JP2007211515A - Prestress introducing method to girder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a prestress introducing method to a girder reducing the number of girder members, girder height and a construction cost and easily coping with the limitation of girder height. <P>SOLUTION: The prestress introducing method to the girder is characterized in that primary prestress to be over-prestress is introduced to the lower edge side of the girder 1 while introducing secondary prestress to the upper edge side of the girder 1 to nullify tensile force generated to the upper edge side of the girder by the over-prestress introduced by a primary prestressed concrete steel member 5 and that the secondary prestress introduced to the upper edge of the girder 1 is released after placing a floor slab 6 on the girder 1 and before placing live load. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for introducing prestress into a girder made of concrete or the like installed on a bridge or the like.

  In conventional bridges, if the number of girder members installed between piers is reduced, the load applied to each girder member increases, so tension members that introduce compressive stress (compression strain) to the girder members This is achieved by increasing the number of (PC steel) and improving the cross-section performance.

  For example, as shown in FIGS. 5 (a) and 5 (b), the girder member 1 is formed with an I-shaped cross section in which an upper edge flange portion 3 and a lower edge flange portion 4 above and below the web portion 2 are integrated. In the case of 1, as shown in FIG.5 (c), before the prestress introduction, the bending moment M1 by the dead weight of the girder member 1 is applied.

When prestress is introduced into such a girder member 1, conventionally, as shown in FIG. 6 (a), a plurality of PC steel materials 5 are arranged in the lower edge flange portion 4, and FIG. 6 (b). By applying a prestress (compressive stress) as shown by a dotted line to the bending moment M1 due to its own weight before the introduction of the prestress shown in FIG. 5C, a bending moment M2 as shown in FIG. After introducing and obtaining a composite bending moment M3 as shown in FIG. 6 (d), as shown in FIG. 7 (a), when the floor slab 6 is loaded on the upper edge flange portion 3, In response to the bending moment M4 due to the floor slab load, the bending moment M4 due to the floor slab load is added to the composite bending moment M3 shown in FIG. 6C to obtain a composite bending moment M5 as shown in FIG. ing.
JP 05-79016 A

  However, in the prestress introduction method to the above-mentioned girder member 1, when prestress is introduced into the girder member only by the primary steel material, prestress can be introduced only to the allowable value limit of the tensile stress acting on the girder edge. As prestressing up to the allowable limit of the tensile stress level, then cast-in-place slabs or precast concrete slabs were constructed, and there was a problem that the girder height including the bending amount of the girder increased. If there is no support for transportation due to high restrictions or increased weight of the girder, it can be handled by increasing the girder height and improving the cross-sectional performance of the girder. When there is a support, it is necessary to increase the girder cross-sectional performance by increasing the number of PC steel materials 5, so the girder height must be increased. Increasing the girder height increases the weight of the girder, making it impossible for factory production to secure a production yard on site. In addition, there is a problem that the construction work becomes very difficult because the girder height cannot be increased in the construction place where the girder height is limited.

  In view of the above-described conventional problems, the present invention aims to reduce the number of girder members and the girder height, reduce the construction cost, and easily cope with girder height restrictions. The purpose is to provide.

  In the prestress introduction method of the girder of the first invention, primary prestress is introduced into the girder as the primary prestress, and over the prestress is introduced to the lower edge side of the girder. Secondary pre-stress was introduced to cancel the tensile force generated on the upper edge of the girders due to over pre-stress introduced by stress. After loading the floor slab on the girders, it was introduced on the upper edge side of the girders before loading the live load. Characterized by releasing secondary prestress

  In the second invention, in the prestress introduction method of the girder of the first invention, the PC steel material for primary prestress is arranged at the lower edge of the girder, and the PC steel material for secondary prestress is arranged at the upper edge of the girder. Characterized by

  In the third invention, in the prestress introduction method of the girder of the first or second invention, the secondary prestress introduced into the upper edge of the girder is at least the upper edge side of the girder when the floor slab is installed on the girder. It is characterized by exceeding the stress applied to.

