JP2004285753A - Bridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of a bridge of a box girder bridge type applied to a long suspension bridge, wherein its natural frequency is low so that flatter is liable to occur, and it is not easy to increase the flatter appearance wind speed. <P>SOLUTION: This bridge includes: a flat bridge body 2 of a double box girder bridge type structure extended in the axial direction of the bridge; a central ventilation opening 3 formed in the central area in the cross direction of the bridge body 2 to vertically penetrate and extended in the axial direction of the bridge; a grating structure provided on the top of the central ventilation opening 3 to allow a vehicle to pass thereon; and a central wind shield structure 7 provided in the state of passing the central area in the cross direction of the central ventilation opening 3 and projected on both upper and lower sides of the bridge body 2 (composed of a central protection fence 7a erected on teh top of the bridge body 2 and a vertical board 7b provided downward from the lower end of the fence). Both end parts in the cross direction of the bridge body 2 are provided with a trapezoidal fairing 8 having a pair of upper and lower inclined plates 8a, 8b and a vertical plate 8c connected to the tips of the inclined plates 8a, 8b. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-box girder bridge applied to a long suspension bridge or a cable-stayed bridge. The fairing at both ends in the width direction of the bridge body is formed in a trapezoidal shape instead of a triangular shape. Also, the present invention relates to a structure in which guide vanes are provided on the upper and lower sides of a bridge body near a fairing to improve flutter resistance.
[0002]
2. Description of the Related Art Conventionally, a bridge applied to a long suspension bridge or a cable-stayed bridge has a low natural frequency of vertical bending and torsion, so that a wind speed at which intense divergent vibration called flutter appears (hereinafter, flutter occurrence). Wind speed) tends to decrease.
For this reason, as the cross-sectional shape of the bridge, a flat box girder cross-sectional shape close to a flat plate wing having excellent dynamic aerodynamic characteristics is adopted. However, even in the case of a bridge having a flat box girder structure, when the natural frequency is extremely low, there is a problem that the flutter onset wind speed is still low. 2 has been proposed.
[0003]
In the bridge of Patent Document 1, a vertical opening is provided at the center of the box girder, and a vertical drift plate is provided from the upper surface of the box girder to the lower surface of the box girder through the center of the opening. Is to deflect the wind flow on the windward side by the deflector plate, prevent the wind from re-adhering to the upper and lower surfaces of the box girder on the leeward side, suppress the self-excited aerodynamic force, Is higher. The ratio of the opening to the entire width of the bridge is about 10%, and a grating that can be used as a road surface is provided on the upper surface of the opening.
[0004]
As fairings formed at both ends of the box girder, an equilateral triangular fairing sharpened laterally with an upper inclined plate and a lower inclined plate, omitting the upper inclined plate and lowering the lower inclined plate to the top of the box girder Extended upper end overhanging fairing, lower lower end overhanging fairing with lower inclined plate omitted and upper inclined plate extended to the lower surface of box girder, upper inclined plate and lower inclined plate wider than this sideways A sharpened trapezoidal triangular fairing, a semicircular fairing, and the like have been proposed.
[0005]
In the bridge of Patent Literature 2, a ventilation wall having ventilation is provided at the center of the upper surface of the box girder, and a part of the wind flow is passed through the ventilation wall to reduce the wind speed near the upper surface of the bridge. , The flutter expression wind speed is increased. In this bridge, a fairing similar to the above-described scalene triangular fairing is employed.
However, in the bridge of Patent Literature 1, since the width of the opening is not so large, the ventilation of the opening is low, and it is difficult to improve the flutter resistance performance. In the bridge of Patent Document 2, it is possible to increase the flutter expression wind speed to some extent, but it cannot be said that it can still be sufficiently increased.
[0006]
In view of such a problem, a bridge (brief presentation bridge) described in the 55th Annual Meeting of the Japan Society of Civil Engineers Lecture Summary IB59 (see FIG. 10) has been proposed. As shown in FIGS. 10 (a) and 10 (b), the bridges 100 and 101 for presenting lectures are bridges of a two-box girder structure, and a central opening 102 is continuous with a central divider of the box girder. The box girder is formed so as to penetrate vertically or vertically without penetrating the pavement part, and a central wind shield wall 103 and an end are provided on the upper surface at the center and both ends of the box girder as means for guiding air to the central opening 102. Partial wind shield walls 104 are provided, and two inspection vehicle rails 105 are provided on the lower surface of the box girder. In the bridges 100 and 101, a fairing 106 similar to the above-described scalene triangular fairing is employed.
