JP7473110B2 - How to install a joist foundation - Google Patents

Description

The present invention relates to a method for constructing a joist foundation to fix the joists that form the foundation of a structure to the ground, and in particular to a method for constructing a joist foundation to fix the joists using spiral piles made of twisted flat steel.

Spiral piles, made of twisted flat steel bars, are used as part of the foundations of structures. Specifically, the spiral piles are buried in the ground and the heads of the spiral piles are fixed to the joists (cross beams) that form the foundation of a building or other structure, and the foundation part including the joists is fixed to the ground.

As shown in Figure 1, Patent Document 1 discloses that a joist 1 is fixed to a spiral pile 2 using a connecting member 3 made of steel material with an L-shaped cross section. The spiral pile is made of a spiral part 2a made of twisted flat steel, and a bolt is joined to the tip of the spiral part 2a by welding or the like.

In the joist foundation of Figure 1, the spiral pile 2 is buried vertically in the ground, and the connection member 3 is attached to the bolt 2b at the head of the spiral pile 2 exposed on the ground surface with a nut 2c. The connection member 3 is then fixed to the joist 1 by other bolts 4, etc.

Compared to normal cylindrical or rectangular piles, spiral piles can be easily embedded by rotating the spiral pile while pushing it in. Furthermore, when buried, soil from the ground seeps into the surface of the twisted flat steel, so there is an advantage in that the action and resistance of the earth pressure in the ground provides extremely strong resistance to forces trying to pull the pile out (or push it in) vertically.

When the ground is relatively strong, the joist foundation shown in Figure 1 can provide a sufficiently stable strength, but when installing a joist foundation on relatively soft ground such as rice fields or tidal flats, even spiral piles may not provide sufficient mechanical strength.

In order to solve this problem, in Patent Document 2, the inventors proposed providing a pivoting connection portion (30, 31) to the connection member 3 that connects the head of the spiral pile 2 to the joist 1, as shown in Figure 2. Specifically, when the joist 1 moves upward (solid arrow) or downward (dotted arrow), the angle of the connection member 3 relative to the joist 1 changes, moving the spiral pile 2 in a substantially horizontal direction and pressing the spiral pile 2 against the ground G, increasing the resistance of the joist 1 against floating or sinking.

The joist foundation in Figure 2 is expected to be effective enough when a sudden force (impact force) is applied to the joist 1, causing it to move up and down, but there is a problem in that it cannot provide sufficient resistance if the joist 1 sinks slowly over a long period of time.

JP 2015-14145 A JP 2015-55053 A JP 2013-163909 A

The problem that this invention aims to solve is to provide a method for constructing joist foundations that can eliminate the above-mentioned problems and provide a stable foundation even on soft ground.

In order to solve the above problems, the construction method for a floor joist foundation of the present invention has the following features.
(1) A construction method for a joist foundation in which a joist is fixed to the ground using a spiral pile formed by twisting flat steel, the method being characterized in that the spiral pile is placed in the ground at an angle with respect to both the horizontal plane of the joist and the vertical direction perpendicular to the horizontal plane, and the joist is fixed to the head of the spiral pile placed in the ground.

(2) The method for constructing a joist foundation described in (1) above is characterized in that when placing the spiral pile in the ground, the spiral pile is tilted and screwed into the ground.

(3) In the construction method for a joist foundation described in (3) above, when placing the spiral pile in the ground, the spiral pile is screwed vertically into the ground, and then the head of the spiral pile is pulled toward the joist and fixed to the joist.

The present invention relates to a construction method for joist foundations in which joists are fixed to the ground using spiral piles formed by twisting flat steel. The spiral piles are placed in the ground at an angle to both the horizontal plane of the joists and the vertical direction perpendicular to the horizontal plane, and the joists are fixed to the heads of the spiral piles placed in the ground, so that the twisted flat steel is placed at an angle in the ground. This makes it easier for soil from the ground to seep into the twisted flat steel, further increasing the holding power of the spiral piles in the ground, making it possible to provide a stable foundation even on soft ground.

