Method of deriving basic shape of structure method of deriving basic shape of structure

Abstract

To reduce damage to a structure caused by an earthquake without using a dedicated member such as a base isolation device or a vibration damper.SOLUTION: This foundation structure of the structure is buried in the ground, and has a concrete foundation having a rectangular cross section for supporting the structure, and a projecting part projecting downward from a bottom surface of the foundation, having an inclined surface inclined to the horizontal direction, and integrally formed with the foundation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a foundation structure of a structure, a support structure of a structure, a method for deriving a foundation shape of a structure, and a method for deriving a support shape of a structure. [Background technology]

[0002] Patent Document 1 describes an earthquake surface wave breakwater in which wave-dissipating blocks are buried in the surface ground around the outside of a structure, and reflecting plates are driven into the ground at a depth from below the wave-dissipating blocks to the bottom end of the base plate of the structure, thereby suppressing the seismic force caused by surface waves in seismic motion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-080277 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to reduce damage to structures during earthquakes, various methods have been proposed to reduce building response due to input seismic motion, such as seismic isolation structures and vibration control structures. However, these methods require specialized components such as seismic isolation devices and vibration control dampers, which are expensive.

[0005] The object of the present disclosure is to reduce damage to structures that occurs during earthquakes without using dedicated components such as seismic isolation devices or vibration dampers. [Means for solving the problem]

[0006] The foundation structure of the structure according to the first aspect is characterized by having a concrete foundation with a rectangular cross section that is buried in the ground and supports the structure, and a protruding portion that protrudes downward from the bottom surface of the foundation, has an inclined surface that is inclined relative to the horizontal direction, and is formed integrally with the foundation.

[0007] According to the above-described embodiment, seismic waves from below are reflected by the inclined surface of the protrusion, which is inclined relative to the horizontal direction. Here, the proportion of reflected waves is greater than when seismic waves from below strike the foundation at an angle of 0 degrees. In other words, the incident waves that strike the structure are reduced. This makes it possible to reduce damage to the structure during an earthquake without using dedicated components such as seismic isolation devices or vibration dampers.

[0008] The support structure for a structure relating to the second aspect is characterized in that it has a ground improvement body formed in the ground in which the lower end portion of the structure is buried and which supports the structure, and a protruding portion which protrudes downward from the bottom surface of the ground improvement body, has an inclined surface inclined relative to the horizontal direction, and is formed integrally with the ground improvement body.

[0009] According to the above-mentioned aspect, seismic waves from below are reflected by the inclined surface of the protrusion, which is inclined relative to the horizontal direction. Here, the proportion of reflected waves is greater than when seismic waves from below are incident on the ground improvement body at an angle of 0 degrees. In other words, the incident waves incident on the structure are reduced. This makes it possible to reduce damage to structures during earthquakes without using dedicated components such as seismic isolation devices or vibration dampers.

[0010] The method for deriving the foundation shape of a structure according to the third aspect is characterized by comprising the steps of: deriving the natural frequency of the structure; and deriving the thickness of the foundation and the inclination angle of the inclined surface, which is inclined relative to the horizontal direction and has a protruding portion protruding downward from the foundation of the structure, so that the proportion of reflected waves of seismic waves of the natural frequency reflected by the inclined surface is increased.

[0011] According to the above aspect, the thickness of the foundation and the inclination angle of the inclined surface are derived so as to increase the proportion of waves reflected by the inclined surface of the protruding portion that is inclined with respect to the horizontal direction. In other words, it is possible to derive the thickness of the foundation and the inclination angle of the inclined surface that reduce damage to the structure caused by an earthquake.

[0012] The method for deriving the support shape of a structure according to the fourth aspect is characterized by comprising the steps of: deriving the natural frequency of the structure; and deriving the thickness of the ground improvement body and the inclination angle of the inclined surface inclined relative to the horizontal direction of the protruding portion protruding downward from the ground improvement body supporting the structure, so that the proportion of reflected waves of seismic waves of the natural frequency reflected by the inclined surface is increased.

