JPH0583694B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for reinforcing prestressed flat plate slabs, and in particular to an improved method for reinforcing around columns and for reinforcing weakened slabs due to the presence of openings. The purpose of this study is to clarify the reinforcement method.

[Background of the invention]

Flat slabs are called beamless plate structures, and are attracting attention because they do not use beams and can reduce the height of buildings. This is a structure that supports the slab by providing a column capital or support plate.

On the other hand, flat plate slabs are similar to the above-mentioned flat slabs in that they do not use beams, but in addition, the slabs are directly connected to the column structure without providing a capital or support plate. Since there is no capital (column head) or support plate, the ceiling area around the columns can have a simple appearance, and it has the advantage that formwork work etc. are easy during construction.

Since both have structures that do not use beams, they have the disadvantage that the slabs are easily warped, but this was initially solved by making the slabs thicker and shortening the spans between the columns. However, later, a prestressed structure using prestressed steel wire was introduced, making it possible to make significant improvements.

However, the prestressed structure used for reinforcing flat slabs was a simple method in which PC wires were stretched in two directions, vertically and horizontally, by bonding or unbonding.

Originally, flat slabs were applied to low-rise buildings, but since flat plate slabs can use space more effectively than flat slabs, they have been improved with prestressed structures, and as a result, they have been applied to high-rise buildings, etc. Its use is being considered. However, unlike flat slabs, flat plate slabs do not use capitals or supporting plates at the joints with columns, so when the load is large or external forces such as earthquakes are applied, the slabs around the columns are There is a high risk of cracking or punching failure.

In conventional slab construction, multiple reinforcing bars are inserted into the slab around the columns, or I
The method used was to insert shaped steel in a criss-cross pattern, but inserting such reinforcing material in places where reinforcing bars would normally be crowded not only made construction difficult, but also made it difficult to fill with concrete, making the reinforcing effect insufficient. It is not recommended to apply it to flat plate slabs.

Conventionally, as a reinforcement method around columns in a flat slab, techniques described in, for example, Japanese Patent Laid-Open Nos. 57-104752 to 58-29961 are known.

In the former method, multiple unbonded PC strands with different curvatures are placed around the column and the tension is used to strengthen the area around the column, but it is also possible to cut the PC strands and roll them up. The construction is complicated, and the PC that has been rolled up and temporarily fixed
If the twisted wires were to become unlatched, there was a danger that it would lead to a serious accident.

Furthermore, the technique described in JP-A No. 58-29961 involves arranging spiral striations around columns in a petal-like manner for reinforcement, but it is difficult to construct them in a petal-like manner. The disadvantage is that there are risks associated with construction.

On the other hand, like slabs of other structures, flat plate slabs may have openings in a portion of the slab, but unlike slabs of frame structures, the slab portion of flat plate slabs does not allow for transmission from the columns. The slab is an important structural element that is responsible for the bending moment and shearing force generated by the slab, so if there is an opening, it is not possible to place the prestressing steel wire, which often weakens the resistance of the slab.

Conventionally, the method of reinforcing the slab around this opening was to insert ordinary opening reinforcing bars into the slab around the opening, but this reinforcing bar only worked to prevent crack propagation at the opening edge. It is not possible to suppress the reduction in slab rigidity due to the absence of prestressing PC steel wire due to openings.

In view of the above, the present inventors have developed a
By devising the placement of the PC steel wires, we were able to complete a new construction method that strengthens the area around the columns and strengthens the weakened slab due to the presence of openings. In other words, in the conventional prestressing construction method, the prestressed steel wires were simply arranged linearly in two directions, vertically and horizontally when viewed from the top, so the prestressed steel wires did not act as reinforcement around the columns.
Furthermore, if there is an opening, the PC steel wire must be placed to avoid this, and therefore the PC steel wire cannot be placed over the length and breadth of the area commensurate with the width of the opening. This led to the weakening of the slab.

Therefore, in the present invention, the PC steel wire itself not only acts to reinforce the surroundings of the column, but also the presence of the opening.
A new PC that does not pose an obstacle to the placement of PC steel wires
The steel wire arrangement solves the above-mentioned problems, and the prestressed frame is easy and safe to construct, and can strengthen around columns and prevent weakening of the slab due to the presence of openings. The purpose of this paper is to provide a reinforcement method for flat plate slabs.

[Means for solving problems]

In other words, the reinforcement method according to the present invention is a method for reinforcing PCs installed in prestressed flat plate slabs.
It is characterized by bending the part of the steel wire located around the column, and arranging the PC steel wire so as to surround the column by crossing two or more points of the bent PC steel wire,
In addition, the reinforcement method according to the present invention can be applied to a PC placed in a prestressed flat plate slab.
A method characterized by bending a portion of the steel wire located around the opening, and arranging the PC steel wire so as to surround the opening by crossing two or more points of the bent PC steel wire. It is.

[Specific structure of the invention]

EMBODIMENT OF THE INVENTION Hereinafter, the specific structure of this invention will be explained in detail according to the Example shown in an accompanying drawing.