FIG. 1 is a structural diagram illustrating a conventional example of a joist foundation using spiral piles. FIG. 1 is a structural diagram illustrating another conventional example of a joist foundation using spiral piles. FIG. 13 is a diagram illustrating the state in which a spiral pile is embedded diagonally relative to the vertical direction (dotted line A). This is a diagram illustrating the state when a spiral pile is embedded vertically (dotted line A) and then pulled toward a joist 1. 5 is a diagram showing a construction procedure for the floor joist foundation of FIG. 4. FIG. 2 is a diagram showing an example of a connecting member (metal fitting) used in the construction method of the floor joist foundation of the present invention. 11A to 11C are diagrams showing other examples of connecting members (metal fittings) used in the construction method of the floor joist foundation of the present invention. 13 is a diagram showing yet another example of a connecting member (metal fitting) used in the joist foundation construction method of the present invention. FIG. This is a diagram illustrating the state in which spiral piles are placed on both sides of a joist 1. FIG. 2 is a diagram explaining the positioning of the spiral pile relative to the joist 1. This is a diagram showing an example of connecting spiral piles arranged in different directions to a joist 1 using a single connecting member (metal fitting). FIG. 13 is a diagram illustrating an example in which the spiral portion and the bolt portion of a spiral pile are constructed as separate bodies.

The construction method for a floor joist foundation according to the present invention will be described in detail below.
The present invention relates to a construction method for a joist foundation in which a spiral pile 2 formed by twisting flat steel is used to fix the joist foundation to the ground, as shown in Figures 3 and 4, and is characterized in that the spiral pile 2 is placed in the ground at an angle with respect to both the horizontal plane of the joist 1 (left-right direction in the drawing) and the vertical direction perpendicular to the horizontal plane (up-down direction in the drawing; see dashed dotted line A), and the joist 1 is fixed to the head of the spiral pile placed in the ground.

As shown in Figure 3, the spiral pile can be easily tilted and placed in the ground by tilting the direction in which the spiral pile is screwed into the ground (dash-dotted line B) with respect to the vertical direction A. The angle θ between the vertical direction A and the tilting direction B can be selected from any angle greater than 0 and less than or equal to 45 degrees. In particular, the softer the ground, the greater the angle θ. The greater the angle θ, the more the spiral pile is prevented from sinking and the more stable the position of the joist. However, as the angle θ increases, the pressure of the ground pressing down on the spiral pile in the vertical direction weakens, so it is preferable to keep the angle θ at 45 degrees or less. More preferably, it is set to a range of ±5 to ±10 degrees with 30 degrees as the center.

Next, the installation method of the spiral pile placed in the ground as shown in FIG. 4 will be explained with reference to FIG. 5. As shown in FIG. 5(a), the spiral pile 2 is buried in a position distance L away from the joist 1 in a substantially vertical direction, and as shown in FIG. 5(b), a metal fitting (distance l between the attachment position to the joist and the attachment position to the spiral pile) which is the connection member 3 is temporarily fixed to the head of the spiral pile 2. The head of the spiral pile is then pulled toward the joist 1, and the metal fitting 3 is attached to the joist 1. This moves the head of the spiral pile in the direction of the joist 1 by a length of "L-l" from the original buried position.

As shown in Figure 4, by moving the head of the spiral pile 2 buried in the ground in a horizontal direction, bending gradually occurs in the part of the spiral pile that is perpendicular to the direction of movement (part shown as node D in Figure 4). As a result, the spiral pile 2 is buried in the ground in an entirely bent state, as shown by the dashed line C in Figure 4.

A spiral pile is made by twisting flat steel, and compared to a normal cylindrical pile, there are parts that are weak in bending in the lateral direction. As shown in Figures 4 and 5, when a spiral pile arranged in the direction of the dashed line A is bent to the left in the drawing, the mechanical strength against bending force is weaker at node D in Figure 4, which is perpendicular to the bending direction, compared to other parts. This characteristic of a spiral pile was previously considered a drawback of spiral piles, but the present invention has been conceived by actively utilizing this weak bending part, discovering that it is possible to greatly bend the entire spiral pile. Moreover, in the spiral pile, in any direction perpendicular to the longitudinal direction, there is always a part corresponding to node D in Figure 4, so the spiral pile can be greatly bent in any direction.

In a spiral pile that is generally bent, the soil in the ground in the direction in which the head of the spiral pile is moved (the inside of the bent spiral pile (left side of Figure 4)) penetrates into the surface of the twisted flat steel of the spiral pile at the top side of the spiral pile, providing a large resistance to the force of embedding the spiral pile into the ground. Also, the restoring force of the spiral pile acts on the bottom side of the spiral pile opposite the direction in which the head of the spiral pile is moved (the outside of the bent spiral pile (right side of Figure 4)), and the surface of the twisted flat steel is pressed against the soil in the ground, providing a large resistance to the spiral pile sinking. The joints of the spiral pile bend, but they also need to have the restoring force to return to their original position, so the flat steel used in the spiral pile needs to have a thickness that is resistant to bending. Also, by setting the width of the flat steel wider, the contact area with the soil in the ground is increased, providing a larger resistance.

