JPH0358890B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a novel PC pile. (Conventional technology) Conventionally, PC piles (prestressed concrete piles) use high-tensile reinforcements as shaft reinforcements to prevent cracks from occurring in the piles and to improve rigidity and bending strength. Place reinforcing bars at required intervals on the circumference, spot weld spiral reinforcing bars on the outer periphery to create a reinforcing bar cage, and then rebar with tensile strength close to high tensile strength.
A tensile force equivalent to 70% is introduced, the concrete is placed in a form, the concrete material is poured into the form and centrifugally formed, and prestressing is introduced after steam aging. And as its high tensile strength reinforcement, generally,
JISG3109 deformed PC steel wire, especially the yield point of D type No. 1
Wire rods with a tensile strength of 130 Kg/mm ² or more, a tensile strength of 140 Kg/mm ² or more, and a breaking elongation of 5% or more were used. However, although JIS stipulates that the elongation at break of steel tension wire rods is 5% or more, generally the twisted reinforcing bars are heated to 400°C to 500°C during spot welding.
The elongation at break was only slightly more than 5% of the high tensile strength material buried in the PC pile, which was known at the time, due to the fact that it was preheated and the electrodes were energized for pot welding. In reality, 8% in this state
There was no high-tensile wire material that exceeded this. Therefore, the elongation at break of the wire embedded in the PC pile was about 6% at most. Moreover, the PC pile obtained by the conventional manufacturing method had a large stress loss. (Problems to be Solved) As mentioned above, in the conventional PC pile, there is a limit to the elongation at break of the wire embedded in the PC pile, and the stress loss is high. Perhaps for this reason, conventional piles have had the disadvantage of being susceptible to brittle rupture of the high-tensile reinforcing bars and breakage of the piles when subjected to impact due to falls or collisions during transportation or construction. The present invention aims to provide a novel PC pile that improves the drawbacks of conventional impact resistance properties. (Means for Solving the Problem) The present invention hot-rolls a wire rod containing 0.4% or less of carbon and then transforms it into martensite by controlled cooling from a temperature of 700°C or less without going through a descaling process. , a pile in which the shaft reinforcement is a high-tensile reinforcing steel that has been drawn with a roller die and then tempered, to which twisted reinforcing bars are spot-welded, the reinforcing steel is tempered, and the high-tensile reinforcing steel is buried in concrete in a tensioned state. The elongation at break of the buried high tensile strength material is 8.1%.
The above is a PC pile characterized in that the stress loss amount ratio of the pile is 0.75 or less. The high-tensile reinforcement used in the present invention is a wire with a carbon content of 0.4% or less, and by using such a wire, the shortcomings in impact resistance seen in conventional PC piles have been improved. It became a PC pile. That is, in the pile of the present invention, by limiting the buried high-tensile reinforcement to wire rods with a carbon content of 0.4% or less, the elongation at break of the high-tensile strength reinforcement embedded in the product pile is 8.1% or more. make it possible to
Furthermore, it is the first to achieve a pile stress loss ratio of 0.75 or less, and the product
By limiting these two properties to values that were previously unimaginable: the elongation at break of the high-tensile reinforcement in the PC pile is 8.1% or more, and the pile stress loss ratio is 0.75 or less, the conventional PC They succeeded in improving the shortcomings of the pile's impact resistance properties. In other words, it is impossible to obtain the PC pile of the present invention using a wire rod with a carbon content of more than 0.4%, and furthermore, even if a wire rod with a carbon content of 0.4% or less is used, the processing method cannot be used. If you make a mistake, the elongation at break of the high-tensile reinforcing bars buried in the product pile may not exceed 8.1%, or the stress loss ratio of the pile may
0.75 or less, the present invention still works.
The PC pile will no longer be able to achieve its full potential. As described above, in the present invention, it is required that the carbon content of the high-tensile reinforcement material used be at least 0.4% or less. In addition, the wire rod has C of 0.10 to 0.04 and Si of 0.05 to 1.50.
%, Mn 0.70 to 2.50%, and Cr 0.10 to 1.50%.
