JP2009097278A - Centrifugal reinforced concrete pile with high bending resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a centrifugal reinforced concrete pile having high bending resistance without increasing the quantity of axial reinforcements. <P>SOLUTION: A prestressed concrete structure 4 into which a prestress is introduced through PC steel members 7 is installed in the hollow part 5 of the centrifugal reinforced concrete pile. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reinforced concrete pile having a high bending strength provided with a prestressed concrete structure in a hollow portion of a centrifugal reinforced concrete pile.

High-strength prestressed reinforced concrete piles (high-strength PRC piles) using high-strength concrete (concrete with design basis strength exceeding 78.5 N / mm ² ) have high cracking resistance and bending fracture resistance and high toughness. Therefore, it is used as an upper pile that requires earthquake resistance.

  As shown in FIG. 2, this conventional high strength PRC pile B is located in a pile body thick portion 10 of a centrifugal high strength prestressed concrete pile (high strength PHC pile), and between the PC steel materials 11, 11. When the reinforcing bars 12 and 12 in the axial direction parallel to this are arranged over the entire length, the amount of the spiral reinforcing bar 13 is larger than that of the PHC pile.

  However, in the conventional high-strength PRC pile B, the PC steel material 11 that gives prestress to the pile body is located in the pile body thick portion 10 of the hollow pile. Therefore, the resistance to bending of this PRC pile B is the high strength concrete 10a of the pile body thick portion 10 of the hollow pile made by centrifugal force forming, and the axial direction arranged in the pile body thick portion 10 It is determined by the reinforcing steel bars 12 of the above. Therefore, in the conventional high-strength PRC pile B, the amount of reinforcing bars such as the reinforcing bars 12 and the spiral reinforcing bars 13 in the axial direction must be increased in order to improve the bending strength.

  The present invention provides a high-strength RC pile by increasing the compressive strength of the concrete and installing a prestressed concrete structure in which prestress is uniformly introduced into the hollow portion of the high-strength RC pile via PC steel. Reinforced concrete piles with high bending strength can be obtained without increasing the number of axial rebars by adopting a structure in which the neutral axis position approaches the tensile edge when bending is applied, and most of the cross section changes to the compression region. The gist is to provide a prestressed concrete structure in which prestress is introduced via a PC steel material in a region having a large total length or a large acting bending moment in the hollow part of a centrifugal reinforced concrete pile (RC pile). It is in a high bending strength centrifugal reinforced concrete pile characterized by that.

  The process of developing a high bending strength centrifugal reinforced concrete pile having the above configuration will be described with reference to FIG. 3. When the centrifugal reinforced concrete pile (RC pile) 14 having a small axial force is subjected to bending, As shown in the strain distribution, the neutral axis position is too close to the compression edge. As a result, the region (compression region) that receives bending compression in the cross section of the hollow pile becomes smaller, and conversely, most of the cross section becomes the tensile region. Therefore, in RC piles, the concrete compressive strength hardly influences the bending strength of the cross section, and the bending strength is determined by the amount and strength of the tension side reinforcing bars.

  In civil engineering structures, the fact that the acting axial force (dead load) is small is used, and as shown in the strain distribution in Fig. 3 (b), uniform axial strain is given to the cross section by pre-stress via PC steel. Thus, when the member (RC pile) is bent, as shown in the strain distribution of FIG. 3 (c), the neutral axis position approaches the tensile edge, and most of the cross section becomes the compression region.

  Therefore, as in the case of the conventional high-strength PRC pile B, the compressive strength of the concrete that forms the pile body thick part of the hollow pile is increased rather than increasing the axial rebar to improve the bending strength. (Use high-strength concrete), and the solid concrete installed in the hollow part of the hollow pile resists that the thick part of the high-strength pile body undergoes bending compression and expands laterally, High strength pile body thick part can bear high bending compression force. Thereby, it becomes possible to obtain the reinforced concrete pile provided with the high bending strength, without increasing an axial direction reinforcing bar.

Hereinafter, the present invention will be described in detail with reference to the explanatory drawings shown in the drawings. In FIG. 1, A is a high-strength PRC pile according to the present invention, and 1 is a pile body thick part of a hollow pile made by centrifugal force molding. Yes, it is made of high-strength concrete with a design standard strength of approximately 50 N / mm ² or more. Reference numeral 2 denotes an axial rebar located in the cross section of the pile body thick portion 1. In the figure, 3 is a high-strength spiral rebar.

4 is a prestressed concrete structure part installed in the hollow part 5 of the hollow pile, and is composed of an intermediate filling concrete 6 filled in the hollow part 5 and a PC steel material 7 in which prestress is introduced into the intermediate filling concrete 6. In this embodiment, a prestress of 0 to 50 N / mm ² is introduced into the filling concrete 6 through the PC steel material 7. In the figure, 8 is a nut or fixing cone, 9 is a washer or anchor plate, and is an example of fixing of the PC steel material 7.

  Next, various conditions of the reinforced concrete pile A (hereinafter referred to as the present invention pile) having a high bending strength according to the present invention will be described based on Table 1 compared with the conventional preformed PHC pile.

