JP2011144550A - Composite floor slab - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite floor slab in which steel materials are integrated with concrete, which is simple in structure, and which has increased fatigue durability. <P>SOLUTION: This composite floor slab includes a bottom steel plate 2, a concrete 5 placed on the bottom steel plate 2, a plurality of ribs 3 which extend in the span direction, which are arranged at intervals on the bottom steel plate 2, and which are buried in the concrete 5, and distributing bars 4 extending in the direction crossing the ribs. The ribs 3 are configured so that the upper ends thereof project further upward than the neutral axis of the composite floor slab 1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a synthetic slab, and more particularly to a steel / concrete composite slab.

Conventionally, in a synthetic slab made of steel and concrete, the steel and concrete are integrated through some kind of stopper.
For example, Patent Document 1 discloses a composite floor slab in which concrete is cast on a bottom steel plate, and a headed stud protruding upward is joined to the bottom steel plate. In this composite floor slab, the bottom steel plate and the concrete are integrated by attaching concrete to the headed stud.
Patent Document 2 discloses a composite floor slab in which a reinforcing steel material made of H-shaped steel or I-shaped steel is disposed on a bottom steel plate, and an opening is provided in a web of the reinforcing steel material. In this composite floor slab, the bottom steel plate and the concrete are integrated by the concrete entering the opening of the reinforcing steel material.
Further, in Patent Document 3, a lattice rib composed of a horizontal rib and a vertical rib is disposed on a bottom steel plate, and the horizontal rib and the vertical rib intersect in a pipe gibber disposed on the bottom steel plate. A floor slab is disclosed. In this synthetic floor slab, the concrete and the bottom steel plate are integrated through lattice ribs and pipe gibbles.

JP 2005-264550 A JP 2001-81729 A Japanese Patent Laid-Open No. 7-119237

  However, the composite floor slabs according to Patent Documents 1 to 3 have a problem in that the structure is complicated in order to integrate the steel material and the concrete, the production period and cost are increased, and the filling property of the concrete is not good. Further, the stud welded portion according to Patent Document 1 and the opening portion of the reinforcing steel material according to Patent Document 2 are structurally weak, which causes a decrease in fatigue durability of the composite floor slab.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a composite floor slab capable of integrating steel and concrete and having a simple structure and improved fatigue durability. To do.

In order to achieve the above object, a composite floor slab according to the present invention includes a bottom steel plate, concrete cast on the bottom steel plate, and extends in a span direction and is arranged at intervals on the bottom steel plate. A composite floor slab comprising a plurality of ribs embedded in the concrete, wherein the rib has an upper end projecting upward from a neutral axis of the composite floor slab.
In the present invention, the upper end of the rib protrudes upward from the neutral axis of the composite floor slab, so that when the bending moment is applied to the composite floor slab from above, the upper side of the rib is on the concrete compression side. Since the bending compressive stress of the concrete acts on the rib, the bending compressive stress of the concrete acts as a frictional force between the rib and the concrete, so that the rib and the concrete can be integrated, and the rib The bottom steel plate and the concrete can be integrated.

In the composite floor slab according to the present invention, it is preferable that a distribution bar extending in a direction orthogonal to an extending direction of the rib is provided on an upper portion of the rib.
In the present invention, the upper part of the rib is provided with a distribution bar extending in a direction orthogonal to the extending direction of the rib, so that the rigidity of the composite floor slab can be increased, and The acting load can be dispersed.

In the composite floor slab according to the present invention, reinforcing fibers may be mixed into the concrete.
In the present invention, since the reinforcing fibers are mixed in the concrete, the strength of the concrete is increased and the rigidity of the composite slab can be increased.

Moreover, the synthetic floor slab according to the present invention is characterized in that no opening is formed in the rib.
In the present invention, since an opening such as a hole is not formed in the rib, the synthetic floor slab can be easily manufactured as compared with a synthetic floor slab provided with a rib formed with an opening. In addition, since stress does not concentrate in the opening, a stable structure with a good stress balance can be obtained.

  According to the present invention, the upper ends of the plurality of ribs erected on the bottom steel plate project to the compression side of the concrete, the compression stress of the concrete acts as a frictional force on the ribs, and the rib and the concrete are integrated, The structure of the composite slab can be made simple, and the production period and cost can be reduced and the fatigue durability can be improved.

