JP6718658B2 - Prestressed concrete floor slab - Google Patents

Description

The present invention relates to prestressed concrete slabs.

Design guidelines have been revised due to large-scale disasters such as the Great Hanshin Earthquake and the Great East Japan Earthquake. On the other hand, some existing bridges do not meet the criteria such as the revised design guidelines. For such bridges, repair work may be carried out for the purpose of seismic strengthening.

Floor slab replacement work may be performed as part of the existing bridge repair work.
If the floor slab used for the replacement work is lightweight, it is possible to reduce the burden on the existing bridge piers, and thus improve the earthquake resistance of the entire bridge.
Further, it is possible to improve the workability by reducing the weight of the precast floor slab.

Currently, prestressed concrete floor slabs are often used as bridge decks.
In a prestressed concrete floor slab, it is common to arrange PC steel materials and reinforcing bars. Considering the arrangement of the PC steel material and the reinforcing bars, it was efficient to use a flat plate structure as the basic shape of the prestressed concrete slab (for example, refer to Patent Document 1).

JP, 2009-264040, A

In the conventional prestressed concrete floor slab, in addition to the arrangement of the PC steel materials, it is necessary to consider the concrete covering of the reinforcing bars and the space between the reinforcing bars or between the reinforcing bars and the PC steel materials. I will end up. If the thickness of the floor slab is large, the weight of the floor slab becomes heavy.
From such a viewpoint, it is an object of the present invention to propose a prestressed concrete floor slab capable of improving the earthquake resistance of the entire bridge by reducing the weight.

In order to solve the above problems, the prestressed concrete floor slab of the present invention uses a fiber reinforced concrete, a plate portion, and a grid-like rib consisting of vertical ribs and horizontal ribs formed on the lower surface of the plate portion, In the plate portion, a thickened portion is formed according to the position of the bridge girder, prestress is introduced into the vertical ribs by a post tension method, and the lateral ribs are prestressed by a pretension method. There have been introduced, the ends of the longitudinal ribs is characterized that you have been formed fixable bolt box end of the tendons.

According to the prestressed concrete floor slab, since the fiber reinforced concrete is used, the reinforcing bar can be omitted. Therefore, as the minimum shape required for disposing the reinforcing material, only the disposition of the PC steel material and the covering should be taken into consideration, so that it is possible to reduce the thickness of the floor slab and thus to reduce the weight. be able to.
By arranging the PC steel material on the grid-shaped ribs, it is possible to reduce the thickness of the plate portion. Therefore, the plate portion may have a minimum member thickness of 40 mm or less, for example.

Before and prestress is introduced by the pre-tensioning the Kiyokori blanking, because not prestress is introduced by post-tensioning method on the longitudinal rib, it is possible to introduce evenly prestress.

In addition, it is preferable that at least a pair of pre-tension PC steel materials are arranged at positions where the vertical ribs and the horizontal ribs intersect each other with the PC steel material for post-tension interposed therebetween.

According to the prestressed concrete floor slab of the present invention, it is possible to improve the earthquake resistance of the entire bridge by reducing the weight of the floor slab.

It is a figure which shows the prestressed concrete floor slab of embodiment of this invention, (a) is a perspective view seen from an upper surface, (b) is a perspective view seen from a lower surface. 1A is a sectional view taken along line AA of FIG. 1, FIG. 1B is a sectional view taken along line BB, and FIG. (A) is an enlarged plan sectional view of a joint portion of a prestressed concrete floor slab, and (b) is a DD sectional view of (a).

In the embodiment of the present invention, a precast prestressed concrete floor slab 1 (hereinafter, simply referred to as “floor slab 1”) using fiber reinforced concrete, which is used for floor slab replacement work of an existing road bridge, will be described. ..

As shown in FIGS. 1A and 1B, the floor slab 1 of the present embodiment has a plate portion 2 formed in a flat plate shape and a grid-shaped rib formed on the lower surface (back surface) of the plate portion 2. 3, a tension member 4 arranged on the grid rib 3, and a joint portion 5 formed at an end portion in the bridge axial direction LG.

The plate portion 2 constitutes an upper portion (road surface side portion) of the floor slab 1, is made of fiber reinforced concrete, and has no reinforcing bars inside.
The plate thickness of the plate portion 2 may be appropriately set according to the assumed loading load, its own weight, etc., but in the present embodiment, the minimum member plate thickness t _{min is set} to 40 mm or less (see (a) of FIG. 2). ). The minimum member plate thickness t _min of the plate portion 2 is not limited to 40 mm or less and may be set appropriately.

