Patent Description:
There are two main situations in which the dynamic behavior of a railway bridge is essential for evaluating its safety and functionality.

The first of said situations is the commissioning of a new work, subjected to high-speed traffic (V><NUM>/h), capable of generating damaging vibrations in the structure if they are not suitably taken into account. Structural calculation during the project phase is performed based on certain hypotheses relative to the properties of the bridge and its materials, which are often verified for safety by means of a load test (prior to accepting the work). Particularly in Spain, this verification is compulsory according to Instruction on Technical Inspections in Railway Bridges (Inspecciones Técnicas en los Puentes de Ferrocarril - ITPF-<NUM>).

The second situation arises in light of the increased loads and/or speeds of a train passing over an already existing bridge. Due to the circulation of heavier and faster railway traffic, the structure may not be prepared to support higher levels of vibration. In such case, load tests are again required to verify the dynamic properties and evaluate the actual bearing capacity of the bridge. If said capacity is not sufficient, it will need to be refurbished or replaced, with the high costs derived therefrom. Infrastructure administrative entities have considerable interest in this sense given the continuous improvement of the rolling stock and the growing demands of transport.

Given the importance of dynamic behavior in both scenarios, some of the inventors of this application already developed an earlier utility model based on counter-rotating masses (reference U <NUM>) for the purpose of reliably measuring:.

In particular, to measure the real damping, structure vibrations that are similar in intensity and duration to the passage of a railway are required, given that this can generate a non-linear response rendering methods based on environmental vibrations (for example, wind) or small manually transportable exciters rather unreliable. The passage of heavy railway axles opens/closes cracks and microcracks, mobilizes friction in the ballast, and of the ballast with the track, further deforms the supports, etc., said complex phenomena being responsible for the non-linearity. In this sense, tests based on recording the free vibration after the passage of trains are normally used, but the short duration thereof and the fact that not all the vibration modes are excited do not allow a complete structure characterization.

Therefore, utility model U201200785 was developed due to the limitations of the methods based on environmental vibration with manually transportable exciters or on free vibrations. However, the practical usefulness thereof is limited by three shortcomings. These three problems to solve by the filed application are the following:.

In conclusion, to solve the three aforementioned problems and confer the apparatus the required functionalities and reliability, it is necessary to design an exciter based on a large hydraulic actuator, and incorporate a fifth load sensor between the plunger and the vehicle frame.

Korean patent with reference number <CIT> describes a machine related to the present invention to a certain degree because it makes use of a piston-type actuator. However, its design is not suitable for testing railway bridges either due to the following reasons:
The machine described in patent <CIT> is prepared to generate vibrations in the railway track, but not while being located on a bridge or viaduct, but in the track on an embankment. The fundamental difference lies in the fact that in the track on an embankment, the movement of the base of the machine will be essentially vertical, with very limited rotation, but in the case of a bridge the situation is clearly different.

Patent <CIT> allows placing vibrating masses in the form of discs, which hang line a pendulum from the actuator. However, if said equipment is to be used in a bridge and the apparatus was located at any point of the structure in which movement was not purely vertical, the hanging masses would oscillate sidewise, damaging the actuator. A typical case would be a double-track bridge: placing the machine in one of the two tracks, in the center of the opening. In that case, the torsional oscillation would cause the lateral rolling of the masses, especially taking into account its significant elevation with respect to the plane of the rail. Something similar would happen even in single-track bridges if it were not used exclusively in the center of the opening or if skew were present.

The invention described in patent <CIT> furthermore presents an additional problem since it is not prepared to be transported long distances along the track given that it only has small wheels that are only suitable for short displacements.

As for patent <CIT>, it discloses an excitation and vibration measurement system intended for analyzing railway track behavior. It is a complex, multipurpose system formed by one or more railway vehicles with on-board excitation and force and vibration measurement systems. However, said invention fails in separating the excitation action applied by the axles and false axles from the presence of other wheels of the vehicle/s in contact with the track, such that not all, but only some of, the forces applied in the structure are monitored. That is a distinguishing aspect of both reference U <NUM> and the filed application: they measure all forces applied on the bridge.