[0007]
In the bridges 100 and 101, the airflow pattern in which the vibration control effect of the central windshield 103 and the central opening 102 is emphasized by the separation interference effect of the end windshield 104 and the inspection car rail 105. Making, increasing the flutter expression wind speed.
[0008]
Patent Literature 1 proposes various types of fairings. However, the relationship between the shape of the fairings and the anti-flutter performance has not been sufficiently studied. There is room for study on the shape of. The same applies to the scalene triangular fairing of the bridge of Patent Literature 2 and the lecture presentation bridge of FIG.
[0009]
In addition, although a technology to provide a shoulder fence or an end windshield near the base end of the bridge fairing has been proposed, the flutter resistance is improved by using a horizontal guide vane that greatly affects aerodynamic characteristics. No technology has been proposed.
An object of the present invention is to improve the anti-flutter performance by making the shape of the fairing trapezoidal in a two-box girder bridge, and to improve the anti-flutter performance by using a guide vane.
[0010]
According to a first aspect of the present invention, there is provided a bridge having a double box girder structure, a flat bridge main body having a double box girder structure extending in the bridge axis direction, and a vertical central portion in the width direction of the bridge main body. A central ventilation opening formed in a penetrating shape and extending in the bridge axis direction, a grating structure provided on an upper surface of the central ventilation opening so that a vehicle can pass therethrough, and a central protective fence erected on a central upper surface in the width direction of the central ventilation opening And a central wind-shielding structure which is provided in a state where the central ventilation opening is inserted from the lower end thereof and is formed of a vertical plate projecting from the lower side of the bridge main body, and at both end portions in the width direction of the bridge main body, A trapezoidal fairing having a pair of inclined plates and a standing plate connected to the tips of these inclined plates is provided.
[0011]
The flutter of the bridge main body is generated by a fluctuating lift acting as a self-excited aerodynamic force acting on the bridge main body, and a fluctuating moment caused by a separation between a center of action of the fluctuating lift and a structural center of the bridge main body. In a two-box girder bridge body, part of the wind blowing from a substantially horizontal direction with a small positive or negative angle of attack flows through the central ventilation opening, so the pressure difference between the upper surface and the lower surface acting on the bridge body Fluctuated lift is reduced to reduce. In addition, since the airflow separates from the downstream box girder together with the upstream box girder, the fluctuating lift acting on each box girder is balanced, and the fluctuating moment acting on the bridge body is reduced. On the other hand, by providing a central windshield structure that protrudes to the upper and lower sides of the bridge body, air flow separates from the central windshield structure, and the balance of the variable lift is improved in the direction of reducing the variable moment. You. Further, it was experimentally confirmed that the fluctuating moment was further reduced by making the shape of the fairing of the double box girder structure trapezoidal. Thus, the fluctuation moment acting on the bridge main body is reduced, so that the fluttering wind speed increases.
[0012]
The bridge according to claim 2 is the invention according to claim 1, wherein a horizontal portion extending near the base end of the trapezoidal fairing of the bridge main body at a predetermined distance from the bridge main body on the upper and lower sides of the bridge main body and extending in the bridge axis direction. Guide vanes are provided. It is presumed that this horizontal guide vane makes it easier for the wind to flow along the upper and lower surfaces of the bridge body, and that the flow strengthens the separation effect of the central windbreak structure, thereby reducing the fluctuation moment acting on the bridge body. Is done.
[0013]
According to a third aspect of the present invention, in the invention of the second aspect, the guide vanes are fixed to upper ends of a plurality of leg plates positioned at predetermined intervals in the bridge axis direction and orthogonal to the bridge axis. Since the plurality of leg plates are orthogonal to the bridge axis, they hardly affect the flow of the wind blowing at a right angle toward the bridge axis, which is a wind direction that should be a problem for the generation of flutter.
[0014]
Embodiments of the present invention will be described below.
The bridge according to the present embodiment is applied to a long suspension bridge having a maximum span of more than 2000 m. As shown in FIG. 1, the bridge 1 includes two box girders, a left box girder 2 a and a right box girder 2 b. This is a flat bridge having a two-box girder structure, and extends a predetermined length (for example, 2300 m) in a direction perpendicular to the paper surface of FIG. 1 (in a bridge axis direction). The length × width of the bridge 1 is, for example, 2300 m × 27 m.
