JPS5825806B2 - Concrete piles and columns using high-strength spiral reinforcement - Google Patents

Description

Detailed Description of the Invention The present invention provides a concrete column with improved torsional strength, shear strength, and toughness by using a reinforcing bar cage in which high-strength spiral reinforcement with a yield point strength of 55 kyf/m4 or more is arranged around a group of vertical reinforcements. It is an attempt to realize the body.

In recent years, as precast concrete piles have been increasingly used as bridge piers, etc., they have sufficient resistance to torsional moments generated by horizontal forces during earthquakes, and they are also used in the latest so-called noise-free and vibration-free construction methods. Prestressed concrete columns (hereinafter referred to as “
There is a demand for the realization of "PC pile").

As shown in Fig. 1, the conventional PC pile has a required number of longitudinal tensile muscles 1 arranged in rows along the circumference of the PC pile.
Around the outer periphery of the longitudinal tension muscle group, a spiral shape with a diameter of 3.2 mm ~
It is manufactured using a reinforcing bar cage in which spiral reinforcements 2 of about 4.07 m are arranged.

That is, the above-mentioned reinforcing bar cage is placed in a formwork, concrete is poured into the above-mentioned formwork, compacted by centrifugal force, the concrete is cured, and then prestress force is introduced into the concrete by longitudinal tension bars using a known method. .

However, since conventional spiral reinforcement is used for assembling reinforcing bar cages to prevent longitudinal tension reinforcement from coming apart, the yield point of the drawn mild steel wire is 30-40K.
Gf/mat has been used.

That is, P manufactured by the conventional centrifugal compaction method
For example, for a C pile with an outer diameter of 300 mm, the wall thickness is 60 mm, and as shown in Fig. 2, longitudinal tension muscles 1 with a diameter of 9.2 mm are arranged along the center line 4 of the wall thickness. A spiral muscle 2 with a diameter of 3.2 mm is arranged around the outer circumference of the longitudinal tension muscle.

In such a configuration, in order to maintain the above-mentioned proof strength required for the PC pile,
It is conceivable to use a thick spiral wire with a thickness of 13 m, but if this is done, the following problems arise before the above objective can be achieved.

That is, as mentioned above, since the spiral reinforcement is placed on the outer periphery of the longitudinal tension reinforcement placed on the center line 4 of the wall thickness, the pure covering 3 of the reinforcement becomes thinner and the risk of corrosion of the reinforcement increases. Rather, as an actual manufacturing problem, the larger the diameter, the more difficult it becomes to process the spiral thread.

If the covering thickness is kept as usual to eliminate the risk of corrosion,
The outer shape of the pile has to be shaped like a dog, and the weight has to be shaped like a dog.

The present invention was made to solve these difficulties, and has a yield point strength of 55. The aim is to realize a concrete pile that can meet the above requirements by using thin spiral reinforcement with high strength of kgf/m4 or more.

The spiral muscle used in the present invention has a yield point strength of 55k.
Use a material with a gf/m4 or higher.

The reason why the yield point strength of the spiral reinforcement was set to 55 kg f /ma or more was to set the compressive limit strain of the concrete column to about 1.5 factor or more, as is clear from the experimental examples described later. This is because it has been found that the compressive toughness can be significantly improved, and the torsional strength and shear strength of the column can be significantly improved compared to conventional ones.

Methods of obtaining reinforcing bars with a yield point strength of 55 kg f 7 m4 or more are known, such as heat treatment, plastic working such as drawing, and changing chemical composition, and the present invention utilizes such known methods. do.

Such high-strength spiral reinforcements are arranged in a spiral around the outer periphery of the longitudinal tension reinforcement group using the same method as described above with reference to Fig. 1 to form a rebar cage, and the rebar cage is placed in a formwork and concrete After centrifugal compaction and curing, prestress force is introduced into the concrete using longitudinal tension bars.

The inventor conducted various experiments regarding the present invention.

Some of them are as follows.