(A) is a figure which shows an example of the composite floor slab by embodiment of this invention, and is the sectional view on the AA line of (b), (b) is the sectional view on the BB line of (a). It is the schematic which shows the bending moment which acts on a synthetic floor slab. It is the schematic which shows the compressive stress of the concrete which acts on a rib. It is a figure explaining the test body in a loading test. (A), (b), (c) is a figure explaining the loading position in a loading test. It is a figure which shows the relationship between the load of a test body, and a displacement. It is a figure which shows the state to displacement 3mm by the relationship between the load and displacement of a test body shown in FIG. (A) is a figure which shows the relationship between the load of the test body 1 after 1 loading, and a distortion | strain, (b) is a figure which shows the relationship between the load of the test body 1 after 300,000 times loading, and a distortion | strain. (A) is a figure which shows the relationship between the load of the test body 2 after 1 loading, and a distortion | strain, (b) is a figure which shows the relationship between the load of the test body 2 after 300,000 times loading, and a distortion | strain. (A) is a figure which shows the relationship between the load of the specimen 3 after 1 loading, and a distortion | strain, (b) is a figure which shows the relationship between the load of the specimen 3 after 300,000 times loading, and a distortion | strain. (A) is a figure which shows the relationship between the load of the specimen 4 after 1 loading, and a distortion | strain, (b) is a figure which shows the relationship between the load of the specimen 4 after 300,000 loadings, and a distortion | strain.

Hereinafter, a composite floor slab according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3.
As shown in FIGS. 1A and 1B, the composite floor slab 1 according to this embodiment includes a bottom steel plate 2, a rib 3 erected on the bottom steel plate 2, and a rib 3 above the rib 3. And a plurality of force distribution bars 4 arranged so as to intersect with each other, and a concrete 5 placed on the bottom steel plate 2.

The rib 3 is formed of a steel material, FRP, or the like, and an I-shaped steel is adopted in the present embodiment. The rib 3 extends in the direction A between the floor slabs shown in the direction of the arrow in FIG. 1A, and a plurality of ribs 3 are arranged at a predetermined interval in a direction orthogonal to the direction A between the floor slabs. The rib 3 has a lower flange welded to the bottom steel plate 2.
Further, as shown in FIG. 1B, the rib 3 is formed so that the upper end projects upward from the neutral shaft 6 of the composite floor slab 1. The neutral shaft 6 means that when a bending moment due to a load from above acts on the composite floor slab 1, compressive stress acts on the upper side of the composite floor slab 1 and tensile stress acts on the lower side. A portion where neither compressive stress nor tensile stress acts is shown.

  The position of the neutral axis 6 of the composite floor slab 1 is calculated by the following equation (1). Formula (2) shows the formula for calculating the second moment of inertia in terms of concrete.

X _n is the distance from the compression edge (upper end) 7 to the neutral shaft 6 in the cross section of the composite slab 1, b is the interval between the ribs 3 (I-shaped steel), n is the Young's modulus ratio, and AS ₁ is the installation of the rib 3 Effective cross-sectional area of bottom steel plate per interval, A _S2 is the cross-sectional area per rib 3, X _S1 is the distance from the neutral axis of the bottom steel plate 2 to the compression edge 7, and X _S2 is the neutral axis of the rib to the compression edge The distance to 7 is shown.
Further, I _S1 represents a bottom steel plate cross-sectional moment per installation interval of the ribs 3, and I _S2 represents a cross-sectional second moment per rib 3.

Next, the stress that acts on the rib 3 when the composite floor slab 1 according to this embodiment having the above-described configuration is loaded from above will be described.
As shown in FIG. 2, when the composite slab 1 is applied from above, a bending moment M acts, compressive stress in the plane direction acts above the neutral shaft 6, and tensile stress below the neutral shaft 6. Works. At this time, as shown in FIG. 3, bending compressive stress (supporting stress) of the concrete 5 acts on the rib 3 on the upper side of the neutral shaft 6.

  The bending compressive stress of concrete acting in the direction orthogonal to the extending direction of the rib 3 is compressed in the bending compressive stress of concrete compressed in the direction orthogonal to the extending direction of the rib 3 and the extending direction of the rib 3. This is the resultant force with the bending compressive stress acting in the direction orthogonal to the extending direction of the ribs 3 determined by the Poisson's ratio among the bending compressive stress of the concrete.

And the bending compressive stress with the concrete 5 which acts on the rib 3 becomes a frictional force between the rib 3 and the concrete 5, and the rib 2 and the concrete 5 are prevented from shifting from each other. And the rib 3 and concrete are integrated when this frictional force exceeds the horizontal shearing force which acts on the synthetic floor slab 1.
At this time, the height at which the rib 3 protrudes above the neutral shaft 6, the shape of the rib 3, the installation interval of the rib 3, and the like are set so that the frictional force exceeds the horizontal shearing force.
In addition, it is preferable that the cover thickness of the concrete 5 of the rib 3 is about 50 to 60 mm.