[0013] According to the above-mentioned aspect, the thickness of the ground improvement body and the inclination angle of the inclined surface of the protrusion are derived so as to increase the proportion of reflected waves from the inclined surface that is inclined with respect to the horizontal direction. In other words, it is possible to derive the thickness of the ground improvement body and the inclination angle of the inclined surface that reduce damage to structures caused by earthquakes. [Effects of the Invention]

[0014] According to the present disclosure, damage to structures caused by earthquakes can be reduced without using dedicated components such as seismic isolation devices or vibration dampers. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a schematic diagram illustrating a foundation structure of the structure according to the first embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing an embodiment model used in analyzing the foundation structure of the structure according to the first embodiment of the present disclosure. [Figure 3] 1 is a drawing showing, in a table, the physical property values ​​of the foundation, first layer, second layer, and third layer used in the analysis of the foundation structure of the structure according to the first embodiment of the present disclosure. [Figure 4] FIG. 2 is a schematic diagram showing a foundation structure of a structure according to a comparative embodiment to the foundation structure of the structure according to the first embodiment of the present disclosure. [Figure 5] FIG. 2 is a schematic diagram showing a comparative form model used in analysis of a structure according to a comparative form with respect to a foundation structure of the structure according to the first embodiment of the present disclosure. [Figure 6]FIG. 2 is a schematic diagram showing a free ground model used in analyzing the free ground configuration for the foundation structure of the structure according to the first embodiment of the present disclosure. [Figure 7] (A) (B) (C) Analysis results of the foundation structure of the structure according to the first embodiment of the present disclosure, showing graphs of acceleration in response waves for the embodiment model, the comparative form model, and the free ground model. [Figure 8] (A)(B) are graphs showing the analysis results of the foundation structure of the structure according to the first embodiment of the present disclosure, illustrating the ratio of the Fourier amplitude spectrum of the embodiment model to the free ground model, and the ratio of the Fourier amplitude spectrum of the comparative shape model to the free ground model, respectively. [Figure 9] FIG. 10 is a schematic diagram showing a support structure for a structure according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0016] First Embodiment An example of a method for deriving a foundation structure of a structure and a foundation shape of a structure according to an embodiment of the present disclosure will be described with reference to Figures 1 to 8. Note that arrow H shown in each figure indicates the vertical direction, which is the up-down direction of the structure, arrow W shown in each figure indicates the width direction of the structure perpendicular to arrow H and also the horizontal direction, and arrow D shown in each figure indicates the depth direction of the structure perpendicular to arrows H and W and also the horizontal direction.

[0017] The drawings used in the following description are all schematic, and the dimensional relationships between elements, ratios, etc. shown in the drawings do not necessarily correspond to the actual ones.

[0018] (Structure foundation 10) The foundation structure 10 (hereinafter referred to as "foundation structure 10") of the structure in this embodiment is a structure that supports the building main body 50a of the structure 50, as shown in Figure 1, and has a concrete foundation 12 that is buried in the ground G and provided on the structure 50, and a protrusion 20 that protrudes downward from the bottom surface of the foundation 12.

[0019] [Basic 12] As shown in Fig. 1, the foundation 12 constitutes the lower end portion of the structure 50, is buried in the first layer 100a, which is the uppermost layer of the ground G, and has a rectangular cross section. Specifically, the foundation 12 is solid and filled with concrete, with no hollows, and has a side surface 12a facing horizontally. Furthermore, reinforcing bars (not shown) are arranged inside the foundation 12.

[0020] In this embodiment, the ground G is made up of multiple layers, and a first layer 100a, a second layer 100b, a third layer 100c, and a fourth layer 100d are formed in this order from top to bottom in the ground G. The density increases from top to bottom.

[0021] [Protrusion 20] As shown in Fig. 1, the protrusion 20 has an inclined surface 20a that is inclined with respect to the width direction (horizontal direction), is formed integrally with the foundation 12, and is buried in the first layer 100a, which is the uppermost layer of the ground G. When viewed from the depth direction, the protrusion 20 has a triangular shape with its apex pointing downward, and is solid and filled with concrete. Specifically, the protrusion 20, which has a triangular cross section, extends in the depth direction, forming a triangular prism shape extending in the depth direction.

