JP6972870B2 - How to design a shaft during an earthquake - Google Patents

Description

The present invention relates to a method for designing a shaft at the time of an earthquake for constructing a shaft having a defect in the main body of the shaft in the ground.

Conventionally, when performing seismic design to construct a cylindrical shaft that is an underground structure, for example, as described in Patent Document 1, the shaft body is modeled in two dimensions, and the response displacement method or 2 A method is used in which the seismic performance is checked after confirming the response during an earthquake by two-dimensional FEM analysis, and the members are determined so that the response value such as the cross-sectional force generated in the shaft body is less than the allowable value such as the bearing capacity of the shaft. ing.

Japanese Unexamined Patent Publication No. 2008-133595

However, when the shaft body has a defect, a verification method for verifying seismic performance has not been established. At present, when confirming the response of the shaft body, the part having the defect (the range of 45 degrees in the radial direction from the axis of the shaft body including the defect when the shaft body is viewed from the plan view) is regarded as the part where the external force is not transmitted. Deemed, the response value is calculated only in the part where there is no defective part excluding these. Then, the shear strength of the portion having the defect is determined so as to exceed this response value.

For this reason, it is difficult to make a rational design for the part of the shaft body that has a defect, and the reinforcement structure around the defect has an excessively thick member or the shear reinforcement becomes overcrowded. The structure was inferior in economic efficiency.

Further, when the defective portion is provided facing the same depth with respect to the shaft main body, as described above, the portion having the defective portion is regarded as a member to which the external force is not transmitted and excluded. Therefore, when modeled, it resists the shearing force. The part does not exist. For this reason, in order to install a tunnel so as to penetrate the shaft, if an opening that is a joint with the tunnel is provided facing the shaft at the same depth, the current seismic design method can cope with it. Instead, we have no choice but to take measures such as installing different depths for the tunnels that join the shaft.

The present invention has been made in view of the above problems, and a main object thereof is to provide a shaft having a defect in the main body of the shaft to be constructed in the ground, which can be rationally seismically designed. It is to provide a design method at the time of an earthquake.

In order to achieve such an object, the shaft earthquake design method of the present invention is a shaft earthquake design method for constructing a shaft having a defect in the shaft body in the ground, and is vertical of the shaft body. The direction is modeled in two dimensions as a vertical beam with equivalent rigidity, and the step of calculating the response value at the time of an earthquake, the step of estimating the shear strength of the shaft body, and the estimated shear strength and the response. It has a step of evaluating the seismic performance by comparing with the value, and the shear strength of the shaft body is measured at the short side of the shaft body and the defect portion on the elevation view on which the shaft body is projected. The opening ratio is calculated based on the maximum length in the direction parallel to the short side, the reduction rate set in advance corresponding to the opening ratio, and the entire plan view cross section with no defect in the shaft body. It is characterized by estimating based on the shear strength of.

Further, in the method for designing a shaft at the time of an earthquake of the present invention, the reduction ratio is the ratio of the proof stress of the state where the shaft has the defect to the state where the shaft has no defect, and the resistance ratio is the ratio. It is characterized in that a plurality of calculations are made by changing the aperture ratio and set from the relationship between the aperture ratio and the proof stress ratio.

According to the above-mentioned method for designing a shaft at the time of an earthquake, the shaft has a defect based on the shear strength of the entire cross section in a plan view with no defect and a preset reduction ratio corresponding to the aperture ratio. Estimate the shear strength of the shaft body.

As a result, it is possible to set an appropriate shear strength according to the opening diameter of the defective portion with respect to the outer diameter of the shaft main body for the shaft main body having the defective portion, so that the shaft can be rationally designed.

Further, since the shear strength can be secured in the shaft body not only when there is only one defect but also when there are two defects, the two defects to be provided in the shaft body, such as so-called double-sided openings, are the same. Even when it is desired to arrange the shaft facing the depth, it is possible to evaluate the seismic performance of the shaft body. This makes it possible to expand the linear options for tunnels that will be joined to the shaft.

According to the present invention, for a shaft having a defect in the shaft body to be constructed in the ground, an appropriate shear strength is set according to the opening diameter of the defect with respect to the outer diameter of the shaft body, and a rational design is made. Can be done.

