JP6661125B2 - Fall prevention device for truss bridge - Google Patents

Description

  The present invention relates to a truss bridge dropping bridge having a structure in which both ends of a columnar girder member are connected to another girder member in a triangular shape and which is formed by repeating the same, and a pair of lower structures supporting both ends of the upper structure. The present invention relates to a prevention device.

In a bridge such as a truss bridge, an upper structure and a lower structure are connected by a bearing. The superstructure has a floor slab and a truss. The substructure has an abutment and a pier.
For example, a device for preventing the upper structure from falling to the ground when a part of the bearing is damaged without damaging the lower structure and the upper structure due to a large earthquake or the like is a fall-fall prevention device.
The bridge prevention device in this case assumes that the superstructure has not caused fatal damage, and functions effectively only in such a case.

Two types are known as fall prevention devices. That is, Patent Literature 1 describes a chain-type bridge prevention device as shown in FIG. The girder fixture 206 provided on the lower surface at the end of the upper structure 202 and the support fixture 207 provided on the side surface of the lower structure 203 are connected by a steel chain 205 to move the upper structure 202. Prevent the bridge from falling by limiting.
Here, the chain 205 is configured by connecting a chain member 251, a connection member 252, and a rubber cushioning member 253.

Patent Literature 2 discloses a cable-type bridge prevention device. That is, in Patent Document 2, as shown in FIG. 18, a girder fixture 106 provided on the lower surface of the end of the upper structure 102 and a support fixture 107 provided on the side surface of the lower structure 103 include: The cables 151 are connected by cable members 105 having connection members 152 provided at both ends of the cables 151, and a bridge is prevented by restricting the movement of the upper structure 102.
Here, the cable member 105 is attached in a loose state so that no tension is applied to an applied load (earthquake, live load, etc.) when the bridge is in a healthy state.

On the other hand, Non-Patent Document 1 discloses a case where a diagonal member of a truss bridge is broken. In this paper, the following points are described.
1) When the tensile oblique material breaks brittlely, the strain is suddenly released at the time of the break. As a result, first, the strain propagates as a longitudinal wave at high speed toward both ends of the member and gives a primary impact to the graduation of the fractured member.
Next, a secondary impact occurs due to a dynamic transition to a new balancing state due to a decrease in rigidity of the entire structural system due to a member break.
2) Dynamic amplification of stress due to primary impact is smaller than stress amplification due to secondary impact. In addition, there is a time difference between the occurrence of the primary impact and the secondary impact, and the influence of the coupling between the two can be ignored. That is, in the redundancy analysis, only the impact due to the secondary impact needs to be considered.
3) Simultaneous and accurate analysis of primary impact and secondary impact Simultaneous analysis of strain propagation by primary impact because the wavelength of longitudinal waves is very short and the propagation speed is fast, resulting in fine element division and time increment, and time history response The analysis requires a huge amount of calculation time.
Since the influence of the primary impact on the impact coefficient is negligible, an approximate analysis method that can analyze only the secondary impact with high accuracy is presented. This technique can greatly reduce the calculation time.

JP 2012-177255 A JP 2012-012867 A

Journal of Structural Engineering, Japan Society of Structural Engineering Vol.56A (March 2010) pp.792-805 Yoshiaki Goto, Naoki Kawanishi, Kazunari Honda "Impact Coefficient of Rigid Steel Truss Bridge at Tension Break in Redundancy Analysis"

However, the conventional fall prevention device has the following problems.
(1) The truss bridge is a truss-structured bridge. The truss structure is a structure in which both ends of an elongated girder member are connected to other girder members in a triangular manner, and the girder is formed by repeating the same. Truss bridges are used for relatively large span lengths. For example, in the case where a girder member near the center of a truss bridge, which is a part of a girder member constituting a truss, is damaged by a large earthquake, the techniques of Patent Documents 1 and 2 cannot cope.
That is, since the techniques of Patent Documents 1 and 2 are structures in which the end of the upper structure and the lower structure are connected by a cable or a chain, the end of the upper structure can be supported. It was impossible to support the bridge, and if the girder member near the center of the truss bridge was damaged, the bridge was dropped.
(2) When the girder member near the center of the truss bridge is damaged, it is necessary to simulate how the truss bridge is displaced in order to prevent the collapse of the truss bridge near the center of the truss bridge. However, Non-Patent Document 1 calculates the impact received by the truss bridge, but does not describe how the truss bridge is displaced when the girder member is damaged.

  SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus for preventing a truss bridge from falling even if a girder member near the center of the upper structure of the truss bridge is damaged.

