Structure of the joint between the spread foundation and the foundation beam

Abstract

To provide structure of a joint part between a spread foundation and a footing beam in the case where the foundation is a reinforced concrete spread foundation.SOLUTION: A structure 10 of a joint part between a reinforced concrete spread foundation and a footing beam includes: a first cylindrical body 34 placed inside a spread foundation 12 and extending vertically; a second cylindrical body 36 joined to the footing beam and extending vertically; and concrete 38 filled inside both the first and second cylindrical bodies. The second cylindrical body has a lower end part 37 positioned inside the first cylindrical body, and the lower end part is surrounded with the first cylindrical body while having an interval therefrom.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This relates to the structure of the joint between a reinforced concrete spread foundation and a foundation beam. [Background technology]

[0002] A joint structure between a pile and a foundation beam has been proposed. This joint structure between a pile and a foundation beam includes a first cylindrical body and a second cylindrical body extending in the vertical direction, respectively, and concrete filled inside the first and second cylindrical bodies. The second cylindrical body surrounds the periphery of the pile head and surrounds all or part of the periphery of the first cylindrical body below the upper end of the first cylindrical body and at a distance from the first cylindrical body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-204172 Summary of the Invention [Problem to be solved by the invention]

[0004] In view of the conventional structure of the joint between a pile foundation and a foundation beam, the present invention provides a structure of the joint between a spread foundation and a foundation beam when the foundation is a spread foundation made of reinforced concrete. [Means for solving the problem]

[0005] The present invention relates to a joint structure between a reinforced concrete spread foundation and a foundation beam. The joint structure includes a first cylindrical body positioned inside the spread foundation and extending vertically, a second cylindrical body joined to the foundation beam and extending vertically, and concrete filled inside both the first and second cylindrical bodies. The second cylindrical body has a lower end located inside the first cylindrical body, and the lower end is surrounded by the first cylindrical body at a distance. The foundation beam and the first and second cylindrical bodies are integrated with each other via the concrete.

[0006] According to the present invention, the vertical load of the superstructure placed on the foundation beam is first borne by the concrete filled inside the first and second cylindrical bodies, and then by the spread foundations around them. This allows the surface area and thickness of the spread foundation to be reduced, i.e., the spread foundation can be made smaller.

[0007] The foundation beam can have a cross-shaped bracket consisting of one H-shaped steel and two H-shaped steels joined to the one H-shaped steel and perpendicular to it, and the second cylindrical body can be joined to the bracket.

[0008] The spread foundation is formed on basal concrete formed on the ground, and the first cylindrical body can be positioned at a height above the basal concrete via three or more temporary support members arranged around it at intervals.

[0009] The first cylindrical body and the second cylindrical body can be made of either a circular steel pipe or a square steel pipe. The first cylindrical body can be made of a circular steel pipe from the viewpoint of avoiding stress concentration. The second cylindrical body can be made of a square steel pipe from the viewpoint of the workability of the first floor slab (deck slab) of the superstructure. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic plan view of the structure of the joint between a spread foundation and a foundation beam according to the present invention. FIG. [Figure 2] FIG. 2 is a schematic cross-sectional view taken along line 2-2 of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1 and 2, the structure of the joint between a reinforced concrete spread foundation 12 formed on basal concrete 16 formed on relatively good ground E and a foundation beam 14 installed above the spread foundation is generally indicated by the reference numeral 10.

[0012] The illustrated spread foundation 12 is made of a plate-like body having an overall rectangular planar shape, and includes concrete 18, a plurality of upper reinforcements 20 arranged vertically at intervals in the concrete in a grid pattern, surrounding a first cylindrical body 34 (described below), and a plurality of lower reinforcements 22 arranged at a height below the first cylindrical body 34. The spread foundation 12 preferably further includes a plurality of opening reinforcement bars 32 arranged around the upper end of the first cylindrical body 34 so as to surround it.

[0013] The foundation beam 14 is made up of a bracket 14A consisting of one H-shaped steel 24 and a pair of H-shaped steels 26 joined together at right angles to the H-shaped steel 24, and a plurality of other H-shaped steels (not shown) attached to the bracket 14A. The foundation beam 14 supports a superstructure, in the illustrated example, a column 30 of the building, above the bracket 14A at the joints between the H-shaped steels 24, 26 that make up the bracket 14A.

[0014] The joint structure 10 between the spread footing 12 and the foundation beam 14 includes a first steel cylindrical body 34 and a second steel cylindrical body 36, each extending in the vertical direction, and concrete 38 filled inside these cylindrical bodies 34, 36. The concrete 38 inside the cylindrical bodies 34, 36 and the concrete 18 that constitutes the spread footing 12 are made of concrete poured simultaneously or in two separate steps to form the joint structure 10.