It is a flow chart of the design method at the time of an earthquake of a shaft in embodiment of this invention. It is a figure which shows the shaft body and the vertical beam model in embodiment of this invention. It is a figure which shows the 3D analysis model of the shaft body in embodiment of this invention. It is a figure which shows the examination case at the time of carrying out the 3D nonlinear analysis of the shaft body in embodiment of this invention. It is a figure which shows the shear stress distribution at the time of the maximum load when the shearing force is applied to the shaft body in embodiment of this invention. It is a figure which shows the damage state of the concrete when the shearing force is applied to the shaft body in the embodiment of this invention. It is a figure which shows the yield state of the shear reinforcing bar when the shearing force is applied to the shaft body in embodiment of this invention. It is a figure which shows the analysis model at the time of changing the size of the defect part with respect to the outer diameter of the shaft body in 4 steps in embodiment of this invention. It is a figure which shows the relationship between the aperture ratio and the proof stress ratio when the 3D nonlinear analysis of the shaft body in the embodiment of this invention is carried out in the study case 1 (reference case). It is a figure which shows the relationship between the aperture ratio and the proof stress ratio when the 3D nonlinear analysis of the shaft body in the embodiment of this invention was carried out in study cases 1-5.

The method for designing a shaft at the time of an earthquake of the present invention is a suitable design method when attempting to construct a shaft having a defect in the shaft body in the ground. The procedure is the same as the conventional design method, in which structural analysis is performed in the vertical direction of the shaft body to check the seismic performance, and then structural analysis is performed in the horizontal direction of the shaft body to evaluate the seismic performance. However, the present invention is a method characterized by a method for verifying seismic performance.

Hereinafter, according to the flow of the flow chart shown in FIG. 1, the method of designing the shaft at the time of an earthquake will be described in detail with reference to FIGS. 2 to 9.

As shown in FIG. 2A, the shaft 1 is a reinforced concrete underground structure constructed so as to extend the shaft body 2 having a cylindrical body having a circular cross section in the vertical direction in the ground, and is a shield tunnel. It is used for starting or reaching shafts, underground station building structures, shafts connecting to tunnels, etc.

Further, in the vicinity of the lower end portion of the shaft main body 2, two defective portions 3 are provided so as to face each other at the same depth. These defects 3 are formed in a circular hole-shaped closed opening, and are joints with linear underground structures extending laterally in the ground, such as tunnels, sewage pipes, power line and communication line caverns, etc. Functions as.

<STEP 1: Vertical structural analysis of the shaft body>
In carrying out the structural analysis of the shaft body 2 of the shaft 1 described above in the vertical direction, first, the design conditions of the shaft body 2 (for example, the member thickness of the shaft body 2, the reinforcing bar arrangement, the compressive strength of the concrete, and the defective portion 3) are first performed. Set the size, position, etc. of

Next, the shaft body 2 is modeled in two dimensions, and assuming that the shaft body 2 has no defect portion 3, the response value, specifically, the displacement at the time of an earthquake and the displacement by the response displacement method, the two-dimensional FEM analysis, etc. Calculate the section force (bending moment, shear).

In the present embodiment, when modeling the shaft body 2 in two dimensions, as shown in FIG. 2 (b), a plurality of beam elements having equivalent rigidity as a whole are modeled as a beam in which a plurality of beam elements are continuously connected in the vertical direction. ing. As the rigidity to be set at this time, the rigidity obtained by the wall of the shaft body 2 per unit width is generally adopted, but in the present embodiment, the plan view cross section of the shaft body 2 as shown in FIG. 2 (c) is adopted. Set to the overall rigidity.

Regarding the height range in which the defective portion 3 is located, such as the BB cross section shown in FIGS. 2 (b) and 2 (c), the rigidity of the entire plan view cross section in which the defective portion 3 does not exist as in the AA cross section is determined by BB. The rigidity of the cross section is set, and it is assumed that the model of the shaft body 2 has no defective portion 3.

The response value calculated using such a vertical beam model is the response value of the entire vertical cross section of the shaft body 2 without the defect portion 3, but the seismic performance is checked in <STEP 3> described later. As the permissible value used in this case, the permissible value of the entire plan view cross section of the shaft main body 2 in consideration of the influence of the defective portion 3 is used.

Therefore, in <STEP2>, a method of calculating the shear strength Vd'of the entire cross section in a plan view will be described among the allowable values of the shaft body 2.