[0015]
The bridge 1 basically has a flat bridge body 2 having a two-box girder structure extending in the bridge axis direction, and a central ventilation opening formed in a central portion in the width direction of the bridge body 2 so as to extend vertically and extend in the bridge axis direction. 3, a grating structure 4 provided on the upper surface of the central ventilation opening 3 and capable of passing vehicles, an upper truss structure 5 provided in the central ventilation opening 3 and connecting the left box girder 2a and the right box girder 2b, and a lower truss structure The truss structure 6, a central protection fence 7 a erected on the upper surface in the width direction center of the central ventilation opening 3 and protruding about 1.0 m above the bridge body 2, and a central ventilation opening 3 from the lower end of the central protection fence 7 a. A central wind shield structure 7 composed of a vertical plate 7b provided so as to be inserted and protruding about 1.0 m below the bridge main body 2, and platforms respectively provided at both ends in the width direction of the bridge main body 2. Shape fairing 8 and trapezoidal fair of bridge body 2 A horizontal guide vane 9 which is spaced apart from the bridge main body 2 by about 1.0 m and extends in the bridge axis direction on both upper and lower sides of the bridge main body 2 near the base end (end on the center side of the bridge 1) of the bridge 8; 2 and two inspection vehicle rails 10 provided on the lower surface side and extending in the bridge axis direction.
[0016]
Although not shown, a plurality of stiffeners extending in the bridge axis direction and rings arranged in a direction perpendicular to the bridge axis are provided inside the left box girder 2a and the right box girder 2b to secure necessary rigidity and strength. A stiffener and a partition wall are provided. In order to increase the airflow (wind) flowing through the central ventilation opening 3 and reduce the lift acting on the bridge main body 2, the width of the central ventilation opening 3 is about 1/3 of the width of the bridge 1 in the present embodiment. It has become. However, the value is not limited to 1/3.
[0017]
Each trapezoidal fairing 8 has a pair of upper and lower inclined plates 8a and 8b, and an upright plate 8c connected to the tips of the inclined plates 8a and 8b. The tip angle between them (the opening angle at the virtual vertex A in FIG. 1; hereinafter, referred to as the fairing tip angle) is about 55 to 65 degrees, and the upright 8c extends from the base ends of the inclined plates 8a and 8b to the virtual vertex A. It is arranged at a position that divides the horizontal width into two equal parts. However, the above position of the standing plate 8c is an example, and is not limited to this position. The guide vanes 9 are fixed at predetermined intervals in the bridge axis direction and are fixed to the upper ends of a plurality of leg plates 9a orthogonal to the bridge axis. A roadside protection fence 11 is provided at the inner end of the left and right guide vanes 9 provided on the upper surface side of the bridge main body 2.
[0018]
The operation of the bridge 1 described above will be described.
As shown in FIG. 2, for example, when the wind blows from the left side of the figure, the air flow is rectified by the guide vanes 9 into the flow along the upper surface and the lower surface of the bridge main body 2, and a part of the air flow on the upper surface side is centered. The air flows through the ventilation opening 3 to the lower surface side, and a part of the air flow on the lower surface side flows through the central ventilation opening 3 to the upper surface side. By the flow passing through the central ventilation opening 3, the pressure difference between the upper surface and the lower surface generated in the bridge main body 2 is reduced, and the lift is reduced. Since the upper end portion of the central wind shield structure 7 (that is, the central protective fence 7a) protrudes from the upper surface of the bridge main body 2, the air flow generated from the central wind shield structure 7 separates right above the bridge main body 2 due to the separation. The fluctuating moment acting on the box girder 2b is reduced by balancing the fluctuating lift acting on the box girder 2b with the fluctuating lift acting on the left box girder 2a.
[0019]
On the lower side of the bridge main body 2, the lower end of the central wind shield structure 7 protrudes from the lower surface of the bridge main body 2 in the same manner as described above. When the fluctuating lift acting on the right box girder 2b is balanced with the fluctuating lift acting on the left box girder 2b due to the separation of the flowing airflow, the fluctuation moment is reduced. In addition, under the bridge main body 2, since the inspection vehicle rail 10 protrudes to the lower surface side of the bridge main body 2, peeling also occurs from the inspection vehicle rail 10, but the inspection vehicle rail 10 is arranged at an appropriate position. It has been experimentally confirmed that the above-mentioned method hardly affects the anti-flutter performance.