[0022] The concrete base 12 and protruding portion 20 have higher rigidity than the first to fourth layers 100a to 100d. In other words, the concrete base 12 and protruding portion 20 have a higher propagation velocity of seismic waves than the first to fourth layers 100a to 100d.

[0023] In other words, the larger the angle of incidence of seismic waves when they enter the inclined surface 20a formed on the protrusion 20, which has a high propagation speed, the greater the proportion of reflected waves reflected from the inclined surface 20a of the protrusion 20.

[0024] In this configuration, seismic waves from below (arrow A shown in Figure 1) are reflected by the inclined surface 20a of the protrusion 20, and the proportion of reflected waves (arrow C shown in Figure 1) is greater than when the angle of incidence of the seismic waves from below onto the foundation is 0 degrees.

[0025] (Evaluation by simulation) Next, we used simulations using the finite element method to compare how much the shaking of the top surface of the foundation changes when the same seismic waves are incident.

[0026] [Evaluation model] First, the evaluation models will be described. The models used for evaluation were an embodiment model according to this embodiment, a comparative form model according to a comparative form, and a free ground model.

[0027] -Embodiment model- As shown in Fig. 2, the embodiment model of the foundation structure 10 includes a base 12 with a rectangular cross section and two protruding portions 20. The base 12 has a width of 30 m and a thickness of 5 m. The protruding portions 20 have a width of 15 m and a height of 3 m, and the length of the inclined surface 20a of the protruding portions 20 is 8 m. As a result, the angle of incidence of seismic waves incident from below on the inclined surface 20a of the protruding portions 20 is 22°.

[0028] As shown in the table of FIG. 3, the density of the protrusion 20 and the base 12 is 2.3 [t / m 3 ], the S-wave velocity is 2100 [m / s], and the attenuation constant is 0.005. Furthermore, in the first layer shown in Figure 2, the depth is 30.0 [m], the density is 1.7 [t / m 3 ], the S-wave velocity is 200 [m / s], and the attenuation constant is 0.017. In addition, in the second layer shown in Figure 2, the depth is 70.0 [m], the density is 1.8 [t / m 3], the S-wave velocity is 300 [m / s], and the attenuation constant is 0.013. Furthermore, in the third layer shown in Figure 2, the depth is 120.0 [m], the density is 1.8 [t / m 3 ], the S-wave velocity is 400 [m / s], and the attenuation constant is 0.007.

[0029] -Comparative morphological model- As shown in Fig. 4, a foundation 60 of a structure according to a comparative example (hereinafter referred to as "foundation 60") has no protrusions, and as shown in Fig. 5, a comparative example model of foundation 60 has a foundation 62 with a rectangular cross section. Foundation 62 has a width of 30 m and a thickness of 5 m. This ensures that the angle of incidence of seismic waves incident on foundation 62 from below is 0°.

[0030] As shown in the table of Fig. 3, the density, S-wave velocity, and attenuation constant of the foundation 62 in the comparative model are the same as those in the embodiment model. Furthermore, the depth, density, S-wave velocity, and attenuation constant of the first, second, and third layers in the comparative model shown in Fig. 5 are the same as those in the embodiment model.

[0031] -Free ground model- The free ground model does not have a foundation, as shown in Fig. 6. As shown in the table of Fig. 3, the depth, density, S-wave velocity, and attenuation constant of the first, second, and third layers in the free ground model shown in Fig. 6 are the same as those in the embodiment model.

[0032] [Evaluation method and items] When the Ministry of Construction's notification wave (extremely rare earthquake) was input to the bottom of the third layer of each model, the foundation top surface response wave in the embodiment model and the comparison model, as well as the ground surface response wave in the free ground model, were evaluated.