Experimental example 1 1) Specimen (1) Rebar cage (a) High-strength wire rods (ψτv = 130 kP f /wM) at pitch 1
001 m (method of the present invention) (b) A CD wire with a diameter of 3 and 2 mm (JV/= 37 kyf/
mA) spirally wound at a pitch of 100 mm (conventional method) % Formula % Using the above reinforcing bar cages (a) and (b), each with an outer diameter of 3
00mm, wall thickness 60mm, and a prestress force of 100kgf/cyyf is introduced into each pile using the pretension method, increasing the strength of the concrete to 600k.
gf/cIL.

2) A torsion test was conducted on each of the above specimens (a) and (b).

3) The test results were as shown in Table 1.

As is clear from the above experimental results, the PC according to the present invention
The pile (a) has a crushing torsional moment that is 0.4 t-m higher than a conventional one with the same shape and dimensions, and it is important to note that the conventional PC pile (b) has a crushing torsional moment of 3 t-m. When reaching .4 t-m, the torsional strength suddenly decreases to 2.8 t-m, leading to destruction, but the PC pile (a) according to the present invention is pulled and the torsional moment) is 3.8 t-m.
Even if it reaches m, the proof strength does not decline, and the ultimate maximum proof stress is 4. Ot-m
It was only then that it was destroyed.

Looking at this in Figure 3, the conventional PC pile (b)
When the moment of bending and twisting reaches point A, it loses its tenacity.
In contrast to the sudden decrease in yield strength leading to failure B, the PC pile (a) according to the present invention has strong tenacity even when the torsional moment C point is reached, and the final maximum strength is not reached. It is important to have sufficient resistance strength as required by the design.

In the above example, JT = 130 kg f /
Diameter of rna6. Although we have described an example using Omrn's spiral reinforcement, depending on the outer diameter and wall thickness of the PC pile to be manufactured, the dimensions of the longitudinal tension reinforcement to be used, etc., it is necessary to It has also been found that the same effect as in the above embodiment can be obtained by using spiral stripes with a diameter smaller than that of a gun by changing the pitch.

Experimental example 2 1) Specimen (1) PC < outer diameter 4001rL7IL, wall thickness 75mm, length 2000mm, each specimen has 80kgf/hi, 120kgf/- and 160 has 9f/art. A model with prestressing force introduced was used.

(2) Conventional spiral reinforcement was placed for shear reinforcing bars PC<1 and floor 2, and high-strength spiral reinforcement with a yield point strength of 130 and 9f/rn4 was used for the other PC piles, and the spacing was changed. In other words, the amount of reinforcing bars was changed and the reinforcement was arranged.

2) A shear failure test was conducted on the above-mentioned PC pile using a 1000t Amsura testing machine using a two-point concentrated loading method.

3) The test results were as shown in FIGS. 4 and 5.

For example, 160 kgf /7ILi in Figure 4
Shear span, with F type pile introducing prestress force
When looking at the case where the outer diameter ratio a/D is 1.5, specimens 1 and NCL2, which had conventional spiral reinforcements, suffered shear failure before reaching the design bending failure moment of 31.5 t-m, but the present invention The fracture pattern changed to bending fracture in cases 3 to 8 (reinforcing bar ratio of 0.53% or more), which were reinforced with high-strength spiral reinforcement.

Moreover, their maximum yield strength is greater than the design value, and it is clear from FIG. 5 that their yield strength is about 30% lower than that of NAL and seat 2, which are constructed using conventional spiral reinforcement.

FIG. 5 shows the relationship between the load and the bending shear deformation angle in the shear span, where the vertical axis shows the load P (ton) and the horizontal axis shows the bending and shear deformation angle b (10 ft).

Although conventional reinforcing bars are used in specimens N[11 and Nl12 in FIG. 4, the high-strength spiral bars of the present invention are not used, so they are expressed as "no shear reinforcing bars."