In order to achieve the above object, a truss bridge fall prevention device of the present invention has the following configuration.
(1) A structure in which both ends of a columnar girder member are connected to another girder member in a triangular shape, and an upper structure constructed by repeating the same and a pair of lower structures supporting both ends of the upper structure, thereby preventing a truss bridge from falling. In the apparatus, at least one cable is provided on each of both sides in the width direction of the upper structure, a guide member for slidably inserting the cables is provided on the side surfaces of the plurality of girder members, and the upper structure has ends at both ends. The vertical member at the end has a fixing member near the upper end, the cable is inserted into the guide member, both ends of the cable are fixed to each of the fixing members, and the cable has a live load. It is characterized by being in a slack state at the time of normal vibration caused by the movement, and being tensed to prevent collapse of the upper structure when the spar member is damaged and the upper structure is deformed.

(2) In the bridge drop prevention device described in (1), the guide member is characterized in that the cable is arranged at a position along the lower chord material grade.
(3) In the bridge fall prevention device described in (1), the guide member is arranged at a position where the cable holds the cable so as to draw a suspension curve.
(4) In the bridge prevention device described in (2) or (3), the cable is strained when the amount of change in the superstructure exceeds the limit displacement during normal vibration.
(5) The truss bridge fall prevention device described in (1) to (4), wherein the truss bridge is a lower road truss bridge, and an end vertical member is added as a reinforcing member. I do.

The truss bridge fall prevention device of the present invention has the following operations and effects.
(1) A structure in which both ends of a columnar girder member are connected to another girder member in a triangular shape, and an upper structure constructed by repeating the same and a pair of lower structures supporting both ends of the upper structure, thereby preventing a truss bridge from falling. In the apparatus, at least one cable is provided on each of both sides in the width direction of the upper structure, a guide member for slidably inserting the cables is provided on the side surfaces of the plurality of girder members, and the upper structure has ends at both ends. The vertical member at the end has a fixing member near the upper end, the cable is inserted into the guide member, both ends of the cable are fixed to each of the fixing members, and the cable has a live load. It is characterized by being in a slack state at the time of normal vibration caused by the movement, and being tensed to prevent collapse of the upper structure when the spar member is damaged and the upper structure is deformed.
The present inventors have approximately evaluated the kinetic energy generated by the spar member fracture and the energy absorption capacity of the fracture system by Pushover analysis using static composite nonlinear analysis. This Pushover analysis is a so-called Model Pushover analysis, in which the inertia force generated by dynamically moving the fracture system to a new balanced state by applying gravity as the external force acting on the mass position of the structural system after the spar member breaks. Approximately evaluated based on the lower order natural vibration mode of the fracture system.
According to this analysis, the behavior of the truss bridge after damage can be accurately evaluated, and the operation timing of the cable can be controlled as a bridge fall prevention device.

The truss structure to which dead load (load due to the weight of the truss bridge) and live load (vehicle load and the like) act is originally supported by a pair of lower structures.
When the truss bridge fall prevention device of the present invention supports a damaged truss bridge, as the truss structure around the damaged girder member is sequentially displaced downward, the dead load and the live load that the truss can no longer bear are reduced. Since the cable bears the load, the tension of the cable increases.
Therefore, if the load acting on the truss structure itself is received by the cable at a time when the downward displacement is as small as possible, the bridge can be prevented without further increasing the displacement.
That is, after the girder member is damaged, the truss structure is supported by the cable while maintaining the state where the lower structure supports most of the load of the upper structure.

Applicants initially considered fixing both ends of the cable to the undercarriage. However, when fixing both ends of the cable to the lower structure, it is necessary to reinforce the structure with respect to the portion where the lower structure is fixed. Reinforcing the substructure of an existing truss bridge is costly and impractical.
Also, in the case of a long bridge having a plurality of piers (continuous truss bridge), it is difficult to fix the cable to the pier as the substructure. Generally, both ends are supported by the abutment, and the middle part is supported by the pier.
According to the invention of (1), since both ends of the cable are fixed in the vicinity of the end vertical member which is the upper structure, only the upper structure can be used for the existing truss bridge without performing reinforcement work on the lower structure. Since this can be realized by reinforcement, the bridge fall prevention device can be implemented at low cost.
Further, the fixing member attached near the upper end of the end vertical member is attached to the end vertical member and the upper chord with high-strength bolts in consideration of construction on site.

(2) In the bridge prevention device described in (1), the guide member is characterized in that the cable is disposed at a position along the lower chord material grade.
The lower chord material is a strength member and has sufficiently high strength, and since there is no other member below the lower chord material, it is convenient to provide a guide member for holding the cable.

