DK169444B1 - System and method for countering wind-induced oscillations in a bridge carrier - Google Patents

Description

DK 169444 B1 i

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a system and method for counteracting wind-induced oscillations in bridge carriers on long cable-borne bridges, wherein a plurality of symmetrically arranged control surfaces 5 arranged along the longitudinal axis of the bridge are adapted to utilize the wind energy to automatically reduce said oscillations in response to the movement of the bridge carrier.

In the case of long-span bridges with insufficient rigidity and damping, oscillations may occur due to aerodynamic instability. In the worst case, these swings can become fatal and cause the bridges to collapse. The fluctuations are also often denoted by the English term flutter. These may be torsional oscillations or vertical oscillations or a combination thereof. Eg. it was the torsion oscillations that in 1940 destroyed the Tacoma Bridge in the United States, which at that time was the world's longest suspension bridge.

Aerodynamic instability occurs when the aerodynamic forces reduce the torsional rigidity of the bridge carrier or the total damping (structural as well as aerodynamic) becomes negative, which means that the bridge is supplied with more energy than is absorbed in the oscillation movement. The wind speed at which aerodynamic instability occurs is referred to as the flutter wind speed or critical wind speed, and it decreases with decreasing structural stiffness and damping.

The problem is traditionally addressed by e.g. to increase the stiffness of the bridge carrier or by mounting mechanical damper devices. For a given cross section of the bridge carrier, its torsional rigidity will decrease with increasing span.

Therefore, as the span increases, it is also necessary to increase the fracture cross-section to establish the sufficient torsional stiffness. However, the increased cross-sectional area gives rise to larger wind loads, which in turn leads to increased demands on the structural strength of the bridge carrier and thus means increased construction costs. Also, of course, for the appearance of the bridge, there are limits to how much one wishes to increase the cross-section of the bridge carrier 5. These conditions have thus set an upper limit on the range of spreads that can be achieved.

US patent 4,741,063 discloses a system which uses control surfaces to counteract wind-induced oscillations in a bridge carrier by utilizing wind energy. A surface is placed on each side of the longitudinal axis of the bridge. The surfaces are preferably fixedly mounted; but they can also be adjustable, possibly using an automatic control system.

15

From an article by H. Kobayashi, et.al. "Active control of the Flutter of a suspension bridge" (Preprint from the Eighth International Conference on Wind Engineering, London, Canada, July 1991) is known a similar system, 20 where two control wings are placed over the bridge carrier in each side of the bridge. The wings are pivotally suspended and can be moved harmoniously in line with the movements of the bridge carrier. The influence of the wind on the wings thereby produces forces which can be transferred to the bridge carrier and counteract its movement. This system means that one can reduce the mechanical dimensions of the bridge carrier and attenuate any oscillations by means of the control wings. However, this system suffers from disadvantages.

The system described is a harmonic control which is associated with a particular oscillation frequency. This is inconvenient as the oscillations in a cable-carried bridge that precede an instability situation are an overlay of several oscillation modes with each oscillation frequency. The combination of these oscillations is not harmonious and thus the described control has no general applicability.

3 DK 169444 B1

The control wings are placed over the bridge and this means that they will sit in an area where the air flow is usually quite turbulent. This is partly due to the fact that the elements which carry the bridge 5, e.g. cables, hangers, etc., partly protects and guides traffic, e.g. railings, auto guard, light screens and light masts. The traffic on the bridge also helps to make the air flow on the top of the bridge turbulent. Thus, it is difficult to make precise adjustments to the movements of the bridge when the control wings are placed in this area. Furthermore, control wings placed in this way over the bridge will significantly affect the aesthetic appearance of the bridge.

15 Furthermore, the system described in the article does not take into account that the control of the control surfaces depends on the direction of the wind relative to the bridge carrier. Reversing the wind direction requires the opposite movement of the control surfaces to achieve the intended effect.

