Design method of foundation footing

Abstract

To accurately calculate a bar arrangement amount required for a main reinforcement of a foundation footing when a position of a semi-fixed pile does not match a position of a column.SOLUTION: A distance in a vertical direction from upper surfaces of foundation beams 15a and 15b to an upper surface of a pile 12 is acquired. A distance in a ±X direction from a pile reaction core of the pile 12 to a column core 41 of a column 14 is acquired. A column axial force that the column 14 should support is acquired. A quotient obtained by dividing a product obtained by multiplying the column axial force by the distance in the ±X direction by the distance in the vertical direction to get a reinforcing force required in the ±X direction. The reinforcement bar arrangement amount of the base reinforcement 31 is calculated based on the reinforcing force thus calculated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for designing a foundation footing semi-fixed to piles. [Background technology]

[0002] Patent Document 1 discloses a support structure for a structure foundation using piles that fit into the inside of a concave bearing portion provided on the bottom surface of the structure foundation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-162259 Summary of the Invention [Problem to be solved by the invention]

[0004] The position of the piles that support the building does not necessarily coincide with the position of the building's columns. If the center position of the semi-fixed pile does not coincide with the center position of the column, the load will be eccentric, so there is no established method for accurately calculating the strength required for reinforcing the foundation footing. The present invention aims to solve such problems, for example. [Means for solving the problem]

[0005] The foundation footing design method is a method for designing a foundation footing semi-fixed to piles. The foundation footing has main reinforcement and is arranged between the pile and a column fixed to the foundation footing. The main reinforcement is arranged near the bottom end of the foundation footing above the top end surface of the pile. The method obtains the vertical distance from the top end surface of a foundation beam fixed to the column and the foundation footing to the top end surface of the pile. The distance in a predetermined horizontal direction from the pile reaction center of the pile to the column center of the column is obtained. The column axial force to be supported by the column is obtained. The quotient obtained by multiplying the column axial force by the predetermined distance in the horizontal direction and dividing the product by the distance in the vertical direction is used as the reinforcing force required in the predetermined horizontal direction. The reinforcing amount of the main reinforcement is calculated based on the calculated reinforcing force. [Effects of the Invention]

[0006] According to the foundation footing design method, when the position of the semi-fixed pile does not match the position of the column, the amount of reinforcement required for the main reinforcement of the foundation footing can be accurately calculated. Since sufficient strength can be obtained using only the main reinforcement, there is no need to reinforce with braces or other reinforcement, which improves the workability of the foundation footing and reduces the construction costs of the building. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 10 is a side cross-sectional view showing an example of a foundation structure. [Figure 2] FIG. [Figure 3] FIG. 10 is a perspective view showing an example of pile reaction force distribution and reaction force core. DETAILED DESCRIPTION OF THE INVENTION

[0008] 1 and 2, the base structure 10 will be described. The foundation structure 10 includes, for example, piles 12, a foundation footing 13, columns 14, and foundation beams 15a to 15d.

[0009] The piles 12 extend in the vertical direction (±Z direction) and support the building. The piles 12 may be newly installed, or may be piles from an old building that has not yet been rebuilt, for example, in a rebuilding project. The pillar 14 is disposed above the pile 12, but the pillar center 41 of the pillar 14 does not necessarily have to be directly above (in the +Z direction) the pile center 21 of the pile 12. For example, the pillar 14 may be disposed at a distance e x , in the Y direction (which is an example of a horizontal direction perpendicular to the predetermined horizontal direction and is also an example of the predetermined horizontal direction), by a distance e y It's off. The foundation beams 15a to 15d extend from the lower end portions of the pillars 14 in the ±X and ±Y directions.

[0010] The foundation footing 13 is disposed between the piles 12 and the columns 14. The foundation footing 13 is fixed to the columns 14 and foundation beams 15a to 15d, but is not fixed to the piles 12, but is semi-fixed via, for example, caps (not shown). Therefore, when a compressive force is applied between the foundation footing 13 and the piles 12, the compressive force is transmitted, but when a tensile force is applied, the tensile force is not transmitted. The foundation footing 13 has, for example, base reinforcement 31 (an example of main reinforcement). However, the foundation footing 13 does not have splay reinforcement. Because the foundation footing 13 does not have splay reinforcement, it does not have reinforcement that connects the foundation footing 13 to the splay reinforcement. In other words, the reinforcement of the foundation footing 13 is flat, not cage-shaped. Note that reinforcement for fixing the columns 14 and foundation beams 15a to 15d to the foundation footing 13, such as reinforcement continuing from the main reinforcement of the columns 14 and foundation beams 15a to 15d, is not shown in the figure, but is present within the foundation footing 13 as usual.