According to the present invention, the primary PC steel material arranged at the lower edge of the girder introduces a primary prestress that causes overprestress to the girder, and the secondary PC steel material arranged at the upper edge of the girder introduces it to the girder. Secondary pre-stress is introduced to cancel the tensile force generated on the upper edge of the girders due to the over pre-stress, and after the floor slab is loaded on the girders, the secondary pre-stress is applied before the live load is loaded. Since it is possible to release the stress up to the allowable limit of the compressive stress applied to the girder edge by using the primary PC steel, it is possible to efficiently prestress the girder without increasing the girder height. In addition to being able to be introduced, the cross-sectional performance of the girder can be remarkably improved, and when a girder with improved cross-sectional performance is used, the floor slab can be supported with a smaller number of girder, so than in the conventional case It is possible to reduce the number of required beam members, it is possible to improve the workability and economy.
Therefore, for example, when the present invention is applied to a prestressed concrete composite floor slab bridge, a prestressed concrete girder member into which prestress is efficiently introduced without increasing the girder height is incorporated. The required girder members can be made into three, and an economical floor slab bridge can be constructed, and the workability of the floor slab bridge can be improved as the number of girders is reduced. .
In addition, the secondary prestress introduced at the upper edge of the girder is designed to exceed the stress applied to the upper edge of the girder at least when the floor slab is installed on the girder. Even if the stress applied to the upper edge side due to the load temporarily occurs, the secondary pre-stress is released later and is almost offset, so the load on the upper edge side can be reduced and effective throughout the girder height direction. It can be a rational and economical digit using a digit, and can be a small and economical digit with a small digit height.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, the same reference numerals are used for the same parts as those in the conventional method shown in FIGS.

  As a girder used in the prestress introduction method of the girder in the present embodiment, for example, as shown in FIGS. 3 and the lower edge flange portion 4 are formed in an integrated cross-sectional I-type or H-type. The cross-sectional shape of the girder member 1 may be a cross-sectional shape such as a rectangle other than those described above. In the case of the spar member 1 as described above, as shown in FIG. 1C, the spar member 1 is subjected to a bending moment M1 due to its own weight before the prestress is introduced.

When prestress is introduced into the girder member 1, first, as shown in FIG. 2A, a plurality of PC steel materials 5 are arranged in the longitudinal insertion of the lower edge flange portion 4 of the girder member 1. The PC steel material 5 is tension-fixed at both ends of the girder member 1 to introduce primary prestress to the girder member 1 so as to cause over prestress. At this time, the primary prestress is introduced up to or near the allowable limit of compressive stress applied to the lower edge flange portion 4.
In the present invention, the primary prestress that causes the overprestress is defined in relation to the girder height of the girder member 1, and the girder height is an allowable value (allowable compressive stress) in a state where a design load is applied. Although it is set so as to satisfy, when the digit height is lowered to a state where the allowable value (allowable compressive stress) is not satisfied when the primary prestress is introduced, the prestress corresponding to the allowable value, Beyond this, it refers to the total prestress including the prestress of the part that does not satisfy the allowable value.
For example, as the over prestress, the stress is introduced up to the allowable value limit of the compressive stress applied to the lower edge of the girder, but it is the maximum value among the over prestresses. In fact, the value is slightly smaller than the maximum value. Within the range up to, it is set appropriately.
By introducing the over prestress to the lower edge side of the spar, stress is applied to the spar member 1 such that the spar member 1 deforms upwardly as indicated by the solid line from the state indicated by the dotted line in FIG. A bending moment M6 due to over prestress as shown in FIG. 2 (c) is introduced into the bending moment M1 due to the weight of the girder before the prestress introduction shown in FIG. 1 (c), as shown in FIG. 2 (d). A composite bending moment M7 can be obtained.
In order to introduce over prestress on the lower edge side of the beam member 1 as described above, for example, as shown in FIG. 8, the lower edge side of the beam member 1 without changing the beam height or changing the beam height. In order to make it possible to arrange the PC steel material 5 on the lower edge side of the girder member 1, a lower edge flange portion 4 or a haunch 8 is provided at a corner portion of the lower edge flange 4 and the web portion 2 to increase the cross-sectional area. Thus, it is preferable to increase the degree of freedom of arrangement of the PC steel material, increase the PC steel material insertion hole, and increase the number of PC steel materials on the lower edge side.