20

The invention provides a system which, far better than the one described in the above-mentioned article, allows the wind energy to be utilized to create stabilizing aerodynamic forces on very long bridges, thus counteracting the forces that set the bridge in oscillations. The system is unaffected by the turbulent air flows that exist on the upper side of such a bridge, as well as being able to take into account changing wind directions and speeds as well as combinations of several types of oscillation. Thus, the float velocity can be significantly increased without the use of a large, inconvenient and expensive torsional rigid bridge carrier.

This is achieved according to the invention by using control surfaces which are divided into sections in the longitudinal direction of the bridge. In addition, there are a number of detectors for measuring the movements of the bridge carrier, and for each control section, DK 169444 B1 4 includes a local control unit which is arranged to control the control section in question depending on information from one or more detectors.

5 By thus dividing the control surfaces into sections, it is possible to give the system a very long extension in the longitudinal direction, just as the division into sections makes it possible to individually regulate the individual sections and thus take into account the oscillating trends that can be observed. the place in question on the bridge, even if the oscillations are not harmonious.

As stated in claim 2, leaving the detectors in the longitudinal direction of the bridge at the same time as each local control unit controls the associated control surface section in dependence on information from the detector (s) nearest to it, a further improvement of the system's ability to take into account is achieved. the local oscillation conditions.

In a particular embodiment described in claim 3, the detectors, like the control surfaces, are arranged substantially symmetrically about the longitudinal axis of the bridge such that there is a detector for each local control unit and this 25 controls the associated control surface section depending on information from the control unit. associated detector.

As stated in claim 4, providing the system with a main control unit capable of receiving information from several 30 detectors in the longitudinal direction of the bridge and sending control signals back to the local control units, it is achieved that the system can also take into account the total oscillation image for the entire bridge.

In a particular embodiment as recited in claim 5, the local control units control the associated control surface portion in dependence on the control signal received from the main control unit 5 DK 169444 B1.

In one embodiment described in claim 6, there are at least two main control units. By allowing each master control unit to receive information from a portion of the detectors and correspondingly transmit control signals to a portion of the local controllers distributed in the longitudinal direction of the bridge, additional security is achieved if any failure of one of the controllers occurs. In this case, the detectors and the local controllers belonging to the other controllers will continue to function. The control section sections are thus divided into groups, each distributed over the length of the bridge, and faults in a control unit will only be able to disable the associated group, thereby significantly improving the safety of the entire bridge.

Further, as stated in claim 7, to provide the system with a number of sensors which can measure the direction of the wind and to use the local control units or the main control units, respectively, to obtain the resulting information on the wind direction, a system is obtained which can adjust the control surfaces below taking into account the wind direction.

Furthermore, as indicated in claim 8, using sensors which can measure the speed of the wind, it is also possible to take this into account in the system.

In one embodiment described in claim 9, the control surfaces are placed below the bridge carrier and at a distance from the latter, where the air flow is almost undisturbed by the bridge carrier. Hereby a system is obtained which is not affected by the turbulent air flows, which are found especially on the upper side of the bridge. Claim 10 describes a particular embodiment in which the control surfaces are attached to the bridge carrier by means of pylons on the underside of the bridge carrier.

DK 169444 B1 6

In an alternate embodiment as claimed in claim 11, the control surfaces are formed by sections of the surface of the bridge carrier itself, the outermost parts of the bridge carrier in the transverse direction of the bridge being movable in such a way that the cross-section of the bridge carrier 5 and thus its aerodynamic properties are changed. This results in an aesthetically pleasing appearance of the bridge carrier, since the control surfaces are not immediately visible.

10 In the method according to the invention, the control surfaces are divided into sections in the longitudinal direction of the bridge. A number of detectors measure the movements of the bridge carrier, whereupon a local controller at each control surface section controls this in reliance on information from one or more detectors.

An improved method is obtained, as described in claim 13, when one or more master controllers receive information from a plurality of detectors and send control signals to a number of local controllers, thus enabling the overall oscillation image of the bridge to be taken into account.

A further improvement of the method is achieved by measuring, as mentioned in claim 14, the direction of the wind at a number of sensors and sending signals thereto to the local controllers or main controllers and using these signals in the control of the control surfaces.