[0011] The base reinforcement 31 is arranged above the upper end surface of the pile 12 and near the lower end of the foundation footing 13, and includes, for example, horizontal reinforcement 32a to 32f and vertical reinforcement 33a to 33f. The horizontal bars 32a to 32f are substantially linear reinforcing bars extending substantially parallel to the ±Y directions and are arranged at intervals in the ±X directions. The vertical reinforcements 33a to 33f are substantially straight reinforcing bars extending substantially parallel to the ±X directions, are spaced apart in the ±Y directions, and are fixed to the horizontal reinforcements 32a to 32f. The vertical reinforcements 33a to 33f may be arranged above or below the horizontal reinforcements 32a to 32f.

[0012] Next, a method for calculating the amount of reinforcement of the base reinforcement 31 will be described. As described above, since the column center 41 of the column 14 is misaligned with the pile center 21 of the pile 12, a larger force is applied to the base reinforcement 31 than when the column center 41 of the column 14 and the pile center 21 of the pile 12 are aligned. For this reason, it is necessary to increase the amount of reinforcement of the base reinforcement 31. Therefore, the amount of reinforcement (reinforcement amount) that should be increased for the base reinforcement 31 in order to obtain sufficient strength is calculated. For example, the reinforcing amount of the vertical reinforcements 33a to 33f is calculated according to the following procedure.

[0013] First, to calculate the amount of reinforcement required for the long-term load under normal conditions, the long-term axial force NCL that the column 14 must support is obtained. Here, the long-term axial force NCL is a force acting vertically downward (in the -Z direction) through the column 14, and can be calculated based on the structural calculations of the building. Next, the vertical distance D between the upper end surfaces of the foundation beams 15a to 15d and the upper end surfaces of the piles 12 (i.e., the difference between the height of the upper end surfaces of the foundation beams 15a to 15d and the height of the upper end surfaces of the piles 12) is obtained. Furthermore, the distance e in the ±X direction between the column center 41 of the column 14 and the pile reaction center of the pile 12 x The pile reaction center is the line of action on which the resultant reaction force from the top end face of the pile acts, and if the reaction force is uniformly distributed on the top end face of the pile, it passes through the center of gravity of the top end face of the pile in the plan view sense. In other words, the pile reaction center coincides with the pile center 21 of the pile 12. Usually, the pile center 21 is designed to coincide with the column center 41, so the distance e x should be 0, but in reality, there is a construction error in pile 12, so the distance e xwill not be 0. Therefore, for example, if the expected construction error (for example, 10 cm) is x In addition, when reusing existing piles or when it is difficult to align the column center 41 and the pile core 21 due to environmental influences, the column center 41 may be designed to be offset from the pile core 21 from the beginning. In that case, for example, the distance e can be calculated by adding an expected construction error (for example, 10 cm) to the designed distance between the column center 41 and the pile core 21. x Calculate.

[0014] The long-term axial force NCL acting vertically downward via the column 14 is supported by a reaction force from the upper end surface of the pile 12. The reaction force from the upper end surface of the pile 12 is a force acting vertically upward, and as described above, this resultant force acts vertically upward from the pile core 21 of the pile 12. Because the pile core 21 of the pile 12 and the column center 41 of the column 14 do not coincide, it is thought that the strut compressive force STL acts diagonally along the diagonal strut core 16 connecting the column center 41 of the column 14 and the pile core 21 of the pile 12, between the upper end surfaces of the foundation beams 15a to 15d and the upper end surfaces of the pile 12. The component force STL in the ±Z direction of this strut compression force STL z is equal to the long-term axial force NCL, so

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[0015] The vertical reinforcement 33a to 33f of the base reinforcement 31 is subjected to this component force STL x It must be reinforced to support the STL. x is the long-term reinforcement force required for the vertical reinforcements 33a to 33f. And, the long-term reinforcement amount AtL of the vertical reinforcements 33a to 33f is x is the long-term reinforcement force STL x The long-term allowable stress of the rebar is ftL (e.g., 215 N / mm 2 ) is calculated by dividing by

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[0016] The same calculation is performed for horizontal bars 32a to 32f, and the long-term reinforcement force STL of horizontal bars 32a to 32f is calculated. y and long-term reinforcement amount AtL y Calculate.

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[0017] Next, to calculate the amount of reinforcement required for the short-term load when an earthquake occurs, the short-term axial force NCS that the column 14 must support is obtained. The short-term axial force NCS is calculated, for example, by adding the load NCE generated by the earthquake to the long-term axial force NCL that the column 14 must support.

[0018] Furthermore, the distance e in the ±X direction between the column center 41 of the column 14 and the pile reaction center of the pile 12 x In the case of a long-term load, the pile reaction center is assumed to coincide with the pile center 21, and the distance in the ±X direction between the column center 41 of the column 14 and the pile center 21 of the pile 12 is defined as the distance e x However, when an earthquake occurs, the pile reaction force is not distributed evenly on the upper end surface of the pile 12, so the pile reaction force center does not coincide with the pile core 21.

