JP7532737B2 - Foundation structure and foundation construction method - Google Patents

Description

The present invention relates to a foundation structure and a foundation construction method.

The following Patent Document 1 shows a pile foundation structure in which a column-under-pillar is installed at the bottom of the foundation beam.

JP 2016-199861 A

In the pile foundation structure of Patent Document 1, the piles exert shear resistance on the ground during an earthquake, but if the seismic force becomes too large, the piles may be subject to shear failure.

Taking the above facts into consideration, the present invention aims to increase the shear resistance of the foundation against the ground.

The foundation structure of claim 1 comprises a concrete floor slab provided on the ground, a foundation beam protruding above the concrete floor slab and having two or more main beam reinforcements in the width direction , an insertion section formed in a part of the foundation beam, protruding below the concrete floor slab and embedded in the ground, stirrups arranged from the upper end of the foundation beam to the lower end of the insertion section and surrounding the main beam reinforcement, and bending reinforcement bars arranged in parallel along the stirrups when viewed from the width direction of the foundation beam in the range from the center of the foundation beam to the lower end of the insertion section, between adjacent stirrups, and along the stirrups when viewed from the longitudinal direction of the foundation beam, to resist bending deformation due to earth pressure.

According to the foundation structure of claim 1, the foundation beam has an embedded portion that protrudes below the concrete floor slab and is embedded in the ground. Therefore, when the foundation beam tries to move relative to the ground during an earthquake, the embedded portion receives the soil shear resistance force from the ground. Therefore, compared to a configuration in which the foundation beam does not have an embedded portion, the shear resistance force of the foundation against the ground can be increased. This makes it difficult for the foundation beam to displace horizontally relative to the ground.

In one embodiment of the foundation structure, the embedded portion is provided with bending reinforcement bars that resist bending deformation caused by earth pressure.

According to one aspect of the foundation structure, the penetration portion is provided with a bending reinforcement bar that resists bending deformation due to earth pressure, so that the penetration portion is less likely to bend and break due to earth pressure.
One embodiment of the foundation structure has bending reinforcement bars arranged parallel to and between adjacent stirrups in the range from the center of the foundation beam to the lower end of the embedded portion, and which resist bending deformation due to earth pressure.
The foundation structure of claim 2 is the foundation structure of claim 1, further comprising a slab joined to the upper end of the foundation beam.
A foundation structure according to claim 3 is the foundation structure according to claim 1 or 2, in which a support pile is fixed to the foundation beam.
The foundation structure of claim 4 is the foundation structure described in claim 3, in which the support piles are provided with a plurality of support piles of different lengths, each having its pile head fixed to a footing integrated with the foundation beam and its lower end fixed to the supporting ground, and the embedded portion is formed in the foundation beam to which at least the longest support pile of the plurality of support piles is fixed, but is not formed in the foundation beam to which the shortest support pile is fixed.

The foundation construction method of claim 5 includes the steps of excavating the ground to form an excavation trench, placing steel bars in the excavation trench, pouring concrete into the excavation trench and into the ground surface in which the excavation trench is formed to form a concrete floor slab and an insertion portion protruding downwardly from the concrete floor slab, and pouring concrete above the excavation trench and above the concrete floor slab where the excavation trench is not formed to form a foundation beam that protrudes upwardly from the concrete floor slab and has a portion of it embedded in the ground, wherein the steel bars are stirrups that are arranged from the upper end of the foundation beam to the lower end of the insertion portion and surround two or more main beam reinforcements arranged in the width direction of the foundation beam .

According to the foundation beam construction method of claim 5, a foundation beam is constructed that is embedded in the ground. Therefore, when the foundation beam attempts to move relative to the ground during an earthquake, the embedded portion receives the soil shear resistance force from the ground. Therefore, compared to a configuration in which the foundation beam is not embedded in the ground, the shear resistance force of the foundation against the ground can be increased. This makes it difficult for the foundation beam to be displaced horizontally relative to the ground.

The foundation structure and foundation construction method of the present invention can increase the shear resistance of the foundation against the ground.