The initial properties of the PC pile are more stable. In the present invention, the stress loss amount ratio of the pile of 0.75 or less means that the ratio of the stress loss amount of the PC pile of the present invention to the stress loss amount of the conventional PC pile is 0.75 or less. In addition, in the present invention, it is desirable that the concrete has high strength, with a compressive strength of 800
It is preferable to set it as Kg/ ^mm2 or more. For this purpose, it is effective to adopt high-temperature, high-pressure steam curing (autoclape curing) as a curing method. However, conventional autoclave-cured piles have a large stress loss. For example, in the case of Type A PC piles, the stress initially applied is greatly reduced,
Normally applied stress will be reduced by about 27%. However, according to the present invention, even when autoclaved, the stress lost is less than 20% of the applied stress.
Loss of stress can be reduced. That is,
According to the present invention, the stress loss ratio of the pile is 20÷27=
It decreases to 0.74, that is, 0.75 or less. In addition, the high-tensile reinforcement material more preferably used for manufacturing the PC pile of the present invention is made by hot rolling a wire rod containing 0.4% or less of carbon and then turning it into martensitic material by controlled cooling from a temperature of 700°C or less. This is a high-tensile reinforcement material that is drawn using a roller die and then tempered without going through a descaling process. In hot rolling, it is necessary to carry out precision rolling using at least a group of finish rolling mills to achieve a deformation difference within 0.1 mm and a dimensional accuracy within ±0.1 mm. Normally, this type of steel wire is subjected to quenching treatment after wire drawing, but the reinforcing material used in the above preferred manufacturing method utilizes the heat retained in the wire during hot rolling, and exceeds the critical cooling rate. Preferably, the material is blast-cooled at a cooling rate of . After rapidly cooling the hot-rolled wire rod to 700°C or less (preferably in the range of 700°C to 500°C) by forced cooling with cold water,
If controlled cooling is performed, even with blast cooling using a normal Stelmor type device, the wire will be sufficiently martensited before convergence, and only a thin scale that can be drawn as is will be produced. A preferred composition for obtaining a high-strength martensitic steel wire by controlled cooling from such a low temperature is as follows. 0.10~0.40% C, Si
0.05~1.50%, Mn 0.70~2.50%, Cr 0.10~
It is preferable to contain 1.50%, and further include Ti: 0.0050 to 0.030% and B: 0.0002 to 0.005% as trace components.
It is more preferable to contain one or two of the following. The remainder is Fe and impurities. Steel wire with the above plasticity can be sufficiently martensited even at a relatively slow cooling rate by blast cooling.
Moreover, the scale produced is preferable as described above. The steel wire that has been turned into martensite by controlled cooling is sent directly to the wire drawing process without going through the descaling process. One of the characteristics of the above-mentioned preferred manufacturing method is that it does not undergo a descaling step. Another feature is that the steel wire is drawn using a roller die. The roller die operates on the same principle as general rolling, and draws the wire by applying pressure to the wire using a combination of VH rolls. The steel wire drawn to a predetermined diameter with a roller die is sent to a tempering process as is, or is tempered after being shaped into a different shape. Conventional high-tensile reinforcement requires heat treatment of quenching and tempering, but in the method of the present invention, the steel wire is already martensited by controlled cooling directly connected to the rolling process, so wire drawing is not necessary. Alternatively, the heat treatment after the irregular shape processing does not require quenching, and only tempering is sufficient. The tensile strength is only martensitic.
Although the specified values for JIS PC steel bars are met, the yield point is low. Tempering is performed to improve this yield point. Preferably, the heating is by high frequency induction heating. In general, straightness and relaxation resistance are important for PC steel bars, and in order to stably provide these properties to the wire used in the preferred manufacturing method described above, warm straightening is performed during the cooling process after tempering. It is more preferable to perform the following. In order to apply the above-mentioned high-tensile reinforcement to PC piles, it is first necessary to organize a reinforcing bar cage. The method of organizing the reinforcing bar cage will be explained below by giving an example. The twisted reinforcing bars used in the present invention are JIS
Among G3505 mild steel wire rods, SWRM8 is particularly preferred. When organizing the reinforcing bar basket, as shown in Fig. 1, high tensile strength bars 1 are arranged at required intervals on the circumference,
A twisted reinforcing bar 2 is wound around the outer periphery, each intersection thereof is spot welded, and immediately tempered. An example of the welding and tempering apparatus is shown in FIG. 2.