A thickened portion may be formed on the plate portion 2 depending on the position of the bridge girder.
The height (thickness) of the thickened part is set so that the road surface height of the bridge constructed using the newly installed floor slab 1 is the same as the road surface height before the renovation.
The cross-sectional shape of the thickened portion is not limited, and may be, for example, rectangular or trapezoidal in cross section.

The lattice-shaped rib 3 is a portion integrally molded with the plate portion 2, and extends along the bridge axis direction LG (the short side direction of the floor slab 1) as shown in FIG. 1(b). The vertical ribs 31 and the horizontal ribs 32 extending along the direction orthogonal to the vertical ribs 31 (the long side direction of the floor slab) are formed.
Prestress is introduced into the vertical ribs 31 and the horizontal ribs 32 by the tension material (PC steel material) 4.

In this embodiment, ten vertical ribs 31 are arranged in parallel in the long side direction of the floor slab 1 (direction orthogonal to the bridge axis direction LG) at intervals. In addition, in the present embodiment, the two horizontal ribs 32 are arranged side by side in the short side direction (bridge axis direction LG) of the floor slab 1 at intervals.

The numbers of the vertical ribs 31 and the horizontal ribs 32 are not limited. Further, the intervals between the vertical ribs 31 and the horizontal ribs 32 may be set as appropriate according to the size of the assumed loading load and the operating location, and are not necessarily equal intervals. Further, the vertical ribs 31 may be inclined with respect to the short side direction of the floor slab 1, and the horizontal ribs 32 may not be orthogonal to the vertical ribs 31.

The intervals of the grid-like ribs 3 are, for example, the maximum value of the tensile principal stress degree that occurs when a T load of the road bridge specification is applied to the position of the minimum member plate thickness t _min of the plate portion, and the fiber reinforcement. It may be determined by comparing with the crack initiation strength of concrete.

Post-stress prestress is introduced into the vertical ribs 31, and pre-stress prestress is introduced into the horizontal ribs 32.

The method of introducing the prestress to the vertical ribs 31 and the horizontal ribs 32 is not limited, but from the viewpoint of more effectively introducing the prestress to the entire floor slab 1, the vertical ribs 31 and the horizontal ribs 32 are provided. It is desirable that either one of them is a pre-tension system and the other is a post-tension system.

As shown in FIG. 2A, a pipe material 40 is embedded in the center of the cross section of the vertical rib 31. A PC steel rod 41 as a tension member 4 for post tension is inserted into the pipe member 40.

The material forming the tube material 40 is not limited, but a sheath tube is used in this embodiment. Further, the material forming the tension member 4 is not limited to the PC steel rod, and may be PC steel strand, for example.

The end portion of the steel rod 41 is fixed to the joint portion 5 as shown in FIG.
A bolt box 50 is formed in the joint portion 5 so as to correspond to the position of the pipe member 40.
Both ends of the steel rod 41 project into the bolt box 50, and the nut 43 is screwed into the bolt box 50 to fix the steel rod 41 to the joint 5.

As shown in FIG. 2( c ), a PC steel stranded wire 42 as a tension member 4 for pretensioning is embedded in the lateral rib 32. In the present embodiment, in each horizontal rib 32, two PC steel strands 42 arranged side by side in the horizontal direction are arranged in upper and lower two stages (four in total).
The PC steel strand 42 is embedded in the cross section of the lateral rib 32 and is fixed in the lateral rib 32.

As shown in FIG. 2C, the upper PC steel twisted wire 42 and the lower PC steel twisted wire 42 face each other across the PC steel rod 41 at the intersection of the vertical rib 31 and the horizontal rib 32. It is located at the position.
The arrangement and the number of the PC steel twisted wires 42 are not limited. Further, the tension member 4 embedded in the lateral rib 32 is not limited to the PC steel strand, and may be a PC steel rod, for example.

As shown in FIG. 1, the joint portion 5 is formed in a rectangular shape in cross section at the end portion of the floor slab 1. In the present embodiment, the height of the joint portion 5 is set equal to the height of the grid-shaped rib 3. The height of the joint portion 5 is not limited, and may be higher or lower than the lattice ribs 3.

As shown in (a) and (b) of FIG. 3, the joint portion 5 is formed with a plurality of through holes 51 along the bridge axis direction LG. The through hole 51 is arranged at a position where it does not overlap the PC steel rod 41 and the PC steel strand 42.

The through hole 51 is parallel to the PC steel rod 41 and is formed by a pipe material (for example, a sheath pipe) embedded in the joint portion 5. A joint PC steel rod 52 for joining with another adjacent floor slab 1 is inserted into the through hole 51.