The invention will be described in more detail below with reference to the drawing, in which: FIG. 1 shows a section of a suspension bridge where the invention can be used; FIG. 2 shows a section of a sloping roof bridge with central slopes in which the invention can be used; FIG. 3 shows a section of a bridge with a first embodiment of controlled control surfaces placed in the free flow under the bridge carrier; FIG. 4 is a detail view of a cross-section of the bridge of FIG. 3, FIG. 5 is a cross-section of the bridge of FIG. 3, 10 FIG. 6 shows how detectors and local controllers can be connected to a main controller; FIG. 7 shows an alternative mode of connection which includes two main control units; FIG. 8 shows a section of a bridge with another embodiment of controlled control surfaces integrated into the edge of the bridge carrier, and FIG. 9 is a detail view of a cross-section of the bridge of FIG. 8th

FIG. 1 and 2 show examples of bridges in which the invention can be applied.

25

FIG. 1 shows a suspension bridge. A bridge carrier 1 is carried by carrier cables 2 and vertical or inclined hangers attached thereto 3. The carrier cables 2 are again carried by a bridge tower 4. Bridges of this type will typically have two towers and the distance between these towers is referred to as the span of the bridge. Thus, on the entire stretch between the two towers 4, the bridge carrier 1 is carried by the carrier cables 2 and the hangers 3.

It can be seen that such a bridge carrier could be subjected to considerable forces at high 35 wind impacts, which may cause fluctuations in the bridge carrier. These may be fluctuations of different types. In the case of vertical oscillations, the oscillation of the bridge carrier will take place in the vertical direction, while in the case of horizontal oscillations, oscillations in the horizontal direction will occur. There may also be torsional oscillations in which the entire bridge carrier "twists" around the longitudinal axis of the bridge. In addition, combinations of these oscillation types may occur. For example, the world's longest suspension bridge, the Tacoma Bridge in the United States, was destroyed in 1940 as a result of torsional fluctuations.

10

In order to counter these oscillations, it has previously been necessary to increase the stiffness of the bridge carrier or to install mechanical damping devices. It can be seen that the larger the span of the bridge, the stiffer the bridge carrier must be built-up in order to avoid oscillations. However, since there is a limit to the dimensions of the cross-section of the bridge carrier and thus to its stiffness, an upper limit is thus also set for how large spans can be built safely. In the invention, it has been found possible to substantially increase this limit.

FIG. 2 shows another bridge type, a so-called oblique bridge, where the oscillation phenomenon can occur and the invention thus applies. Here, a bridge carrier 5 of 25 carries a number of so-called slopes 6, which in turn is carried by a bridge tower 7. Also in this bridge type one or two bridge towers are used, and the span of the bridge is the distance between two supports for the bridge carrier. Those for the suspension bridge of FIG.

The oscillation conditions described in 1 also apply to this bridge type. There are also combinations of the two bridges, as well as other variants. As a common term, these bridges are often referred to as cable-borne bridges.

FIG. 3 is a perspective view of a section of a suspension bridge of the same type as that of FIG. 1. Again, carrier cables 8, 9 are attached to which are attached a number of hangers 10 carrying the bridge carrier 11. On the upper side of the bridge carrier there are lanes 12, and various handrails and guardrail 13 are arranged.

As can be seen, the bridge here is provided with a plurality of control surface sections 14, 15, 16, 17. Each section is arranged on two two aerodynamically shaped pylons 18 and, as will be further described below, can be individually controlled. There are control surface sections on both sides of the bridge carrier.

10 When these control surface sections are exposed to the wind, they will, depending on their position, affect the bridge carrier with an upward or downward force.

Both the direction and magnitude of the force can be changed by changing the position of the control surface section. Thus, at wind direction 15 towards sections 14, 15, 16, the control surface section ion 14 will provide an upward force on the bridge carrier, while section 16 will correspondingly provide a downward force. In this way, it becomes possible to counteract oscillations that may occur in the bridge. Thus, if the bridge carrier at a given location is pivoting upwards, by adjusting the corresponding control surface section, the bridge carrier at that location can be influenced by a downward force and thus attenuate the pivot.