[0015] In the illustrated example, the first and second tubular bodies 34, 36 are made of large-diameter and small-diameter circular steel pipes, respectively. More specifically, both circular steel pipes have the same thickness, and the circular steel pipe constituting the first tubular body 34 has inner and outer diameters larger than those of the circular steel pipe constituting the second tubular body 36. Instead of the illustrated example, the first and second tubular bodies 34, 36 can be made of square steel pipes. However, from the perspective of avoiding stress concentration, it is desirable to make the first tubular body 34 made of a circular steel pipe, as in the illustrated example. Furthermore, from the perspective of constructability of the first floor floor slab (deck slab) 40 of the superstructure, the second tubular body 36 can be made of a square steel pipe instead of the illustrated example.

[0016] The first cylindrical body 34 is disposed inside the spread foundation 12. In the illustrated example, the first cylindrical body 34 is located approximately in the center of the spread foundation 12 in a plan view. In the illustrated example, the first cylindrical body 34 is disposed at a height above the basal concrete 16 via three or more temporary support members 42 arranged around the first cylindrical body 34 at intervals, and its upper end surface 34a is located on the flat top surface 12a of the spread foundation 12. Each of the illustrated temporary support members 42 is made of an L-shaped steel piece, and one end 42a is fixed to the outer peripheral surface 34b of the first cylindrical body 34 by welding or alternatively by bolts and nuts (not shown), and the other end 42b is fixed to the basal concrete 16 by bolts and nuts 44 or by welding. Each temporary support member 42 is embedded in the concrete 18 of the spread foundation 12.

[0017] On the other hand, the illustrated second cylindrical body 36 is made up of four arc-shaped plate members 36a and four arc-shaped plate members 36b assembled into a cylindrical shape and joined to the bracket 14A by welding. The four arc-shaped plate members 36a are respectively positioned between one H-shaped steel 24 and two H-shaped steels 26 that make up the bracket 14A. The four plate members 36b are positioned directly below the four plate members 36a.

[0018] More specifically, each plate member 36a has a cross-sectional shape that is an arc of approximately 1 / 4 of a circle, and extends in the vertical direction between the upper and lower flanges 24a, 24b of the H-shaped steel 24 and the upper and lower flanges of the H-shaped steel 26 (however, only the upper flange 26a is shown in FIG. 1). Each plate member 36a defines a partial cylindrical space 46 that is approximately 1 / 4 of a circle between one H-shaped steel 24 and each H-shaped steel 26 that are adjacent to each other in the circumferential direction. A total of four partial cylindrical spaces 46 define a cylindrical space that is approximately equivalent to one cylindrical space.

[0019] The four plate members 36b located directly below the four plate members 36a define one cylindrical space 48 (FIG. 2) that communicates with the four partial cylindrical spaces 46. The four plate members 36b are welded to the bottom flange 24b of one H-shaped steel 24 and the bottom flanges (not shown) of the two H-shaped steels 26 that make up the bracket 14A. The four plate members 36b extend downward from these bottom flanges toward the flat top surface 12a of the direct foundation 12, with a portion 37 extending through the flat top surface 12a of the direct foundation 12 and into the first cylindrical member 34. The portion 37 of the second cylindrical body 36 forms the lower end of the second cylindrical body 36 and is surrounded by the first cylindrical body 34 at a distance from the first cylindrical body 34. In the illustrated example, the portion 37 of the second cylindrical body 36 overlaps the upper end of the first cylindrical body 34 at an equal distance from the upper end of the first cylindrical body 34. The length (vertical length) of the overlap between the part 37 of the second cylindrical body 36 and the first cylindrical body 34 can be determined arbitrarily. In the illustrated example, the axis of the first cylindrical member 34 and the axis of the second cylindrical member 36 extend on a single straight line L that extends in the vertical direction. Instead of the illustrated example, the axis of the first cylindrical member 34 and the axis of the cylindrical member 36 can extend on two straight lines (not shown) that are parallel to each other.

[0020] The bracket 14A of the foundation beam 14 and the second cylindrical body 36 can be manufactured in advance in a factory and delivered to the construction site of the building.

[0021] The concrete 38 filled inside the first cylindrical body 34 and filling the four partial cylindrical spaces 46 and cylindrical space 48 defined by the second cylindrical body 36 defines a flat surface that is located at the same level as the surface of the upper flanges 24a, 26a of the H-shaped steel beams 24, 26 or the surface of the first floor floor slab (deck slab) 40.