For this reason, patent <CIT> is not suitable for analyzing bridges by means of the powerful techniques known as SIMO/MIMO (Single/Multiple Input, Multiple Output). Another serious drawback of this system is that the coupling between the vehicle and the track through the wheels does not allow accurately and repeatedly reproducing all the forces that were applied on the track, given that part of said forces is never controlled by the user.

It is also relevant to discuss patent <CIT>, which discloses a device that performs the function of causing the excitation of an infrastructure located under a road vehicle. However, this device suffers the same drawback as the one disclosed by patent <CIT>: when the exciter acts on the infrastructure while the vehicles arranged thereon, coupling between the vehicle and the infrastructure through contact forces in the wheels takes place, said forces being unknown (not measured). This patent therefore gives rise to the same drawbacks already described for patent <CIT>.

Finally, patent <CIT> is also discussed. This document discloses an invention for applying static forces on bridges by means of a road vehicle with a movable rail and a traveling bogie which can be positioned arbitrarily, thus allowing to vary the position and weight to which the load is applied. In comparison with the device disclosed in the filed application, patent <CIT> shares the idea of lifting the vehicle in such a way that forces are not applied to the bridge through the vehicle wheels. For the device in patent <CIT>, which is intended to perform static tests, lifting the vehicle is important to apply the static loads only at the desired positions. In contrast, the device disclosed in the filed application is lifted in such a way that all four points in contact with the bridge are monitored, which provides the complete description of all dynamic forces acting on the bridge, at all times.

Moreover, the action of a train on a bridge presents a considerable pseudostatic component because loads always act downwards, and furthermore there is usually one or more loads on the structure (according to the span of the bridge). This causes the vertical displacement of the bridge to be similar to that of <FIG> upon passage of the train.

This effect is of special importance in bridges. <FIG> shows a TGV passing a <NUM>-meter opening at <NUM>/h. A clear mean value component indicated by the horizontal line (pseudostatic value equal to <NUM>) and causing the bridge to depart from its initial configuration (deformed by the actual weight alone) upon the entry of loads, is seen. Oscillation, which may even exhibit a resonant character depending on the speed, is created from then on: the characteristics of the response will be affected by the base pseudostatic value, since the latter determines the degree of opening of the cracks and microcracks, as well as the work of the supports at full load and at greater friction mobilization in the ballast layer.

To reproduce an effect of this type and to enable applying at the same time intense dynamic forces with an exciter, there is a need to be able to ballast same with a variable weight that is readily adapted to each bridge, a feature which is found in the machine to be patented herein.

In summary, in the field of exciter systems for railway infrastructures, there is currently no suitable system for railway bridges which is capable of applying general forces, with an adjustable static component, and of suitably supporting lateral and torsional oscillations of the bridge. Utility model U <NUM> can only produce harmonic forces but not general impulsive or transient forces, and given the wide range of frequencies of interest, the eccentricity of the machine needs to be varied by a ratio of <NUM>:<NUM> which complicates both the construction and the operation thereof. Moreover, Korean patent <CIT> cannot be used either because it would deteriorate due to the lateral/torsional oscillation of the bridge, requiring an actuator with masses that are guided by linear bearings. Furthermore, the apparatus in the Korean patent is not prepared for being ballasted, nor is it prepared for being transported long distances along a railway track, making the use thereof in real railway bridges completely impractical. Patents <CIT> and <CIT> fail to identify all forces acting on the structure, since only some of the contact points of those devices with the bridge are monitored with force sensors. That prevents the use of SIMO/MIMO techniques in a convenient manner, because all input forces to the structure ought to be known at all times in order to apply such techniques.