(3) In the bridge fall prevention device described in (1), the guide member is arranged at a position where the cable holds the cable so as to draw a suspension curve.
You.
The present inventors simulated the displacement of the truss structure due to the breakage of the truss member of the truss, and studied how to arrange the cables. When both ends were fixed and the cable was not restrained by the guide member, it was found that the tension was applied to the entire cable only after the cable was positioned in a catenary curve. Until the cable is in the state of a suspension curve, the cable is partially tensioned, the cable is partially stretched, and the displacement of the truss structure increases. After the cable draws a suspension curve, the cable supports the truss.
Therefore, in the normal state, if the guide member is arranged at a position where the cable holds a hanging curve, the cable immediately draws a hanging curve when the girder member is damaged, so that the cable is drawn. The truss structure can be supported with little extension and the displacement of the truss structure can be minimized. Thereby, the partial elongation of the cable can be minimized, and a cable having a small diameter can be used.

(4) In the bridge prevention device described in (2) or (3), the cable is strained when the amount of change in the superstructure exceeds the limit displacement during normal vibration.
The truss bridge vibrates up and down, for example, due to the movement of a live load such as an automobile or a railway car. The limit displacement during such normal vibration is specified by the Ministry of Land, Infrastructure, Transport and Tourism. Since the limit displacement amount during normal vibration is a value that does not exceed during normal vibration, if the slack amount of the cable is set to the limit displacement amount, the cable will not be tensioned by vibration due to live load, The cable is not affected by fatigue or the like. On the other hand, immediately after the girder member is damaged, the slackness of the cable is set so that the cable becomes taut before the displacement of the truss structure increases because the lower structure is supporting most dead load and live load. Then, the force applied to the cable can be minimized, and a cable having a small diameter can be used.

(5) The bridge fall prevention device according to any one of (1) to (4), wherein the truss bridge is a lower road truss bridge, and an end vertical member is added as a reinforcing member. The present invention is characterized by adding a reinforcing member not only to an upper truss bridge having an end vertical member at the end but also to a lower truss bridge having no end vertical member at the end. Can be applied.

It is a side view of the upper road type truss bridge in the first embodiment of the present invention. It is a side view of the upper road type truss bridge in 2nd Embodiment of this invention. FIG. 3 is an enlarged view of a portion C in FIGS. 1 and 2. FIG. 3 is an enlarged view of a portion A in FIGS. 1 and 2. FIG. 3 is an enlarged view of a portion B in FIG. 2. It is the figure which modeled the truss bridge of FIG. FIG. 7 is a diagram showing specifications and material constants of each girder member in FIG. 6. It is a partial view which shows the magnitude of the dead load and live load applied to a truss bridge. It is a figure showing distribution of a live load in the direction perpendicular to a bridge axis. It is a figure which shows the distribution of the live load in the bridge axis direction of a truss bridge. It is a figure showing a simulation result when a part 50 of lower chord material 15 is damaged in a conventional truss bridge not using cable 5. FIG. 4 is a diagram showing an analysis model when a cable 5 is used. FIG. 4 is a diagram showing a sag amount of a cable 5; It is a figure showing a simulation result when a part of lower chord material 15 is damaged in a truss bridge using cable 5. It is a figure showing a simulation result in case guide parts 21aB, 21aC, 21aD, and 21aE are provided in the lower end of perpendicular members 11B, 11C, 11D, and 11E. It is the figure which predicted the simulation result at the time of making the cable 5 draw a suspension curve by the guide part 31aB, 31aC, 31aD, 31aE. It is a figure which shows the structure at the time of applying this invention to an underpass truss bridge. It is a figure showing the conventional cable type fall prevention device. It is a figure which shows the conventional chain type fall prevention device.

An apparatus for preventing a bridge from falling according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a side view of an upper road type truss bridge, and is a view schematically showing a structure of an embodiment of the present invention.
The upper road type truss bridge is of a type in which a floor slab 1 through which automobiles, pedestrians, or railway vehicles pass is disposed above a truss structure 2. An upper structure is formed by the floor slab 1 and the truss structure 2. The upper structures 1 and 2 are arranged on the upper surface of the step portion of the pair of left and right lower structures 3 via a bearing 4 which is a connecting portion between the two.
The truss structure 2 has six columnar vertical members 11A, 11B, 11C, 11D, 11E, and 11F. The upper ends of the vertical members 11A to 11F are fixed to the upper chord member 14 located from the upper end of the vertical member 11A to the upper end of the vertical member 11F. The lower ends of the vertical members 11A to 11F are fixed to a lower chord member 15 located from the lower end of the vertical member 11A to the lower end of the vertical member 11F. In the space between the vertical member 11A and the vertical member 11B, oblique girder members 12A and 13A having different inclination directions are fixed obliquely. The oblique girder members 12B to 12E and 13B to 13E are sequentially fixed.
The truss structure 2 is constituted by these.