In soft ground such as organic soil, highly organic soil (humus soil), clayey soil with an N value of 3 or less, and sandy soil with an N value of 5 or less, the flat steel can be thin as long as the mechanical strength is sufficient to screw the spiral pile into the ground. However, for soft ground, it is more preferable for the flat steel to be wider. Also, when the ground is strong, it is generally better for the flat steel of the spiral pile to be thicker and wider. When screwing a spiral pile into the ground, heavy machinery is essential to rotate the tip of the pile and drive it into the ground, but in soft ground, the strength required to screw the pile in is low, so lighter machinery can be used. Furthermore, in softer ground, it is also possible to screw the pile in by hand.

For a spiral pile to bend, the ground must be hard enough to allow the head of the spiral pile to move horizontally. The advantage of using the joist foundation construction method of the present invention is particularly great on soft ground such as fields, tidal flats, and areas with layers of sand and gravel.

The joists 1 in Figures 3 and 4 are made of square timber with a rectangular cross section, but the joists 1 are not limited to these materials and can be made of various materials such as H-shaped steel.

Figures 6 to 8 show examples of connection members (metal fittings) that connect the spiral pile to the joist. Figure 6 shows flat steel that has been bent and has screw holes 32 and 33 drilled in it. The screw hole 32 is a hole for attaching the metal fitting 3 to the joist 1 with a bolt and nut, and by providing an oval hole in the longitudinal direction of the joist, it is possible to set it so that the position between the joist and the metal fitting can be adjusted.

In addition, the shape of hole 33 in FIG. 6(a) is circular, but as shown in Patent Document 1, the shape of hole 33 can also be elliptical, like hole 32. As shown in FIG. 6(a), the surface on which hole 33 is formed is slightly bent with respect to a surface parallel to the ground in accordance with the angle at which the spiral pile is buried.

Figure 6 (b) shows the spiral pile 2 fixed to the joist 1 using the metal fitting 3 in Figure 6 (a). The bolt 2b at the head of the spiral pile is inserted into the hole in the metal fitting 3, and the two are connected using a nut 2c. Furthermore, the joist 1 and the metal fitting 3 are connected using another connecting member such as a bolt 4.

In Figure 7, the connecting member (metal fitting) is made by bending a rod-shaped steel material 300. The rod-shaped steel material 300 is bent as shown in Figure 7(a) and threads are formed at both ends. The tip of the steel material is passed through a hole pre-formed in the joist 1 and is fastened and fixed with nuts 301 from both sides of the joist 1. Washers can also be placed between the joist and the nuts if necessary.

The connecting member (metal fitting) shown in Figure 7 is relatively easy to manufacture, since it is made by simply bending a bar-shaped steel material 300 into a U-shape and tilting the tip (the part that holds the spiral pile). Moreover, the position of the head of the spiral pile can be adjusted by moving it within the range of the tilted U-shape. Figure 7(b) shows the spiral pile 2 fixed to the joist 1 using the metal fitting 300. When fixing the metal fitting 300 to the spiral pile, if necessary, a washer 2d can be used to apply the tightening force of the nut 2c to a wide area of the metal fitting, making it possible to exert a more reliable holding force.

The connecting member (metal fitting 310) shown in FIG. 8 reduces the load applied to the bolt 2b when the spiral pile is pulled toward the joist using a bolt provided at the head of the spiral pile. The spiral pile is prevented from being damaged by being configured to pull not only the bolt 2b but also the tip of the twisted flat steel of the spiral pile. Specifically, as shown in FIG. 8(a), a cylindrical portion 311 capable of accommodating the tip of the spiral pile is fixed to one end of the connecting portion 312 of the connecting member (metal fitting 310). It is preferable that the tip of the spiral pile accommodated in the cylindrical portion 311 is set so that the twisted portion of the spiral portion includes at least half a turn. The other end of the connecting portion 312 is joined to a fixing portion 313 that is fixed to the joist. When the metal fitting 310 is fixed to the joist, the spiral pile is held tilted with respect to the vertical direction of the ground, so the cylindrical portion 311 is fixed to the connecting portion 312 at an angle.

Figure 8 (b) shows the state in which the spiral pile is fixed to the connection member. However, the connecting part 312 in Figure 8 (a) uses a rotating connection part as shown in Patent Document 2. Specifically, the connecting part is divided into two parts (reference numbers 312-1 and 312-2), and the two are rotatably connected by a rotating shaft 312-3. By using such a rotating connection part, even if the angle at which the spiral pile is buried changes, it is possible to respond with the same connecting part. In addition, as described in Patent Document 2, the head of the spiral pile can be moved horizontally in response to the vertical movement of the joist, and the spiral pile can be pressed against the ground.