(Example 1) In this example, as shown in FIGS. 1 and 2, among the PC steel wires 2 arranged in a lattice pattern, the steel wires 2A, 2B
are bent into an arch shape in opposite directions in the lateral direction of the column 1 (left and right direction in the drawing, the same applies hereinafter), and are made to intersect between the adjacent columns 1, 1, and the lateral steel wire 2A, 2B is also bent into an arch shape in opposite directions at the top and bottom of the pillar 1, and intersects between the adjacent pillars 1, 1. In other words, the PC steel wire is bent at four locations on the top, bottom, left and right around the pillars so as to intersect between adjacent pillars 1 and 1, so that the intersection of the bent portions surrounds pillar 1. .

In this embodiment, the PC steel wire 2 is bent horizontally around the pillars as described above, and is located approximately at the center between the plurality of pillars 1 as shown in FIG.
is preferably suspended below the cross section of the slab 3 (downward in the drawing).

As shown above, the PC steel wire is bent in an arch shape at four points on the top, bottom, left, and right around the pillars so that it intersects between adjacent pillars 1, 1, and the pillar is formed by crossing the four arch-shaped bent parts. As a result of surrounding 1, when prestressing this steel wire, a hoop tension effect (force acting in the Y direction of the drawing) occurs in addition to the normal crimping effect (force acting in the X direction of the drawing). These combined forces generate reinforcing force and prevent punching cracks.

In addition, in FIG. 1 showing this embodiment, adjacent columns 1,
Although the crossing is performed between horizontally adjacent columns, it may also be performed between adjacent columns at an oblique position.

(Embodiment 2) FIG. 3 is a schematic plan view of main parts showing a second embodiment.

In this embodiment, as shown in FIG.
B is bent outward in an arch shape on the left and right sides of the column 1 and inflated, and the lateral PC steel wires 2A and 2B are also bent outward in an arch shape at the top and bottom of the column 1 and inflated. be. That is, by crossing these four arch-shaped bending parts, the adjacent pillars 1, 1 are bent in an arch-shape without crossing each other as in Example 1,
It is designed to surround pillar 1.

In this example, the vertical PC steel wire is
It may be placed above or below the PC steel wire.

Although only one PC steel wire is shown in each of the vertical and horizontal directions in the drawing, a plurality of PC steel wires may be used as in the first embodiment. The same applies to the following examples. Furthermore, this embodiment may be implemented between pillars at diagonal positions. The same applies to the following examples.

(Example 3) In this example, as shown in FIG. 4, the horizontal PC steel wires 2A of the PC steel wires 2 arranged in a lattice pattern surround the columns 1A and 1B. The PC steel wire 2D is bent inward and the PC steel wire 2D is also
Each side is bent inward at 90 degrees so as to surround the sides. 2X and 2Y are PC steel wires formed by bending, each with connection 4.
connected by. Also, 2 of pillars 1C and 1D
The bent PC steel wires 5A and 5B surrounding the sides are the same as the bent PC steel wire 2Y rotated left and right by 90 degrees, that is, the bent PC steel wire 5A is the same as the bent PC steel wire 2Y. is rotated 90 degrees counterclockwise (left) around column 1C and moved downward by the distance between column 1A and column 1C in Fig. 4, and the bent PC steel wire 5B is This is the same as the state in which the bent PC steel wire 2Y is rotated 90 degrees clockwise (to the right) about the column 1D and moved downward by the distance between the columns 1B and 1D in FIG. That is, the PC steel wire is bent at two opposite locations around the column, and the column 1 is surrounded by the intersection of at least two bent portions.

Note that in this embodiment, the PC steel wire to be bent is not limited to that shown in the drawings, and any wire that has a configuration in which the PC steel wire is bent at two opposing locations around the column may be used. Furthermore, if the bent PC steel wires 2X and 2Y are formed of one PC steel wire, it goes without saying that only one connection 4 is required.

(Embodiment 4) FIG. 5 is a schematic plan view of main parts showing a fourth embodiment.

In this embodiment, as shown in Fig. 5, bent PC steel wires are installed on the left and right and upper and lower columns 1, 1, and at least three sides of the column (top, bottom, left and right) are installed.
The PC steel wire is bent so that the pillar is surrounded by the intersection of at least two bent parts.

In the above examples, the PC steel wire is unbonded PC
Stranded wire is preferably used, but bonded wire
It is also possible to carry out using PC steel wire.

Further, the shape of the PC steel wire 2 after being bent is not limited to that shown in the drawings, and may be any shape as long as it is curved in an arch shape (including a semicircular shape, etc.).

The pillar 1 may be made of a steel frame or the like as a support, but it may also be a concrete column (by RC construction method or the like) without a steel frame and reinforced with reinforcing bars or the like.

The method for bending the PC steel wire in the above embodiments may be a combination of two or more of the above embodiments, or in addition to the above embodiments, the PC steel wire may be bent in the diagonal direction.
It may also have a steel wire.

(Example 5) Next, in the present invention, a case in which a PC steel wire is arranged around an opening will be explained based on FIGS. 8 and 9. In Examples 1 to 4 above, the reinforcement method for the surrounding area of the column was explained, but the above reinforcement method is for placing PC steel wire around the opening provided in the slab for arranging the elevator etc. The same can be applied to.