[0019] The pile reaction core 22 will be described with reference to FIG. If an earthquake applies a horizontal force to a building, causing it to vibrate along the shaking direction 91, the pile reaction force will have an uneven distribution 92, while the value of the overall resultant force 93 will remain unchanged. That is, at a certain moment, the pile reaction force will be large on the side of the building that shook along the shaking direction 91, and small on the opposite side. Then, when the building sways to the opposite side, the side where the pile reaction force was large will become small, and the opposite side will become large. This process will be repeated until the vibration ends. Therefore, at a certain moment, the pile reaction force core 22 is positioned at a position displaced from the pile core 21 in the direction along the shaking direction 91. In this way, the distance e between the pile core 21 and the pile reaction core 22 e changes in the short term as the building shakes due to the earthquake. e is largest when the pile reaction force is distributed so that it becomes 0 at one end. This is because the pile 12 is semi-fixed, so the pile reaction force cannot become smaller than 0. If the upper end surface of the pile 12 is rotationally symmetrical about the pile core 21, the distance e e The maximum value of is the same in any direction, but if the pile 12 is not rotationally symmetric, it will differ depending on the direction.

[0020] Since it is not known where an earthquake will occur, the shaking direction 91 at the time of the earthquake is unknown. However, the distance e between the column center 41 and the pile reaction center 22 along the ±X direction x becomes maximum when the shaking direction 91 is parallel to the ±X direction. Furthermore, this is the case when the distance between the column center 41 and the pile core 21 and the distance between the pile core 21 and the pile reaction force center 22 are added together rather than being cancelled out. For example, if the pile core 21 is located on the -X side of the column center 41 as in the example of Figure 1, the pile reaction force becomes 0 at the +X side end of the top surface of the pile 12 and becomes maximum at the -X side end, and the distance e x Conversely, when the pile core 21 is located on the +X side of the column core 41, the pile reaction force becomes 0 at the end of the -X side of the top surface of the pile 12 and becomes maximum at the end of the +X side. x becomes maximum.

[0021] As mentioned above, the amount of reinforcement required for the vertical reinforcements 33a to 33f is determined by the distance e x is proportional to the distance e x It is sufficient to calculate it based on the maximum value of Therefore, assuming that the pile reaction force applied from the top end surface of the pile 12 to the foundation footing 13 is distributed in the ±X direction so that it becomes 0 at the end closer to the column center 41 of the column 14 and becomes maximum at the end farther from the column center 41 of the column 14, the position of the center of gravity of the pile reaction force is calculated as the position of the pile reaction force core 22, and based on the calculated position of the pile reaction force core 22, the distance e x Calculate.

[0022] Based on the calculated values, the short-term reinforcement force STS required for the vertical reinforcement 33a to 33f is calculated. x and vertical reinforcement 33a to 33f short-term reinforcement AtS x Calculate.

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[0023] Similarly, for the horizontal bars 32a to 32f, the short-term reinforcement force STS of the horizontal bars 32a to 32f y and short-term reinforcement amount AtS y Calculate.

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[0024] The foundation footing 13 must be able to withstand both long-term loads and short-term loads due to earthquakes. Therefore, the calculated long-term reinforcement amount and short-term reinforcement amount are compared, and the larger one is determined as the required reinforcement amount. In other words, the reinforcement amount At x is the amount of long-term reinforcement AtL x and short-term reinforcement AtS x The larger of these is the amount of reinforcement At of horizontal bars 32a to 32f. y is the amount of long-term reinforcement AtL y and short-term reinforcement AtS y It is the larger of the two.

[0025] In this way, the amount of reinforcement for the base reinforcement 31 is determined. As a result, sufficient strength can be obtained with the base reinforcement 31 alone, so there is no need to reinforce it with braces or the like. This improves the workability of the foundation footing 13 and reduces the cost of building construction.

[0026] The above calculations may be performed using a device specially designed to perform such calculations (an example of a foundation footing design device), or may be performed by a general-purpose computer running a computer program specially programmed to perform such calculations.

[0027] The above-described embodiment is an example for facilitating understanding of the present invention. The present invention is not limited thereto, and includes various modifications, changes, additions, or omissions without departing from the scope defined by the appended claims. This can be easily understood by those skilled in the art from the above description.