Next, as shown in FIG. 3A, a plurality of PC steel materials 7 are inserted into the plurality of PC steel material insertion holes in the longitudinal direction of the upper edge flange portion 3 of the girder member 1. Is fixed at both ends of the girder member 1 to introduce secondary prestress that counteracts the tensile force generated on the upper edge side of the girder due to overprestress by the PC steel material 5 disposed in the lower edge flange portion 4. . The amount of the secondary pre-stress is set in consideration of these because the bending moment acting on the girder member 1 due to a dead load (at least floor slab load or the like) loaded on the girder member 1 is replaced with a bending moment acting on the girder member 1 later.
At this time, the girder member 1 has a downward compressive stress as shown by a dotted line in FIG. 3B, and as shown in FIG. 3C, the upper edge side of the girder due to the over-prestress shown in FIG. A bending moment M8 by introducing a secondary pre-stress that cancels the tensile force generated in FIG. 3 is applied to obtain a combined bending moment M9 as shown in FIG.

  In the state shown in FIG. 3D, since the bending deformation of the girder member 1 is small, the floor slab 6 is disposed on the upper edge of the girder member 1 in this state as shown in FIG. Then, as shown in FIG. 4 (c), the bending moment due to the floor slab 6 is added to the bending moment M9 shown in FIG. 3 (c), and the resultant bending moment M10 shown in FIG. 4 (d) can be obtained.

Next, by removing the tension of the PC steel material 7 in the upper edge flange portion 3, the secondary prestress is released, and the release of the secondary prestress releases M11 shown by a dotted line in FIG. 4 (e). As shown in FIG. 4B, the bending moment of the girder member 1 becomes the load of the girder's own weight, primary prestress, floor slab 6 and the like, and the compressive stress is released as shown in FIG. As shown by a bending moment M12 shown in FIG. 4 (f), a larger composite bending moment M12 is efficiently borne on the beam member 1 as compared with the conventional composite bending moment shown in FIG. 7 (d).
As described above, when the secondary prestress is released, at least the floor slab 6 is loaded on the beam member 1 and before the live load is loaded. By doing in this way, the load of the floor slab 6 at least among dead loads can be efficiently borne by the girder member 1. After the dead load other than the load of the floor slab 6 is loaded, it may be before the live load is loaded.

  As described above, when prestress is efficiently introduced into the girder member 1, the design of the conventional precast concrete floor slab bridge 9 requires five prestressed concrete girder members 1a as shown in FIG. 9 (a). However, as shown in FIG. 9 (b), the number of girders 1 made of precast concrete or the like can be reduced to about three, and the number of installed girders 1 can be reduced. Can be built.

  In addition, about the construction procedure which actually introduces pre-stress, if all the PC steel materials 5 in the girder member 1 are first tension-fixed and all primary pre-stress is introduced, an allowable value is provided on the upper edge side of the girder member 1. In order to avoid this, a part of the primary prestress is introduced, or a secondary prestress is introduced by the PC steel material 7 arranged on the upper edge side of the girder member 1 in order to avoid this. Therefore, the following construction procedure 1 or 2 in which primary prestress is introduced using the PC steel material 5 on the lower edge side of the girder member 1 may be used.

<First example of construction procedure>
(1) As primary pre-stress, using a part of a plurality of PC steel materials 5 arranged on the lower edge side of the girder member 1 to fix them in tension, the allowable value of the compressive stress degree of the lower edge of the girder member 1 or Stress is introduced to the lower edge side of the girder member 1 up to the allowable value of the tensile stress of the upper edge.
(2) Thereafter, as secondary prestress, all the PC steel materials 7 arranged on the upper edge side of the girder member 1 are tension-fixed, and stress is introduced to the upper edge side of the girder member 1.
(3) Thereafter, the remaining PC steel material 5 that is not tension-fixed on the lower edge side is tension-fixed, and the remaining primary prestress is introduced.
(4) A floor slab 6 is formed on the girder member 1 to form a floor slab portion.
(5) Before the live load is loaded, the tension of all the PC steel materials 7 fixed on the upper edge side of the girder member 1 is released, and the secondary prestress is released.