In the conventional prestressing method, the PC steel wires are arranged in a grid-like straight line, so there are openings 6 in the middle.
If there is, it is impossible to arrange the PC steel wire across the opening 6, so it has to be arranged avoiding the opening 6. Since it is not possible to arrange the PC steel wires 2 over the entire area, the resistance of the slab to stress becomes weaker. According to the construction method of the present invention, even if an opening 6 exists, the structure is curved in an arched manner to bypass only the opening 6 and surround it, similar to the above-mentioned method of reinforcing the surrounding area of a column.
It is possible to arrange the PC steel wires 2P to 2U and 2p to 2u, and it is possible to cover the weaknesses of the conventional construction method.

In addition, during actual construction, PC steel wire 2P ~
Since the tightening operation for 2U and 2p to 2u is performed after the poured concrete has cured, there is no need for any particular difference in the formwork installed in the opening 6. However, PC steel wire 2P ~
In order to prevent the concrete around the opening 6 from being crushed by the tightening operation of 2U and 2p to 2u, it is preferable to sufficiently space the PC steel wires 2P to 2U and 2p to 2u from the opening end.

Arranged around the opening 6 as described above
The PC steel wires 2P to 2U and 2p to 2u are connected to the opening 6
Because it has the effect of improving the degree of compressive stress in the surrounding area,
This is effective not only for simply preventing cracks but also for ensuring the rigidity of the slab around the opening 6.

(Other configurations) It should be noted that in the present invention, “a structure arranged in a grid”
"Bending the part of the prestressed steel wire around the column or around the opening" includes bending the existing prestressed steel wire, as well as bending the part of the prestressed steel wire that is located around the pillar or the opening. This includes adding new bent PC steel wire while leaving the steel wire intact.

Incidentally, as an application of the present invention, bending means as shown in FIGS. 6 and 7 can also be considered.

〔Effect of the invention〕

According to the present invention, the portion of the prestressed steel wire placed around the column is bent in a prestressed flat plate slab, and the column is formed by crossing the bent prestressed steel wire at two or more points. Since the pillars are placed in a surrounding manner, the hoop tension effect increases the concrete compressive stress in the slab around the pillars, and according to experiments and analysis, it increased by approximately 30%. Therefore, the resistance to punching failure increases as the degree of compressive stress increases, making it easier to design slabs around columns, eliminating the need to use reinforcing bars and reinforcing steel frames as in the past, and eliminating the need for crowded reinforcement in slabs. It has the effect of being easy to work with and has good workability.

Furthermore, as a preferred embodiment, it is possible to use the PC steel wire that is normally placed for reinforcing the slab around columns without cutting it, which saves labor in construction. There is no need to roll up the steel wire, so the construction can be carried out safely.

Furthermore, according to the present invention, despite the presence of an opening, the PC steel wire can be placed substantially across the opening, which only increases the stress resistance of the entire slab. In addition, the compressive stress around the opening becomes larger than the concrete tensile stress, and it has the effect that reinforcement can be performed without ordinary opening reinforcing bars. Furthermore, since the entire area around the opening is compressed, there is an effect of preventing a decrease in the rigidity of the opening. Furthermore, similar to the case around the pillars, it is possible to save labor in construction.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view showing the first embodiment;
3 is a schematic plan view of the main part showing the second embodiment, FIG. 4 is a schematic plan view of the main part showing the third embodiment, and FIG. 5 is a schematic plan view of the main part showing the third embodiment. 6 is a schematic plan view of the main part showing an application example of the present invention; FIG. 7 is a schematic plan view of the main part showing an application example of the present invention; FIG. 8 is a schematic plan view of the main part showing an application example of the present invention. FIG. 9 is a schematic plan view showing the fifth embodiment of the invention, and is also a schematic cross-sectional view. In the figure, each symbol indicates the following. 1...
Pillar, 1A...Column, 1B...Column, 1C...Column, 1D
...Column, 2...PC steel wire, 2A...PC steel wire, 2B
...PC steel wire, 2a...PC steel wire, 2b...PC steel wire, 2X...bent PC steel wire, 2Y...bent PC
Steel wire, 2P~2U...Bent PC steel wire, 2P~2
u...bent PC steel wire, 3...slab, 4...connection, 5A...bent PC steel wire, 5B...bent PC
Steel wire, 6...opening.

Claims (1)

[Claims] 1. A part of a prestressed flat plate slab that is placed around a column is bent, and the bent prestressed steel wire intersects at two or more points to form a column. A method for reinforcing slabs around columns in a prestressed flat plate structure, which is characterized by arranging PC steel wires to surround the pillars. 2. Bend the part of the PC steel wire arranged in the prestressed flat plate slab around the opening, and surround the opening by crossing two or more points of the bent PC steel wire. A method for reinforcing slabs around openings in prestressed flat plate structures, which is characterized by installing PC steel wires. 3. Reinforcement of a slab around a column in a prestressed flat plate structure according to claim 1, characterized in that a PC steel wire located approximately at the center between a plurality of columns is suspended below the cross section of the slab. Construction method.