Due to their different lengths and rigidities, railway bridges require an adjustable supplementary static force that must be controlled by means of ballasts that are suited for each bridge. Furthermore, in certain situations it may be appropriate for dynamic testing to be performed prior to track installation to verify the structural characteristics of a new work. Accordingly, in the present invention, it is also relevant to propose an embodiment such that the apparatus can be moved to the structure in a rubber-tyred rolling vehicle.

<CIT> discloses a system to excite a bridge using a swinging mass.

The exciter systems according to the invention are defined in claims <NUM> and <NUM>. The exciter is made up of a servo-hydraulic actuator connected to a railway wagon designed for such purpose so as to be able to transport same over the tracks. The exciter can also be connected to a (towed or self-propelled) rubber-tyred vehicle suitable for circulating on a road or a line of railway or highway. The actuator generates a force by moving a variable-weight reaction mass guided by linear bearings.

The value of the reaction mass will be the function of the type of infrastructure to be analyzed by means of the application of the exciter, taking into account load requirements for the excitation. The engine design will be adapted to said requirements.

Additionally, it will comprise hydraulic equipment enabling direct transmission of the vibrations to the infrastructure, independently of the rolling gear of the wagon or the rubber-tyred vehicle, via false wheels. This is necessary to prevent wear in the rolling elements and to prevent excitation energy loss in the suspension elements of the wagon or vehicle (suspension dampers). The wagon or vehicle will allow a variable-weight ballast for the purpose of exerting variable forces of different intensity, without losing contact with the rails or the structure and where the pseudostatic effect can be reproduced.

The movement of the piston of the actuator will be controlled by a computer system programmable for such purpose, allowing the actuator to apply general forces on a bridge, such that they do not exceed the maximum acceptable displacement of the piston: harmonic, impulsive, and transient forces.

Lastly, the equipment will be equipped with the necessary load control elements to know, at all times, the force actually transmitted to the infrastructure, by means of a sensor located between the actuator and the wagon and additional sensors in the false wheels. Said sensors in the false wheels will also measure the vibratory movement of the bridge in order to know its response using the smallest number of external sensors possible. The simultaneous presence of the sensor located between the actuator and the wagon, plus the additional sensors in the false wheels, enable to compare their force measurements with an external algorithm that verifies Newton's second law of motion, in such a way that it is possible to detect when any of those five force sensors is miscalibrated, without the need to either move the machine from its position or remove the sensors. This is the main distinguishing feature of the filed application.

A series of drawings which help to better understand the invention, some of which are expressly related with the embodiments of said invention as non-limiting examples thereof, are very briefly described below.

The preferred embodiment is shown in <FIG> in which a railway wagon (<NUM>) houses a frame (<NUM>) integral therewith, on which a weight-adjustable reaction mass (<NUM>) can slide vertically guided by linear bearings (<NUM>) having a very low friction. The reaction mass (<NUM>) is driven with a piston or plunger (<NUM>) which is part of the hydraulic actuator (<NUM>), the movement of the piston being controlled by means of ad-hoc software and hardware, with the functionalities necessary for producing general load functions, such that they do not exceed the maximum acceptable displacement of the piston: harmonic, impulsive, and transient forces.

The precise measurement of the load function is essential, so a novel dual device is proposed, consisting of a first aggregate sensor (<NUM>), located between the actuator (<NUM>) and the wagon (<NUM>), and additional sensors (<NUM>) directly measuring the specific force transmitted at each contact point of the machine with the train track located on the bridge. This dual device allows detecting miscalibration of the sensors without the need to either move the machine from its position or remove the sensors, and thereby increases measurement quality and reliability. The direct measurement of the forces exerted on the track allows performing maintenance operations without having to clear the track of ballast, thereby saving considerable time and costs. The wagon and the track come into contact by means of false wheels (<NUM>), which are contacted with the rails by means of hydraulic actuators (<NUM>) capable of blocking vertical movement, while at the same time also blocking the suspension systems of the wagon so that they do not oscillate during movement. The sensors (<NUM>) located in the false wheels also measure the vibratory movement of the bridge in order to know its response using the smallest number of external sensors possible.