In this example, the high-tensile reinforcement is set in a reinforcement guide 4 fixed on a fixed electrode ring 3 serving as a cathode, and the twisted reinforcing bar 2 can be wound around the outer circumference of the reinforcement guide 4. A movable electrode 5 for spot welding and a movable electrode 6 for tempering are brought into pressure contact with the outside of the spiral reinforcing bar 2. Furthermore, the electrostatic electrodes 5 and 6 are constructed by reducing the weight of the welding head and increasing the force of the spring that presses them, so that even if centrifugal force and weight act on the electrodes as they rotate, they will always be in constant pressure contact. In a preferred manufacturing method for manufacturing the PC pile of the present invention, a wire rod containing 0.4% or less of carbon is hot-rolled, then turned into martensite by controlled cooling from a temperature below 700°C, and then subjected to a descaling process. After drawing with a roller die, tempered high-tensile reinforcements are placed at required intervals on the circumference.
A twisted reinforcing bar is wound around the outer circumference, and a current of 2500 to 3250 A is applied to the spot welding electrode of the movable electrode for 2 to 4 cycles, and the twisted reinforcing bar is pressurized at a constant pressure to spot weld the high-tensile reinforcement. , Immediately after that, apply a current of 2750 to 3500A to the tempering electrode for 2 to 4 hours.
The hardened layer produced in the high-tensile reinforcement by the spot welding is tempered by cyclic energization, and then the high-tensile reinforcement of the reinforcing bar basket produced as described above is brought into tension and embedded in concrete. The reason why movable electrodes are used for the spot welding electrode and the tempering electrode is that tempering can be performed directly after welding.
Then, first use the spot welding electrode of the electromechanical electrode 5.
A current of 2,500 to 3,250 A is applied for 2 to 4 cycles to spot weld the twisted reinforcing bars 2 to the high-tensile reinforcement 1 by applying a constant pressure, and then the movable electrode 5 is rotated and the movable electrode is attached to the spot welded part. Immediately after the spot welding, e.g.
After 0.5 seconds, the movable electrode 6 is heated to a temperature of 2750 to the tempering electrode.
A current of 3500 A is applied for 2 to 4 cycles to temper the hardened layer formed in the high-tensile reinforcement by electric spot welding. The basis for limiting these numbers is shown below. First, Table 1 shows the results of tests on changes in elongation caused by the relationship between welding current, electrode pressurization force, and energization amount for high-tensile reinforcement B produced by the method of Examples described later. Incidentally, spot welding and tempering were conducted in the same two cycles, and tempering was carried out at 250 A higher than the welding current.

[Table] Even when the number of energization cycles was varied within the range of 2 to 4 cycles, there was no significant difference from the results shown in this table. Therefore, from the results in this table, welding requires 2 to 4 cycles of 2500 to 3250 A current, and tempering requires 2750 to 3250 A.
It has been found that applying a current of 3500 A for 2 to 4 cycles is necessary to ensure a high elongation at break (8.1 or more, usually 8.5% or more) of the high-strength steel. In addition, in the present invention, the measurement of elongation at break is based on JIS
Z 2241. By the way, since it is difficult to adjust the pressing force of the electrode appropriately, it is preferable to set the pressing force to a constant value, for example, 40 kg. Next, the pressure of the spot electrodes was set to 40 kg, welding was carried out by cycling at a current of 2,700 A, and after about 0.5 seconds, the high tensile strength material of 10 reinforcing bar baskets was knitted by being electrically tempered at a current of 3,000 A. It is as shown in Table 2. A similar test was conducted under different conditions, but the results were not significantly different from those shown in Table 2.

