JPS6045567B2 - Method for manufacturing ultra-high strength PC pile with improved shear strength - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing prestressed concrete piles manufactured by the pretensioner method, in which a prestressed concrete pile is manufactured by a pretensioner method, in which a steel material for prestressed concrete (hereinafter referred to as "PC steel material") is placed around a group of longitudinal reinforcements. Constructed by winding a steel wire with a descending point strength of 80 to 9/1 or more in a spiral shape with a reinforcement ratio (Pw) to the vertical cross-sectional area of the pile body of 0.53% or more and a pitch interval of 10 cm or less. P
q After pre-stressing the steel material, it is compacted by centrifugal force using a cement containing an ultra-early strength admixture that can quickly obtain a compressive strength of 80 Ok9/c or more through atmospheric pressure steam curing. After forming the concrete pile body, it is cured with atmospheric pressure steam, and then the concrete is 80 to 9/d.
The bending strength is significantly high, which is characterized by the introduction of a press dress that can obtain the above effective press dress.
Prestressed steel with dramatically improved shear strength.
This invention relates to a method for manufacturing a concrete pile.

The present invention will be explained in detail below with reference to FIGS. 1 and 2.

First, the background of the present invention will be described.

In order to improve the bending strength of prestressed concrete piles (hereinafter referred to as "PC piles"), it is possible to increase the amount of prestress introduced into the concrete. The amount of stress is limited to an appropriate amount depending on the compressive strength of the concrete used. Therefore, in order to increase the bending strength, it is necessary for the concrete to have high compressive strength in order to increase the amount of prestress introduced. Autoclave curing (high temperature, high pressure steam curing) has traditionally been used as a method to improve the compressive strength of concrete. According to this method, a compressive strength of 800k9/Clt or more can be obtained.

However, since this is a special curing method in which the concrete is kept at a high temperature close to 200℃ for several hours, the amount of relaxation of the pre-tensioned prestressed steel material increases excessively, and the amount of prestress introduced into the concrete after curing decreases abnormally. However, it is nearly impossible to introduce high prestress. If a post-tensioning method is used in which prestress is introduced after autoclave curing, the prestressing steel material will not be adversely affected by the high temperature conditions mentioned above, and therefore the loss of prestress amount can be prevented, but the prestressing pile basically cuts the ends. For this reason, post-tensioning PC stakes are not generally used at present.

In view of the above-mentioned circumstances, and in connection with the recent development of super-fast-strengthening admixtures, the inventor of the present application has conducted various experiments, and has found that an admixture that can be obtained by autoclave curing instead of autoclave curing has been found. As described above, we have invented a method for effectively obtaining a concrete body with significantly improved bending strength (Showa era patent application No. 155748).

In this method, the compressive strength of concrete used in the manufacturing method of prestressed concrete piles produced by the pretensioning method is simply subjected to normal pressure steam curing to achieve a compressive strength of 800 k9/cm at an extremely early stage.
Use an admixture that contains an ultra-early strength admixture that can give a strength of at least c. The compressive strength of concrete is about <0.
It is characterized by being 1 to 0.3 times larger.

According to this method, it is possible to introduce high prestress into high-strength concrete, which is very effective in increasing bending strength, and it is also possible to manufacture concrete piles that exhibit sound mechanical properties. During the experimental process of the invention, doubts remained regarding the shear strength. This is because in the above method, in an experiment using a reinforcing bar cage made of iron wire with a descending point strength of about 40 kg/d, which is used in a normal PC pile as a spiral bar wound around the outer circumference of a group of longitudinal bars, the shear span In the shear region where the ratio a/D = 1.5, a much lower load was applied due to the bending failure strength, and the shear failure occurred.On the other hand, the inventor of the present application A reinforcing bar cage in which high-strength spiral bars with a point strength of 55 kg/d or more are placed around the outer periphery of the longitudinal bar group is placed in the formwork, and after the concrete is centrifugally compacted, it is cured, and then the longitudinal tension bars are used to tighten the concrete. , for example 100
Experiments have confirmed a method for obtaining columns with excellent torsional strength, shear strength, and toughness by introducing a k9/Cli prestressor.

The present invention has been made based on the previous two inventions mentioned above.

In other words, the former invention, which is a high-strength, high-prestress pile with high bending strength, has a low shear strength, which is the only questionable point, and the latter invention, which uses ordinary strength concrete, However, by using a spiral reinforcement with a descending point strength of 55k9/d or more, it is difficult to see whether this can be improved by using technology to create columns with significantly improved torsional strength and shear strength. We investigated various conditions and conducted numerous experiments to find out under what conditions, if improvements could be made, we could obtain a body with high bending strength and high shear strength. A part of it is shown below with reference to FIGS. 1 to 2b. Example 1 Specimen (1) Rebar cage Specimen T. P. NO. As the reinforcing bar cage for 3 to NOl4, vertical bars 1 and reinforcing bars (spiral bars) 2 with the following dimensions were used, and for each specimen, the pitch interval was changed as shown in Table 2, and the vertical bars were Reinforcing bars 2 were spirally wound around the outer periphery of the group to form a reinforcing bar cage with a diameter of 33 cm.

Vertical reinforcement 1: Outer diameter and number are as shown in Table 2 Reinforcement reinforcement 2: Outer diameter 7.4T$L Both have a descending point strength of 130k9/d or more and breakage Strength... 145kg/i or more Specimen T.
P. NO. l and NO. As for the reinforcing bar cage for 2, vertical bar 1 is NO. 3~NO. A reinforcing bar cage was knitted in the same manner as above, using the same reinforcing bars as in No. 8, and using wire rods having a diameter of 3.27 Tr1Tt1 and a descending point strength of 37 kg/d.