The pseudostatic effect of the weight of a train, shown in <FIG>, is reproduced by means of the actual weight of the wagon (<NUM>), which may have to be ballasted depending on the bridge, its span, and its rigidity. For such purpose, the wagon (<NUM>) is provided with the possibility of incorporating additional ballast (<NUM>), until reaching the required weight.

A second embodiment is shown in <FIG> in which, in this case, it is a rubber-tyred vehicle (<NUM>) which houses the frame (<NUM>) integral therewith, on which a weight-adjustable reaction mass (<NUM>) can slide vertically guided by linear bearings (<NUM>) having a very low friction. The vehicle may be a towed or self-propelled vehicle, as appropriate. This type of vehicle makes it possible to transport the system to the bridge along a line of the railway, prior to track installation, to perform acceptance tests or tests of another type. Likewise, due to its configuration, it allows testing road bridges, if necessary.

The reaction mass (<NUM>) is driven with a piston or plunger (<NUM>) which is part of the hydraulic actuator (<NUM>), the movement of the piston being controlled by means of ad-hoc software and hardware, with the functionalities necessary for producing general load functions, such that they do not exceed the maximum acceptable displacement of the piston: harmonic, impulsive, and transient forces.

Like in the first embodiment, the precise measurement of the load function is essential, so a novel dual device is proposed, consisting of a first aggregate sensor (<NUM>), located between the actuator (<NUM>) and the rubber-tyred vehicle (<NUM>), and additional sensors (<NUM>) directly measuring the specific force transmitted at each contact point of the machine with the deck of the bridge on which it is located. This dual device allows detecting miscalibration of the sensors without the need to either move the machine from its position or remove the sensors, and thereby increases measurement quality and reliability. The rubber-tyred vehicle and the bridge come into contact by means of false wheels (<NUM>), which are contacted with the deck by means of hydraulic actuators (<NUM>) capable of blocking vertical movement, while at the same time also blocking the suspension systems of the rubber-tyred vehicle so that they do not oscillate during movement. The sensors (<NUM>) located in the false wheels also measure the vibratory movement of the bridge in order to know its response using the smallest number of external sensors possible.

Claim 1:
Exciter system for inducing vibrations in railway bridges based on harmonic forces which can be transported long distances by railway and is capable of carrying out dynamic testing prior to track installation, by inducing vibrations based on harmonic, impulsive, and transient forces, said system being made up of a vertical hydraulic actuator (<NUM>) and a variable-weight reaction mass (<NUM>) vertically guided by linear bearings (<NUM>) preventing any horizontal movement of said mass (<NUM>) with respect to a frame (<NUM>) and driven by a piston (<NUM>) of the hydraulic actuator (<NUM>), which is integrally assembled on a railway wagon (<NUM>) designed for such purpose, which system incorporates a variable-weight ballast (<NUM>) for the purpose of applying variable forces of different intensity without losing contact with the rails, wherein a movement of the piston (<NUM>) of the actuator (<NUM>) is controlled by a computer system programmable for such purpose, allowing the actuator (<NUM>) to apply general forces, in particular harmonic, impulsive, and transient forces, on the bridge, such that they do not exceed a maximum acceptable displacement of the piston (<NUM>), wherein forces which the actuator (<NUM>) applies on the bridge are aggregately measured via a sensor (<NUM>) located between the actuator (<NUM>) and the wagon (<NUM>), the wagon (<NUM>) comprises hydraulic equipment (<NUM>) capable of transmitting excitation directly to the bridge, without going through a rolling system of the wagon, via false wheels (<NUM>), the system further comprises additional force and vibration sensors (<NUM>) arranged at each of the false wheels (<NUM>).