JPH0320524B2 - - Google Patents

Description

[Detailed description of the invention]

For example, when constructing a composite girder bridge, the reinforced concrete deck slab is combined with a steel girder to form a composite girder, compressive stress is applied to the reinforced concrete deck slab in advance, and then the reinforced concrete deck slab and the steel girder are combined. The present invention relates to a construction method capable of generating a desired amount of tensile force and bending moment in the entire composite girder by integrating steel girders and then releasing the compressive stress by a desired amount. 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 deck 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 stress-adjustable method for forming synthetic structural members that can reduce the size and weight of synthetic structural members. We provide a method for forming composite structural members that involves stress adjustment, which reduces the man-hours and costs required for slab construction, and makes steel girders lighter and smaller, making it possible to construct economical composite girder bridges. It is to be. 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. The concrete slab 7 is installed so that the PC steel wire 8 buried therein is parallel to the steel girder 4. In addition, PC steel wire 8
A PC steel bar may be used instead. FIG. 3 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 side view seen from the arrow A side, FIG. 5 is a plan view seen from the arrow B side, and FIG. 6 is a sectional view taken from the cutting plane line - in FIG. A steel girder 4 extending in the horizontal direction has a web 9 extending in the vertical direction,
The web 9 includes an upper flange 10 and a lower flange 11 extending perpendicularly to the web 9 at both ends thereof.
A slip prevention member 12 is provided on the upper surface of the upper flange 10 to prevent the concrete slab 7 from slipping. This anti-slip member 12 is, for example, a dowel, and is made up of a plurality of rod-shaped protrusions 13, and is fixed by welding on the upper surface of the upper flange 10. A plurality of these anti-slip members 12 are arranged at intervals on the upper surface of the upper flange 10. A plurality of elongated holes 14 into which the anti-slip members 12 can fit when installed between the steel girders 4 are formed in the concrete slab 7 along the width direction of the concrete slab 7 in correspondence with the positions of the protrusions 13. has been done. Further, a plurality of sheath pipes 15 are inserted in advance into the concrete slab 7 to penetrate in the width direction. The diameter of this sheath tube 15 is selected to a value that allows the PC steel wire 8 to be inserted gently. The process of laying the concrete slab 7 on the steel girder 4 to form the passage board 6 will be described below. First, the concrete slab 7 is temporarily joined between the steel girders 4 without any gaps. After that, adhesive is applied to the joint part 40 of each concrete floor slab 7, or cement mortar is injected or poured into each concrete floor slab 7.
Aiming for unification between the two. Next, prestress along the member axis direction of the steel girder 4 is introduced into the concrete slab 7, and compressive stress is applied to the concrete slab 7. Specifically, the PC steel wire 8 is inserted into the sheath pipe 15. Thereafter, tension is applied to the PC steel wire 8 by jacking or the like, and the PC wire 8 is fixed by the support plate 16 and the fixing member 17. At this time, support plate 1 is placed on the concrete.
Compressive force acts through 6, and compressive stress is generated inside. The fixing member 17 is a means for fixing compressive stress to the concrete floor slab 7, and also functions to arbitrarily adjust the compressive stress within the concrete floor slab 7, as will be described later. The concrete deck slab 7 into which prestress has been introduced in this way is integrated with the steel girder 4. Specifically, the long holes 14 of the concrete slab 7 are filled with concrete, cement mortar, or the like. As a result, the concrete deck slab 7 and the steel girder 4 are fixed to each other and integrated. In this way, the steel girder 4 and the concrete slab 7 become a composite girder. After the concrete deck slab 7 is combined with the steel girder 4 in this way, tensile force and bending moment can be generated in the steel girder 4 by unloading the prestress in the axial direction of the concrete deck slab 7. . Specifically, the tension in the PC steel wire 8 is released by loosening the fixing member 17.
As a result, the concrete slab 7, which had been contracted by prestress (compressive stress generated in advance), attempts to extend in the axial direction of the bridge. However, since the concrete deck slab 7 and the steel girder 4 are integrated, their extension is restricted, and therefore the beam of the steel girder 4 is curved upward. That is, this bending moment and tensile force act. Therefore, ordinary concrete slabs that are not prestressed are