1 is a cross-sectional elevation view showing a building to which a foundation structure according to an embodiment of the present invention is applied. FIG. 2 is a foundation plan showing a foundation beam to which the foundation structure according to the embodiment of the present invention is applied. FIG. 2 is a cross-sectional elevation view showing a foundation structure according to an embodiment of the present invention. (A) shows the state after excavation of the surface ground in a foundation construction method according to an embodiment of the present invention, (B) shows the state after construction of a beam formwork, and (C) shows the state after backfill material has been filled between the excavated trench and the beam formwork. (A) shows the state in which the beam reinforcement of the foundation beam has been arranged in the foundation construction method according to an embodiment of the present invention, and (B) shows the state in which the concrete of the pressure plate, foundation beam, and slab has been poured. 1 is a cross-sectional elevation view showing a modified example in which a building to which a foundation structure according to an embodiment of the present invention is applied is built on a site where the depth of the supporting ground is approximately constant.

(building)
A building 10 to which the foundation structure according to the embodiment of the present invention is applied is a structure standing on a site on which an inclined supporting ground G2 is formed below a surface ground G1, as shown in Fig. 1. The building 10 is of a spread foundation type in which a foundation beam 12 is directly placed and supported on the supporting ground G2 at a position where the supporting ground G2 is shallow (on the right side in the X direction in Fig. 1).

In addition, where the supporting ground G2 is deep (on the left side in the X direction in FIG. 1; in other words, where the foundation beam 12 and the supporting ground G2 are vertically spaced apart), the foundation is supported by a pile foundation in which the support piles 20 extend from the lower end of the foundation beam 12 to the supporting ground G2. In the following explanation, the entire foundation structure including the foundation beam 12 and the support piles 20 is referred to as the "foundation".

(Support piles)
The support piles 20 are cast-in-place concrete piles. If the support piles 20 are designated as 20A, 20B, 20C, 20D, 20E, 20F, and 20G in order from the left side in the X direction in Fig. 1, their lengths correspond to the distance from the foundation beam 12 to the supporting ground G2 at the respective installation positions, and the order of the support piles is 20A > 20B > 20C > 20D > 20E > 20F > 20G.

The heads of the support piles 20 (support piles 20A, 20B, 20C, 20D, 20E, 20F, 20G) are fixed to a footing 14 that is integrated with the foundation beam 12. The lower end of a column 40 is embedded in the head of each support pile 20. The column 40 is a permanent column of the building 10, formed from a concrete-filled square steel pipe (CFT). The column 40 can be formed from a square steel pipe or H-shaped steel without being filled with concrete (so-called steel frame construction), or it can be a steel-reinforced concrete construction in which the H-shaped steel is covered with concrete.

Note that in Figure 1, one each of support piles 20A, 20B, 20C, 20D, 20E, 20F, and 20G are shown, but in the following explanation, support piles 20A, 20B, 20C, 20D, 20E, 20F, and 20G refer collectively to support piles 20 shown in Figure 2 that are on the same axis (axis along the Y direction).

(Foundation beam)
As shown in Figure 2, the foundation beam 12 comprises a foundation beam 12X extending along the Y direction and arranged at intervals in the X direction, and a foundation beam 12Y extending along the X direction and arranged at intervals in the Y direction.

The foundation beams 12X are, in order from the left side in the X direction in FIG. 2, foundation beams 12X1, 12X2, 12X3... 12X10, 12X11. The foundation beams 12Y are, in order from the top side in the Y direction in FIG. 2, foundation beams 12Y1, 12Y2, 12Y3... 12Y6, 12Y7.

As shown in FIG. 1, foundation beams 12X1, 12X3, and 12X5 have a larger beam depth than the other foundation beams 12X (foundation beams 12X2, 12X4, 12X6, 12X7...12X10, 12X11). More specifically, the height position of the upper end surface of foundation beams 12X1, 12X3, and 12X5 is the same as that of the other foundation beams 12X, and the height position of the lower end surface is lower than that of the other foundation beams 12X.

A pressure plate 16 and a slab 18 are placed between adjacent foundation beams 12X. The pressure plate 16 is positioned so that the lower surface of the foundation beams 12X (foundation beams 12X2, 12X4, 12X6, 12X7...12X10, 12X11) other than foundation beams 12X1, 12X3, 12X5 is aligned with the same height. As a result, the lower ends of the foundation beams 12X1, 12X3, 12X5 protrude below the pressure plate 16 and are embedded in the surface ground G1. In the following description, this embedded portion is referred to as the embedded portion 12XE (see FIG. 3).