(2) Cement, etc. used Using the compounding ratio shown in Table 1 Ta.

Note: The admixture is an ultra-fast and strong admixture, manufactured by Ono 1) Cement Co., Ltd., trade name: Onoda Σ1,000 (chemical composition, S
lO2, 6-17, Al2O3; 5 or less, Fe2O32
Below, CaO: 31-41, SO3: 43-53, specific gravity: 2.5 or more, specific surface area: 5000 cIL/da or more, I
g-10ss; 5 or less) was used.

(3) Place the above-mentioned reinforcing bar cage in a formwork, pour cement etc. made of the above-mentioned mixture ratio into the formwork, then, after pre-tensioning the vertical reinforcements, form concrete by centrifugal force forming method,
Four hours after concrete was placed, atmospheric pressure steam curing was carried out according to the cycle shown in Figure 1, and immediately pre-preparation**
Stress was introduced and the effective prestress amounts shown in Table 2 were applied, and specimen No. 1 was prepared as shown in Figure 2a, consisting of the following dimensions. l~NO. 14 was obtained.

2. Experimental Method A loading test was carried out on each of the 14 specimens on the 28th day of the test using a loading method in which the shear span ratio was set to a/D = 60/40 = 1.5 as shown in Figure 2b.

The strength of concrete is O~28=890~1080k9
/CIL had been reached. In addition, in Figure 2a, L is 5
00cm1D is 40α, the supporting points Fl, f2 and the specimen T. P. The distances 11 and 12 from the end face of 50C7n1 are respectively the load points P. The distances A and a of the intervals P-Fl and P-F2 between P and the fulcrums Fl and f2 are 60c, respectively.
It was m.

3 Experimental results It was as shown in Table 2.

As is clear from the above experimental results, specimen No. l～N
O. 8, specimen No. 8 does not use spiral auxiliary bars with high descending point strength. l and NO. No. 2 underwent shear failure at a load far below the calculated bending failure load, and the others underwent bending failure when the calculated bending failure load was reached.

That is, the above specimen No. l and NO. No. 2 is based on the present invention, in which the amount of effective prestress introduced is the same, but reinforced with spiral reinforcement with high descending point strength. 3~NO. 8
Failure occurred at a much lower load than the PC pile body.

In addition, NO. with a small amount of effective prestress. 9~NO. It is also clearly shown that sufficient effects are obtained with respect to l4. The above experiments have shown that the former invention, which is a high-strength, high-prestress pile, and the latter invention, which is a high-strength spiral reinforcement that improves the torsional strength and shear strength of ordinary strength concrete, have been developed. It is clearly recognized that the effect is working effectively.

That is, in the case of the present invention using high-strength spiral auxiliary reinforcement, even at a shear spy ratio such as a/D = 1.5, bending failure precedes shear failure, or bending failure and shear failure occur simultaneously. - It was confirmed that the fracture occurred at a high load almost equivalent to the bending fracture load. From the above, the effective prestress amount is 80k.
In the case of the present invention, in which the reinforcing bars are made of steel wire with a descending point strength of 80k9/i or more and are used as spiral reinforcing bars, the pitch interval of the spiral reinforcing bars is at least 10
cm or less, the reinforcement ratio is set to 0.53% or more, preferably the pitch interval is 7cm or less, and the reinforcement ratio is set to 0.76% or more. By using a reinforcing bar cage, high strength and high prestress with high bending strength can be achieved. It is possible to improve/increase the shear strength of the pile body and prevent shear failure from occurring under a load that is less than the tear strength. Furthermore, according to other experiments conducted by the present inventor, if the reinforcement ratio of spiral reinforcing bars is the same, shear strength is improved by arranging reinforcements with smaller diameter steel wires and smaller pitch intervals. It has been confirmed to be effective.

According to the present invention, the process is simpler compared to the case of manufacturing a wedge body by autoclave curing using a post-tensioning method, and simple atmospheric pressure steam equipment is sufficient, and early demolding is possible. Therefore, it is possible to obtain a highly prestressed concrete pile that has both high bending strength and high shear strength at an economical cost, and is able to withstand sudden and high horizontal loads such as those received in the early stages of an earthquake. It became possible to realize the body.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of a normal pressure steam curing cycle in the present invention, Fig. 2a is a sectional view of a specimen used in an embodiment of the present invention, and Fig. 2b is an experiment in an embodiment of the present invention. It is a front view for explaining a method. 1... Vertical reinforcement, 2... Steel wire wound in a spiral around the vertical reinforcement group, C... Cement.

Claims (1)

[Claims] 1 Based on the pretension method, prestressed concrete piles are formed by pre-tensioning the prestressed steel, forming the concrete using the centrifugal forming method, and introducing prestress into the concrete after steam curing. When manufacturing, steel wire (spiral reinforcement) is spirally wound around a group of longitudinal reinforcements made of prestressed steel to form a reinforcing bar cage, and the descending point strength of the spiral reinforcement used in this case is 80 kg/mm^
2 or more, the reinforcement ratio (Pw) of the spiral reinforcement to the longitudinal cross-sectional area of the pile body is set to 0.53% or more, and the spiral pitch is set to 10cm or less. After that, tension is applied to the longitudinal reinforcement, and then centrifugal force forming is performed. A concrete pile is obtained by the method. The concrete used is cement containing an ultra-early strength admixture, and the obtained concrete pile is subjected to normal pressure steam curing, and the concrete has a weight of 80 kg/cm^2 or more. A method for manufacturing an ultra-high strength PC frame with improved shear strength, characterized by introducing effective prestress.