JPH03881B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming composite structural members using prestressed concrete members, and more specifically, it can be suitably implemented, for example, for forming composite girders in which reinforced concrete deck slabs and steel girders are combined in composite girder bridges. Regarding construction methods. An example of what has traditionally been widely used as a composite structural member is composite girder (beam), which is a composite of reinforced concrete slabs and steel girders in composite girder bridges.
There is. This is done by integrating the reinforced concrete slab and steel girder using connectors such as dowels.
Both of them jointly resist the subsequent load. In this conventional construction method, the reinforced concrete slab is constructed by first erecting steel girders,
Next, the formwork is constructed and then concrete is poured. Therefore, the number of man-hours required for constructing the formwork and floor slabs is large and the cost is high. Therefore, it is desired to reduce the weight and size of steel girders. The purpose of the present invention is to solve the above-mentioned technical problems,
It is an object of the present invention to provide a construction method for forming a composite structural member using prestressed concrete members that can realize miniaturization and weight reduction of the composite structural member, and more specifically, by applying the present invention to, for example, a composite girder bridge. It is possible to reduce the man-hours and costs required for constructing reinforced concrete slabs, and to make the steel girder lighter and smaller, making it possible to construct an economical composite girder bridge. An object of the present invention is to provide a method for forming a composite structural member using prestressed concrete members. FIG. 1 is a side view of an embodiment of a bridge in which the present invention is used, and FIG. 2 is a plan view thereof. The bridge 1 is supported by abutments 2 and 3 at both ends. The bridge 1 has a framework including a plurality of main girders 4 made of steel girders with a shaped cross section extending in the axial direction, and steel members 5 called transverse girders or anti-tilt structures supported by these main girders. has. A passage plate 6 is installed on the upper surface of the steel girder 4. The right half of the passage plate 6 is omitted in FIG. 2 for ease of illustration. This passage board 6 is constructed by connecting a plurality of concrete floor slabs 7. As will be described later, a plurality of PC steel (high tensile strength steel) wires 8 extending in the width direction are embedded in the concrete slab 7 in parallel with each other. In addition, concrete floor slab 7
is installed so that the PC steel wire 8 buried therein is parallel to the steel girder 4. Note that a PC steel rod may be used instead of the PC steel wire 8. FIG. 3 is a plan view of the prestressed concrete floor slab 7 according to the present invention, and FIG. 4 is a sectional view taken along the section line - in FIG. 3. A PC steel wire 8 is buried in the concrete slab 7 and extends in the width direction (left and right direction in FIG. 3) with a turnbuckle 9 interposed therebetween. Furthermore, a long hole 10 is formed in the concrete slab 7 so as to surround the turnbuckle 9 and open upward. The internal compressive stress of the concrete slab 7 is released by operating the turnbuckle 9 from the outside through the elongated hole 10. Instead of the turnbuckle 9, a coupler may be used in which a screw is formed inside the main body along the axial direction. Moreover, it is not necessary to interpose a connecting means such as a turnbuckle 9 or a coupler in the PC steel wire 8, and in this case, the PC steel wire 8 may be cut at the elongated hole 10 to release the internal compressive stress. The long holes 15 are used to integrate the steel girder 4 and the concrete slab 7 by filling them with high-strength mortar or the like. Such a concrete floor slab 7 is manufactured in advance at a factory or the like by the following method. As shown in FIG. 5, a formwork indicated by an imaginary line 16 is installed, and forms for the long holes 9 and 15 are also installed as necessary. Next, unbonded PC steel wires 8 that do not adhere to concrete are placed in this form together with necessary reinforcing bars, and concrete is poured. After curing for a specified period, the PC is
Tension is applied to the steel wire 8 and it is fixed by bearing plates 11, 12 and fixing members 13, 14. At this time,
A compressive force acts on the concrete via the bearing plates 11 and 12, and compressive stress is generated inside the concrete. As described above, the concrete floor slab 7 in which compressive stress is generated in advance is manufactured. FIG. 6 is a simplified perspective view showing the state in which the concrete slab 7 is attached to the steel girder 4.
The figure is a front view seen from the arrow A side in FIG. 6. The horizontally extending steel girder 4 includes a vertically extending web 20, and an upper flange 21 and a lower flange 22 extending perpendicularly to the web 20 at both ends of the web 20. A slip prevention member 23 is provided on the upper surface of the upper flange 21 to prevent the concrete slab 7 from slipping. This anti-slip member 2
3 is a scibel, for example, and has a plurality of rod-shaped protrusions 2
