JP4453857B2 - Outside cable truss PC outside cable tensioning device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an external cable extension device for a PC bridge provided with an external cable .
[0002]
[Prior art]
Recently, the “Eccentric Cable” has been designed to make lighter and more rational PC bridges (prestressed concrete bridges) by using prestress effectively by placing the outer cables more eccentric than the PC bridge girder. Several structural forms of “PC bridge” have been proposed. One of them is known as the Extradosed PC Bridge (Fig. 1), which has a structure that lowers the main tower of the cable-stayed bridge. While the main girder is lifted and supported diagonally, the main focus is on giving prestress and eccentric moment to the main girder by diagonal materials. Also known is a stringed PC girder bridge (Fig. 2), which is connected to the main girder and supports the outer cable by decentering it below the main girder by a vertical strut in the direction of the bridge axis. Since the outer cable protection pipe is rigidly connected or pin-coupled, and the outer cable is tensioned and cemented in the protection pipe, the connection structure between the strut and the outer cable (at least against bridge load and live load) A) It is in a state close to fixing or pin connection.
[0003]
Furthermore, the structural type of the “large eccentric cable PC bridge” is also applied to the cable trust bridge (Fig. 3), which is a simple girder bridge of steel bridge, and is slightly inclined with respect to the bridge axis direction and the direction perpendicular thereto. Cables are arranged eccentrically with diagonal struts. As this outer cable, a galvanized steel wire bundle coated with polyethylene is used, and it is fixed to a cable saddle (deflection part) using a jig such as a bolt or a cable band as shown in FIG. ing.
[0004]
[Problems to be solved by the invention]
In the extradosed PC bridge, the diagonal is located on the upper side even near the center of the span where the lower tensile bending moment is generated. There is an inconvenience that a construction step such as adjustment is required. In addition, in the case of a tension string PC girder bridge, the amount of strut steel is basically determined by the vertical component of the outer cable tension as the largest determinant, but in addition, the strut steel material amount depends on the horizontal component of the outer cable tension. Is bent in the direction of the bridge axis. If only struts perpendicular to the direction of the bridge axis are provided, the amount of strut steel material increases, which is uneconomical. In addition, when the connection between the cable saddle and the outer cable is fixed or pinned, there is a tendency for greater bending due to the tension difference of the outer cable before and after the cable saddle. It is impossible to confirm whether the cement cement grout alone is actually fixed or pinned. Furthermore, in the case of cable trust bridges, the cable saddle and the polyethylene-coated outer cable are fixed using a special jig such as a bolt or cable band. The entire cable saddle is covered with a cover, and a rubber-based sealing material is filled therein, and a waterproof rubber boot is applied to the boundary between the outer cable and the steel cover.
[0005]
It is an object of the present invention to provide an external cable tensioning device that can easily construct a lightweight and reasonable external cable truss PC bridge.
[0006]
[Means for Solving the Problems]
In the present invention, in an external cable truss PC bridge in which a cable saddle is supported on a strut extending from a bridge girder, and the outer cable is stretched by being greatly eccentric from the bridge girder by the cable saddle, the outer cable is slid on the cable saddle. The above-mentioned object is achieved by freely inserting and stretching. The cable saddle is composed of a double pipe having a curvature matching the arrangement shape of the outer cable, and the outer cable can be slid through the double pipe, thereby simplifying the structure of extending the outer cable. Enforcement is also easier. In addition, by using an unbonded cable that allows the outer cable and the steel stranded wire to slide relative to each other, the sliding performance between the outer cable jacket and the double pipe inner tube has decreased over the years. However, the sliding performance of the steel stranded wire itself can be secured. The cable saddle for extending the outer cable of the outer cable truss PC bridge is constituted by a double pipe having a curvature matching the arrangement shape of the outer cable, and the inner pipe constituting the double pipe is supported by a spacer or the like. By using the outer cable tensioning device that is attached to the outer pipe through the means and the end of the inner pipe is formed in a trumpet shape, the outer cable can be reasonably tensioned and the workability is improved.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. FIGS. 5 to 8 schematically show an outer cable truss PC bridge. A cable saddle 3 is supported on a strut 2 extending from a continuous bridge girder 1 and the bridge girder is supported on the cable saddle 3. The outer cable 4 is stretched so as to be close to the distribution of the bending moment with a large deviation from 1. Since the outer cable 4 is disposed below the main girder near the center of the span, prestress can be used more effectively than a conventional extradosed PC bridge, and a lighter and more rational PC bridge can be constructed. .
[0008]
The strut 2 is not perpendicular to the bridge axis direction like a string PC girder bridge, but is connected to the outer cable by diagonal struts inclined in the bridge axis direction and in a direction perpendicular to the bridge axis strut like a cable trust bridge strut. 4 is arranged eccentrically from the bridge girder so that the amount of steel material of the strut 2 is reduced. Since it is reasonable to arrange the outer cable 4 in an eccentric manner close to the distribution of bending moment, a plurality of struts 2 are arranged between the supports to support the outer cable 4. As a result, it is possible to avoid the arrangement of large struts, so that workability is also improved.
[0009]