Next, a fall prevention device which is a feature of the present embodiment will be described. In the present embodiment, a pair of cables 5 are stretched around both sides in the width direction of the upper structures 1 and 2 (truss structure 2). One end of the cable 5 is fixed to an intermediate position of the fixing member 8A having one end fixed to the end vertical member 11A and the other end fixed to the upper chord material 14. The other end of the cable 5 is fixed at an intermediate position of the fixing member 8B having one end fixed to the end vertical member 11F and the other end fixed to the upper chord material 14.
FIG. 3 is an enlarged view of a portion C in FIG. FIG. 3A is a cross-sectional view showing the mounting structure, and FIG. 3B is a view taken in the direction of arrow C in FIG. FIG. 4 shows an enlarged view of a portion A in FIG. 4B is an enlarged partial cross-sectional view, and FIG. 4A is a DD cross-sectional view of FIG. FIG. 5 is an enlarged view of a portion B in FIG. FIG. 5B is an enlarged partial cross-sectional view, and FIG. 5A is an EE cross-sectional view of FIG.

Next, the fixing member 8 (8A, 8B) will be described with reference to FIG. FIG. 3A is an enlarged view of the fixing member 8A.
The end vertical member 11A is an H-shaped steel material, and an outer frame member 111 for reinforcement is fixedly provided. Specifically, an inwardly facing bracket 113 erected at both ends of the outer frame member 111 and a parallel plate of the end vertical member 11A are fastened by bolts and nuts.
A bracket 81a extends from a portion where one end 81 of the fixing member 8A is connected to face the entire surface of the parallel plate, and is fastened to the parallel plate with bolts and nuts over the entire surface. At the other end 82 of the fixing member 8A, a bracket 82a superimposed on the upper chord material 14 is extended, and is fastened to the upper chord material 14 by bolts and nuts over the entire surface.
As shown in FIG. 3B, a pair of extending portions 83 are provided on both sides at an intermediate position of the fixing member 8. The extension portion 83 has a through hole formed therein, the cable 5 is inserted through the through hole, and the cable fastener 51 is fixed to an end of the cable 5.

As shown in FIG. 4, a guide member 21D is fixed by welding or the like at a position directly below the lower chord member 15 provided below the vertical member 11D. The guide member 21D includes a mounting bracket 21cD having a shape surrounding both side surfaces and a bottom surface of the lower chord material 15, a guide bracket 21dD having a pair of groove-shaped guide portions 21aD formed on a lower surface, and extending upward from the mounting bracket 21cD. And has a welding bracket 21bD that is welded to the vertical member 11D. The inner peripheral surface of the guide portion 21aD is formed as a curved surface following the cable 5.
A guide member 21C is fixed to the vertical member 11C at the same height position as the guide member 21D. Similarly, the guide member 21B is fixed to the vertical member 11B at the same height position as the guide member 21D. Similarly, a guide member 21E is fixed to the vertical member 11E at the same height position as the guide member 21D. The shapes of the guide members 21C, 21B, and 21E are the same as those of the guide member 21D.

The cable 5 having both ends fixed to the fixing member 8 is inserted into the guide portions 21aB, 21aC, 21aD, and 21aE. The cable 5 is in a state of slack, and is in a state of slack while being in contact with the inner upper curved surface of the guide portions 21aB, 21aC, 21aD, and 21aE.
The slack amount is set to a slack amount that does not cause the cable 5 to be strained in a range where the displacement of the upper structures 1 and 2 (truss structure 2) does not exceed the limit displacement amount during normal vibration. According to the standards of the Ministry of Land, Infrastructure, Transport and Tourism, the limit displacement amount during normal vibration is L / 600. Here, L is the length of the bridge. In the present embodiment, L = 60 m, and the limit displacement amount during normal vibration is 60 m / 600 = 0.1 m.
The slack amount is specifically controlled by the sag amount. This will be described later.