Table 1

  In the pile according to the present invention, pre-stress is applied to the filling concrete 6 by the PC steel material 7. The PC steel material is arranged so that the resultant stress of prestress applied thereto is approximately at the center position, and resistance to bending is not expected, and is used only for prestressing. This is in contrast to the conventional off-the-shelf PHC piles that also expected the PC steel to be bent.

  Thereby, (1) Since the PC steel material 7 remains in an elastic state, it is possible to expect a reduction in crack width and residual displacement after unloading. (2) In the conventional off-the-shelf PHC pile, even if the prestress is increased, the bending strength does not change that much. On the other hand, in the structure of the pile of the present invention, the size of the prestress directly leads to the improvement of the bending strength.

Moreover, in this invention pile, the resistance with respect to a bending is the concrete of the thick part of a pile body produced by centrifugal force shaping | molding, and the axial direction reinforcing bar arranged in it. As described above, in the structure of the pile of the present invention, since the magnitude of the concrete compressive strength is directly linked to the improvement of the bending strength, high-strength concrete of approximately 50 N / mm ² or more is generally used. For axial rebars, use high-strength rebars of SD345 or higher to effectively improve bending strength.

In addition, although a normal ready-made PHC pile becomes a hollow structure after centrifugal force shaping | molding, in the structure of this invention pile, a hollow part is filled with concrete. In ordinary off-the-shelf PHC piles, bending strength is hardly improved even if concrete is packed in the hollow part (thick part concrete will not expand because the area subjected to bending compression in thick part concrete is small). In the case of the structure of the pile according to the present invention, the prestressed filled concrete 6 resists the high-strength concrete of the thick part 1 of approximately 50 N / mm ² or more from bending and compressing and laterally expanding. The concrete of the thick part 1 can bear a high bending compression force. The concrete filled in the hollow portion 5 does not need to be high-strength concrete, and concrete having a normal slump of approximately 30 N / mm ² or more or concrete excellent in self-filling and easy to construct may be used.

In the pile structure of the present invention that exhibits high bending strength, the acting shear force is inevitably increased. Therefore, it is necessary to use a high-strength spiral reinforcement for the spiral reinforcement 3. In addition to shear reinforcement, the spiral rebar 3 is also expected to prevent the axial rebar 2 from sticking out and to have a restraining effect on the thick-walled concrete 1. In order to expect these, the product of the spiral reinforcement ratio (ρ _S ) and the yield point strength (σ _y ) needs to be 5.0 N / mm ² or more.

  In addition, in this invention pile, in order to prevent peeling of covering concrete, a bending proof stress further improves by coat | covering with a carbon fiber sheet.

  Next, the calculation method of the bending strength of the pile according to the present invention can be described under the following conditions. (1) The cross-sectional strain distribution is assumed to be flat. (2) Although the PC steel material arranged at the center position of the cross section slightly fluctuates from the strain state immediately after the prestress is introduced due to an increase in the bending load, the influence is small. Therefore, PC steel is not considered in the calculation of bending strength, but only prestress given from PC steel is considered.

  The constitutive rules are as follows. (3) Cover concrete: Constitutive law of plain concrete. (4) Core concrete: “Matsuyoshi Akiyama, Masatoshi Watanabe, Atsushi Abe, Matsuoka Tsuji, Naoki Maeda, Motoyuki Suzuki: Research on fracture properties and mechanical properties of high-strength RC piles subjected to uniaxial compression. Vol.62, No.3, pp.477-496, 2006.8 "etc., to evaluate the stress-strain relationship appropriately. (5) Axial rebar: bilinear model

It is a description top view of the high bending strength centrifugal force reinforced concrete pile which concerns on this invention. It is a description top view of the conventional high intensity | strength PRC pile. It is action explanatory drawing when a hollow pile receives a bending load.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pile body thick part 2 Axial rebar 3 Spiral rebar 4 Prestressed concrete structure part 5 Hollow part 6 Filled filling concrete 7 PC steel material 8 Nut or fixing cone 9 Washer or anchor plate 10 Pile body thick part 11 PC steel material 12 Axial rebar 13 Spiral rebar 14 Centrifugal reinforced concrete pile A Reinforced concrete pile B High strength PRC pile

Claims (4)

  A high bending strength centrifugal reinforced concrete pile characterized in that a prestressed concrete structure part in which prestress is introduced via a PC steel material is provided in a hollow region of a centrifugal reinforced concrete pile in a region where the entire length or acting bending moment is large. ^2. The high bending strength centrifugal reinforced concrete pile according to claim 1, wherein a thick part of the pile body of the centrifugal reinforced concrete pile is formed of high strength concrete having a compressive strength of approximately 50 N / mm ² or more. High bending strength centrifugal force reinforced concrete piles of claim 1 or 2, wherein the size of the introduced prestress of the prestressed concrete structure is 0~50N / mm ^2.   4. The high bending strength centrifugal reinforced concrete pile according to claim 1, 2 or 3, wherein the concrete of the prestressed concrete structure part is a concrete having a normal slump or a concrete excellent in self-filling property.

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