JPS59328Y2 - Intermediate fulcrum raising device for prestressed concrete embedded formwork - Google Patents

Description

[Detailed description of the invention] This invention relates to a device for raising the intermediate fulcrum of a buried formwork made of prestressed concrete (hereinafter referred to as PC) for concrete structures, when pouring concrete in place. After increasing the calculated warping and curing the concrete while maintaining that state, the warping means is removed to increase the residual compressive stress on the bottom surface of the formwork, creating girders, beams, floors, etc. that are resistant to cracking. It is something.

Hereinafter, embodiments of this invention will be described with reference to the drawings.

Figure 1 shows an example of applying this idea to a floorboard with a span of 5m.

The PC-embedded formwork 1 is a mass-produced flat plate material, with a length of 5m plus extra length and a fixed width, usually 1 to 2m widths lined up (see drawing 1) to obtain the required width. It is something.

The thickness is 4cm, and on top of that is cast-in-place concrete 1-2.
The concrete is cast to a thickness of 8 cm, making the total cost 12 crn.

Two pillars 3 are set up on the ground and supported at four points: A and B at both ends, the middle glue, and E.

In the first drawing, 1a is a PC steel bar, and 1b is a welded wire mesh.

In this way, after extending the embedded formwork 1 over the beam or original shape at the required position and supporting the intermediate part at - or several points (in this case, two points) at appropriate intervals, raise E at each intermediate fulcrum, As shown in Figure 1, which is slightly exaggerated, the formwork 1 is given a gentle upward curvature.

The screw jack at the lower end of the column 3 is turned to raise its upper end, and the screw jack is equipped with a reaction force adjustment and measuring device 4 (FIG. 9), which will be described later.

After giving the formwork 1 an appropriate warp, cast-in-place concrete notebook is poured as usual.

This increases the weight of the entire floor slab, and the reaction force of each support column 3 also increases accordingly.

Therefore, the fulcrum is adjusted up and down so that the indicated value of the device 4 that measures the reaction force reaches the expected value obtained in advance through design calculations for that support.

Wait for the concrete to harden, and after the embedded formwork 1 and cast-in-place concrete 2 are integrated, the support at the intermediate support E is removed.

To outline the design calculations for the embodiment shown in Figure 1, the dimensions of the floor slab are as described above, with an AD distance of 1.8m and a DC and CE distance of 0.7m.
Let it be m.

The PC embedded formwork 1 that forms the bottom of the floor slab is a mass-produced product, and its maximum bending moment is 184 kg-m, so D, E
The bending moment at both supporting points) MdMe should be -184 kg-m.

Then, by calculation, due to the weight of formwork 1 and cast-in-place concrete 2, reaction force at point A = 168 kg, reaction force at point D =
582 kg, bending moment MC at point C (center) = -1
10 kg-m, Mx = +47 kg, m can be calculated (x = 0.s6m is the point where the maximum moment occurs).

Therefore, after pouring concrete 2, immediately move to point D and E.
When the column reaction force is adjusted so that the support reaction force at the point becomes 582 kg, the embedded formwork 1 is given the maximum bending moment - camber.

Figure 1A is a moment diagram of this state.

Also, Fig. 2 7゜work, Ki is Fig. 1 X (X = 0.56
Stress diagrams of formwork 1 before use at point m), point D, and point C. Figures A, E, and R show the stress when cast-in-place concrete is cast and warped when the entire slab weight is applied. It is a diagram.

Before use, the formwork 1 has a prestressed compressive stress of 6 on the entire cross section.
9 kg/cm2 is evenly distributed.

When cast-in-place concrete 2 is applied while giving an upward warp and is hardened by adjusting to the support reaction force calculated above, at point X (Figure A), the upper surface is 87, the lower surface is 51. At point D (Figure O), the upper surface is 0, the lower surface is 138, and at point C (Figure 7), the upper surface is 2.
8. The lower surface has changed to 110kg/cm".

Cast-in-place concrete 2 is placed on top of this curved formwork 1 to complete the floor slab, and after the supports 3 are removed, the maximum load allowed for this floor slab is placed on top of it. .

In this case, the maximum load is the allowable compressive stress at the center of the top surface of the floor plate, that is, the top surface of the cast-in-place concrete 2 - 80 kg.
/Cm”, maximum load = 347 kg
/m (calculated based on a width of 1m).

When this maximum load is applied, the stress diagram at points X, D, and C in Figure 1 becomes as shown in Figure 2.

In other words, at point X, the stress on the top surface of cast-in-place concrete 2 is 42 kg.
/cm2, the lower surface is -8, the upper surface of the formwork 1 is 79, and the lower surface is 18 kg/Cm''.

At point D, stress 113 on the top surface of cast-in-place concrete 2 (converted stress 113 x 0.675 = 76 kg/
cm2), the lower surface is -22, the upper surface of the formwork 1 is also -22, and the lower surface is 48.

At point C, the stress on the top surface of cast-in-place concrete 2 is 118 (converted stress 80 kg/cm2), the stress on the bottom surface is -23, and the stress on the bottom surface of formwork 1 is 118 (converted stress 80 kg/cm2).
5 kg/cm2 on the upper surface and 16 kg/cm2 on the lower surface, both of which leave compressive stress on the lower surface of the slab.

The stress on the lower surface of the floor slab without this idea is shown by the chain line, and the tensile stress would be -33 at point X, -90 at point D, and -94 at point C, resulting in cracks.

