JP2012127053A - Prestressed concrete bridge structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a prestressed concrete bridge structure capable of constantly detecting a state of tension in an outer cable, acquiring an increase in the tension and restoring load bearing capacity of the outer cable by reapplying the tension to the outer cable when the load bearing capacity of a bridge is reduced.SOLUTION: A prestressed concrete bridge structure 10 provided with outer cables 13 tightened with low tension enough to make an anchorage device 16 and a bearing plate of a prestressed concrete bridge 11 closely contact each other comprises: a tension mechanism 14 to tighten the outer cables; and detection means 15 to detect a tension fluctuation of the outer cables. The detection means quantitatively monitors the tension of the outer cables. When detecting a predetermined increase in the tension, the prestressed concrete bridge structure 10 enables the tension mechanism to restore load bearing capacity of the bridge by reapplying the tension to the outer cable.

Description

  The present invention detects a physical change of an outer cable in order to quantitatively detect a decrease in load bearing capacity of a prestressed concrete bridge (PC bridge), detects a risk of bridge collapse due to a decrease in load bearing capacity in advance, and The present invention relates to a prestressed concrete bridge structure capable of appropriately recovering the reduced load bearing capacity and extending the life by re-tensioning.

In general, the load resistance of prestressed concrete bridge structures decreases due to various factors. For example, when chloride ions enter concrete and the PC steel material is broken due to corrosion or the like, the load bearing capacity of the bridge decreases.
However, conventionally, there has been no method or bridge structure for monitoring the lowering process quantitatively and reinforcing the reduced load immediately when the load bearing capacity of the bridge is reduced.
In addition, it is difficult to properly predict changes in the load caused by changes in traffic volume in bridges, etc., and when the load applied is greater than the preset load, the load capacity of the bridge is reduced. Invite you.

  In addition, there is a method of applying additional prestress by an external cable as a method of reinforcing a bridge having a reduced load bearing capacity due to the fracture of the PC steel material.

FIG. 6 is an explanatory view schematically showing an example of a conventional prestressed concrete bridge structure. The prestressed concrete bridge 1 is given compressive stress by PC steel 2 arranged inside the concrete or by an external cable. With such a structure, the prestressed concrete bridge 1 is superior in durability and safety compared to general concrete bridges. Long span and light weight can be achieved.
However, when the existing PC steel material 2 of the prestressed concrete bridge 1 is broken, the load resistance is lowered, and cracks 3 may occur on the lower surface of the bridge as shown in FIG. FIG. 7 is an explanatory diagram showing a case where a crack 3 occurs in the conventional prestressed concrete bridge 1 as the load bearing capacity decreases. FIG. 8 is an explanatory diagram showing a case where a conventional prestressed concrete bridge structure is dropped due to a decrease in load bearing capacity.

However, the conventional outer cable is tensioned at a tensile strength of about 80% of the tensile strength of the PC steel material arranged as the outer cable, and aims to restore the necessary performance.
Further, in the conventional prestressed concrete bridge structure, it is necessary to quantitatively grasp the amount of decrease in the load bearing capacity due to the breakage of the existing PC steel material in advance and to apply the prestress corresponding to the amount of decrease. In this method, when the fracture amount of the existing PC steel material is estimated to be larger than the actual amount, the prestress applied becomes excessive and adversely affects the load resistance of the bridge. On the contrary, if the estimate is small, the amount of prestress applied is too small and the amount of reinforcement is insufficient. Thus, in order to reinforce by the outer cable construction method, it is indispensable to accurately grasp the amount of decrease in the load bearing capacity due to the breakage of the existing PC steel material. However, since the existing PC steel is hidden inside the concrete, there is a problem that the amount of decrease in the load bearing capacity cannot be accurately grasped in reality.
The present invention has been proposed in view of the above circumstances. The amount of breakage of the PC steel material within an assumed period is determined, and an outer cable corresponding to the amount of breakage is installed in close contact with the fixing tool and the bearing plate. The purpose is to provide a prestressed concrete bridge structure that can constantly monitor and quantitatively grasp the decrease in load bearing capacity, and can immediately re-tension and restore the load bearing capacity when load bearing capacity decreases. To do.

  In order to achieve the above object, the present invention is a prestressed concrete bridge structure in which an outer cable that is tensioned with such a degree that the fixing tool and the bearing plate are in close contact with each other, and a tension mechanism that tensions the outer cable; Detection means for detecting a tension variation of the outer cable is provided, and the outer cable is re-tensioned by the tension mechanism when the detection means detects an increase in a predetermined tension.

  Since this invention consists of an above-described structure, there can exist an effect which is demonstrated below.