[0020]
Regarding the operation of the trapezoidal fairing 8, according to the experimental results described below, when the trapezoidal fairing 8 is provided, compared to the case where the triangular fairing is provided, the wind blows from a substantially horizontal direction with a small positive or negative angle of attack. While there is almost no difference in the steady lift acting on the bridge body 2, the steady moment is greatly reduced. This is presumed to be due to the fact that the trapezoidal fairing caused a subtle change in the airflow pattern and the center of lift acting on the bridge main body 2 moved to the center of the width of the bridge main body 2. To reduce the fluctuating moment. As can be seen from the experimental results described below, according to the bridge 1, the anti-flutter performance is improved, and the wind speed at which flutter occurs is increased.
[0021]
Next, experimental results obtained by performing a wind tunnel test on the bridge model of the bridge 1 in a state where the bridge model is spring-supported and a state where the bridge model is fixedly supported will be described with reference to FIGS. FIG. 9 is a cross-sectional view of a bridge model 20 used as a comparative example in this experiment. This bridge model 20 is different from the bridge model of the bridge shown in FIG. Other structures are the same except for the ring 21.
[0022]
3 to 7, "trapezoid" indicates a bridge model having a trapezoidal fairing 8 as shown in FIG. 1, and "triangle" indicates a bridge model of a comparative example having a triangular fairing 21 as shown in FIG. Is shown.
[0023]
FIG. 3 shows an experimental result of obtaining a k value (shape correction coefficient) indicating a degree of difficulty in generating flutter for a model without guide vanes by changing the tip angle of the fairing. This k value is the k value = experimental limit wind speed / limit wind speed of the flat plate blade section obtained by the Selberg equation. In the range of the tip angle of 55 to 65 degrees, the trapezoidal fairing has a significantly higher k value than the triangular fairing, and the flutter resistance performance is improved.
[0024]
FIG. 4 shows the experimental results for the model without guide vanes and the model with guide vanes, in which the tip angle of the fairing was changed and the angle of attack was changed in the range of -3 deg to +3 deg to determine the k value. "Angle" in the figure indicates the tip angle of the fairing, and "GV" indicates that the guide vane is provided. At an angle of attack of -3 deg, all models tend to have reduced flutter resistance, but the addition of guide vanes significantly improves flutter resistance, and the combination of trapezoidal fairings and guide vanes provides better flutter resistance. Is obtained. Among them, a model of a trapezoidal fairing having a tip angle of 55 degrees shows the most excellent anti-flutter performance.
[0025]
FIGS. 5 to 7 show three models of a bridge model provided with a trapezoidal fairing having a common fairing tip angle of 55 degrees and a bridge model provided with a triangular fairing by changing the angle of attack in the range of −15 deg to +15 deg. This is a summary of the results of measurement of component forces (stationary drag, lift, and aerodynamic moment). As shown in FIG. 5, the drag coefficient of the bridge model with the trapezoidal fairing is somewhat larger than the drag coefficient of the bridge model with the triangular fairing, but as shown in FIG. Has little difference between the two.
[0026]
However, as shown in FIG. 7, in the range of the angle of attack of 6 deg or less, the aerodynamic moment coefficient of the bridge model with the trapezoidal fairing is significantly smaller than that of the bridge model with the triangular fairing. For example, at an attack angle of 0 deg, the value is about 1/3. This is presumably because the trapezoidal fairing caused a subtle change in the airflow pattern, and the center of lift acting on the bridge model moved to the center of the width of the bridge model. In the case of a long suspension bridge, since the torsional deformation is likely to occur in the bridge body, the characteristic that the moment coefficient is reduced is very advantageous for the long suspension bridge.
[0027]
FIG. 8 shows torsional displacement (twist at the center of the span) when the wind speed is changed using the three-component force obtained for the two types of bridge models for a long suspension bridge with a maximum span of 2300 m. 3 shows the results of a three-dimensional static deformation analysis in which the displacement) was obtained analytically. As can be seen from this figure, the torsional displacement of the bridge with the trapezoidal fairing is significantly reduced compared to the torsional displacement of the bridge with the triangular fairing. In addition, according to the results of the three-dimensional flutter analysis in consideration of the static torsional displacement, the fluttering wind velocity is about 80 m / s for a bridge having a triangular fairing and about 100 m / s for a bridge having a trapezoidal fairing. . Compared with the triangular fairing, in the case of the trapezoidal fairing, the fluttering wind speed can be increased by about 20%, and the torsional displacement can be significantly reduced as shown in FIG.