<STEP2: Estimating the shear strength Vd'of the shaft body>
When estimating the shear strength Vd'of the shaft body 2 having the defective portion 3, first, as shown in FIG. 2 (d), the shaft body 2 is projected from the elevation in the vertical direction. The short side r _{0 and the maximum length r 1} of the defective portion 3 in the direction parallel to the short side r ₁ are calculated. The aperture ratio R is calculated from the mathematical formula (1) based on _{the short side r 0} of the shaft body 2 and the maximum length r _{1 of the defective portion 3.}
R = r ₁ / r ₀ ... (1)
r ₀ : Short side on the elevation of the shaft body 2
r ₁ : Maximum length of defect 3 in the direction parallel to the short side r ₀

In the present embodiment, since the shaft body 2 is a tubular body having a circular cross section and the defect portion 3 is circular, the outer diameter of the shaft body 2 is the short side r of the shaft body 2 on the elevation view. _{It corresponds to 0,} and the opening diameter of the defective portion 3 corresponds to _{the maximum length r 1 of the defective portion 3.} Further, the mathematical formula (1) is a case where two defective portions 3 are present in the shaft main body 2, and when there is one defective portion 3, the aperture ratio R of the above mathematical formula (1) may be divided by 2. ..

Next, the shear strength Vd of the entire cross section in a plan view with no defect 3 in the shaft body 2 is calculated (see mathematical formula (2)).
Vd = Vc + Vs ... (2)
Vd: Shear strength of the shaft body 2 without the defect 3.
Vc: Shear force of concrete
Vs: Shear force of the shear reinforcement

Then, the shear strength Vd of the entire cross section in a plan view without the defective portion 3 is multiplied by the reduction ratio D set in advance corresponding to the aperture ratio R. The calculated value thus calculated is estimated as the shear strength Vd'of the shaft body 2 having the defective portion 3 (see mathematical formula (3)).
Vd'= D × Vd ・ ・ ・ ・ (3)
Vd': Shear strength of the shaft body with a defect
D: Reduction rate set corresponding to the aperture ratio R

The reduction ratio D is a quantity set corresponding to the aperture ratio R, and is the shear strength Vd'of the shaft body 2 having the defect portion 3 with respect to the shear strength Vd of the entire plan view cross section without the defect portion 3. It can be obtained by the mathematical formula (4) derived from the relationship between the yield strength ratio (Vd'/ Vd), which is the ratio of the above, and the aperture ratio R. The calculation method of the reduction rate D will be described later.
D = α (1-R) + β ... (4)
α, β: Parameters for evaluating shear strength

<STEP3: Seismic performance check>
After that, the response values calculated in <STEP 1> and the permissible values of the shaft 2 are compared for each of the bending moment and the shear force, in the same manner as the seismic design method of the shaft, which has been conventionally carried out as a seismic performance check. At this time, since the shaft body 2 is modeled as a beam in which a plurality of beam elements are continuously connected in the vertical direction in the present embodiment, the response value generated in each beam element in the seismic performance verification of the shear force is performed. Check the cross-sectional force, which is the allowable value, and the shear strength, which is the allowable value.

Then, among the beam elements continuous in the vertical direction, the shear strength Vd'estimated in <STEP2> is adopted as an allowable value when checking the beam element at the height position where the defect portion 3 is provided.

If it is determined in the above seismic performance check that the safety and function of the shaft body 2 cannot be maintained after the earthquake, the process returns to the process of setting the design conditions of the shaft body 2 and the design conditions are changed as appropriate. Repeat the examination of. On the other hand, if it is determined that the safety and function of the shaft 2 can be maintained, a horizontal structural analysis of the shaft body 2 is performed.

<STEP 4 and 5: Horizontal structural analysis and seismic performance verification>
Horizontal structural analysis and seismic performance verification of the shaft body 2 may be performed by the same procedure as the conventional seismic design method, and the general part and the defect in the shaft body 2 where the defect 3 does not exist and the defect For each of the openings in which the part 3 is located, a two-dimensional frame analysis is performed to calculate the cross-sectional force which is the response value.

After that, as a seismic performance check, the calculated response value and the allowable value of the shaft body 2 are compared for each of the bending moment and the shearing force. If it is determined in these seismic performance checks that the safety and function of the shaft body 2 cannot be maintained, the process returns to the process of setting the design conditions of the shaft body 2, and the design conditions are changed as appropriate in the vertical direction of the shaft body 2. Repeat the examination from the structural analysis of. On the other hand, if it is determined that the safety and function of the shaft main body 2 can be maintained, the shaft main body 2 is determined under the current design conditions.

According to the above-mentioned method for designing a shaft at the time of an earthquake, it is possible to set an appropriate shear strength according to the aperture ratio R for the shaft body 2 having the defective portion 3, so that the shaft 1 can be rationally designed. It will be possible.

Further, since the shear strength Vd'can be secured in the shaft body 2 not only when there is only one defect 3 but also when there are two, there are two defects with respect to the shaft body 2 such as so-called double-sided openings. Even when it is desired to provide the portions 3 facing each other at the same depth, it is possible to evaluate the seismic performance of the shaft main body 2. This makes it possible to expand the linear options for the tunnel to be joined to the shaft 1.