The control surfaces are located on the underside of the bridge because the air flow here is relatively undisturbed by the presence of the bridge. On the upside, the flow is more turbulent, due, among other things, to cables, hangers, handrails, guardrails and windscreens as well as the traffic on the bridge.

30

In order to measure the movements that occur in the bridge, a number of detectors are placed in the bridge carrier. These detectors are e.g. of accelerometers. On the basis of the measurements from these detectors, the control surface sections are controlled in such a way as to counteract oscillations.

DK 169444 Bl 10 In fig. Figure 4 shows a detail section of a cross-section of a cable-carried bridge. Again, the bridge carrier 11 is shown, on which is a lane 12 and a railing / guardrail 13. The bridge carrier is, as previously described, suspended in hangers or slopes 5 10, and a control surface section 17 is placed on a pylon 18. A detector 19 measures the movement of the bridge or accelerates that location and sends a signal to a controller 20. This controller may e.g. is made up of a computer. Based on a control algorithm, control unit 20 then sends a signal to a servo pump 21 which controls a hydraulic cylinder 22. The hydraulic cylinder 22 can then rotate the control surface section 17 by means of an exchange plate 23 and a control rod 24. In this way, the control surface section 17 is constantly adjusted depending on the movements of the bridge carrier at that point as measured by the detector 19.

As seen in FIG. 5, which shows a cross section of the entire bridge carrier, the controller 20 can be connected to the corresponding controller 25 on the opposite side of the bridge carrier. The system in this page is also quite similar to the one just described. By allowing the two controllers 20, 25 to exchange information, it is possible to better take into account the type of oscillation that may arise from the applicable location. For example, if both detectors 19, 26 detecting an upward movement, there will be an initial vertical oscillation, and both of the control surface sections 14, 17 will therefore be adjusted to give a downward force. On the other hand, if the detector 30 measures an upward movement, while the detector 26 measures a downward movement, it is a torsional oscillation, and the control surface section 17 will therefore be set to provide a downward force, while the section 14 is set to provide an upward force. , 35 to counteract the torsional oscillation.

XI

DK 169444 B1

However, in order to make these settings of the control surface sections, the control units 20, 25 must know the wind direction, since this is crucial to how the control surface sections must be adjusted to give the desired force effects. In FIG. 5, there is also shown a wind sensor 27 which can provide the control units with information on the direction of the wind. The sensor 27 may also be arranged to provide information on the current wind speed. In the figure, the wind sensor 27 is connected to the control unit 20. Another possibility would be that each of the control units 20, 25 has its own wind sensor. As shown, the sensor 27 can be placed on the underside of the bridge, as the air flow here is most undisturbed by the bridge, but other locations are possible.

Similarly, detectors 19, 26 can also be replaced by a common detector which can be utilized by both controllers 20, 25, since this common detector must then also only be able to measure angular turns of the bridge about the longitudinal axis of the bridge carrier 20.

As shown in FIG. 3, the control surfaces are divided into longitudinal sections of the bridge, and FIG. 4 and 5 show the structure of such a section. Each of these sections 25 can operate independently, as just described; but improved control can be achieved if all sections are additionally connected to a common master controller. FIG. 6 shows an example of how the local controllers and detectors can be connected to a main controller 30 28. The overall information contained in considering all sections simultaneously provides important information on the type of swing (or combination of several) the bridge moves look for. This information can be used to optimize the overall control of the overall system of control surfaces. The main controller 28 can provide the local controllers with this information, after which they can take this into account when controlling the respective control surface sections. However, it is also possible to let the main control unit 28 take over the entire control, thus it itself obtains information from all the detectors and then directly controls the control section sections. In FIG. 6, the wind sensors are not shown, but these can be connected in the same way as the motion detectors.

In the case where the main control unit 28 is responsible for controlling the control surface sections, it will be seen that the number of detectors need not be the same as the number of control plate sections. Thus, it is conceivable that a smaller number of detectors evenly distributed in the longitudinal direction of the bridge will be able to provide the main controller 28 with sufficient information about the current oscillation state of the bridge, while the control surface sections must be placed at less distance to provide optimal control. Also, for mechanical reasons, there may be a limit to how long guide recharge sections you want to use.