[0033] [Evaluation results] Figure 7(A) shows a graph of the response waves on the foundation surface of the embodiment model, Figure 7(B) shows a graph of the response waves on the foundation surface of the comparative model, and Figure 7(C) shows a graph of the ground surface response waves on the free ground model. Specifically, the vertical axis of the graph is the acceleration of the response waves [cm / s 2 ] and the horizontal axis of the graph is time [sec].

[0034] As can be seen from a comparison of the graphs shown in FIG. 7, the acceleration of the response waves decreases in the order of the free ground model, the comparative model, and the embodiment model.

[0035] 8(A) shows a graph of the ratio of the Fourier amplitude spectrum of the embodiment model to the free ground model, and FIG. 8(B) shows a graph of the ratio of the Fourier amplitude spectrum of the comparative form model to the free ground model. Specifically, the vertical axis of the graph represents the ratio of the Fourier amplitude spectrum, and the horizontal axis of the graph represents the period [s].

[0036] 8(A) and 8(B), for seismic waves with a period of 0.2 s, the ratio of the Fourier amplitude spectra of the embodiment model is 0.6, while the ratio of the Fourier amplitude spectra of the comparative model is 0.75. In other words, for seismic waves with a period of 0.2 s, the amplitude of the response waves of the embodiment model is reduced to about 80% of the amplitude of the response waves of the comparative model.

[0037] Furthermore, for seismic waves with a period of 0.3 [s], the ratio of the Fourier amplitude spectra of the embodiment model is 0.8, while the ratio of the Fourier amplitude spectra of the comparative model is 0.9. In other words, for seismic waves with a period of 0.3 [s], the amplitude of the response waves of the embodiment model is reduced to about 90 [%] of the amplitude of the response waves of the comparative model.

[0038] 1 and 4, if arrow A represents a seismic wave, arrow B represents an incident wave that has entered the structure, and arrow C represents a reflected wave that has been reflected from the foundation structures 10 and 60, the proportion of incident waves that are incident on the structure 50 by the foundation structure 10 according to the present embodiment shown in Fig. 1 is smaller than the proportion of incident waves that are incident on the structure by the foundation structure 60 according to the comparative embodiment shown in Fig. 4. In other words, the proportion of reflected waves that are reflected by the foundation structure 10 according to the present embodiment shown in Fig. 1 is larger than the proportion of reflected waves that are reflected by the foundation structure 60 according to the comparative embodiment shown in Fig. 4.

[0039] (Method of deriving the basic shape of a structure) Next, a method for deriving the foundation shape of a structure (hereinafter referred to as "foundation shape derivation method") will be described. Specifically, seismic waves from below are reflected by the inclined surface 20a of the protrusion 20. A method for deriving the foundation shape will be described, which derives the thickness of the foundation 12 and the inclination angle of the inclined surface 20a so that the proportion of the reflected waves is increased.

[0040] First, the natural frequency of the structure is derived through known simulations. In other words, the frequency of seismic waves that easily shake the structure is derived. In other words, the frequency of reflected waves that can suppress the shaking of the structure by reflecting them is derived.

[0041] Furthermore, as described in the above-mentioned "Evaluation by Simulation," an embodiment model, a comparative form model without a protrusion, and a free ground model without a foundation are created. Then, the ratio of the Fourier amplitude spectrum of the embodiment model to the free ground model is compared with the ratio of the Fourier amplitude spectrum of the comparative form model to the free ground model, and it is determined at which frequency the amplitude is reduced.

[0042] Furthermore, for the embodiment model, the inclination angle of the inclined surface is changed to multiple values ​​and the thickness of the foundation is changed to multiple values, and the foundation thickness and inclination angle of the inclined surface that effectively reduce the amplitude at the natural frequency of the structure are derived.

[0043] (summary) As described above, in the foundation structure 10, seismic waves from below (arrow A in FIG. 1 ) are reflected by the inclined surface 20a of the protruding portion 20. The proportion of reflected waves (arrow C in FIG. 1 ) is greater than when the angle of incidence of seismic waves from below onto the foundation is 0 degrees. In other words, the proportion of incident waves that are incident onto the structure 50 is smaller than when the angle of incidence of seismic waves from below onto the foundation is 0 degrees. This makes it possible to reduce damage to the structure 50 that occurs during an earthquake without using dedicated components such as seismic isolation devices or vibration dampers.