[0022] According to this, the first cylindrical body 34 and the second cylindrical body 36 are integrated via the concrete 38, the bracket 14A and the first and second cylindrical bodies 34, 36 are integrated via the concrete 38, and the first and second cylindrical bodies 34, 36 and the spread foundation 12 are integrated via the concrete 18, 38. In this way, the spread foundation 12 and the foundation beam 14 are joined to each other via the joint structure 10.

[0023] In the illustrated example, a composite (first composite) consisting of a second cylindrical body 36 and concrete 38 filling it is reinforced by a composite (second composite) consisting of a first cylindrical body 34 surrounding a portion 37 of the second cylindrical body 36 and a portion of the concrete 38 filling the annular cross-sectional space between the first and second cylindrical bodies 34, 36, thereby increasing the shear resistance of the first composite. As a result, when an external shear force acts on the first composite, the external shear force is transmitted to the second composite, which is integral with the first composite. More specifically, the shear force is transmitted sequentially from the second cylindrical body 36 constituting the first composite to the portion of the concrete 38 constituting the second composite and the first cylindrical body 34. This eliminates the need to install a shear force transmission member inside the second cylindrical body 36, which would otherwise be required to increase the shear resistance.

[0024] Instead of the illustrated example, the second cylindrical body 36 can be formed from a single cylindrical member. In this case, the single cylindrical member constituting the second cylindrical body 36 has four recesses (not shown) opening to its upper end. These four recesses receive and allow insertion of a portion of the H-shaped steel 24 and portions of the two H-shaped steels 26 constituting the bracket 14A. Similarly, the gaps between the single cylindrical member constituting the second cylindrical body 36 and the portions of the H-shaped steels 24, 26 received in the respective recesses, more specifically, portions of their webs, can be temporarily blocked with an appropriate steel plate member (not shown), thereby preventing leakage during pouring of the concrete 38 to be filled. Alternatively, four H-shaped steels (not shown) constituting the bracket of the foundation beam can be joined to the circumferential surface of the cylindrical member constituting the second cylindrical body 36 at 90-degree angular intervals.

[0025] In this joint structure 10, the vertical load of the superstructure installed on the foundation beam 14 is first borne by the concrete 38 filled inside the first and second cylindrical bodies 34, 36, and then by the spread footing 12 around these cylindrical bodies 34, 36. This allows the spread footing 12 to be reduced in both surface area and thickness, i.e., the spread footing 12 can be made more compact. Furthermore, because the vertical load is borne by the first and second cylindrical bodies 34, 36 and the concrete 38, the magnitude of the tensile force acting on the lower reinforcement bars 22 in the spread footing 12 due to the vertical load is reduced. This allows for a reduction in the amount of reinforcing bars (the number of lower reinforcement bars 22, the length of the lower reinforcement bars 22, and the cross-sectional area of ​​the lower reinforcement bars 22) that need to be placed. [Explanation of symbols]

[0026] 10 Joint structure 12 Direct foundation 14 Foundation beam 14A Brackets constituting foundation beams 18 Concrete 24 One H-beam 26 Two H-beams 30 pillars 34 First cylindrical body 36 Second cylindrical body 36a Arc-shaped plate member 37 Lower end of second cylindrical body 38 Concrete

Claims

1. A structure of a joint between a reinforced concrete spread foundation and a foundation beam, a first cylindrical body disposed inside the spread foundation and extending in the vertical direction; a second cylindrical body joined to the foundation beam and extending in the vertical direction, the second cylindrical body having a lower end portion, the lower end portion being located inside the first cylindrical body and being surrounded by the first cylindrical body at a distance from the first cylindrical body; and concrete filled inside both the first and second cylindrical bodies, A structure of a joint between a spread foundation and a foundation beam, in which the foundation beam and the first and second cylindrical bodies are integrated via the concrete.

2. 2. The structure of the joint between a spread foundation and a foundation beam as described in claim 1, wherein the foundation beam has a cross-shaped bracket consisting of one H-shaped steel and two H-shaped steels joined to the one H-shaped steel and perpendicular to it, and the second cylindrical body is joined to the bracket.

3. 3. The joint structure between a spread foundation and a foundation beam according to claim 1, wherein the first cylindrical body is made of a circular steel pipe or a square steel pipe.

4. A structure of a joint between a spread foundation and a foundation beam as described in any one of claims 1 to 3, wherein the spread foundation is formed on basal concrete formed on the ground, and the first cylindrical body is positioned at a height above the basal concrete via three or more temporary support members arranged at intervals around it.

5. The structure of a joint between a spread foundation and a foundation beam according to any one of claims 1 to 3, wherein the second cylindrical body is made of a circular steel pipe or a square steel pipe.

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