  In the present invention, a prestressed concrete bridge structure in which an outer cable that is tensioned with such a tension that the fixing tool and the bearing plate are in close contact with each other is provided, and a tension mechanism that tensions the outer cable and a tension variation of the outer cable. Detecting means for detecting, and when the detecting means detects an increase in a predetermined tension, the tensioning mechanism re-tensions the outer cable, so that the load bearing force can be recovered in a short period of time and the prestress amount is excessive. There is no danger of becoming too small. Therefore, it is possible to apply an appropriate tension force that matches the reduction in the load bearing capacity of the bridge.

FIG. 1 is a perspective view showing an embodiment of a prestressed concrete bridge structure according to the present invention. FIG. 2 is an explanatory view schematically showing the prestressed concrete bridge structure. FIG. 3 is an explanatory view showing one of the sensors used in the prestressed concrete bridge structure. FIG. 4 is an explanatory diagram showing a reduced load bearing capacity in the prestressed concrete bridge structure. FIG. 5 is an explanatory view showing a state in which the load bearing capacity is restored by re-tensioning in the prestressed concrete bridge structure. FIG. 6 is an explanatory view schematically showing an example of a conventional prestressed concrete bridge structure. FIG. 7 is an explanatory diagram showing a case where cracks occur with a decrease in load bearing capacity in a conventional prestressed concrete bridge structure. FIG. 8 is an explanatory diagram showing a case where a conventional prestressed concrete bridge structure is dropped due to a decrease in load bearing capacity.

The prestressed concrete bridge structure of the present invention is provided with an outer cable that is strained to such an extent that the fixing tool and the bearing plate are in close contact with each other, and is provided with a detecting means for detecting physical fluctuations of the outer cable, and the detecting means has a predetermined tension When the increase is detected, the outer cable is re-tensioned by the tension mechanism, so that the tension force to be accurately applied can be grasped and the load bearing force can be recovered in a short period of time.
Therefore, it is possible to quickly apply tension according to the amount of decrease in the load bearing capacity of the bridge.

  Hereinafter, the present invention will be described in detail with reference to the drawings illustrating an embodiment. FIG. 1 is a perspective view showing an embodiment of a prestressed concrete bridge structure according to the present invention, and FIG. 2 is an explanatory view schematically showing the prestressed concrete bridge structure of the present invention. Here, the prestressed concrete bridge structure 10 of the present invention is provided with the outer cable 13 that is tensioned to such an extent that the fixing tool 16 of the prestressed concrete bridge 11 and the bearing plate are in close contact with each other. A tension mechanism 14 that detects the physical fluctuation of the outer cable 13 is provided.

  The outer cable 13 is stretched between the fixing portions 16 installed in the vicinity of the end portion of the prestressed concrete bridge 11, and the prestress applied to the outer cable 13 by the deflecting portion 17 provided between the fixing portions 16. Is transmitted to the concrete bridge 11. Here, the fixing unit 16 applies a compressive stress to the concrete member by fixing a fixing tool made of metal, concrete, or the like to the concrete member and tensioning the inserted outer cable 13 or the like. The deflecting unit 17 fixes a deflecting tool made of metal, concrete, or the like to the concrete member, and applies a component of tension applied to the outer cable 13 to the concrete member.

  Moreover, the tension | tensile_strength according to the load-bearing force anticipated beforehand to the prestressed concrete bridge 11 is given to the tension | tensile_strength of the PC steel material 12, and the tension | tensile_strength is tensioned to the outer cable 13 with the small tension | tensile_strength which adheres the fixing tool 16 and a bearing plate. . That is, the outer cable 13 is applied with a small tension and a tension within a range in which the tension can be measured by the detection means 15. This is because it is difficult to measure a change in the tension of the outer cable 13 when no tension is applied to the outer cable 13 from the beginning. Further, when the outer cable 13 is tensioned to the bridge in which the bending crack has occurred and prestress is applied, and the crack is closed, it can be determined that the stress around the cracked portion has become zero.

  The detection unit 15 may be, for example, an EM sensor 18 that detects a change in magnetostriction of the outer cable 13. As shown in FIG. 3, the EM sensor 18 has an insertion hole 21 for inserting a cable through the metal casing 20, and is disposed in the casing 20 and concentrically from the insertion hole 21. The secondary coil 22, the primary coil 23, the temperature sensor 24, and the like are provided, and the axial stress (tension) of the outer cable 13 can be detected using magnetostriction. The EM sensor 18 does not need to contact the outer cable 13 and can directly measure the actual stress. Further, since the stress is directly measured, the stress can be measured regardless of the extension of the cable, and long-term durability is obtained.