In the case of the spiral pile 2 in Figure 3, as the joist 1 sinks, the spiral pile 2 exerts an upward pushing force close to the dashed line B, so the joist 1 is pushed to the left in the figure. Also, in the case of the spiral pile 2 in Figure 4, the longer the pile is, the greater the force that tries to return it from the position of the dashed line C to the position of the dashed line A, and the force that pulls the joist 1 to the right in the figure acts. In this way, since horizontal forces act on the joists using the construction method of the joist foundation of the present invention, it is preferable to use multiple spiral piles and adopt a configuration in which the horizontal forces cancel each other out.

In FIG. 9, two spiral piles (2, 2') are arranged facing each other with respect to one joist 1, and are fixed to the joist 1 with connecting members (3, 3'). With this configuration, the horizontal force applied to the joist 1 by one spiral pile can be set to be cancelled by the other spiral pile. Furthermore, as shown in FIG. 10, when the joist 1 is viewed from above in a plan view, as shown in the area from the dashed line to the arrow E in FIG. 10(a), the spiral piles (only the metal fittings fixing the heads of the piles are shown in the figure) can be arranged in positions facing each other with respect to one joist 1. In addition, if more spiral piles can be provided, it is also possible to arrange the spiral piles in a staggered pattern (alternate state) on the left and right of one joist 1, as shown in the area of the dashed line arrow F in FIG. 10(a). Furthermore, as shown in Figure 10(b), it is also possible to determine the arrangement of multiple spiral piles for a joist 1 (a square joist assembly in the figure) assembled on a plane so that the horizontal forces acting on the entire joist 1 cancel each other out. In Figure 10(b), the spiral piles are arranged in opposing positions across the entire joist 1 assembly.

Furthermore, as shown in Figure 11, there is also a method of fixing multiple spiral piles (two in the figure) with one connecting member (metal fitting 3) to counteract the horizontal force generated by the spiral piles. As shown in Figure 11(a), the connecting member (metal fitting 3) has the tip portion of the metal fitting 3 (the portion with the holes (33, 33') for inserting the heads of the spiral piles) bent in different directions. As shown in Figure 11(b), by burying multiple spiral piles (2, 2') in different directions and fixing the bolts at the heads of each spiral pile integrally with one metal fitting 3, it is possible to install an extremely strong and stable foundation.

The spiral pile used in the present invention is not limited to a spiral pile with a bolt welded to the tip of twisted flat steel. As disclosed in Patent Document 3 and shown in Figure 11, it is also possible to use a spiral pile in which a polygonal plate 2f such as a circle or hexagon is welded to the head of twisted flat steel 2a, and the head 2g of a bolt 2b is inserted and fixed into the gap 2e in the head of the flat steel 2a. With the spiral pile in Figure 11, when embedding, it is first screwed in by hand, and then the plate 2f is hit with an impact wrench or the like, making it easy to embed the spiral pile in the ground.

The joist foundation described in this invention can be used as a pile foundation for various structures, but since the foundation can be constructed with simple construction work in a short construction period, it is suitable for use as a pile foundation for simple structures such as agricultural greenhouses for growing agricultural crops, observation towers installed on reclaimed land or tidal flats, and solar panel support racks. Furthermore, the "joist" used in this invention includes not only cross beams for supporting floorboards, but also cross beams for supporting posts without supporting flooring. For example, when applying this invention to the foundation of a simple structure without a floor, such as a vinyl greenhouse for growing agricultural crops, it can also be applied to a pile foundation for installing and fixing cross beams (joists) that run along the ground to support the posts of the greenhouse.

The present invention makes it possible to provide a method for constructing joist foundations that can provide a stable foundation even on soft ground.

1 Joist 2 Spiral pile 3 Connection member (metal fitting)

Claims (1)

A method for constructing a joist foundation in which a joist is fixed to the ground using a spiral pile formed by twisting flat steel,
A method for constructing a joist foundation, comprising: placing a spiral pile in the ground at an angle with respect to both the horizontal plane of the joist and a vertical direction perpendicular to the horizontal plane; and fixing the joist to the head of the spiral pile placed in the ground,
This method for constructing a joist foundation is characterized in that when placing the spiral pile in the ground, the spiral pile is screwed vertically into the ground, and then the head of the spiral pile is pulled toward the joist and fixed to the joist .

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