Next, the effect of the composite floor slab 1 described above will be described with reference to the drawings.
According to the composite floor slab 1 according to the present embodiment, the rib 3 protrudes above the neutral shaft 6 of the composite floor slab 1 so that when a load is applied to the composite floor slab 1 from above, the neutral shaft 6 The bending compressive stress of the concrete 5 acts on the rib 3 on the upper side, and this bending compressive stress becomes a frictional force between the rib 3 and the concrete 5, so that the rib 3 and the concrete 5 are integrated and the rib 3 is interposed. Thus, the concrete 5 and the bottom steel plate 2 are integrated.

Then, the bottom steel plate 2 and the concrete 5 are integrated with a simple structure without providing a complicated structure in which an opening is provided in the rib or a stud gibber or a grid-like rib is provided in the bottom steel plate as in the prior art. Therefore, the production cost and the production period can be shortened.
Further, since there is no structurally fragile portion such as an opening provided in the rib or a welded portion between the bottom steel plate and the stud gibber, the fatigue durability of the composite floor slab 1 can be enhanced.

Here, the test which confirms the integrity of the rib and the concrete of the synthetic floor slab by this Embodiment was done.
The specimen is a composite floor slab of the form shown in FIGS. 1 (a) and 1 (b), and is formed with a width of 1.5 m, a floor slab span of 1.2 m, and a floor slab thickness of 160 mm. The ribs 3 were I-shaped steel, and the interval between the adjacent ribs 3 was three times the height of the ribs 3 and was 300 mm.
As shown in FIG. 4, there are four types of specimens having different forms, and the specimen 1 uses a perforated gibber in the rib 3 and a plurality of openings are formed in the web. The specimen 2 is the synthetic floor slab 1 according to the above-described embodiment of the present invention, in which the rib 3 has no opening. In the specimens 1 and 2, an inorganic zinc rich paint 30 μm is applied to the surface of the rib 3.
The specimen 3 has a form in which a Teflon (registered trademark) sheet is attached to the surface of the rib 3 and adhesion and friction between the rib 3 and the concrete 5 are eliminated. The specimen 4 has a shape in which the rib 3 has no opening and 0.5% polyolefin reinforcing fiber (length 30 mm) is mixed into the concrete 5 of the specimen 2.
In each of the specimens 1 to 4, the upper end portion of the rib 3 protrudes above the neutral shaft.

In order to reproduce the use for a certain period of time, the specimens 1 to 4 are repeatedly subjected to a fixed point loading test while moving the loading point, and then punched out at the center of the specimens 1 to 4 Perform a proof test.
In the fixed point loading test, the loading position P1 corresponding to the central portion of the rib 3a installed at the center of the specimens 1 to 4 shown in FIG. 5A, the rib installed at the center shown in FIG. 5B. Loading position P2 at the midpoint between the center portion of 3a and the center portion of the two ribs 3b adjacent to the rib 3a, two ribs adjacent to the rib 3a installed at the center shown in FIG. 5 (c) The loading is repeatedly performed in order at a loading position P3 corresponding to the central portion 3b.
Each loading position P1, P2, P3 is loaded about 100,000 times, and the load value is as follows according to the road bridge specification I.2.2.2 and the steel road bridge fatigue design guideline 2.4.2 (2). From the formula (3), it is set to 120 KN per location.

  When loading at the loading position P2 and the loading position P3, there is an influence due to the loads adjacent to each other. Therefore, the reduction rate to calculate the cross-sectional shearing force of the rib cross section similar to that when the basic load of 120 kN is loaded is calculated by analysis. Then, a load in consideration of this is loaded. Further, except for the specimen 3 in which a Teflon (registered trademark) sheet is adhered to the surface of the rib 3, after loading at the loading positions P2 and P3, the loading at the loading position P1 is returned to 2.5 to 5 of the design load. The double load was repeatedly loaded about 100 to 10,000 times.

Then, after the fixed point loading test, a punching strength test is performed in which loading is repeated until the design load 120 kN is gradually increased 1.5 times, 3 times, etc., to the loading position P1 until punching shear failure occurs.
In this test, displacement near the center of specimens 1 to 4 and strain distribution in the cross section were confirmed as measurement items.

Next, the results of the above test will be described.
FIG. 6 shows the load-displacement relationship of each specimen 1-4, and FIG. 7 shows the load-displacement relationship of each specimen 1-4 up to a displacement of 3 mm.
The line L1 in the figure indicates the bending rigidity of the composite section effective for all sections, the dotted line L2 indicates the bending rigidity of the composite section (RC calculation section) ignoring the tensile side of the concrete, and the two-point difference line L3 indicates steel (ribs and ribs). Only the bottom steel plate shows bending rigidity.