[0044] In addition, in the method for deriving the foundation shape, the thickness of the foundation 12 and the inclination angle of the inclined surface 20 a are derived so as to increase the proportion of the reflected waves reflected by the inclined surface 20 a. In other words, it is possible to derive the thickness of the foundation 12 and the inclination angle of the inclined surface 20 a that reduce damage to the structure 50 that occurs during an earthquake.

[0045] Second Embodiment An example of a support structure for a structure and a method for deriving a support shape for a structure according to an embodiment of the present disclosure will be described.

[0046] (Support structure 110 of the structure) The support structure 110 (hereinafter referred to as the "support shape") for the structure in this embodiment is a structure that supports the structure 150, as shown in Figure 9, and is composed of a ground improvement body 200a and a protrusion 210.

[0047] [Structures 150] 9, the structure 150 has a building main body 150a and a concrete foundation 150b that supports the building main body 150a. The foundation 150b has a rectangular cross section.

[0048] [Soil improvement body 200a, protrusion 210] 9, the ground improvement body 200a is formed from ground improvement soil, and the foundation 150b of the structure 150 is buried in the ground improvement body 200a. Here, the ground improvement soil is soil that has the required strength, for example, obtained by mixing and stirring a cement-based solidification material and surface ground soil.

[0049] The protruding portion 210 protrudes downward from the bottom surface of the ground improvement body 200a, has an inclined surface 210a that is inclined relative to the horizontal direction, and is formed integrally with the ground improvement body 200a. In other words, the protruding portion 210 is formed from ground improvement soil. Furthermore, the protruding portion 210 has a triangular cross section and extends in the depth direction, forming a triangular prism shape extending in the depth direction.

[0050] As a result, the ground improvement body 200a and the protruding portion 210 have higher rigidity than the second layer 200b provided below the ground improvement body 200a, the third layer 200c provided below the second layer 200b, and the fourth layer 200d provided below the third layer 200c. In other words, the ground improvement body 200a and the protruding portion 210 have a higher propagation velocity of seismic waves than the second layer 200b, the third layer 200c, and the fourth layer 200d. In other words, in the ground improvement body 200a and the protruding portion 210, which have a high propagation velocity of seismic waves, the proportion of reflected waves increases as the angle of incidence of seismic waves increases.

[0051] In this configuration, seismic waves from below (arrow A in FIG. 9) are reflected by the inclined surface 210a of the protrusion 210. The proportion of reflected waves (arrow C in FIG. 9) is greater than when the angle of incidence of the seismic waves from below onto the ground improvement body is 0 degrees.

[0052] (Method of deriving the support shape of a structure) Next, a method for deriving the support shape of a structure (hereinafter referred to as "support shape derivation method") will be described. Specifically, seismic waves from below are reflected by the inclined surface 210a of the protrusion 210. A support shape derivation method will be described, which derives the thickness of the ground improvement body 200a and the inclination angle of the inclined surface 210a so that the proportion of these reflected waves is increased.

[0053] First, the natural frequency of the structure is derived through known simulations. In other words, the frequency of seismic waves that easily shake the structure is derived. In other words, the frequency of reflected waves that can suppress the shaking of the structure by reflecting them is derived.

[0054] Furthermore, taking into consideration the contents described in "Evaluation by Simulation" in the first embodiment, an embodiment model, a comparative model without protrusions, and a free ground model without soil improvement bodies or protrusions are created. Then, the ratio of the Fourier amplitude spectrum of the embodiment model to the free ground model is compared with the ratio of the Fourier amplitude spectrum of the comparative model to the free ground model, and it is determined at which frequency the amplitude is reduced.