[Table] The aperture in Table 2 is the diameter of the point where the 7.28 mm high-tensile reinforcement material is cut, and is the "parallel part" at the break point.
indicates that there was a break between the spot welds, and a "spot" indicates that the break occurred at the weld location.From this table 2, no matter where the break is, it is considered that the high-tensile reinforcement of the rebar cage is broken. It can be seen that the elongation at break is 8.1% or more. By repeating such tests, the high tension welding conditions for manufacturing the PC pile of the present invention were determined as described above. In order to manufacture the PC pile of the present invention,
The reinforcing bar cage organized under these conditions is placed in a formwork, the high-tensile reinforcement is tensed, concrete is poured into the formwork, centrifugally formed, and when the concrete hardens to a predetermined strength, it is released. It is molded, prestressed, and steam cured to obtain a PC pile. It is preferable to perform autoclave curing during this curing because the curing time of the concrete is shortened and stable strength can be obtained in a short period of time. By the way, the PC pile manufactured as described above uses a special steel material, has a high elongation at break near high tensile strength of 8.1% or more, and has low stress loss as described later. ,
These factors combine to give the pile significantly superior impact performance. In other words, in the case of conventional PC piles, the stress loss of the pile after autoclave cultivation was about 27% compared to the amount of stress when prestressing was introduced, but the stress loss of the PC pile of the present invention was less than 20%. The stress loss amount ratio of the present invention shows an excellent value of 20÷27=0.75 or less. Therefore, in the present invention, when conventional piles and co-workers' reinforcing materials are used, the amount of effective prestress is much larger, and the elongation at break and this effective prestress act synergistically, resulting in outstanding impact resistance as a PC pile. Show your gender. Furthermore, if the same amount of effective prestress as conventional products is sufficient, the amount of high tension reinforcement material used can be reduced. The amount of prestress is measured by measuring the force generated in the reinforcement using a wire strain cage.
It is calculated by converting it into a concrete cross section. The tension force of the reinforcement (initial tension force when it is fixed in the formwork) is
It is calculated from the tensile strain occurring in the wire strain cage, and to measure the effective press toilet after training, cut this reinforcement and measure the amount of residual strain using a wire strain gauge. The stress loss rate is calculated by the following formula. Stress loss rate (%) = amount of strain at initial tension - amount of residual strain / amount of strain at initial tension x 100 Examples of the present invention will be described below along with their manufacturing method. Example Steel type A (composition: C0.10, Si0.49, Mn1.51, P.021,
S0.018, Ti0.010, b0.000%) and steel type B (composition: C0.30, Si0.55, Mn1.49,
Two types of steel materials (P0.020, S0.018, Ti0.035, b0.000%) were hot rolled into wire rods with a diameter of 7.5 mm, and rapidly cooled to 650°C with straightening cold water.
This was formed into a ring shape using a laying cone, spread on a conveyor, and cooled in a controlled manner by blast air having a cooling capacity of 0.4°C/sec. The length of the conveyor is 40 m, and the cooling time is 100 seconds. Using roller dies (2 sets, tandem) with scales, these wires were processed at a processing speed of 90
The wire was cold drawn to a diameter of 7.5 to 7.28 mm at m/min without lubrication. The drawn wire was cold-processed into an oval shape, and then tempered (450℃) using high frequency (250KW, 3KHz). Furthermore, a spinner straightening machine was placed at a position 5 m from the output side of the high-frequency coil, and the wire was straightened so that the bending was within 2 mm/1.5 m. The inlet temperature of the straightening machine was 440°C. The process from roller die wire drawing to warm straightening was performed continuously on the same line, and the speed was 90 m/min.
It was hot in minutes. High tensile strength bars A and B with a diameter of 7.28 mm manufactured as described above and deformed PC steel bars of conventional diameter 7.28 standard products (JIS G 3109) as comparative examples, especially D
Type 1 yield point 130Kg/ ^mm2 or more, tensile strength 145Kg/
mm ² or more, elongation 5% or more) are used as axial reinforcements, and these are placed at a constant interval on the circumference at a constant time interval, and twisted reinforcing bars (SWRM) are placed on the outer periphery.