Compared to the case where the composite girder is installed on a steel girder, the positive bending moment of the composite girder according to the present invention is reduced by this bending moment. As a result, even if a positive bending moment is applied due to a live load such as an automobile or a person, there is sufficient margin up to the allowable bending stress, and it is therefore possible to reduce the cross section of the steel girder. Note that after the prestress is removed, the sheath pipe 15 is grouted with cement paste or the like. Note that when releasing the prestress, by releasing the desired amount using the fixing member 17,
It becomes possible to adjust the stresses acting on the composite structural member as a whole. In this embodiment, the concrete slab 7 was manufactured in advance at a factory, but it may also be formed by pouring concrete into a form using a form, as in conventional cast-in-place concrete. FIG. 7 is a plan view of another embodiment of the concrete slab, and FIG. 8 is a partially enlarged perspective view. This concrete floor slab 7a has an uneven surface 21 formed at both ends along its longitudinal direction. This uneven surface 21 has a plurality of recesses 22 formed along its width direction. For example, if the width of this concrete slab 7a is 1.5m,
The depth d1 of this recess 22 is 2 m, and the pitch d
2 is 20cm. Note that the shape of this uneven surface 21 is not limited to the shape shown in FIG.
Furthermore, it goes without saying that the values of the depth d1 and pitch d2 are not limited to these values. The concrete slab 7a having such a shape is placed on the upper flange 10 of the steel girder 4 so as to face each other at a constant interval. Thereafter, prestress is introduced in the same manner as in the previous embodiment, and after compressive stress is generated, the fixing member 17 is used to fix the structure. After that, when integrating the concrete slab 7a with the steel girder 4, a bonding agent such as concrete or cement mortar is applied to the space 23 between the uneven surface 21 of the concrete slab 7a and the opposing uneven surface 21. By filling the concrete slab 7a and the steel girder 4
and integrate them. The subsequent method of unloading the prestress is similar to the previous embodiment. In this way, in this embodiment, the uneven surface 21 is provided on the concrete floor slab 7a.
Since the concrete slab 7
a is reliably integrated with the steel girder 4, so that even when the prestress is released, a situation such as the concrete deck slab 7a slipping on the steel girder 4 is prevented from occurring. FIG. 9 is a diagram for explaining the stress level of the steel girder 4 and the concrete deck slab 7 when the concrete deck slab 7 shown in the first diagram is installed on the steel girder 4, and FIG. The corresponding bending moment diagram is shown. In FIG. 9, in order to simplify the explanation, it is assumed that the steel girder 4 is supported at both ends by simple supports 26 and 27. The state in which the steel girder 4 is supported by the fulcrums 26 and 27 is shown in FIG. 91. In this state, a positive bending moment l1 represented by a parabola acts on the steel girder 4 due to the uniformly distributed load due to its own weight, as shown in FIG. 10. The state in which the concrete deck slab 7 is installed and integrated with the steel girder 4 is shown in FIG. 92. The bending moment l2 in this state is shown in FIG. 102. Next, when the prestress generated inside the concrete slab 7 is released, a tensile force p that tries to return the concrete to its original shape acts on the steel girder 4, as shown in Figure 9. Therefore, a negative bending moment l3 acts on the steel girder 4. That is, the negative bending moment l3 due to prestress shown in FIG. 10 3 is added to the bending moment shown in FIG. 10 2, and as a result, the steel girder 4 experiences a bending moment l 4 as shown in FIG. Become. 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. 10 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. 11 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 is released. 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. δsu=N/Av-M/Ivyvsu δsl=N/Av-M/Ivyvsl...(3) Here, Av is the cross-sectional area of the composite cross section, Iv is the second moment of area of the composite cross section, and yvsu is the composite cross-sectional area. The distance between the center of gravity of the cross section and the upper flange, 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. δsu=-pc/Av+pc・dc/Ivyvsu δsl=-pc/Av+pc・dc/Ivyvsl ...(4) Edge stress δcu of concrete slab 7, δcl is initially prestressed PC/compression of cross-sectional area Ac of concrete slab Since a force is generated, it is expressed by the fifth and sixth equations. δcu=pc/Av+N/nAv−M/n・Ivyvcu=pc/Ac−pc/n・Av+pc・dc/n・Ivyvcu……(5
) δcl=pc/Ac+N/n・Av−M/n・Ivyvcl=pc/Ac−pc/n・Av+pc・dc/nIvyvcl ……(6) Here, n is the elastic modulus of concrete Ec and the elastic modulus of steel girder is the ratio of n=Es/Ec,
yvcu is the center of gravity v of the composite section and concrete slab 7
is the distance from the top surface of , and yvcl is the center of gravity v of the composite cross section
and the distance from 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 formwork is not 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】