The joining portion PC steel rod 52 is disposed over the joining portions 5 and 5 of the adjacent floor slabs 1 and 1. One end portion of the joining portion PC steel rod 52 has the joining portion 5 of one floor slab 1. Of the floor slab 1 and the other end of the floor slab 1 protrudes from the end of the joint 5. The floor slabs 1 are connected to each other by screwing nuts 53 onto both ends (protruding portions) of the joint PC steel rod 52.

Next, a method of constructing the floor slab 1 of the present embodiment will be described.
First, the floor slab 1 to which prestress has been introduced in advance in the direction orthogonal to the bridge axial direction LG by the PC steel wire 42 is placed on the bridge girder. The floor slab 1 is installed in a state in which other floor slabs 1 placed on the bridge girder in advance and the joint portions 5 are in contact with each other.

After the floor slab 1 is placed, the steel rod 41 is used to introduce prestress in the bridge axial direction LG, and the through holes 51 are used to join adjacent floor slabs 1 to each other.
The steel rod 41 may be inserted into the pipe 40 in advance, or may be inserted into the pipe 40 after the floor slab 1 is placed on the bridge girder.

Further, the floor slabs 1 are joined to each other by inserting the joining portion PC steel rod 52 across the joining portions 5 (through holes 51) of the adjacent floor slabs 1 and screwing the nut 53 ( (See FIG. 3A).

According to the floor slab 1 of the present embodiment, since the fiber reinforced concrete is used, the reinforcing bar can be omitted in the plate portion 2. Furthermore, since the tension members 4 are arranged on the grid-shaped ribs 3, it is possible to reduce the thickness of the plate portion 2 and thus to reduce the weight of the floor slab 1 as a whole.

Further, the size and shape of the grid-like ribs 3 may be any size and shape that can secure a necessary covering around the PC steel material 4, so that the floor slab 1 can have a small cross section.
By reducing the weight of the floor slab 1, the dead load can be reduced, and by extension, the seismic performance of foundations such as piers and footings can be improved.

Since the pre-stress is introduced into the vertical ribs 31 by the post-tension method and the pre-stress is introduced into the horizontal ribs 32 by the pre-tension method, the pre-stress can be uniformly introduced into the entire floor slab 1. ..

When the post-tension method is adopted, it is not necessary to consider the fixing loss length of the PC steel material 4, so prestress is effectively introduced.
Further, since the prestress is introduced through the grid-shaped ribs 3, the prestress introduction efficiency is higher than that of the conventional slab having a flat plate structure.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the respective constituent elements described above can be appropriately modified without departing from the spirit of the present invention.
For example, in the above-described embodiment, the case where the prestressed concrete slab of the present invention is used to replace the slab of the existing bridge has been described, but the purpose of use of the prestressed concrete slab is not limited to this. , For example, may be used for a new bridge.

Further, in the above-described embodiment, the case where the prestressed concrete slab of the present invention is used for the repair work of the road bridge has been described, but the type of the bridge to be repaired is not limited, and for example, a bridge for a railway. May be

Further, in the above-described embodiment, two PC steel materials for pre-tensioning are arranged above and below the PC steel material for post-tensioning at the intersections of the vertical ribs and the horizontal ribs. It suffices that the PC steel materials for pre-tension face each other with the PC steel material for post-tension interposed therebetween, and the number of PC steel materials for pre-tension is not limited.

1 Floor slab (prestressed concrete floor slab)
2 Plate part 3 Lattice rib 31 Vertical rib 32 Horizontal rib 4 Tension material (PC steel material)
41 PC steel rod (PC steel material for post tension)
42 PC steel stranded wire (PC steel material for pretension)

Claims (3)

A prestressed concrete floor slab using fiber reinforced concrete,
A plate portion and a grid-like rib formed of vertical ribs and horizontal ribs formed on the lower surface of the plate portion,
In the plate portion, a thickened portion is formed according to the position of the bridge girder,
Pre-stress is introduced into the vertical ribs by the post-tension method, and pre-stress is introduced into the horizontal ribs by the pre-tension method ,
Wherein the ends of the longitudinal ribs, characterized that you have fixable bolt box end of the tension member is formed, prestressed concrete slab. At the intersection of the vertical ribs and the horizontal ribs,
The prestressed concrete floor slab according to claim 1 , wherein at least a pair of pre-tensioned PC steel materials are arranged at positions facing each other with the post-tensioned PC steel material interposed therebetween. The prestressed concrete floor slab according to claim 1 or 2 , wherein the minimum member thickness of the plate portion is 40 mm or less.

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