This difference shows the effectiveness of this invention in improving crack resistance.

Here, the reaction force adjustment used as a means of increasing the intermediate fulcrum,
The measuring device 4 will be explained with reference to FIG.

In this case, a coil spring is inserted into the upper part of the prop elevation device using a commercially available screw jack, and the magnitude of the reaction force is measured by the amount of contraction of the spring.

A screw shaft 11 fixed to the base plate 10 is fitted into the lower end of the steel pipe support 3.

When the bundle 13 of the female screw 12 screwed onto the screw shaft 11 is turned, the female screw 12 moves up and down.

Between this female screw 12 and the lower end of the column 3, there are upper and lower flanges 14, 15 that can slide on the female screw 12, and a coil spring 16 interposed between them.

When the female screw 12 is moved up and down by the bundle 13, the lower tsuba 1
4. The coil spring 16 and the upper flange 15 move up and down, and the column 3 mounted on the upper flange 15 moves up and down.

When a load is applied to the support column 3, the coil spring 16 contracts by that amount, so the amount of contraction can be measured using the mortar scale 17 fixed to the lower flange 14 and calculated from the spring constant, or it can be calculated from the load-shrinkage line in advance. Make a diagram and know the load value.

The load value may be placed in the scale 17 as a mortar.

The LT spring used in the experiment has a compression rate of 25 kg per 1 mm.
It was proportional.

In the embodiment shown in Fig. 3, the intermediate supports E, F, and G are supported by bidet type supports 3a, and the embedded formwork 1 is of the first design.
Span 5m, AD 1.4m, DE 1.2m, Total thickness 15
cm, load capacity 180 kg/m C width 1 m),
The reaction force is adjusted so that the reaction force at each intermediate fulcrum is equal and the upward bending moment at the center point C is -60 kg-m.

Calculated from the above conditions, the required reaction force at each intermediate support is 437
kg.

At that time, the moment distribution of the formwork 1 becomes as shown in Fig. 3A, and as a result of pour-in-place concrete placement and the addition of the above-mentioned live load, the stress diagram becomes as shown in Fig. 4.

FIG. 5 shows the same floor slab as in FIG. 1, and the intermediate fulcrum E is at the same position, but the upward reaction force of the left and right supports 3 that cause the formwork 1 to warp upward is reduced.

X in the diagram. The stress diagram at points D and C is as shown in Figure 6.

FIG. 7 shows an embodiment in which the embedding form 1' is made of a PC board having reinforcing ribs as shown in FIG. 10, which is more resistant to bending.

The A, I, and TS in the upper row of Figure 8 are the X points in Figure 7, and the O in the lower row.
Force, Ki, and Ri indicate stress changes at point C in the figure.

Although the above has been explained using decimal examples, this invention is
This method is characterized by pouring and hardening cast-in-place concrete using PC-fabricated formwork on-site with appropriate reaction force and upward warping based on design calculations to increase bottom surface stress. Naturally, the aspects will vary widely depending on design conditions and site conditions.

This idea takes advantage of the wide elasticity range of the factory-manufactured high-quality, tough PC embedded type, and applies the compressive stress of prestressing to the underside of the formwork, which forms the bottom surface of the completed floor slab, during on-site work. Provides the simplest means for further growth.

In other words, the device for raising the intermediate fulcrum of this invention is the simplest, cheapest, and easiest to handle because the threaded shaft is inserted into the steel pipe support to serve as a lifting guide and lifting drive adjustment mechanism for the support, and it also serves as the core material of the coil spring for measuring reaction force. Easy height and reaction force adjustment device.

Furthermore, since the coil spring is equipped with a deformation measurement scale, it can be calibrated to immediately determine the fulcrum reaction force.

Considering that other reaction force adjustment devices and stress measurement devices are used to adjust the height of the fulcrum and measure the reaction force, the simplicity of this heightening device is revolutionary.

[Brief explanation of drawings]

Figure 1 A, B, TS and TE are a schematic explanatory diagram of the embodiment of this invention, a moment diagram at the time of warping, an elevation view, and a cross-sectional view of the floor slab, respectively, and Figure 2 A → KE are the same. Stress diagrams for each part and each condition,
Figure 37. A is an explanatory diagram and a moment diagram of another embodiment, FIG. 4 A→F is its stress diagram, FIG. Its stress diagram, Figure 77. A is an explanatory diagram and moment diagram of another embodiment, FIG. FIG. 3 is a cross-sectional view of a floor slab using a different embedded formwork. 1...PC concrete embedded formwork, 2...
...cast-in-place concrete.

Claims (1)

[Scope of utility model registration request] The middle supporting point of the prestressed concrete embedded formwork is raised higher than both ends of the formwork to give the formwork an upward curvature, and while maintaining this state, cast-in-place concrete concrete is poured onto the formwork. In the hardening equipment, a screw shaft with a part fitted onto the end of the steel pipe support of the intermediate fulcrum and a plywood attached to the end, a female thread with a rotating drive part screwed onto this screw shaft, and a female screw mentioned above that fits on the outer periphery of the screw shaft. A coil spring with upper and lower flanges interposed between the upper and lower flanges and a spring deformation measuring scale attached to either of the upper and lower flanges is provided, and the female screw is rotationally driven to raise the intermediate fulcrum and is supported by the measuring scale. A device for raising the intermediate fulcrum of a prestressed concrete embedded formwork, which is characterized by calculating the reaction force.