The slab 18 is also positioned so that its upper surface is at the same height as the foundation beams 12X (foundation beams 12X1, 12X2...12X10, 12X11). The space between the pressure plate 16 and the slab 18 is used as an underground pit P for the building 10.

Figure 2 shows the foundation plan of the building 10, which shows in a shaded area the foundation beams 12X1, 12X3, and 12X5 with embedded sections 12XE that are embedded in the surface ground G1.

Similarly, in the foundation beams 12Y1, 12Y3, 12Y5, and 12Y7 extending along the X direction, the portions sandwiched between the foundation beams 12X1 and 12X5 are also shown shaded. That is, in the foundation beams 12Y1, 12Y3, 12Y5, and 12Y7, the portions sandwiched between the foundation beams 12X1 and 12X5 also have portions that are embedded in the surface ground G1, similar to the foundation beams 12X1, 12X3, and 12X5. In the following description, this embedded portion is referred to as the embedded portion 12YE.

As a result, as shown by the dashed line in Figure 2, an area V is formed at the bottom of the building 10 that is substantially rectangular in plan view and is surrounded by the penetration sections 12XE, 12YE. Area V is surrounded on all four sides by penetration sections 12XE, 12YE and is arranged in a lattice pattern. Furthermore, each of these areas V is filled with soil that forms the surface ground G1.

Figure 3 shows a cross section of a foundation beam 12X5 with an insertion section 12XE. Stirrups 34 are wrapped around the foundation beam 12X5, surrounding the main beam reinforcement 32, in the range from the upper end to the lower end (the lower end of the insertion section 12XE) of the foundation beam 12X5. Furthermore, bending reinforcement 36 is arranged between the stirrups 34 in the range from the center to the lower end of the foundation beam 12X5. In the following description, the main beam reinforcement 32, the stirrups 34, and the bending reinforcement 36 are collectively referred to as beam reinforcement 30.

In FIG. 3, the footing 14 is omitted in order to clarify the configuration of the foundation beam 12X5. However, as shown in FIG. 1, the footing 14 to which the foundation beams 12X1, 12X3, and 12X5 having the insertion portion 12XE are joined has a lower end surface located at a lower height than the lower end surfaces of the foundation beams 12X1, 12X3, and 12X5.

Foundation beams 12X1 and 12X3 are configured similarly to foundation beam 12X5, and foundation beams 12Y1, 12Y3, 12Y5, and 12Y7 equipped with recessed portion 12YE are configured similarly to foundation beam 12X5.

(Foundation Construction Method)
A method for constructing the foundation beams 12X1, 12X3, and 12X5 having the insertion portion 12XE and the foundation beams 12Y1, 12Y3, 12Y5, and 12Y7 having the insertion portion 12YE will be described. Note that the construction methods of these foundation beams 12X and 12Y are similar, but the foundation beam 12X5 will be described here as an example.

First, as shown in FIG. 4(A), the surface ground G1 is excavated to form an excavation trench 50. The excavation trench 50 is formed along the extension direction of the foundation beams 12X5 (not shown), the trench bottom 52 is leveled substantially horizontally, and the trench wall, which is a slope 54, is formed at an incline relative to the trench bottom 52.

Next, as shown in FIG. 4(B), crushed stone and concrete 56 are laid in the trench bottom 52, and then a beam formwork 58 is constructed. The beam formwork 58 is made of galvanized steel plate and is erected in a position spaced apart from the slope 54, approximately vertically.

Next, as shown in FIG. 4(C), backfill material 60 is filled between the beam formwork 58 and the slope 54. The backfill material 60 is improved soil made by mixing cement with the soil and sand excavated when forming the excavation trench 50 (soil and sand that forms the surface ground G1), and has an increased shear strength compared to the surface ground G1 before excavation.

Next, as shown in FIG. 5(A), crushed stone and concrete 62 are laid on top of the backfill material 60 and on top of the surface ground G1, and then the beam reinforcing bars 30 are placed inside the beam formwork 58 and on the part protruding upward from the inside of the beam formwork 58. In addition, the slab main reinforcement bars (not shown) of the pressure plate 16 are placed.