[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 one. 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 concrete slab and steel girder, which have internal compressive stress, are integrated, tensile force and negative bending moment are applied to the steel girder by releasing the stress in the concrete slab. , both the compressive stress on the upper edge side and the tensile stress on the lower edge side are smaller than in the normal construction method. Therefore, it is able to withstand greater loads than conventional construction methods. In other words, if we compare the two for the same vertical load, this method requires a smaller cross-sectional area for the steel girder, making the steel girder lighter and smaller. Furthermore, by reducing the cross section of the steel girder, the height of the girder can be lowered, making it possible to reduce loads such as wind pressure applied to the side surfaces 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 with this method, precast slabs that have been manufactured in advance at a factory etc. can also be used, and in this case, formwork is not required. It is possible to reduce the man-hours and costs required for constructing the floor slab. 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 concrete members, tensile force will be applied to the foundation members.
This will cancel out the compressive force generated by the load. In other words, similar to when applied to composite girder bridges,
By omitting formwork construction, man-hours and costs can be reduced, and components can be made lighter and smaller, making it possible to create economical composite structural components. In addition, in the above-mentioned example, when forming a composite structural member, a steel member was used as the foundation member and a concrete member was used as the auxiliary member. A steel member may be used as
Further, steel members may be used as the foundation member and the auxiliary member, and furthermore, concrete members may be used as the foundation member and the auxiliary member. Further, the base member and the auxiliary member may be members made of a composite material made of concrete and steel. As described above, according to the present invention, when forming a composite structural member, by releasing the compressive stress generated inside the composite structural member, the compressive force or bending force generated in the member due to the load considered in the design can be reduced. A force in the opposite direction to the moment is applied, so the member can be made lighter and smaller.

[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 simplified perspective view showing a concrete deck 7 attached to a steel girder 4. 4 is a side view seen from the arrow A side in FIG. 3, FIG. 5 is a plan view seen from the arrow B side in FIG. 3, and FIG. 6 is a section line - Figure 7 is another plan view of the concrete slab, Figure 8 is a partially enlarged perspective view, Figure 9 is a cross-sectional view as seen from
The figure is a diagram for explaining the stress degree of the rope girder 4 and the concrete deck slab 7, FIG. 10 is a bending moment diagram corresponding to FIG. 9, and FIG. FIG. 3 is a diagram that serves as a basis for specifically analyzing stress levels. 1...Bridge, 4...Tie girder, 7,7a...Concrete floor slab, 8...PC cable wire, 12...Slip prevention member, 14...Long hole, 16...Support plate, 17...
...Fixing member, 40... Seam.

Claims (1)

[Claims] 1 Temporarily join the auxiliary member to the foundation member, then generate compressive stress in the auxiliary member by means of a compressive stress generating means, and then attach the auxiliary member to the foundation member in the direction of action of the compressive stress and the members of the foundation member. The base member is fixedly installed so that it is parallel to the axial direction, and then the amount of compressive stress released is adjusted by the compressive stress adjustment means, so that the foundation member is subjected to tensile force along the acting direction corresponding to the amount of release. A method of forming composite structural members with stress adjustment characterized by the generation of forces and bending moments.