The details of the strut 2 and the cable saddle 3 are as shown in FIGS. 9 and 10, and the cable saddle 3 is supported by four inclined struts 2, and the cable saddle 3 is arranged in the shape of the outer cable 4. It comprised with the double pipe which consists of the inner pipe | tube 3a and the outer pipe | tube 3b which have the curvature combined. The outer cable 4 is slidably inserted into the inner tube 3a, prestressed, and both ends thereof are fixed to the fixing block. To disperse and transmit the prestressing force of the outer cable 4 applied to the inner tube 3a to the outer tube 3b, it is attached via support means 5 such as plate-like and shaft-like stiffener spacers, gutters, grouts, etc. did. Further, in order to prevent sudden breakage and wear of the outer cable 4, the end portion of the inner tube 3a was processed into a trumpet shape. Further, the gap between the inner and outer pipes is sealed by welding to the end of the outer pipe 3b using a steel plate seal 6 to prevent the invasion of rainwater and the like to prevent corrosion. If necessary, grout is injected into the gap. Thus, even if the outer cable 4 slides along the inner surface of the inner tube 3a, the reaction force component due to the tension of the outer cable 4 is dispersed to the outer tube 3b and the strut 2 via the support means 5 of each spacer tube. Is transmitted.
[0010]
The dimensions of the outer tube 3b are determined in consideration of the dimensions of the struts 2 determined from strength requirements, and the inner diameter of the inner tube 3a is determined to be slightly larger than the outer diameter of the polyethylene-coated outer cable 4. In general, the diameter of the outer tube 3b is considerably larger than the diameter of the outer cable 4. If the cable saddle 3 is constituted only by the outer tube 3b and the outer cable is in direct contact with this, the diameter of the outer tube 3b is compared with the diameter of the outer tube. Since the contact area is small, the thickness of the outer tube is determined by local stress rather than the stress determined from the performance of the entire cross section of the outer tube. However, the local stress is remarkably reduced by making the inner and outer double pipes as shown in the figure, and the inner pipe 3a and the outer pipe 3b are integrally resisted against the reaction force of the outer cable more equalized. can do. Since the outer cable 4 looks like it passes through the center of the cable saddle 3, the appearance is improved, and the end portions of the inner and outer tubes are sealed and filled with grout, so that corrosion resistance and durability can be secured relatively easily.
[0011]
As shown in FIG. 11, the outer cable 4 includes a plurality of PC stranded wires 9 coated with a rust preventive grease 7 and a polyethylene sheath 8, and is further bonded with a high-density polyethylene coating 10. Although a cable is used, a cable having a general structure may be used. The outer cable 4 of the unbonded cable is configured such that the PC stranded wire 9 is slidable with respect to the covering 10. By using the outer cable 4, the inner surface of the inner tube 3a polished after many years is rusted. Even if the sliding performance is deteriorated between the outer cable 4 and the covering 10, the sliding performance of the PC stranded wire 9 itself is ensured. Therefore, the precondition of the slide coupling as a design condition is permanently maintained with a simple configuration, and the function of the outer cable can be exhibited accurately.
[0012]
The example shown in FIG. 5 shows an example in which the present invention is applied to an external cable PC bridge having a total length of about 60 m provided with one pier 11 in the middle, and each of the external cables 4 composed of two unbonded cables is connected to a bridge girder. 1, each cable saddle 3 was attached to the bridge girder 1 by four diagonal struts 2. On the bridge girder 1, the outer cable 4 was inserted into an insertion hole 13 formed in the dovetail-shaped supporting wall 12.
[0013]
The outer cable 4 is provided so as to be greatly decentered from the bridge girder 1 and is slidably inserted into the cable saddle 3, so that it slides away from the cable saddle 3 even if the tension of the outer cable 4 changes. Therefore, a reasonable load distribution can be obtained for the outer cable 4, and the strut 2 can be configured to be lightweight. Further, by configuring the cable saddle 3 with inner and outer double pipes, the load of the outer cable 4 can be evenly distributed, and the outer cable 4 can be inserted into the central portion of the cable saddle 3, so that the appearance is improved. .
[0014]
【The invention's effect】
As described above, according to the present invention, since the outer cable is slidably inserted into the cable saddle of the large eccentric type outer cable truss PC bridge, it is possible to easily construct a lightweight and rational cable truss PC bridge. is obtained, it can be easily construction by the tensioning device and the configuration of claim 1.
[Brief description of the drawings]
FIG. 1 is a side view of a conventional extradosed bridge. FIG. 2 is a side view of a conventional stringed PC girder bridge. FIG. 3 is a side view of a conventional cable trust bridge. FIG. 5 is a side view showing an embodiment of the present invention. FIG. 6 is a plan view of FIG. 5. FIG. 7 is a cross-sectional view taken along line 1-1 and line 2-2 in FIG. 5 is a sectional view taken along the line 3-3 of FIG. 5. FIG. 9 is an enlarged view of the cable saddle portion of FIG. 5. FIG. 10 is an enlarged perspective view of the cable saddle of FIG. Explanation of symbols]
1 continuous bridge girder, 2 struts, 3 cable saddle, 3a inner tube, 3b outer tube, 4 outer cable, 5 spacer, 9 PC stranded wire, 10 sheathing,

Claims (1)

The cable saddle for extending the outer cable of the outer cable truss PC bridge is constituted by a double pipe having a curvature matching the arrangement shape of the outer cable, and the inner pipe constituting the double pipe is supported by a spacer or the like. An outer cable tensioning device for an outer cable truss PC bridge, characterized in that the outer tube is attached to the outer tube via an end and the end of the inner tube is formed in a trumpet shape.

Images