[0028] The foundation footing, where the pile head reinforcement is fixed, is subject to complex stress exchanges, so reinforcement is arranged to encase the outer periphery of the footing in a cage-like manner. In contrast, semi-rigid piles without pile head reinforcement do not require the same reinforcement arrangement for the foundation footing as fixed piles. This is because semi-rigid piles do not have rebar at the pile head, and the force exchange between the pile and the superstructure is a very simple one, consisting only of compressive force. In other words, no complex force exchange occurs. Therefore, in the case of semi-fixed pile heads, the force required for reinforcing the foundation footing is calculated from the mechanical relationship with the columns and other structural members, and the reinforcement of the foundation footing is limited to the base reinforcement only, with other reinforcement being eliminated. The amount of reinforcement required at the bottom end of the feeding column for the long term due to pile eccentricity, AtL, is calculated as follows: If the total strut compressive force generated between the pile and column due to long-term eccentricity is STL (however, the first floor foundation beam shear force QFGL and the footing weight are considered to flow directly to the pile and are therefore excluded from the strut axial force), then:

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[0029] 10 Foundation structure, 12 Pile, 13 Foundation footing, 14 Column, 15a-15d Foundation beam, 16 Strut core, 21 Pile core, 22 Pile reaction core, 31 Base reinforcement, 32a-32f Horizontal reinforcement, 33a-33f Vertical reinforcement, 41 Column core, 91 Sway direction, 92 Distribution, 93 Resultant force.

Claims

1. A method for designing a foundation footing semi-fixed to piles, comprising: The foundation footing has a main reinforcement and is disposed between the column fixed to the foundation footing and the pile; The main reinforcement is arranged above the upper end surface of the pile and near the lower end of the foundation footing, The method comprises: The vertical distance from the upper end surface of the foundation beam fixed to the column and the foundation footing to the upper end surface of the pile is obtained; A predetermined horizontal distance from the pile reaction center of the pile to the column center of the column is obtained, Obtain the column axial force that the column should support, The product of the column axial force and the predetermined distance in the horizontal direction is multiplied and divided by the distance in the vertical direction to calculate the quotient, which is the reinforcement force required in the predetermined horizontal direction, Calculate the reinforcing amount of the main reinforcement based on the calculated reinforcing force. Foundation footing design methods.

2. The main reinforcement has a plurality of vertical reinforcements extending in the predetermined horizontal direction and a plurality of horizontal reinforcements extending in a horizontal direction perpendicular to the predetermined horizontal direction, The method comprises: Obtain the allowable stress of the vertical reinforcement, The quotient obtained by dividing the reinforcing force by the allowable stress is calculated as the reinforcing amount of the vertical reinforcement. The foundation footing design method of claim 1.

3. The method comprises: As the reinforcement force, a long-term reinforcement force against a long-term load and a short-term reinforcement force against a short-term load due to an earthquake are calculated, As the allowable stress of the vertical reinforcement, a long-term allowable stress for a long-term load and a short-term allowable stress for a short-term load are obtained, The quotient obtained by dividing the long-term reinforcement force by the long-term allowable stress is calculated as the long-term reinforcement amount, and the quotient obtained by dividing the short-term reinforcement force by the short-term allowable stress is calculated as the short-term reinforcement amount, The larger of the calculated long-term reinforcement amount and short-term reinforcement amount is set as the reinforcement amount of the vertical reinforcement. The foundation footing design method of claim 2.

4. In calculating the long-term reinforcement force, The position of the pile core of the pile is acquired as the position of the pile reaction core of the pile, As the column axial force to be supported by the column, a long-term axial force to be supported by the column is obtained. The foundation footing design method of claim 3.

5. In calculating the short-term reinforcement force, Assuming that the pile reaction force applied to the foundation footing from the upper end surface of the pile is distributed so that it becomes 0 at the end closer to the column center in the predetermined horizontal direction and becomes maximum at the end farther from the column center in the predetermined horizontal direction, calculate the position of the center of gravity of the pile reaction force and set it as the position of the pile reaction force center, Calculate the short-term column axial force that the column should support during an earthquake and use it as the column axial force that the column should support. A method for designing a foundation footing according to claim 3 or 4.

6. A computer program that, when executed by a computer, implements the foundation footing design method according to any one of claims 1 to 4.

7. A foundation footing design device that implements the foundation footing design method according to any one of claims 1 to 4.

8. In foundation footings that are semi-fixed to piles, The foundation footing has a main reinforcement and is disposed between the column fixed to the foundation footing and the pile; The main reinforcement is arranged above the upper end surface of the pile and near the lower end of the foundation footing, The main reinforcement has a plurality of vertical reinforcements extending in a predetermined horizontal direction and a plurality of horizontal reinforcements extending in a horizontal direction perpendicular to the predetermined horizontal direction, The reinforcing amount of the main reinforcement is the quotient obtained by multiplying the column axial force to be supported by the column by the predetermined horizontal distance from the pile reaction center of the pile to the column center, and dividing the product by the vertical distance from the upper end surface of the foundation beam fixed to the column and the foundation footing to the upper end surface of the pile, and dividing the reinforcing force required in the predetermined horizontal direction by the allowable stress of the vertical reinforcement. Foundation footing.

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