Next, displacement analysis of the truss when the lower chord material 15 is partially damaged will be described.
First, the initial conditions will be described. FIG. 6 shows a model of a truss bridge. (B) is a side view, (a) is a plan view, and (c) is a view as viewed from below.
FIG. 7 shows the member specifications and material constants of the truss bridge model. The member numbers correspond to the member numbers described in FIG. Here, σy is the yield stress in the axial direction of each member.
FIG. 8 shows the magnitude of the dead load and the live load applied to the truss bridge. Specifically, the load equivalent to the mass acting on the point of the truss bridge model is indicated by the size of a black circle.
FIG. 9 shows the distribution of the live load in the direction perpendicular to the bridge axis, and FIG. 10 shows the distribution of the live load in the direction of the bridge axis of the truss bridge.

The present inventors have approximately evaluated the kinetic energy generated by the spar member fracture and the energy absorption capacity of the fracture system by Pushover analysis using static composite nonlinear analysis. This Pushover analysis is a so-called Model Pushover analysis in which the inertia force generated by dynamically shifting the fracture system to a new balanced state by applying gravity as an external force acting on the mass point of the structural system after the spar member breaks. Approximately evaluated based on the lower order natural vibration mode of the fracture system.
According to this analysis result, it is understood that the truss structure around the damaged girder member is sequentially displaced downward. In the truss structure, a pair of lower structures originally support a total dead load (a load due to the own weight of the truss bridge) and a live load (such as a vehicle load).
As the truss structure around the damaged girder member is sequentially displaced downward, the superstructure cannot support the load, leading to a falling bridge.

FIG. 11 shows a simulation result when a part of the lower chord material 15 is damaged in a conventional truss bridge not using the cable 5. (A) shows a state after 0.5 seconds, (b) shows a state after 1.0 seconds, (c) shows a state after 1.5 seconds, and (d) shows a state after 2.0 seconds. Show the later state.
It is assumed that a part 50 of each of the lower chord members 15 is damaged on both sides. It can be seen that the bending of the truss bridge progresses after 1 second, that it bends greatly after 1.5 seconds, and that it collapses after 2.0 seconds.

FIG. 12 shows an analysis model of a simulation when the cable 5 is used. (A) is a bridge fall prevention device of the present invention, and the end vertical members 11A and 11F are reinforced in the case of an existing vertical member. Also, when designing from the beginning, it has sufficient strength. (B) shows a case in which the end vertical members 11A and 11F are designed with the same strength as the conventional one in the bridge fall prevention device of the present invention. (C) is a case where both ends of the cable 5 are fixed to the lower structure.
In FIG. 12, a cable located between the fixing member 8A of the end vertical member 11A and the guide member 21B is represented by 5A, a cable located between the guide member 21B and the guide member 21C is represented by 5B, and the guide member 21C is provided. A cable positioned between the guide member 21D and the guide member 21D is denoted by 5C, a cable positioned between the guide member 21D and the guide member 21E is denoted by 5D, and positioned between the guide member 21E and the fixing member 8B of the end vertical member 11F. The cable to be connected is represented by 5E.

FIG. 13 shows the sag amount of the cable 5. Here, the sag amount is the amount of deflection of a cable suspended between two points in a vertical direction from a straight line connecting the two points.
Case 1 is a case where the sag amount of the cables A to E is set to a small value of 0.4 or less in the case of FIG. Case 2 is a case where the sag amount of the cables A to E is set to a small value of 0.4 or less in the case of FIG. Case 3 is a case where the sag amount of the cables A to E is as large as 0.45 or more in the case of FIG. Case 4 is a case where the sag amount of the cables A to E is set to a small value of 0.4 or less in the case of FIG. Case 5 is a case where the sag amount of the cables A to E is as large as 0.45 or more in the case of FIG.
FIG. 14 shows a simulation result when a part of the lower chord material 15 is damaged in the truss bridge using the cable 5. (A) is the case of case 1 and shows a state after 1.1 seconds. (B) is the case of Case 2 and shows the state after 1.5 seconds.
In case 1, it can be seen that the deformation of the truss structure 2 is smaller than that of FIG. In case 2, it can be seen that the end vertical member is deformed and loses proof stress, and the truss structure 2 is greatly deformed.

Next, the tension applied to the cable will be described.
FIGS. 15A and 15B show simulation results when the guide portions 21aB, 21aC, 21aD, and 21aE are provided at the lower ends of the vertical members 11B, 11C, 11D, and 11E. The horizontal axis is the time axis (second), and the vertical axis is the tension applied to the cable 5. (A) is the case of case 1 and (b) is the case of case 3. In the case of the case 2, the vertical member at the end is broken and the cable 5 is not subjected to a load.
The left figure shows the result of the cable R arranged on the right side of the bridge, and the right figure shows the result of the cable L arranged on the left side of the bridge.