Furthermore, the detection means 15 may be an AE sensor 19 that detects an elastic wave that is generated when the PC steel material 12 or the outer cable 13 is partially broken.
Here, the AE sensor 19 detects an elastic wave (vibration, sound wave) generated along with breakage such as occurrence or progress of a crack in the cable, and by installing a plurality of AE sensors, the elasticity that reaches from the breakage point. The breakage point can be estimated using the time difference of the waves.
Furthermore, the detection means 15 may be a load cell. The load cell has no moving parts and a small amount of mechanical displacement, so the structure is simple, excellent in responsiveness, inexpensive, and has a long life. Moreover, it can be used semi-permanently if properly used and managed.

Next, operation | movement of the prestressed concrete bridge structure 10 of this invention comprised as mentioned above is demonstrated. First, after constructing the prestressed concrete bridge structure 10, physical detection of the outer cable 13 is always detected by the detection means 15. The outer cable 13 is tensed with a small tension such that the fixing tool 16 and the pressure plate are in close contact with each other at the beginning of construction, and has a margin in tension.
Specifically, the prestress equivalent to be lost due to creep, relaxation, etc. after the introduction of prestress at the time of construction of the existing bridge. The amount of reduction in prestress lost due to creep, relaxation, etc. can be determined with relatively high accuracy by calculation. Therefore, even when the PC steel material fracture amount of the existing bridge cannot be accurately grasped, there is no problem due to overpress stressing.

  Moreover, since the physical fluctuation | variation of the outer cable 13 is always detected, the re-tensioning force introduced into the outer cable 13 does not become excessive or too small. When the prestressing force to be introduced is excessive, cracking occurs exceeding the allowable compressive stress of concrete, and the load bearing capacity of the prestressed concrete bridge is significantly reduced. Furthermore, if the prestressing force to be introduced is too small, the amount of increase in the load bearing force is insufficient and the risk of destruction cannot be removed.

Next, the case where the AE sensor 19 is used for the detection means 15 in the prestressed concrete bridge structure 10 of the present invention will be described.
The AE sensor 19 detects an elastic wave generated due to a crack or breakage of the cable, and installs a plurality of AE sensors to estimate a breakage point using a time difference between elastic waves reaching from the breakage point. Can do. When a crack or breakage of the outer cable 13 is detected, the outer cable 13 is reinforced and the outer cable 13 is re-tensioned by the tension mechanism 14 to recover the load resistance.

As described above, according to the prestressed concrete bridge structure of the present invention, after construction, when the PC steel material of the existing bridge is broken for some reason, the strain of the concrete shortened by the tension force is released, and the elongation occurs. The interval between fixings at both ends of the outer cable is widened. This extends the outer cable and increases the tension. If this change in tension is measured by a detection means arranged in advance, it can be known that the PC steel material of the existing bridge has broken.
Moreover, the increase in the tension of the outer cable indicates that the outer cable compensated for the load resistance lost due to the breakage of the existing PC steel material. In other words, the outer cable has undergone reinforcement corresponding to the decrease in the load bearing capacity while monitoring the decrease in the load bearing capacity of the existing bridge.

  In the future, if the amount of fracture of the PC steel material of the existing bridge increases, bending cracks will occur in the bridge. In principle, when bending cracks occur, the amount of increase in the tension of the outer cable increases. If the tension is constantly monitored, the occurrence of bending cracks can be detected. In addition, when a prestress is applied to the bridge in which a bending crack has occurred with an external cable and the crack is closed, the stress around the cracked portion is zero. That is, by knowing the amount of prestress, the amount of PC steel material fracture of the existing bridge can be accurately known. If the amount of prestress remaining in the existing bridge can be accurately grasped, an accurate reinforcement design can be achieved.

  In addition, although the said description demonstrated the example of the box girder bridge, it can apply similarly not only to this but another T girder bridge. Further, the installation of the external cable and the detection means according to the present invention can be adapted not only at the time of construction of the bridge but also by addition after construction.

DESCRIPTION OF SYMBOLS 10 Prestressed concrete bridge structure 11 Prestressed concrete bridge 12 PC steel material 13 Outer cable 14 Tension mechanism 15 Detection means 16 Fixing part (fixing tool)
17 Deflection part 18 EM sensor 19 AE sensor 20 Housing 21 Insertion hole 22 Secondary coil 23 Primary coil 24 Temperature sensor

Claims (2)

  A prestressed concrete bridge structure in which an outer cable tensioned with a tension low enough to allow the anchorage of the prestressed concrete bridge and the bearing plate to be in close contact with each other, and a tension mechanism for tensioning the outer cable and a tension variation of the outer cable. A prestressed concrete bridge structure comprising: a detecting means for detecting, and monitoring a load-bearing force of the prestressed concrete bridge by measuring a tension variation of the outer cable by the detecting means.   2. The prestressed concrete bridge structure according to claim 1, wherein when the detection unit detects an increase in a predetermined tension, the tension mechanism re-tensions the outer cable.

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