4, and is fixed by welding on the upper surface of the upper flange 21. A plurality of these anti-slip members 23 are arranged on the upper surface of the upper flange 21 at intervals. One panel of the concrete deck slab 7 is laid on such a steel girder 4 so that the PC steel wire 8 and the steel girder 4 are parallel to each other without any gaps. When fixing the steel girder 4 and the concrete slab 7, the protrusion 24 of the anti-slip member 23 is placed in advance at a predetermined position on a locking part 7a called a haunch that projects below the concrete slab 7. After that, high-strength mortar is injected into the long hole 15 for construction, and the concrete slab 7 and the steel girder 4 are firmly fixed and integrated. Next, the tension in the PC wire 8 is released, such as by loosening the turnbuckle 9 or the fixing member 13 or 14. As a result, the concrete slab 7, which had been contracted due to prestress (compressive stress generated in advance), attempts to expand in the width direction. However, since the concrete slab 7 and the steel girder 4 are integrated, their elongation is restricted, and therefore a negative bending moment and tensile force act on the steel girder 4, which causes the beam to curve upward. Therefore, compared to the case where a normal concrete slab without prestress is installed on a steel girder to form a composite girder, the composite girder according to the present invention has a smaller positive bending moment by the amount of negative bending moment. .
As a result, even if a positive bending moment is applied due to live loads such as automobiles or people, there is sufficient margin up to the allowable bending stress, and it is therefore possible to reduce the cross section of the steel girder. In addition, such concrete deck slabs 7 are manufactured in advance at the factory, and are used to construct the walkway boards at the bridge assembly site, so concrete is poured into the formwork on site using formwork as in the past. Compared to forming passage boards by pouring, it is more economical because no formwork is required. Furthermore, when designing a bridge, there is no need to consider the load of the formwork, and the cross section of the steel girder can be made smaller accordingly. FIG. 8 is a plan view of another embodiment of the prestressed concrete floor slab 7, and FIG. 9 is a sectional view taken from the cutting plane line - in FIG. 8. This embodiment is similar to the embodiment shown in the third figure, and corresponding parts are provided with the same reference numerals. It should be noted that turnbuckle 9 is not used in this embodiment. Therefore, the elongated hole 10 in the embodiment shown in the third figure is also not formed. In releasing the internal compressive stress of such prestressed concrete slab 7,
This is done by loosening the fixing members 13 and 14 of the PC steel wire 8 by jacking or the like. Note that long hole 15
is used for the same function as in the embodiment shown in the third figure. Figure 10 shows the steel girder 4 when the concrete slab 7 shown in Figure 3 or Figure 8 is installed on the steel girder 4.
FIG. 11 shows a bending moment diagram corresponding to FIG. 10. In Fig. 10, in order to simplify the explanation, the steel girder 4 has simple supports 2 at both ends.
Assume that it is supported by 6.27. The state in which the steel girder 4 is supported by the fulcrums 26 and 27 is the first state.
0 is shown in Figure 1. In this state, the steel girder 4 receives a positive bending moment l expressed by a parabola as shown in FIG.
1 comes into play. The state in which the concrete slab 7 is installed and integrated with the steel girder 4 is shown in FIG. 10 2.
The bending moment l2 in this state is shown in FIG. 112. Next, when the prestress generated inside the concrete slab 7 is released, the 10th
As shown in FIG. 3, a tensile force p that causes the concrete to return to its original shape acts on the steel girder 4, thereby causing a negative bending moment l3 to act on the steel girder 4.
That is, the negative bending moment l3 due to the prestress shown in FIG. 113 is added to the bending moment shown in FIG. 112, and as a result, the steel girder 4 is
A bending moment l4 as shown by is generated. The bending moment 13 due to prestress is smaller than the bending moment of a normal composite girder, which is indicated by the imaginary line 15 in FIG. 11 and 4. In this way, when compared with a normal composite girder, according to the present invention, the positive bending moment can be reduced, so the cross section of the steel girder 4 can be made smaller. FIG. 12 is a diagram that serves as a basis for specifically analyzing the degree of stress acting on the concrete deck slab 7 and the steel girder 4 after prestress release. The cross-sectional force, that is, the axial stress N and bending moment M acting on the composite cross section are expressed by the first equation and the second equation. N=-pc...(1) M=Ndc=-pc・dc...(2) However, pc is prestress, and dc is the center of gravity c of the cross section of the concrete slab 7 and the center of gravity v of the composite cross section.
Indicates the distance from The edge stresses δsu and δsl of the steel girder 4 are expressed by the third equation. Here, Av is the cross-sectional area of the composite section, Iv is the second moment of area of the composite section, yvsu is the distance between the center of gravity of the composite section and the upper flange, and yvsl
is the distance between the center of gravity of the composite cross section and the lower flange. Therefore, by substituting the first and second equations into the third equation, the edge stresses δsu and δsl are expressed by the fourth equation. The edge stresses δcu and δcl of the concrete slab 7 are expressed by Equations 5 and 6 since a compressive force of prestress PC/cross-sectional area Ac of the concrete slab is initially generated. δcu=pc/Ac+N/nAv-M/n・Ivyvcu=pc/Ac−pc/n・Av+pc・dc/n・Ivyycu…(5) δcl=pc/Ac+N/nAv−M/n・Ivyvcl=pc/Ac −pc/n・Av＋pc・dc/n・Ivyycl…(6) Here, n is the ratio of the elastic modulus of concrete Ec to that of the steel girder, that is, n=Es/Ec, and yvcu is the center of gravity v of the composite cross section. and the upper surface of the concrete slab 7, and yvcl is the distance between the center of gravity v of the composite cross section and the upper flange. When assembling a road bridge using formwork using simple live load composite girders, the loads to be considered before forming the composite structure are generally shown in Table 1.