Next, the procedure for deriving the reduction rate D and the method for calculating the optimum reduction rate D will be described in detail below.

<Calculation method of reduction rate D>
First, for the shaft 1 having the defective portion 3 in the shaft body 2, as shown in FIG. 3, the concrete, the main reinforcing bar, and the distribution reinforcing bar constituting the shaft body 2 are modeled in three dimensions, respectively, and the behavior until shear failure. Is grasped by three-dimensional nonlinear analysis. In this embodiment, the material nonlinear finite element analysis is adopted as the three-dimensional nonlinear analysis.

In carrying out this analysis, the cross-sectional shape of the shaft body 2 was set to a circular cylinder, and the shape of the defect 3 was set to a circular hole-shaped opening, and the design conditions were as shown in the study case of FIG. bottom. In addition, when modeling the shaft body 2 in three dimensions, the vertical displacement of the top of the analysis model was constrained and the bottom surface was fixed so that bending fracture did not precede.

In the same procedure as above, a three-dimensional nonlinear analysis was performed for the shaft 1a in the state where the shaft body 2 has no defect 3 in order to understand the behavior up to the shear failure. 5 (a) and 5 (b) show the central positions of the shaft body 2 and the defect 3 when a load acts on each of the shafts 1 and 1a in a direction parallel to the opening surface of the defect 3. The shear stress distribution at the maximum load in the horizontal cross section is shown.

In the shaft body 2 where the shear stress is predominant, in the shaft 1a without the defect portion 3, when looking at FIG. 5A, the location where the shear stress is predominant is distributed diagonally according to the shear deformation, whereas the defect portion 3 is distributed. Looking at FIG. 5B in the shaft 1 having the shaft 1, it can be seen that shear stress is flowing diagonally above the defect portion 3 and to the left and right of the defect portion 3 below the defect portion 3.

Further, the shear stress in the horizontal cross section at the center position of the defect portion 3 is large in the range parallel to the load acting direction of the shaft body 2 in FIG. 5A in the shaft 1a without the defect portion 3. You can see the situation. On the other hand, in FIG. 5B in the shaft 1 having the defective portion 3, it can be seen that the shaft 1 has an increase in the range orthogonal to the load acting direction of the shaft main body 2.

In the shaft body 2 having the defect portion 3 in this way, the shearing force is transmitted to a range orthogonal to the load acting direction of the shaft body 2 adjacent to the defect portion 3 via the vicinity of the upper portion of the shaft body 3 in the shaft body 2. Has been done. Therefore, it can be said that the shear strength can be ensured for the entire shaft body 2 even when the two defective portions 3 are present at the same depth while facing the shaft body 2.

Next, FIGS. 6 (a) and 6 (b) show the state of concrete damage at the maximum load leading to shear failure in the shaft body 2, and FIGS. 7 (a) and 7 (b) show the state of shear failure in the shaft body 2 of the shaft 1. The damage status of the horizontal reinforcing bar at the maximum load up to is shown.

Regarding the state of concrete damage, in the shaft 1a without the defective portion 3, when looking at FIG. 6A, the entire shaft body 2 is sheared and deformed. On the other hand, in FIG. 6B in the shaft 1 having the defective portion 3, it can be seen that the deformation is concentrated in the vicinity of the defective portion 3 and the concrete is compressed and softened around the defective portion 3.

Regarding the damage status of the shear reinforcing bar, in the shaft 1a without the defective portion 3, when looking at FIG. 7A, the yield range is diagonally distributed in the entire shaft main body 2 according to the shear deformation. On the other hand, in FIG. 7B in the shaft 1 having the defective portion 3, it can be seen that the distribution of the yield range according to the shear deformation is generated in the vicinity of the defective portion 3.

As a result, the shaft body 2 of the shaft 1 having the defect portion 3 has the shaft body 2 of the shaft 1a in a state where there is no defect portion 3 due to the concentration of shear deformation around the defect portion 3 in which the concrete or the reinforcing bar is defective. It can be said that the shear strength Vd'is lowered as compared with the above.

Next, in order to understand the relationship between the aperture ratio R and the shear strength Vd', the shaft 1 having the defect portion 3 in the shaft body 2 has been described above as shown in FIGS. 8 (a) to 8 (d). Four shafts 1 having different aperture ratios R, in which the opening diameter of the defective portion 3 was changed in four stages, corresponding to the maximum length r _{1 of the defective portion 3, were prepared.} Then, for the shaft 1a without these and the defective portion 3, the behavior up to the shear failure is grasped by the three-dimensional nonlinear analysis by the same procedure as above, and the maximum load leading to the shear failure in the load displacement relationship is grasped. do.