The PC pile according to the present invention is compared to the conventional PC pile,
This shows that not only can the shear fracture strength be significantly increased, but also that the toughness of the pile can be significantly improved by strongly binding the concrete with high-strength spiral reinforcement.

Experimental example 3 1) Yield point strength 130 kgf/ma and 35 kgf
/ma square spiral reinforcement reinforced cross section 20x20,
When central axial pressure was applied to a rectangular column specimen with a length of 60 CrrL, the specimen using square spiral reinforcement with a yield point strength of 35 kgf/1 rLd yielded before a sufficient compressive strain of the concrete was obtained, but the yield point strength was 130kgf/m
In the specimen using the square spiral reinforcement of A, the compressive limit strain of concrete was obtained which was more than twice that of the above-mentioned specimen.

In addition, in order to investigate in more detail, a compression test was conducted on a specimen in which spiral reinforcement with various yield point strengths, wire diameters, and pitches were wrapped around a concrete cylinder with a diameter of 15 crn and a height of 30 cIIL, and the specimen was restrained in the lateral direction. The yield point strength of the spiral muscle was 55 kgf/mA.
It was found that with the above concrete, a compressive strain of about 1.5% could be easily obtained at a normal pitch, and the toughness was significantly improved.

On the other hand, the ESP relationship between the longitudinal strain of the concrete and the stress generated in the spiral reinforcement that restrains the column is expressed as Jma = ε.

Here, 〒 is the stress generated in the restraining reinforcement in the column direction, ε is the strain in the concrete, m is Poisson's number 5,
ESP has a Young's modulus of 20,000 kgf/ma.

It has been found that the high-strength spiral reinforcement according to the present invention can easily impart a compressive limit strain of 1.5 degrees or more to concrete.

Therefore, the yield point strength of the spiral muscle to obtain sufficient restraint is from the above formula, and it can be proven from the calculation formula that it is more than q 60 kgf /ma, and in reality, the compression limit is around 1.5% or more. In order to obtain Df-+, as the above experimental example proves, the lower limit of the yield point strength of the high-strength spiral muscle of the present invention must be 55k.
It is necessary to make it more than gf/ma.

Since Experimental Example 3 was an experiment on the toughness of concrete, it was conducted on a specimen without introducing prestress, but similar results were obtained when prestress was introduced.

Experimental Examples 1 and 2 are experiments on PC concrete IJ-to columns, Experimental Example 3 is an experiment on concrete columns in which no prestress is introduced, and the present invention is applicable to either concrete column.

The torsional strength of the concrete column according to the present invention is improved compared to the conventional one, and it is highly tenacious even when the torsional moment is reached, and has a considerable amount of extra strength until the final maximum torsional moment is reached. Because of this, it has sufficient resistance to the torsional moment generated by horizontal force during an earthquake, and also has sufficient torsional resistance and shear resistance required for torsional penetration construction methods.

In addition, since the spiral reinforcing bars used in the present invention have a small diameter, there is no fear of corrosion due to thinning of the pure covering of the reinforcing bars, and in addition to being durable, they are easy to process, and meet the current requirements for concrete columns. It has most of the features listed above.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing a reinforcing bar cage for PC piles, Fig. 2a is a front view of the PC pile, Fig. 2 is a sectional view taken along the line - in Fig. 2a, and Fig. 3 is an experiment of the present invention. A diagram showing the results,
Line a shows the torsional strength of the PC pile according to the present invention, line b shows the torsional strength of the conventional PC pile, Figure 4 is a table showing other experimental results of the present invention, and Figure 5 shows the load and shear span. It is a diagram showing the relationship between bending and shear deformation angles in FIG. 1...Longitudinal muscle group, 2...Spiral muscle group.

Claims (1)

[Claims] 1. A concrete column that has improved torsional strength, shear strength, and toughness by using a reinforcing bar cage in which high-strength spiral reinforcement with a yield point strength of 55 kgf/sit or more is arranged around a group of vertical reinforcements.