[0028]
The above embodiment is merely an example, and the size (length, width, and height) of the bridge main body 2, the width of the central ventilation opening 3, the amount of vertical protrusion of the central ventilation structure 7, and the height of the guide vanes 9 are shown. The position, the position of the standing plate 8c of the trapezoidal fairing 8 and the like can be appropriately changed by a person skilled in the art without departing from the spirit of the present invention.
[0029]
According to the bridge of the first aspect, the fluctuating lift and the fluctuating moment acting on the bridge body can be reduced by the central ventilation opening. The balance of the variable lift can be improved in the direction of reducing the variable moment by the separation action by the central wind shield structure protruding to the upper and lower sides of the bridge body. Furthermore, even with the trapezoidal fairing, the moment acting on the bridge main body can be reduced by changing the action center of the variable lift toward the center of the width of the bridge main body. In this manner, the fluctuating lift acting on the bridge body can be reduced, and the fluctuating moment can be reduced.
[0030]
According to the bridge of claim 2, the horizontal guide vanes make it easier for the wind to flow along the upper surface and the lower surface of the bridge body, and the flow enhances the peeling action of the central wind shield structure. As a result, the bridge body Is estimated to be reduced.
[0031]
According to the bridge of claim 3, since the guide vanes are located at predetermined intervals in the bridge axis direction and are fixed to the upper ends of the plurality of leg plates orthogonal to the bridge axis, the wind direction which should be a problem with respect to the occurrence of flutter is provided. The guide vanes can be supported on the bridge body by a plurality of leg plates that hardly affect the flow of the wind blowing at a right angle toward the bridge axis.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a bridge according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram illustrating a behavior of a wind flow.
FIG. 3 is a diagram showing a relationship between a fairing tip angle and a k value obtained in an experiment.
FIG. 4 is a diagram showing a relationship between an angle of attack and a k value obtained in an experiment.
FIG. 5 is a diagram showing a relationship between an angle of attack and a drag coefficient obtained in an experiment.
FIG. 6 is a diagram showing a relationship between an angle of attack and a lift coefficient obtained in an experiment.
FIG. 7 is a diagram showing a relationship between an angle of attack and a moment coefficient obtained in an experiment.
FIG. 8 is a diagram showing the relationship between wind speed and torsional displacement obtained by analysis.
FIG. 9 is a cross-sectional view of a bridge model of a comparative example used for an experiment.
10A is a cross-sectional view of a bridge according to the related art, and FIG. 10B is a cross-sectional view of the bridge according to the related art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Bridge, 2 Bridge main body 3 Central ventilation opening, 4 Grating structure 5 Upper truss structure, 6 Lower truss structure 7 Central windbreak structure, 7a Central protective fence 7b Vertical plate, 8 Trapezoidal fairings 8a, 8b Inclined plate, 8c Upright plate 9 Guide vane, 9a Leg plate 10 Inspection car rail 11 Road fence

Claims (3)

In a bridge with a two-box girder structure, a flat bridge main body with a two-box girder structure extending in the bridge axis direction, a central ventilation opening formed in the center in the width direction of the bridge main body and extending vertically and extending in the bridge axis direction, A grating structure provided on the upper surface of the central ventilation opening so that vehicles can pass therethrough, a central protective fence erected on the upper surface in the width direction center of the central ventilation opening, and a bridge body provided in a state where the central ventilation opening is inserted from the lower end thereof And a central wind-shield structure composed of a vertical plate projecting from the lower side of the bridge main body. At both ends in the width direction of the bridge main body, a pair of upper and lower inclined plates are respectively connected to the tips of these inclined plates. A bridge comprising a trapezoidal fairing having a standing plate. The horizontal guide vanes which are spaced apart from the bridge main body by a predetermined distance and extend in the bridge axis direction are provided on the upper and lower sides of the bridge main body near the base end of the trapezoidal fairing of the bridge main body. Bridge. The bridge according to claim 2, wherein the guide vanes are located at predetermined intervals in the bridge axis direction and are fixed to upper ends of a plurality of leg plates orthogonal to the bridge axis.

Images