In the cases of FIGS. 15A and 15B, it is understood that a large tension is partially applied to the cables 5A and 5E. However, as can be seen from FIG. 15, since the tension applied to the cable 5 is lower than the cable yielding tension in any case, the cable 5 is not damaged.
Comparing the case 1 shown in (a) with the case 3 shown in (b), it can be seen that the maximum tension applied to the cables 5A and 5E of the case 1 is clearly smaller in the case 1. .
The reason is that, in the case 1 and the case 3, as the truss structure 2 around the damaged girder member is sequentially displaced downward, the load supported by the lower structure 3 decreases, and the load borne by the cable 5 is reduced. Increase.
At this time, since the sag amount in Case 1 is smaller than 0.4 in comparison with Case 3, the truss structure 2 is supported by the cable 5 at the time when the downward displacement is as small as possible. Smaller. In that case, the load supported by the lower structure 3 is larger than that of the case 3. In addition, reducing the displacement after the rupture reduces the kinetic energy after the rupture and reduces the impact force (dynamic amplifying force).

FIG. 15C illustrates the case 4 and FIG. 15D illustrates the case 5. In the cases of FIGS. 15C and 15D, it is understood that a large tension is partially applied to the cables 5A and 5E. However, as can be seen from FIG. 15, since the tension applied to the cable 5 is lower than the cable yielding tension in any case, the cable 5 is not damaged.
Comparing the case 4 shown in (c) with the case 5 shown in (d), it can be seen that the maximum tension applied to the cables 5A and 5E of the case 4 is clearly smaller in the case 4. .

Comparing case 1 and case 4, both ends of cable 5 are fixed to lower structure 3 and both ends of cable 5 are fixed to fixing members 8A and 8B attached to end vertical members 11A and 11F. In case 1 in which the tension is applied, the tension applied to the cable 5 is almost similar.
Similarly, when comparing the case 3 with the case 5, the case 5 in which both ends of the cable 5 are fixed to the lower structure 3, the fixing member 8A in which both ends of the cable 5 are attached to the end vertical members 11A and 11F, It can be seen that the tension applied to the cable 5 is almost the same as that of the case 3 when the cable 5 is fixed to 8B.
Therefore, for example, when installing an anti-fallover device on an existing truss bridge, in Case 5, it is necessary to perform additional work on the lower structure 3, which complicates the work and raises the cost. In No. 1, since no additional work is required for the lower structure 3, the work can be simplified and the cost can be reduced.
Further, in the case of a long bridge having a plurality of piers, it is difficult to fix the cable 5 to the pier which is the lower structure 3 as in Cases 4 and 5, but in Cases 1 and 3, The construction is easy because it is sufficient to use the vertical member at the end of the bridge.

As described in detail above, according to the present embodiment,
(1) A truss bridge having a structure in which both ends of a columnar girder member are connected to other girder members in a triangular manner and which is constructed by repeating the same, and a pair of lower structures 3 supporting both ends of the upper structure 1. In the device for preventing a bridge from falling, the upper structure 1 has at least one cable 5 on each side in the width direction, and the side surfaces of the plurality of girder members have guide members 21 through which the cables 5 are slidably inserted. The upper structure 1 has end vertical members 11A and 11F at both ends, and the end vertical members 11A and 11F have fixing members 8A and 8B near the upper end. The cable 5 is inserted into the guide member 21 and the cable 5 Are fixed to the fixing members 8A and 8B, respectively. The cable 5 is in a slack state during normal vibration caused by the movement of the live load, and the girder member is damaged and the upper structure 1 is deformed. And when, to prevent collapse of the upper structure 1 nervous, characterized.
The present inventors have approximately evaluated the kinetic energy generated by the spar member fracture and the energy absorption capacity of the fracture system by Pushover analysis using static composite nonlinear analysis. This Pushover analysis is a so-called Model Pushover analysis in which the inertia force generated by dynamically shifting the fracture system to a new balanced state by applying gravity as an external force acting on the mass point of the structural system after the spar member breaks. Approximately evaluated based on the lower order natural vibration mode of the fracture system.
According to this analysis, the behavior of the truss bridge after damage can be accurately evaluated, and the operation timing of the cable can be controlled as a bridge fall prevention device.