The reinforcing bar cage was made by spot welding. In spot welding, the convoluted muscle is pressed against the shaft muscle with a constant pressure (40 kg), and a movable voltage spot welding electrode is used.
This was done by applying a current of 2750 A for 2 cycles, and immediately after that, tempering was performed by applying a current of 3000 A to the tempering electrode for 2 cycles. In this way the diameter
A 250mm and 10m long steel cage was manufactured. Further, as a comparative example, reinforcing bar cages with the same dimensions were manufactured by the same method as above except that the high-tensile reinforcement materials A and B were used and the welding currents were changed to 2000 A and 3500 A. Using various reinforcing bars designed in this way,
Manufactured PC pile. That is, one of the above-mentioned reinforcing bar cages was placed inside the frame, the reinforcing bars were tension-fixed to the frame with an initial tension of 4.06 t/piece, and centrifugal force forming was performed according to the conventional method.
After 5 hours of normal pressure steam aging at 65°C, the tension was released from the mold and stress was introduced into the pulse. Put this in an autoclave (gauge pressure 10Kgcm ² ) and
A product with a diameter of 300 mm, a wall thickness of 55 mm, and a length of 10 m was obtained by curing for 3 hours (pressure increase 3 hours, constant pressure 4 hours, pressure decrease 2 hours), and the effective prestress amount was measured for each.
The stress loss rate (%) of the pile was calculated. The results are shown in Table 3. Table 3 also shows the stress loss ratio of the pile. However, the stress loss rate was set at 100, which was 26.0% of the average stress loss rate of the three types of conventional standard products. Breaking elongation of steel wire is JIS
Measurements were made in accordance with the regulations of Z2241, and the prescribed results are shown in Table 3. In addition, in order to test the impact resistance of the pile, as shown in Fig. 3, one end of the PC pile A was supported by a support frame 7, the other end was suspended with a wire rope 8, and the falling height H was determined as appropriate. Wire rope 8 was cut and PC pile A was dropped. Then, the height of the fall leading to destruction was measured. The results are shown in Table 3.

[Table] (Note) The first and second comparative examples also use new high-strength steel materials, but the performance obtained is rather weak, so they are intentionally shown as comparative examples.
(Effects of the Invention) The shaft reinforcement of the present invention is a high-tensile reinforcement, a spiral reinforcement is welded to the shaft reinforcement, and the high-tensile reinforcement is buried in concrete in a tensioned state. The buried high-tensile reinforcement is a wire rod with a carbon content of 0.4% or less, the water elongation at break of the buried high-tensile reinforcement is 8.1% or more, and the stress loss ratio of the pile is
As can be seen in Table 3, the PC pile, which is characterized by a hardness of 0.75 or less, exhibits significantly improved impact resistance compared to conventional PC piles.

[Brief explanation of drawings]

FIG. 1 is a front view showing an overview of the reinforcing bar cage, FIG. 2 is a schematic view of the welding device, and FIG. 3 is a side view of the impact test state. DESCRIPTION OF SYMBOLS 1...High-tensile reinforcement material, 2...Spiral reinforcing bar, 3...Fixed electrode ring, 4...Reinforcement guide, 5...Fixed electrode, 6...Fixed electrode, 7...Support frame, 8...Wire rope , A...PC pile.

Claims (1)

[Scope of Claims] 1. After hot rolling a wire rod containing 0.4% or less carbon content, it is turned into martensite by controlled cooling from a temperature of 700°C or less, and the wire is drawn with a roller die without going through a descaling process. A pile in which a high-tensile reinforcing steel that has been tempered and tempered is used as the shaft reinforcing steel, a spiral reinforcing reinforcing steel is spot-welded to the reinforcing steel, the reinforcing steel is tempered, and the high-tensile reinforcing steel is buried in concrete under tension,
The elongation at break of the buried high-tensile joints is 8.1% or more,
A PC pile characterized by a pile stress loss ratio of 0.75 or less. 2 The wire rod contains 0.10 to 0.40% C, 0.05 to 1.50% Si,
The PC pile according to claim 1, which is a wire rod containing 0.70 to 2.50% Mn and 0.10 to 1.50% Cr.