JPH0216406B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a prestressed concrete bridge,
That is, it relates to construction girders used in PC bridge construction work.

One of the construction methods for PC bridges is the P&Z construction method, which involves suspending formwork from construction girders installed on the bridge superstructure, as shown in Figure 1.
This is a construction method in which the superstructure is sequentially extended and constructed in sections on both sides of the pier. The weight of concrete for one block to be cast, the weight of the hanging frames and formwork, and the dead weight of the girder itself act as loads on the girder used in this construction method.

By the way, the structure and cross-sectional strength of the construction girder are as follows:
determined by one of the following conditions:

(1) The state immediately before the auxiliary column at the tip of the erected girder reaches the next pier (Fig. 2 A) (2) The state in which the first block or the second block is extended and constructed on both sides of the pier (Fig. 2) B) In the condition (1), it is determined only by the self-weight of the erected girder, and even in the condition (2), the self-weight of the erected girder is a major factor. Therefore, reducing the self-weight of the erected girder also reduces the load acting on the erected girder, which in turn allows the cross section of the erected girder to be made smaller, and as a result, the self-weight of the erected girder can be further reduced. This can synergistically reduce the weight of the erected girder, reduce the influence of the erected girder's own weight on the superstructure and substructure, and make it possible to reduce the cross section of the superstructure and substructure. However, as the span of the superstructure becomes longer, the span of the erection girder also becomes longer.
As a result, there was a drawback that the self-weight of the erection girder became heavy.

The present invention was devised in view of the above-mentioned circumstances, and its purpose is to provide a diagonal tension cable that can reduce the weight of an erection girder used when the span of a superstructure is long. The aim is to provide an erection girder that uses both.

The structure of the present invention will be explained with reference to one embodiment shown in the drawings from FIG. 3 onwards. 1 is an existing bridge (PC bridge) constructed on piers 2 and constitutes a superstructure. Note that the pier 2 constitutes a substructure. Above the existing bridge 1, an erection girder 4 directly supported by a pedestal 3 is placed. The construction girder 4 has a fifth section located on the pedestal 3a at the position where the bending moment is maximum, that is, when the construction girder 4 protrudes to the maximum from the pedestal 3a located at the tip of the overhanging part of the existing bridge 1. As shown in the figure, struts 5 having an isosceles triangular shape when viewed from the direction of the construction girder 4 are attached. Both base ends 5a of this support column 5 are attached to reaction force receiving brackets 6 provided protruding from the upper edges of both side plates 4a of the construction girder 4, so that the pillar 5 can be raised and rotated in the direction of the girder axis of the construction girder 4. It is installed.

7 is a cable stretched in the direction of the girder axis of the construction girder 4, and the cable 7 is on both sides of the support column 5,
Both ends are fixed to cable attachment parts 4b provided equidistantly apart on the upper edges of both side plates 4a of the construction girder 4, and the cables are inserted through holes 5b opened in the tip of the support column 5 in the direction of the girder axis. It is slanted on both sides. One of the cable attachment parts 4b is located at or near the center of gravity of the construction girder 4 as a protruding part when the construction girder 4 protrudes to the maximum from the frame 3a.

Reference numeral 8 denotes a hydraulic jack attached to both side plates 4a of the construction girder 4 near the reaction force receiving bracket 6, and the tip of the hydraulic jack 8 is connected to the vicinity of the base end 5a of the support column 5. By extending and contracting the hydraulic jack 8, the support column 5 can be raised and rotated.

In this embodiment, the support column 5 has an isosceles triangular shape, but is not limited to this shape.

Next, the operation of the present invention constructed as described above will be explained. As shown in Fig. 1, concrete is poured on both sides of the pier 2 and the superstructure is extended one after another, and after one overhang is closed with the overhang of the existing bridge 1, a girder 4 is placed on the next pier 2a. When moving the support column 5, the support column 5 is erected by extending the hydraulic jack 8 prior to the movement. As the column 5 stands up, the cable 7 inserted through the hole 5b at the tip of the column 5 forms triangular sides on both sides of the column 5, and when the column 5 stands completely upright, the cable 7 passes through the hole 5b at the tip of the column 5. A cable 7 is formed between the hole 5b and the cable attachment part 4b on the construction girder 4 on both sides of the support column 5, and is stretched downwardly. After that, the erection girder 4
start moving. When the movement of the construction girder 4 is completed, the support column 5 is lowered so as not to get in the way during construction of the superstructure. This operation is performed by retracting the extended hydraulic jack 8.

By the way, during the movement of the construction girder 4, the mount 3a
The bending moment caused by the weight of the construction girder of the protruding part from above is divided by the cable 7 which is stretched downwardly, and is transferred to the above-mentioned frame 3 via the support column 5.
Unlike conventional construction girders, the negative weight of the construction girder itself can be reduced.
The cross section of the construction girder 4 can be made small so that the resistance can be reduced, and the weight of the construction girder 4 itself can be reduced.

However, on the other hand, since the struts 5 and cables 7 are newly used, the dead weight increases accordingly, but generally speaking, when the length of the protruding part of the erection girder 4 increases, the increase in dead weight due to the struts 5 and cables 7 is outweighed by the increase in dead weight. digit 4
Since the amount by which the dead weight of the construction girder 4 is reduced is greater than that of the construction girder 4, the present invention can reduce the dead weight of the entire construction girder 4 compared to the conventional one.

In short, the present invention is a movable construction girder used in a method of constructing a prestressed concrete bridge section by section between piers that have been constructed in advance. At the top of the erected girder supported by the erected girder, a column is attached so as to be able to raise and lower freely, and is positioned above the frame when the erected girder is protruded to its maximum extent, and the girder shaft is attached from the top of the erected column. Since the tips of the cables that are stretched downward in the direction are attached to the above-mentioned construction girder, the longer the span of the superstructure, the more the dead weight of the entire construction girder is reduced compared to conventional construction girders. Moreover, the load that is supported by the columns and reduced is all supported by the existing superstructure through the trestle directly below them, making it possible to strengthen and modify existing girders when applying them to larger spans. It is a powerful idea. By reducing the weight of the entire erected girder, it becomes easier to move the erected girder, and the influence of the weight of the entire erected girder on the superstructure and substructure can be reduced, so The cross section can be made smaller. In addition, the supports and cables can be used only when necessary and stored in the construction girder when not needed, so there is no risk of them getting in the way during the construction of the superstructure, resulting in extremely novel effects. It is something to play.

[Brief explanation of drawings]

The drawings show an example of an erected girder using diagonal tension cables according to the present invention, in which Fig. 1 is a construction drawing of the P&Z construction method, and Fig. 2 A and B show the cross-sectional strength of the erected girder determined. 3 is an overall side view, FIG. 4 is a side view of essential parts, and FIG. 5 is a view taken along the line A--A in FIG. 4. In the figure, 3 is a frame, 3a is a frame at the tip, 4 is an erection girder, 5 is a column, and 7 is a cable.

Claims (1)

[Claims] 1. A movable construction girder used in the method of constructing a prestressed concrete bridge section by section between pre-built piers, which is supported by a frame installed at the tip of an existing bridge superstructure. At the top of the erected girder, a strut is attached so that it can be raised and rotated freely, and the strut is placed above the frame when the girder protrudes to its maximum extent. An erection girder using diagonal tension cables, characterized in that the tips of the cables to be strung are attached to the erection girder to reduce the weight of the erection girder.