the paper, a new method for evaluating the dissipating characteristics of a TLCD based on an energy approach is presented. This new methodology allows direct linking of the TLCD to be directly linked to the increased damping acting on the structure, facilitating the preliminary design of these devices.

A comparison of the aeroelastic response of four 1:220 aeroelastic models representing three different construction stages and the completion stage of the Izmit Bay suspension bridge in Turkey is presented. Wind tunnel tests were performed in the same laboratory both in smooth and turbulent flow conditions to investigate the aeroelastic stability and the buffeting response. Completion bridge results are used as a reference for considerations on how the variation of the structural characteristics and the different aerodynamics of the various construction stages influence the bridge stability and the buffeting response.

Nonlinear aerodynamic effects on a multi-box deck section are both numerically and experimentally investigated. The basic hypothesis of the band superposition approach, a methodology to model the aeroelastic and buffeting terms of the wind loads acting on a bridge deck, is validated through specific wind tunnel tests on a sectional model. An improved version of the band superposition approach is proposed, introducing a rheological model for high frequency unsteady forces. The numerical model is validated against wind tunnel tests performed by means of an active turbulence generator and a multi-box deck sectional model. Finally, the linear and nonlinear approaches are compared with full scale simulations of the numerical response of a sectional bridge to an incoming real turbulent wind.

The pedestrian bridge over the Swan River in Perth (Australia) is designed to be a three-span arch structure. A unique feature of this bridge is that each span has two crossed arches with triangular cross-sections that vary dimensions along the arch. In addition, two cantilever extensions are connected to the crown of the central arch for aesthetic purposes. For this kind of unique structures, with complex shape and bluff sections, wind effects are challenging and their effects should be studied by wind tunnel tests, as required by most design codes. Both static and dynamic wind loads were studied in wind tunnel using scale models of the full bridge (rigid model in 1:50 scale), of portions of the arches (two aeroelastic sectional models in 1:15 scale), and of the deck (one aeroelastic sectional model in 1:10 scale). Experimental results are analysed and a procedure to assess wind effects on the whole structure is outlined.

An experimental double multi-modal flutter instability was recorded during wind tunnel tests on a full bridge aero elastic model. The analysis of this instability is presented in this paper, and it is studied with a multi-modal eigenvalue approach. It is shown that two different coupling mechanisms, one involving the symmetric modes and the other involving the anti-symmetric modes, lead to two different instabilities that occur at the same wind speed. The numerical analysis shows that a multi-modal framework and a complete set of aerodynamic coefficients are necessary to correctly estimate the flutter onset. The effect on flutter of structural and aerodynamic characteristics is discussed thoroughly, with a focus on structural modes and on the dependence of the aerodynamic coefficients upon the reduced velocity and upon the angle of attack.

Traditional aeroelastic models rely only on good mechanical design and accurate crafting in order to match the required structural properties. This paper proposes an active regulation of their structural parameters in order to improve accuracy and reliability of wind tunnel tests. Following the design process steps typical of a smart structure, a damping tuning technique allowing to control a specific set of vibration modes is developed and applied on the aeroelastic model of a long-span suspended bridge. Depending on the testing conditions, the structural damping value can be adjusted in a fast, precise and repeatable way in order to highlight the effects of the aerodynamic phenomena of interest. In particular, vortex-induced vibration are taken into consideration, and the response of a bridge section to vortex shedding is assessed. The active parameter regulation allows to widen the pattern of operating conditions in which the model can be tested. The paper discusses the choice of both sensors and actuators to be embedded in the structure and their positioning, as the control algorithm to obtain the desired damping. Experimental results are shown and results are discussed to evaluate the performance of the smart structure in wind dunnel tests.

In this chapter, continuous body models (i.e. systems with infinite degrees of freedom, governed by partial differential equations, functions of both time and space) are introduced. As is known, closed form solutions can only be obtained in some simple applications. For this reason, the study was conducted mainly for educational purposes, in preparation for the discretization methods described in the following chapter. In particular, vibrations in continuous systems, using both the direct (the “propagative” solution) and modal approach in principal coordinates (the “stationary” solution), have been studied. At the end of the chapter, the bending vibrations of cables, beams and “taut beams” are shown as examples.

Estimates of the buffeting response of long-span bridges rely on numerical models that require as input the dynamic finite element model of the bridge, the turbulence characteristics of the incoming wind, and the model for the fluid-structure interaction. Nowadays the first two inputs are reliable and do not require deeper investigations, but fluid-structure interaction models have margins for improvement in their accuracy. While from a numerical and analytical point of view these models have been developed and studied in detail, their experimental validation is still an open issue. Indeed, the numerical-experimental comparison is often done against the response wind-tunnel models, either full-aeroelastic or sectional models, which have some intrinsic limitations: for example, uncertainties related to the small geometrical scale for full-aeroelastic models, or the non-deformability of the deck in sectional models. To overcome some of the current limitations, in this paper a large-scale deformable aeroelastic model is proposed. The experimental results should be used as a benchmark study for the accuracy of numerical models for the buffeting response of long-span bridges.

Long span bridges crossed by railway traffic require proper runnability analysis, based on different modelling levels. In this paper the influence of global, medium scale and local deck deformation on the stresses induced on the bridge structure is investigated, by adopting a proper combination of models, with different dimensions and detail levels. What makes a bridge with railway traffic different from bridges crossed by road traffic only is the need to install a track system which involves local stress concentration related both to higher axle loads and specific connection devices. Special attention is given to the influence of the track system on the locally transmitted loads and consequent stresses, by making reference to the case of an embedded rail system directly installed on the top plate of a railway box girder and to the related fatigue resistance of the deck structural elements. Simulation and laboratory tests can be a synergic combination for properly guiding the bridge structural design.