The truss structure 2 to which a dead load (a load due to the own weight of the truss bridge) and a live load (such as a vehicle load) act is originally supported by a pair of lower structures 3.
When the truss bridge fall prevention device of the present invention supports a damaged truss bridge, as the truss structure around the damaged girder member is sequentially displaced downward, the dead load and the live load that the truss can no longer bear are reduced. Since the cable bears the load, the tension of the cable increases.
Therefore, if the load acting on the truss structure itself is received by the cable 5 when the downward displacement is as small as possible, the bridge can be prevented from being dropped without further increasing the displacement.
That is, after the girder member is damaged, the truss structure 2 is supported by the cable 5 while maintaining the state where the lower structure 3 supports most of the load of the upper structure 1.

The applicants initially considered fixing both ends of the cable 5 to the lower structure. However, when both ends of the cable 5 are fixed to the lower structure 3, it is necessary to reinforce the structure of the portion where the lower structure 3 is fixed. Reinforcing the substructure 3 of an existing truss bridge is costly and impractical.
In the case of a long bridge having a plurality of piers, it is difficult to fix the cable 5 to the pier which is the lower structure 3.
According to this embodiment, since both ends of the cable 5 are fixed near the end vertical members 11A and 11F, which are the upper structures 1, the reinforcing work on the lower structure 3 is not performed on the existing truss bridge. Since this can be realized by replacing only the upper structure 1, the fall prevention device can be implemented at low cost.

The guide member 21 is characterized in that the cable 5 is arranged at a position along the lower chord material grade.
The lower chord material 15 has a sufficiently high strength, and since there is no other member below the lower chord material 15, it is convenient to provide the guide member 21 for holding the cable 5.
Further, when the amount of change of the upper structure 1 exceeds the limit displacement amount during normal vibration, the cable 5 is strained.
The truss bridge vibrates up and down, for example, due to the movement of a live load such as an automobile or a railway car. The limit displacement during such normal vibration is specified by the Ministry of Land, Infrastructure, Transport and Tourism. Since the limit displacement amount during normal vibration is a value that does not exceed during normal vibration, if the slack amount of the cable 5 is set to the limit displacement amount, the cable 5 will not be strained by vibration due to live load. Therefore, the cable 5 is not affected by fatigue or the like. On the other hand, when the girder member is damaged, an increase in displacement of the truss structure 2 can be stopped while the lower structure 3 supports most dead loads and live loads, so that the force applied to the cable 5 is minimized. The cable 5 can also be of a small diameter.

Next, a second embodiment of the present invention will be described. Since the entire contents are the same as in the first embodiment, only different points will be described in detail, and description of the same points will be omitted.
As shown in FIG. 2, guide members 31B, 31C, 31D and 31E are arranged at positions where the cable 5 is held so as to draw a hanging curve.
The structure of the guide members 31C and 31D is the same as that shown in FIG. FIG. 5 shows the structure of the guide member 31B. FIG. 5 is an enlarged view of a portion B in FIG.
As shown in FIG. 5, a guide member 31B is fixed to the vertical member 11B. The guide member 31B includes a mounting bracket 31cB integrally fixed around the entire periphery of the vertical member 11B, and a guide bracket 31dB having a pair of groove-shaped guide portions 31aB formed on the lower surface.

In FIG. 2, the inner peripheral surface of the guide portion 31aB is formed as a curved surface following the suspension curve so as to be inclined downward to the right. In this embodiment, it is formed as a curved surface, but may be formed as an approximated inclined straight line. The reason why the cable is formed by a curved surface or an approximated inclined straight line is to prevent the concentration of stress on a part of the cable 5 due to the entire inner peripheral surface being in contact with the cable.
A guide member 31E is fixed to the vertical member 11E at the same height position as the guide member 31B. The inner peripheral surface of the guide portion 31aE fixed to the guide member 31E is formed as a curved surface so as to incline upward to the right in the opposite direction to the guide portion 31aB.
The cables 5 having both ends fixed to the steel brackets 81a and 82a are inserted into the guide portions 31aB, 31aC, 31aD and 31aE. The cable 5 is in a state of being slackened, and is slightly separated from the upper inner curved surface of the guide portions 31aB, 31aC, 31aD, and 31aE and is slackened.

Next, FIG. 16 shows a diagram predicting a simulation result in a case where the cable 5 draws a suspension curve by the guide portions 31aB, 31aC, 31aD, and 31aE as shown in FIG. The horizontal axis is the time axis (second), and the vertical axis is the tension applied to the cable 5.
In the case of FIG. 2, since the cable 5 is in a state of drawing a substantially catenary curve from the beginning, the cable 5 is not partially tensioned, the cable 5 is not partially stretched, and the entire cable 5 is not stretched. Since the tension applied to the cables 5A, 5B, 5C, 5D, and 5E, which are the portions of the cable 5, is substantially equal to and less than the cable yield tension, there is no possibility that the cable 5 will be damaged.