Next, as shown in FIG. 5(B), the concrete that forms the embedded portion 12XE and the concrete that forms the pressure plate 16 are poured together (up to the portion indicated by dotted line P1). A beam formwork 64 is constructed on top of the pressure plate 16, and concrete that forms the foundation beam 12X5 is poured (up to the portion indicated by dotted line P2). Furthermore, a slab formwork 66 is constructed, and concrete that forms the slab 18 is poured.

Through the above steps, a foundation beam 12X5 is constructed, which protrudes above and below the pressure plate 16. In this foundation beam 12X5, the portion protruding below the pressure plate 16 is embedded in the surface ground G1 to form an embedded portion 12XE. In addition, a slab 18 is joined to the portion protruding above the pressure plate 16. Note that the basin concrete 56, 62 and the beam formwork 58 are not shown in Figure 3.

(Action and Effects)
In the foundation structure of this embodiment, the foundation beams 12X1, 12X3, and 12X5 have an insertion portion 12XE that protrudes below the pressure plate 16 and is embedded in the surface ground G1. Also, the foundation beams 12Y1, 12Y3, 12Y5, and 12Y7 have an insertion portion 12YE that protrudes below the pressure plate 16 and is embedded in the surface ground G1.

Therefore, when a force acts in the X direction shown in Figure 2 during an earthquake, and the foundation beams 12X1, 12X3, and 12X5 attempt to move relative to the ground, the embedded portion 12XE receives the soil shear resistance force from the surface ground G1. Also, when a force acts in the Y direction, and the foundation beams 12Y1, 12Y3, 12Y5, and 12Y7 attempt to move relative to the ground, the embedded portion 12YE receives the soil shear resistance force from the surface ground G1.

In contrast, if the foundation beam does not have an embedded portion, the foundation beam cannot obtain soil shear resistance from the surface ground G1. Therefore, the foundation beams 12X and 12Y can increase the shear resistance of the foundation to the ground compared to foundation beams that do not have embedded portions 12XE and 12YE.

In addition, in the foundation structure of this embodiment, the penetration parts 12XE, 12YE are arranged to surround the surface ground G1 on all sides. Therefore, regardless of the direction from which a force acts during an earthquake, one of the foundation beams 12 will receive the soil shear resistance force from the surface ground G1. This increases the shear resistance force of the foundation against the ground compared to when the penetration parts 12XE, 12YE do not surround the surface ground G1 on all sides (for example, when they surround it on three sides, or when they are in contact with it on two sides, etc.).

In addition, in the foundation structure of this embodiment, as shown in FIG. 3, the insertion portions 12XE, 12YE are part of the foundation beams 12X, 12Y, and inside the insertion portions 12XE, 12YE, in addition to the stirrups 34 of the foundation beams 12X, 12Y, bending reinforcement bars 36 arranged between the stirrups 34 are provided.

As a result, a bending moment due to earth pressure is applied to the embedded sections 12XE, 12YE, but these stirrups 34 and bending reinforcement bars 36 suppress bending deformation of the embedded sections 12XE, 12YE. As a result, the embedded sections 12XE, 12YE are less likely to bend and break under earth pressure.

In addition, in the foundation structure of this embodiment, a slab 18 is joined to the upper end of the foundation beam 12X5. Therefore, even if earth pressure acts on the embedded portion 12XE and a rotational moment acts on the upper end of the foundation beam 12X5, deformation of the foundation beam 12X5 is suppressed by the reaction force received from the slab 18. The same applies to the foundation beams 12X1 and 12X3, and also to the foundation beams 12Y1, 12Y3, 12Y5, and 12Y7 equipped with the embedded portion 12YE.

In addition, in the foundation beam 12X5 formed by the foundation construction method of this embodiment, the beam formwork 58 is made of galvanized steel plate, so it is less susceptible to corrosion than a wooden formwork. Therefore, gaps are less likely to occur between the embedded portion 12XE of the foundation beam 12X5 and the backfill material 60, and when the foundation beam 12X5 moves relative to the surface ground G1 during an earthquake, the surface ground G1 can immediately exert shear resistance. The same is true for the foundation beams 12X1 and 12X3, and also for the foundation beams 12Y1, 12Y3, 12Y5, and 12Y7 equipped with the embedded portion 12YE.