  The specimen 3 in which the Teflon (registered trademark) sheet is attached to the rib 3 has almost no adhesion and friction between the rib 3 and the concrete 5, so it is displaced from the start of loading, and the composite is ignored with the tensile side of the concrete 5 ignored. It is lower than the bending rigidity of the cross section (RC calculated cross section) and slightly higher than the bending rigidity of the steel material alone, and it can be seen that the rib 3 and the concrete 5 are not integrated. Further, the punching shear strength is 650 kN, which does not reach the designed punching shear strength of 681 kN of the 16 cm reinforced concrete plate of the concrete standard specification [design edition] 9.2.2.3.

Further, when comparing the specimen 1 in which the opening is formed in the rib 3 and the specimen 2 in which the opening is not provided in the rib 3, the specimen 1 has a slightly higher rigidity and a punching shear force of about 6%. I understand that it goes up. As for the unloading gradient, both of them were in accordance with the gradient of RC calculation, and integration was attempted up to 1,000 kN, which is about eight times the design load.
After that, the load decreases with the breakage of adhesion near the maximum proof stress, but the proof stress again increases with deformation, rises to a load value slightly smaller than the maximum proof stress, then becomes a constant value at about 850 kN, and only the displacement tends to increase. become.
Thus, the difference by the presence or absence of the opening part of a rib is small, and a composite floor slab provided with the rib without an opening part can also ensure sufficient proof stress.

In addition, the specimen 4 in which the reinforcing fibers are mixed into the concrete 5 has the same gradient as the bending rigidity of the composite cross section effective for all cross sections up to about 500 kN, which is about four times the design load. The bending rigidity of the composite cross section (RC calculated cross section) ignoring the tension side is approximately the same.
The maximum shear strength improved by about 7% compared to Specimen 1, and improved by about 13% compared to Specimen 2, but the load decreased with the break of adhesion near the maximum proof stress, and the subsequent behavior was Specimen 1. 2 was the same.

FIG. 8 to FIG. 11 show the load-strain relationship of each specimen 1-4.
As shown in FIGS. 10 (a) and 10 (b), the specimen 3 in which the Teflon (registered trademark) sheet is attached to the rib 3 has a low position of the neutral axis (position where the strain becomes 0) from the beginning of loading, and the steel material. It can be seen that the behavior is not integrated with concrete. On the other hand, as shown in FIGS. 8, 9, and 11, in the specimens 1, 2, and 4, the position of the neutral axis is the design position of the RC cross section, and the position of the neutral axis is 300,000 loads. It can be seen that there is almost no change even after repeated loading. It can also be seen that the strain at each part increases as the load increases thereafter, but the position of the neutral shaft does not change.

  In addition, it can be seen that in the specimen 1 in which the rib 3 has an opening, there is variation in strain between the portion with the opening and the portion without the opening. On the other hand, it can be seen that the specimen 2 in which no opening is formed in the rib 3 has less strain variation than the specimen 1 because the variation in strain is small.

  From the above results, there is almost no difference in the strain distribution and bending rigidity in the cross section between the conventional composite floor slab having an opening in the rib 3 and the synthetic floor slab 1 having no opening in the rib 3, and the rib 3 and the concrete 5 It can be seen that the ribs 3 and the concrete 5 are integrated by frictional conduction.

As mentioned above, although embodiment of the synthetic floor slab 1 by this invention was described, this invention is not limited to said embodiment, In the range which does not deviate from the meaning, it can change suitably.
For example, in the above-described embodiment, the rib 3 is an I-shaped steel, but an H-shaped steel, an angle steel, or a flat steel material may be used instead of the I-shaped steel.
Moreover, you may mix a reinforcement fiber in the concrete 5 of said embodiment.

DESCRIPTION OF SYMBOLS 1 Composite floor slab 2 Bottom steel plate 3 Rib 4 Reinforcement bar 5 Concrete 6 Neutral axis

Claims (4)

A composite floor slab comprising a bottom steel plate, concrete placed on the bottom steel plate, and a plurality of ribs extending in the span direction and arranged at intervals on the bottom steel plate and embedded in the concrete There,
An upper end portion of the rib protrudes upward from a neutral axis of the synthetic floor slab.   The synthetic floor slab according to claim 1, wherein a distribution bar extending in a direction orthogonal to an extending direction of the rib is provided on an upper portion of the rib.   The composite floor slab according to claim 1 or 2, wherein reinforcing fibers are mixed in the concrete. The synthetic floor slab according to any one of claims 1 to 3, wherein an opening is not formed in the rib.

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