[Table] Therefore, the load to be considered for ordinary composite girders is 0.700t/m ² to 1.050t/m ² , but in this case, where no formwork is used, the load to be considered is 0.600t/m ² to 1.050t/m 2
It becomes 0.950t/ ^m2 . Therefore, the dead load during floor slab construction can be reduced by 14% to 10%. Further, Table 2 shows an example in which the present inventor designed and calculated a normal composite girder and a composite girder according to the present invention using the above-mentioned results and Equations 4 to 6. In addition, in Table 2, the allowable stress is ±2100Kg/ ^cm2 , and the concrete cross section is 2736cm in width and 230cm in length.
shall be.

[Table] According to Table 2, the weight ratio of the steel girder is shown by equation 7. 388.2−341.6/388.3×100=12.0% (7) That is, according to the present invention, the weight of the steel girder can be reduced by 12.0% compared to the conventional method. Normally, a positive bending moment acts on the steel girder part of a composite girder bridge due to vertical loads such as dead loads and live loads of the steel girders, deck slabs, ground covering, handrails, pavement, etc., causing compression on the upper edge side. Tensile stress is generated on the lower edge side. In this construction method, after the precast prestressed concrete slab, which has internal compressive stress, and the steel girder are integrated, tensile force and negative bending moment are applied to the steel girder by releasing the stress in the concrete slab. As a result, both the compressive stress on the upper edge side and the tensile stress on the lower edge side are smaller than in normal construction methods.
Therefore, it is able to withstand greater loads than conventional construction methods. In other words, if we compare the two methods for the same vertical load, this method requires a smaller cross-sectional area of the steel girder, which reduces the weight of the steel girder.
Can be made smaller. In addition, by reducing the cross section of the steel girder, the height of the girder can be lowered.
It is possible to reduce loads such as wind pressure that are applied to the side of the bridge. Moreover, it can be applied to places where the space under the girder is limited, and it is economically advantageous by lowering the height of the access road. In addition, with conventional construction methods, it is necessary to assemble formwork in order to construct reinforced concrete slabs, but this method uses precast slabs that are pre-fabricated in a factory, etc., so no formwork is required.
The man-hours and costs required for floor slab construction can be reduced. Furthermore, when the present invention is applied to a composite structural member on which compressive force acts, compressive stress is generated inside the foundation member on which compressive force acts due to the load taken into consideration when designing the member. By releasing the stress in the precast prestressed concrete member, a tensile force will act on the foundation member, counteracting the compressive force generated by the load. In other words, as in the case of applying it to a composite girder bridge, the number of man-hours and costs can be reduced by omitting formwork construction, and the components can be made lighter and smaller, making it possible to create an economical composite structural component. As described above, according to the present invention, when forming a composite structural member, a precast prestressed concrete member is used, and by releasing the compressive stress generated inside the member, the load considered in the design can be reduced. A force in the opposite direction to the compressive force or bending moment generated in the member is applied, so that the member can be made lighter and smaller. Furthermore, by using precast members, it is possible to reduce man-hours and costs, and improve quality.

[Brief explanation of the drawing]

FIG. 1 is a side view of an embodiment of a bridge in which the present invention is used, FIG. 2 is a plan view thereof, and FIG. 3 is a plan view of a prestressed concrete slab 7 according to the present invention.
Fig. 4 is a sectional view taken from the cutting plane line - in Fig. 3, Fig. 5 is a diagram for explaining the manufacturing method of the prestressed concrete deck slab 7, and Fig. 6 shows that the concrete slab 7 is a steel girder 4. 7 is a front view seen from the arrow A side of FIG. 6, and FIG. 8 is a plan view of another embodiment of the prestressed concrete floor slab 7. Figure 9 is a sectional view taken from the cutting plane line - in Figure 8, Figure 10 is a diagram for explaining the stress of the steel girder 4 and concrete slab 7, and Figure 11 is a bending moment corresponding to Figure 10. 12 are diagrams that serve as the basis for specifically analyzing the degree of stress acting on the concrete deck slab 7 and the steel girder 4. 1... Bridge, 4... Steel girder, 7... Prestressed concrete slab, 8... PC steel wire, 9... Turnbuckle.

Claims (1)

[Claims] 1. Prepare in advance a prestressed concrete member in which compressive stress is generated and which has means for releasing the compressive stress, and place the concrete member on a steel or concrete foundation member in the direction in which the compressive stress acts. By installing the foundation member in a fixed manner so that its axial direction is parallel to the member axis, and then releasing the compressive stress in the concrete member using a compressive stress release means, the tensile force along the acting direction is applied to the foundation member. A method for forming composite structural members using prestressed concrete members, which is characterized by generating bending moments.