As shown in FIG. 1, the building 10 according to this embodiment is a structure standing on a site with an inclined supporting ground G2 formed below the surface ground G1. The building 10 is supported by a direct foundation on the right side in the X direction in FIG. 1, and by a pile foundation on the left side in the X direction. The supporting piles 20 are longer as they move toward the left in the X direction. For this reason, the foundation of the building 10 has a large bias in shear stiffness, and the shear stiffness is higher as it moves closer to the right side of the building 10.

In the building 10 according to this embodiment, the embedded portions 12XE and 12YE are provided in the foundation beam 12 in the portions where the support piles 20A, 20C, and 20E, which are longer than the support piles 20F and 20G, are installed, i.e., the portions where the shear stiffness of the foundation is lower than the other portions. This equalizes the shear stiffness of the foundation. Therefore, the support piles 20 are less likely to be damaged by shear.

In contrast, if the embedded sections 12XE and 12YE are not provided, during an earthquake, shear forces will be concentrated on the support piles 20F and 20G, which are shorter than the other support piles, and they will be more likely to undergo shear failure.

In the foundation beam 12X5 of this embodiment, bending reinforcement bars 36 are provided between the stirrup bars 34, but the embodiment of the present invention is not limited to this. For example, instead of bending reinforcement bars 36, bending reinforcement may be achieved by making the pitch of the stirrup bars 34 finer than that of foundation beams 12X2, 12X4, etc. that do not have an insertion portion 12XE.

Alternatively, the number of stirrups 34 may be left unchanged, but the diameter may be increased. This configuration also makes it difficult for the embedded portion 12XE to bend and break due to earth pressure. The same applies to the foundation beams 12X1 and 12X3, and also to the foundation beams 12Y1, 12Y3, 12Y5, and 12Y7 equipped with the embedded portion 12YE.

If the embedment depth of the embedded sections 12XE, 12YE is not large (for example, less than 1 m), the maximum earth pressure received by the bottom of the embedded sections 12XE, 12YE will be small. In such a case, bending reinforcement is not necessarily required.

In addition, in this embodiment, the slab 18 is joined to the upper end of the foundation beam 12X5, but the embodiment of the present invention is not limited to this, and the slab 18 may or may not be provided in the center of the foundation beam 12X5. Even if the slab 18 is not provided, the foundation beam 12Y extending in the X direction is joined to the foundation beam 12X5, so that when earth pressure acts on the embedded portion 12XE, the rotation suppression effect of the foundation beam 12X5 can be obtained.

In this embodiment, galvanized steel plates are used as the beam formwork 58, but the present invention is not limited to this embodiment. For example, even if stainless steel plates, resin plates, precast concrete plates, etc. are used, they are less susceptible to corrosion than wooden formwork, and the surface ground G1 is more likely to exhibit shear resistance.

In addition, in this embodiment, improved soil made by mixing cement with the soil and sand that forms the surface ground G1 is used as the backfill material 60 between the beam formwork 58 and the slope 54 of the excavation trench 50, but the embodiment of the present invention is not limited to this. For example, improved soil made by mixing quicklime with the soil and sand that forms the surface ground G1, or improved soil mixed with a solidification material, etc. may also be used. In other words, it is sufficient that the shear strength of the backfill material 60 is not lower than that of the soil and sand that forms the surface ground G1 around it.

Furthermore, the beam formwork 58 and backfill material 60 can also be omitted. In this case, after forming the excavation trench 50 shown in FIG. 4(A), the beam reinforcing bars 30 shown in FIG. 5(A) are placed, and concrete is poured into the top of the excavation trench 50 and the surface ground G1 up to the position shown by P1 in FIG. 5(B). After that, the beam formwork 64 is assembled and concrete is poured to form the foundation beam. In this way, a foundation beam with an embedded portion embedded in the surface ground G1 can also be formed.

The foundation structure according to this embodiment is applied to the foundation beams 12X1, 12X3, 12X5, 12Y1, 12Y3, 12Y5, and 12Y7 in the portions of the building 10 equipped with multiple support piles (support piles 20A, 20B...20G) of different lengths, where support piles 20A, 20C, and 20E are longer than the other support piles, but the embodiment of the present invention is not limited to this. For example, it may be applied to any location where it is desired to increase the shear resistance of the foundation.