20

A system such as that of FIG. 6 will, of course, be vulnerable to errors in the main controller 28. A more secure system can therefore be obtained by using multiple main controllers. In FIG. 7, there is shown an example where there are two main control units 28 and 29. In order to provide the greatest possible security if one of the units 28, 29 becomes faulty, each other section is connected to the main control unit 28, while the remaining ones are connected to the main control unit 29. Each main control unit 29 is thus connected to 30 a group of sections. In FIG. 7, it is seen that the sections 30, 32 are connected to the main control unit 28, while the sections 31, 33 are connected to the main control unit 29. The distribution of sections between the two control units can of course also be done according to other criteria. If more than two main controllers are used, the sections are distributed equally among the controllers. The overall security of the total system is increased by the number of main units and thus the number of independent sections.

In the system described here, as also shown in FIG. 3, separate control charge sections are each controlled by a local control unit 20, 25. However, embodiments may also be envisaged using a long, continuous control surface on each side of the bridge. This control surface may then be constructed of a flexible material so that the local control units can move a portion of the control surface.

There need not be control surfaces throughout the length of the bridge. The placement of these can be restricted to those areas of the bridge where their power will be optimal, and these positions will typically be the areas that can be subject to severe oscillations. This will normally be the middle portion of the bridge for symmetrical swing shapes and near the quarter points of bridge buckles for asymmetrical swing-shape shapes.

In FIG. 8 shows an alternative embodiment of the invention. Instead of placing the control surfaces on pylons under the bridge carrier, the surfaces here are integrated into the bridge carrier itself. Here, the outer edge of the bridge carrier itself is divided into sections, which can be moved vertically and thus change the geometry of the bridge. Similarly, as previously described, these surfaces utilize the energy of the wind to give the bridge carrier a force effect in the up or down direction. The figure shows sections 34, 35, 36 where section 34 is set to change the forces on the bridge carrier downwards, while section 36 is adjusted to change the forces on the bridge carrier in an upward direction with the sections 35 shown.

14 DK 169444 B1

The sections are arranged to be able to rotate about an axis of rotation 37, and the operation is more clearly seen in FIG. 9th

It can be seen from this that the outermost part 34 can be rotated about the axis of rotation 37. The dashed line 38 shows the upper position of the section, while 39 correspondingly shows the lower position of the section. As before, the movement of the section is controlled by a hydraulic cylinder 40 and a control rod 41. As previously described, the hydraulic cylinder 40 is controlled by a servo pump 10 which is again controlled by a local control unit. the steering is similar to the one previously described.

In this embodiment, the additional guide surfaces which are suspended under the bridge are avoided. This has a cost-15 significance, and it will give the bridge an aesthetically pleasing appearance.

The control algorithm used in the local controllers and the main controllers, respectively, will depend on the current bridge concept, taking into account many factors such as e.g. the span of the bridge and the dimensions of the bridge carrier. The control algorithms are based on the fact that the control surfaces must constantly supply forces which are opposite to the direction of the bridge edge movements. In the case of torsional movements 25 of the bridge carrier, this can e.g. This is done by, in principle, allowing the control surfaces to move at the same frequency as the torsion movement of the bridge carrier, but merely phase-shifted in relation thereto. Typically these will be phase shifts of 60 to 90 °. The actual design of the control surfaces will also depend on the bridge concept in question.

The above are examples of how a system according to the invention can be implemented, and it will be appreciated that details can be changed in many ways within the scope of the invention. Thus, e.g. other designs of the control surfaces than those described herein are used and the control system can be expanded to take into account additional measured parameters.