This chapter of the book describes the large motion non-linear dynamics of multi-body discrete 1, 2 and “n” degree-of-freedom systems using scalar and matrix methodologies (Lagrange’s equations) to write the related equations of motion. Concepts regarding the degrees of freedom of mechanical systems (associated with constraints and their schematization), physical variables and independent coordinates are introduced. The equations of “motion in large” and their linearization in the neighborhood of the equilibrium position (static or steady state) are introduced and described. For 3D motions, the basic concepts of multi-body methods are shown. Several examples are shown in the text.

This chapter deals with the study of the dynamics of continuous mechanical systems using the approximated finite element discretization approach. The general methodology used to define the matrix equations of motion in the case of vibration problems is described. Cable, beam and “taut beam” finite elements are analysed as examples of application; notions regarding two-dimensional and three-dimensional finite elements are shown. The basics concepts regarding the finite element method approach for nonlinear systems and methods of numerical integration of the nonlinear equations of motion are introduced.

This chapter outlines the dynamic behaviour of discrete systems described by linear or linearized equations of motion. From an engineering point of view, this approach simplifies the modelling of machines and mechanical systems subject to vibrations. One, two up to n-degree-of-freedom (d.o.f.) systems are considered, by writing the related equations of motion both in scalar and matrix form. Solution methods for the resulting equations are described for both free and forced motion. Several numerical examples are shown. At the end of the chapter the modal approach in principal coordinates for discrete n d.o.f. systems is illustrated.

An overview of wind tunnel activities and methodologies to support the design of long-span suspension bridges is proposed. The most important aspects of the wind-bridge interaction are investigated considering the aerodynamic phenomena affecting the different parts of the bridge (mainly deck and towers). The experimental activities and results are proposed in the framework of a synergic approach between numerical and experimental methodologies that represent the common practice in defining the full scale aeroelastic behaviour of the bridge starting from scaled reproduction of the wind-bridge interaction. Static and dynamic wind loads, aeroelastic stability, vortex-induced vibrations will be investigated.

The basic concepts related to parameter identification techniques are summarized in this final chapter. These methodologies allow for the identification of some unknown parameters of numerical simulation models of machines and structures, starting from experimental tests on prototypes or real structures. In particular, the text describes modal identification techniques, both in the time and frequency domain. Some examples are given.

This chapter introduces the mechanical systems subjected to force fields, where the excitation depends on the state of the system. As known, these force fields can change the stability characteristics of the mechanical system. The analyses is conducted by introducing the force field characteristics (positional or velocity dependent forces) obtained by linearizing the equations of motion (for 1, 2 and “n” degree-of-freedom systems) in the neighborhood of the static equilibrium position. Stability is analyzed by applying the eigenvalues-eigenvector approach. Some real applications are presented: aerodynamic forces on airfoils, contact force effects in cutting tools, hydrodynamic lubrication in journal bearings and contact force effects in rail and road vehicles. Some real applications are presented: aerodynamic forces on airfoils, contact force effects in cutting tools, hydrodynamic lubrication in journal bearings and contact force effects in rail and road vehicles.

Vortex-induced vibrations are not negligible while evaluating the aerodynamic and aeroelastic behavior of a long-span suspension bridge. This kind of forcing, that can produce high vibration levels, occurs at very low reduced velocities concerning low wind speed and high-frequency modes. This work presents results of experimental tests performed on the multibox deck shape of the Messina Strait bridge investigating vortex shedding phenomena and developing a numerical model to reproduce the vortex shedding forcing. The experimental tests, focused on low reduced velocities, highlight the typical non-linear pattern of the vortex shedding.

Urban rail vehicles can present peculiar problems that require specific analysis of both vehicle dynamics and wheel–rail contact phenomena. This article deals with the numerical–experimental investigations that were performed to evaluate derailment risk, showing the mechanism of flange climb and the conditions that can mainly influence derailment occurrence. In particular, the influence of the dynamic effects related to the vehicle response to track irregularities is investigated, showing that the track’s geometrical defects play a key role with respect to derailment risk.

An analysis refinement of the Messina Strait suspension bridge project has been recently required, concerning mainly the yaw angle effects on the multi-box deck section aerodynamics and the vortex shedding at low reduced velocities V*. In particular the possible interaction of the axial flow with the large cross beams has been investigated. An original test rig has been designed at this purposernallowing for both forced motion and free motion aero elastic tests, varying the average angle of attack a and the deck yaw angle b. The hydraulic driven test rig allowed for both dynamic and stationary tests so that both the stationary coefficients and the flutter derivatives have been evaluated for each yaw angle. Specific free motion tests, taking advantage from the aeroelastic features of the section model, allowed also the study of the vortex shedding induced phenomena.

The Tacoma Bridge disaster, in the 40s, has opened a new interesting chapter in the study of suspension bridges. This is still open today, as the need of making connections easier leads to bridge spans which are longer and longer. Table I gives a list of the suspension bridges with the longest main span, while Figure 1 shows the trend in the main span length for different kind of bridges: a sharp growth is clear in the last years. The complex development of the Messina Strait Bridge project is part of this scenario, in which longer and longer bridges are being built. The project has been brought to an end by 1992 (Ponte sullo Stretto di Messina, 1992): it is a road and railway crossing, with a main span of 3300 m. This paper resumes the huge research carried out about the wind actions on the bridge, which is for sure one among the most critical aspects of the project. Into details, the main purpose has been a careful design and improvement in the shape of both the deck and the towers. An outline of the research carried out on this topic is going to be presented, together with the main results (see also Diana et al., 1999b;Diana et al., 1998;Cigada, 1994;Brancaleoni, 1993;Simiu and Scanlan, 1986).