For example, by applying the embedded sections 12XE and 12YE to the portions of the foundation beams 12X2, 12X4 and the foundation beams 12Y2, 12Y4, and 12Y6 that are sandwiched between the foundation beams 12X1 and 12X5, the shear resistance can be increased compared to the above embodiment.

Alternatively, if the insertion portions 12XE, 12YE are applied only to the portions of the foundation beams 12X1, 12X5 and the foundation beams 12Y1, 12Y7 sandwiched between the foundation beams 12X1 and 12X5, the shear resistance will be higher than a configuration that does not have the insertion portions 12XE, 12YE at all, but the shear resistance can be lower than the above embodiment. In this way, the foundation beams to which the foundation structure according to this embodiment is applied can be selected appropriately depending on the required shear resistance.

The building to which the foundation structure according to this embodiment is applied is a building built on a site where a supporting ground G2 is formed, which is inclined below the surface ground G1, but the embodiment of the present invention is not limited to this. For example, the building may be a building built on a site where the depth of the supporting ground G2 is approximately constant, as in the case of building 70 shown in FIG. 6. The shear resistance against the surface ground G1 can also be increased for any foundation beam 12 of such a building 70.

Specifically, for example, if the center of gravity and center of rigidity of the building 70 are different, the foundation structure according to this embodiment can be applied to the foundation beams 12 located away from the center of rigidity, thereby bringing the center of rigidity closer to the center of gravity and suppressing torsional deformation of the building 70.

Furthermore, the foundation structure according to the embodiment of the present invention does not need to include support piles 20 as long as it includes a foundation beam 12 having an embedded portion 12XE or 12YE. In other words, it can be applied to buildings that are directly supported on the supporting ground. In this case, the embedded portion 12XE or 12YE receives shear resistance from the supporting ground, which is relatively hard, so it is easy to obtain the effect of improving the shear resistance of the foundation.

16 Pressure plate (concrete floor plate)
12X1, 12X3, 12X5 Foundation beam 12Y1, 12Y3, 12Y5, 12Y7 Foundation beam 12XE, 12YE Root section 36 Bending reinforcement bar 50 Excavation trench 54 Trench wall 58 Beam formwork 60 Backfill material G1 Surface ground (ground)

Claims (5)

A concrete floor slab provided on the ground;
A foundation beam protruding above the concrete floor slab and having two or more beam main reinforcements in the width direction ;
An embedded portion formed in a part of the foundation beam, protruding downward from the concrete floor slab and embedded in the ground;
A stirrup is arranged from the upper end of the foundation beam to the lower end of the penetration portion and surrounds the beam main reinforcement ;
A bending reinforcement bar is provided between adjacent stirrups in a range from the center of the foundation beam to the lower end of the embedded portion, parallel to the stirrups as viewed in the width direction of the foundation beam, and is provided along the stirrups as viewed in the longitudinal direction of the foundation beam, and resists bending deformation due to earth pressure;
A base structure having: A slab is provided which is joined to the upper end of the foundation beam.
The base structure of claim 1 . The foundation structure according to claim 1 or 2, in which support piles are fixed to the foundation beams. The support piles include a plurality of support piles of different lengths, each having a pile head fixed to a footing integrated with the foundation beam and a lower end fixed to the supporting ground,
The embedded portion is formed in the foundation beam to which at least the support pile having the longest length is fixed among the plurality of support piles, and is not formed in the foundation beam to which the support pile having the shortest length is fixed,
The base structure according to claim 3. A step of excavating the ground to form an excavation trench;
A step of placing reinforcing bars in the excavation trench;
A step of pouring concrete into the excavation groove and the ground surface on which the excavation groove is formed to form a concrete floor slab and a root portion protruding downward from the concrete floor slab;
A step of pouring concrete above the excavation trench and above the concrete floor slab where the excavation trench is not formed to form a foundation beam that protrudes above the concrete floor slab and has a portion embedded in the ground;
having
The reinforcing bars are arranged from the upper end of the foundation beam to the lower end of the penetration portion and are stirrups surrounding two or more main beam reinforcements arranged in the width direction of the foundation beam .
How to build a foundation.