Claims (14)

A system for countering wind-induced oscillations in a bridge carrier (11) on long cable-borne bridges, wherein a number of substantially symmetrically arranged control surfaces (14, 15, 16, 17, 34, 35, 36) arranged symmetrically about the bridge axis utilizing the wind energy to automatically reduce said oscillations in response to the movement of the bridge carrier 10, characterized in that the control surfaces (14, 15, 16, 17, 34, 35, 36) are divided into sections in the longitudinal direction of the bridge and that there is also a the number of detectors (19, 26) for measuring the movements of the bridge carrier, and that one local control unit (20, 25) belonging to each control surface section (14, 15, 16, 17, 34, 15 35, 36) is arranged to control the respective control section (14, 15, 16, 17, 34, 35, 36) depending on information from one or more of said detectors (19, 26). System according to claim 1, characterized in that said detectors (19, 26) are distributed in the longitudinal direction of the bridge and that each local control unit (20, 25) controls the associated control surface section (14, 15, 16, 17, 34). 35, 36. depending on information from the detector (s) nearest 25 (19, 26). System according to claim 1 or 2, characterized in that the detectors (19, 26) are arranged substantially symmetrically about the longitudinal axis of the bridge such that a detector (19, 26) is provided for each local control unit, (20, 25. and that each control unit (20, 25) controls the associated control surface section (14, 15, 16, 17, 34, 35, 36) depending on information from the associated detector (19, 26). System according to claims 1-3, characterized in that there is furthermore a main control unit (28) which is arranged in DK 169444 B1 to receive information from a number of said detectors (19, 26) and, as a result, send control signals to a number of said local controllers (20, 25). 5 System according to claim 4, characterized in that each local control unit (20, 25) controls the associated control section (14, 15, 16, 17, 34, 35, 36) depending on one received from the main control unit (28). control signal. System according to claim 4 or 5, characterized in that there are at least two main control units (28, 29) and that each main control unit (28, 29) is arranged to receive information from a number of said detectors (19, 26). ) and transmit control signals to a number of said local controllers (20, 25). System according to claims 1-6, characterized in that there are a plurality of sensors (27) for measuring wind direction and that the local control units (20, 25) or the main control units (28, 29) also control said control. surface sections (14, 15, 16, 17, 34, 35, 36) depending on signals from these sensors (27). 25 System according to claim 7, characterized in that said sensors (27) can further measure wind speed. System according to claims 1-8, characterized in that the control surfaces (14, 15, 16, 17) are arranged below the bridge carrier (11) and at a distance therefrom, where the air flow is almost undisturbed by the bridge carrier. System according to claim 9, characterized in that the control surfaces (14, 15, 16, 17) are attached to the bridge carrier (11) by pylons (18) on the underside of the bridge carrier (11). DK 169444 B1 System according to claims 1-8, characterized in that the control surfaces (34, 35, 36) are formed by sections of the surface of the bridge carrier (11) itself, the outer parts of the bridge carrier (11) being arranged in the transverse direction of the bridge to is moved so that the cross-section of the bridge carrier (11) and thus its aerodynamic properties are changed. A method for counteracting wind-induced oscillations in a bridge carrier (11) on long cable-supported bridges, wherein a number of substantially symmetrically arranged control surfaces (14, 15, 16, 17, 34, 35, 36) symmetrically about the bridge axis energy for automatically reducing said oscillations depending on the motion of the bridge carrier, characterized in that the control surfaces 15 (14, 15, 16, 17, 34, 35, 36) are divided into sections in the longitudinal direction of the bridge and that a number of detectors (19, 26 ) measures the movement of the bridge carrier, whereupon one local control unit (20, 25) of each control surface section (14, 15, 16, 17, 34, 35, 36) controls the respective control surface-20 section (14, 15, 16, 17 , 34, 35, 36) depending on information from one or more of said detectors (19, 26). Method according to claim 12, characterized in that one or more main control units (28, 29) receive information from a plurality of said detectors (19, 26) and, as a result, send control signals to a number of said local control units (20, 25). Method according to claim 12 or 13, characterized in that a plurality of sensors (27) measure wind direction and transmit signals thereto to the local control units (20, 25) or the main control units (28, 29), after which they further control said control surface sections. 35 (14, 15, 16, 17, 34, 35, 36) depending on the signals from the wind sensors (27).