As described above, the fall prevention device for a truss bridge according to the second embodiment is characterized in that the guide member 31 is arranged at a position where the cable 5 is held so as to draw a suspension curve.
The present inventors simulated the displacement of the truss structure due to the breakage of the truss member of the truss, and studied how to arrange the cables. If both ends are fixed and the cable 5 is not constrained by the guide member 31, it is found that the tension is applied to the entire cable 5 after the cable 5 is positioned so as to draw a suspension curve. did. Until the cable 5 draws a suspension curve, the cable 5 is partially tensioned, the cable 5 is partially stretched, and the displacement of the truss structure 2 increases. After the cable 5 has drawn the suspension curve, the truss structure 2 is supported by the cable 5.
Therefore, in the normal state, if the guide member 31 is arranged at a position where the cable 5 is held so as to draw a suspension curve, when the girder member is damaged, the cable 5 immediately enters a state of drawing a suspension curve. In addition, the cable 5 is less likely to be partially stretched, and can support the truss structure 2, thereby minimizing the displacement of the truss structure 2. Thereby, the partial elongation of the cable 5 can be minimized, and a small-diameter cable 5 can be used.

Next, a third embodiment of the present invention will be described. Since the entire contents are the same as in the first embodiment, only different points will be described in detail, and description of the same points will be omitted.
As shown in FIG. 17, the present embodiment is a truss bridge with a floor slab installed at the position of the lower chord material 15 in the truss bridge. In this case, there is no end vertical member. Therefore, in order to implement the present invention, it is necessary to add end vertical members 41X and 41Y at both ends and upper girder extension members 42X and 42Y obtained by extending the upper chord member 14 as reinforcing members. If a reinforcing member is added, the rest is the same as in the first and second embodiments. In FIG. 17, the conventional bridge-preventing devices 44A and 44B shown in FIGS. 18 and 19 are used together.

  As described above, in the truss bridge fall prevention device of the third embodiment, the truss bridge is a lower truss bridge, and the end vertical members 41X and 41Y are added as reinforcing members. Since it is characterized by not only the upper truss bridge having an end vertical member at the end but also the lower truss bridge having no end vertical member at the end, the end vertical member 41X which is a reinforcing member, The present invention can be applied by adding 41Y.

The truss bridge fall prevention device of the present invention can be variously modified without being limited to the above embodiment.
For example, in the present embodiment, a pair of cables 5 is used. However, the number of cables may be three or more. For example, when the lower chord is in an arch shape, only one cable may be used.

DESCRIPTION OF SYMBOLS 1 Floor slab 2 Truss structure 3 Substructure 4 Bearing 5 Cable 8 Fixing member 11 Vertical member 11A, 11F End vertical member 12 Diagonal girder member 13 Diagonal girder member 21, 31 Guide member 21a, 31a Guide part 21c, 31c Mounting bracket 21d , 31d Guide bracket 41 End vertical member (reinforcing member)
42 Upper girder extension member (reinforcing member)

Claims (5)

In a structure in which both ends of a columnar girder member are connected to another girder member in a triangular manner, an upper structure formed by repeating the same, and a truss bridge fall prevention device having a pair of lower structures supporting both ends of the upper structure. ,
Having at least one cable on each side of the width of the upper structure in the width direction;
On the side surfaces of the plurality of spar members, having a guide member that slidably inserts the cable,
The upper structure has an end vertical member at both ends, and the end vertical member has a fixing member near an upper end,
The cable is inserted through the guide member, and both ends of the cable are fixed to each of the fixing members,
The cable is in a slackened state during normal vibration caused by movement of a live load, and when the girder member is damaged and the upper structure is deformed, it is tensioned to prevent the upper structure from collapsing,
A fall prevention device for a truss bridge characterized by the following features. The bridge fall prevention device according to claim 1,
The guide member, wherein the cable is disposed at a position along the lower chord material grade,
A fall prevention device for a truss bridge characterized by the following features. The bridge fall prevention device according to claim 1,
The guide member is arranged at a position where the cable holds the cable so as to draw a suspension curve,
A fall prevention device for a truss bridge characterized by the following features. In the fall prevention device according to claim 2 or 3,
When the change amount of the upper structure exceeds the limit displacement amount during the normal vibration, the cable is tensioned,
A fall prevention device for a truss bridge characterized by the following features. The fall prevention device for a truss bridge according to any one of claims 1 to 4,
The truss bridge is a lower truss bridge, and the end vertical member is added as a reinforcing member;
A fall prevention device for a truss bridge characterized by the following features.

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