[0055] Then, for the embodiment model, the inclination angle of the inclined surface is changed to multiple values, and the thickness of the ground improvement body is changed to multiple values, and the thickness of the ground improvement body and the inclination angle of the inclined surface that effectively reduce the amplitude at the natural frequency of the structure are derived.

[0056] (summary) As explained above, in the support structure 110 for a structure, seismic waves from below (arrow A in FIG. 9 ) are reflected by the inclined surface 210a of the protrusion 210, and the proportion of reflected waves (arrow C in FIG. 9 ) is greater than when the angle of incidence of the seismic waves is 0 degrees. In other words, the proportion of incident waves that enter the structure 150 is smaller than when the angle of incidence of the seismic waves is 0 degrees. This makes it possible to reduce damage to the structure 150 that occurs during an earthquake without using dedicated components such as seismic isolation devices or vibration dampers.

[0057] Furthermore, in the method for deriving the support shape, the thickness of the ground improvement body 200a and the inclination angle of the inclined surface 210a are derived so as to increase the proportion of the reflected waves reflected by the inclined surface 210a. In other words, it is possible to derive the thickness of the ground improvement body 200a and the inclination angle of the inclined surface 210a that reduce damage to the structure 150 that occurs during an earthquake.

[0058] While the present disclosure has been described in detail with respect to specific embodiments, it will be apparent to those skilled in the art that the present disclosure is not limited to such embodiments and that various other embodiments are possible within the scope of the present disclosure. For example, in the above embodiments, the inclined surface is a flat surface, but it may be a curved surface or the like as long as it is inclined relative to the horizontal direction.

[0059] Furthermore, in the above embodiment, the protrusions 20, 210 are triangular prisms extending in the depth direction, but they may be protrusions protruding in a lattice pattern from the bottom surface as long as they have an inclined surface.

[0060] In addition, although the above embodiment does not specifically mention the number of protrusions 20, 210, the number may be one or two or more. When there are two or more protrusions, the embedding depth can be made shallower than when there is one protrusion.

[0061] Furthermore, in the second embodiment, no particular description was given regarding the range of the soil improvement body 200a in the horizontal direction, but it is sufficient that the soil improvement body 200a covers the structure 150 when viewed from above.

[0062] Furthermore, although not specifically explained in the above embodiment, the thickness of the foundation (ground improvement body) and the size of the inclined surface can be designed according to the natural frequency of the structure to be reflected, and the angle at which total reflection occurs can be set using geometrical optics theory or numerical simulation, taking into account the physical properties of the foundation and the ground directly below the foundation. [Explanation of symbols]

[0063] 10 Foundation structure (foundation structure of structure) 12 Basics 20 Protrusion 20a Slope 110 Support structure (support structure of structure) 150 Structures 200a Ground improvement body 210 Protrusion 210a Slope

Claims

1. a concrete foundation with a rectangular cross section that is buried in the ground and supports the structure; a protruding portion that protrudes downward from the bottom surface of the foundation, has an inclined surface that is inclined with respect to the horizontal direction, and is formed integrally with the foundation; The foundation structure of a structure having

2. A ground improvement body formed in the ground, in which a lower end portion of a structure is buried and which supports the structure; A protruding portion protruding downward from the bottom surface of the ground improvement body, having an inclined surface inclined with respect to the horizontal direction, and formed integrally with the ground improvement body; A support structure for a structure having the above structure.

3. deriving the natural frequency of the structure; a step of deriving a thickness of the foundation and an inclination angle of the inclined surface of the protruding portion protruding downward from the foundation of the structure so that a proportion of reflected waves of seismic waves of the natural frequency reflected by the inclined surface inclined with respect to the horizontal direction is increased; A method for deriving the basic shape of a structure comprising:

4. deriving the natural frequency of the structure; A step of deriving the thickness of the ground improvement body and the inclination angle of the inclined surface so that the proportion of reflected waves of seismic waves of the natural frequency is increased by the inclined surface inclined with respect to the horizontal direction of the protruding portion protruding downward from the ground improvement body supporting the structure; A method for deriving a support shape of a structure comprising:

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