<Second example of construction procedure>
(1) First, all PC steel materials 7 arranged on the upper edge side of the girder member 1 are tension-fixed, and secondary prestress is introduced into the girder member 1. However, since the secondary pre-stress at this time has a smaller tension than the primary pre-stress, the stress does not exceed the allowable value on the upper edge side and the lower edge side of the girder member 1.
(2) Next, as primary pre-stress, all of the plurality of PC steel materials 5 arranged on the lower edge side of the girder member 1 are used to fix the tension and introduce stress into the girder member 1.
(3) A floor slab 6 is formed on the girder member 1 to form a floor slab portion.
(4) Before the live load is loaded, the tension of all the PC steel materials 7 fixed on the upper edge side of the girder member 1 is released, and the secondary prestress is released.

  In carrying out the present invention, the cross-sectional shape of the girder member may be an appropriate cross-sectional shape such as a rectangle in addition to the I-type or H-type cross-sectional shape, and may be a steel-concrete composite girder member. There may be.

When carrying out the present invention, after releasing the tension of the secondary PC steel material 7 for introducing secondary prestress, a filler such as an adhesive is filled between the PC steel material 7 and the PC steel material insertion hole. Then, the secondary PC steel material 7 and the girder member 1 may be integrated to increase the ultimate strength of the girder member 1.

1 shows an embodiment of a prestress introduction method for a girder according to the present invention, in which (a) is a front view of the girder member, (b) is a side view thereof, and (c) is a bending moment diagram due to the girder's own weight. (A) is a front view showing a state in which primary prestress is introduced to the lower edge side of the girder member, (b) is a side view, and (c) is a bending moment when primary prestress is introduced into the bending moment due to the girder's own weight. FIG. 4D is a composite bending moment diagram of the bending moment due to the girder weight and the primary prestress. (A) is a front view showing a state in which secondary prestress is introduced to the upper edge side of the girder member, FIG. (B) is a side view thereof, and (c) is a secondary prestress in bending moment and primary prestress due to the girder's own weight. Bending moment diagram when stress is introduced, (d) is a combined bending moment diagram of bending moment due to girder weight, primary prestress and secondary prestress. (A) is a front view showing a state in which a floor slab is loaded on the girder upper edge of the girder member, FIG. (B) is a side view, and (c) is a girder's own weight, primary pre-stress and secondary under a floor slab loading load. Bending moment diagram based on prestress and slab loading load, (d) is a composite bending moment diagram, (e) is a moment diagram when secondary prestress is released, and (f) is a girder weight and primary prestress. FIG. The prestress introduction method in the conventional bridge is shown, (a) is a front view of a girder member, (b) is the side view, (c) is a bending moment diagram by girder weight. (A) is a front view showing a state where primary prestress is introduced to the lower edge side of the girder member, (b) is a side view thereof, and (c) is a moment when primary prestress is introduced into the bending moment due to the girder's own weight. FIG. 4D is a composite bending moment diagram of the bending moment due to the girder weight and the primary prestress. (A) is a front view showing a state in which a floor slab is loaded on the upper edge of the girder member, (b) is a side view thereof, and (c) is a floor slab loading load due to bending moment and primary prestress due to the girder's own weight. (D) is a composite bending moment diagram of a floor preload, a bending moment due to the girder's own weight, and a primary prestress. It is a front view which shows one form of the girder member used in this invention. It is the longitudinal front view compared with the case where the prestress introduction construction method of the girder of the present invention is adopted, and (a) is a longitudinal front view in the conventional case, (b) is the longitudinal front view in the case of the present invention. It is.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Girder member 2 Web part 3 Girder upper edge flange part 4 Girder lower edge flange part 5 PC steel material 6 Floor slab 7 PC steel material 8 Haunch part 9 Floor slab bridge

Claims (3)

  Primary prestress is introduced into the girders as primary prestress on the lower edge side of the girders, and the upper edge side of the girders is placed on the upper edge side of the girders due to the overprestress introduced by the primary prestress. A secondary prestress that cancels the generated tensile force is introduced. After loading the floor slab on the girders, the secondary prestress introduced on the upper edge side of the girders is released before the live load is loaded. Prestressing method.   2. The prestress introduction method for a girder according to claim 1, wherein the PC steel material for primary prestress is arranged at the lower edge of the girder, and the PC steel material for secondary prestress is arranged at the upper edge of the girder.   The secondary pre-stress introduced into the upper edge of the girder is configured to exceed the stress applied to the upper edge side of the girder at least when the floor slab is installed on the girder. Prestress introduction method of the indicated digit.

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