In the present embodiment, this maximum load is treated as shear strength Vd'and Vd, and the results are obtained by representing the aperture ratio R on the horizontal axis and the proof stress ratio (Vd'/ Vd) on the vertical axis as shown in FIG. It was plotted on the graph taken.

Looking at the graph of FIG. 9, the proof stress ratio (Vd'/ Vd) decreases as the aperture ratio R increases, and the linear relationship between the aperture ratio R and the proof stress ratio (Vd'/ Vd) can be seen. be able to. Therefore, the proof stress ratio (Vd'/ Vd) is expressed by a linear function based on the aperture ratio R, and this is defined as the reduction ratio D (see (4) above). Thereby, the reduction ratio D corresponding to the aperture ratio R can be calculated by appropriately substituting the quantity corresponding to the aperture ratio R into the mathematical formula (4).

Further, the inventors have found that in the shaft body 2 having the defect portion 3, the shear strength Vd'is affected by at least the member thickness of the shaft body 2, the shear reinforcing bar ratio, the compressive strength of concrete, and the number of openings. Is getting. Therefore, we prepared an analysis model of the shaft body 2 with the design conditions changed as appropriate for these four points, and performed a three-dimensional nonlinear analysis in the same procedure as above to grasp the shear strength Vd'from the maximum load leading to shear failure. The results were plotted in the graph shown in FIG.

Specifically, three-dimensional nonlinear analysis was carried out for each of the four types of shafts 1 shown in FIGS. 8 (a) to 8 (d) under the eight design conditions of the study cases 1 to 5 in FIG. Each study case is based on Case 1, Cases 2-1 and 2-2 are member thicknesses, Cases 3-1 and 3-2 are shear reinforcement ratios, and Cases 4-1 and 4-2 are concrete compressive strengths. Was changed respectively.

Further, the case 5 has the same member thickness, shear reinforcement ratio and concrete strength as the reference case 1, but has only one defective portion 3. In addition, in order to calculate the yield strength ratio (Vd'/ Vd) under all the above design conditions, the shear strength Vd is also calculated for the shaft body 2 assuming that there is no defect portion 3.

Looking at the graph of FIG. 10, it can be seen that in any of the cases 2 to 5, there is a generally linear relationship between the aperture ratio R and the proof stress ratio (Vd'/ Vd). Further, since the inclinations of the cases 2 to 5 are different from those of the standard case 1, the member thickness of the shaft body 2, the shear reinforcement ratio, the compressive strength of the concrete, and the quantity of the defective portion 3 each have a proof stress ratio. It can also be confirmed that (Vd'/ Vd) is affected. Furthermore, among Cases 2 to 4, the difference in linear inclination is remarkable between Case 3-1 and Case 3-2 in which the quantity of the shear reinforcement ratio is changed, and the shear reinforcement ratio is the proof stress ratio (Vd). It can be seen that it has a great influence on'/ Vd).

Therefore, when setting the reduction rate D, it is a parameter α according to the member thickness of the shaft body 2 in the shaft 1 to be constructed, the shear reinforcement ratio, the compressive strength of concrete, the quantity of the defective portion 3, and the like. And β (see the above equation (4)) may be appropriately adjusted to set the optimum reduction rate D according to the design conditions of the shaft 2. The adjustment method of α and β may be either, but for example, α or β is set as the objective variable, and the member thickness of the shaft body 2, the shear reinforcing bar ratio, the compressive strength of concrete, and the quantity of the defective portion 3 are used as explanatory variables. It is also conceivable to perform multiple regression analysis and set the reduction rate D.

In this way, when calculating the shear strength Vd'of the shaft body 2 using the mathematical formulas (3) and (4), the member thickness of the shaft body 2 to be constructed, the shear reinforcing bar ratio, the compressive strength of concrete, and the defect portion 3 By using the optimum reduction rate D according to the design conditions of the shaft 2 such as the quantity, the shaft 1 can be designed more rationally.

In the present embodiment, the member thickness of the shaft body 2 used in Cases 2-1 and 2-2 includes the member thickness (1.0 to 2.5 m) of the existing deep shaft, and Case 3-. The shear reinforcement ratios used in 1 and 3-2 include the minimum and maximum values specified in the concrete standard specification. As for the concrete strength used in cases 4-1 and 4-2, examination cases are set in consideration of the application of high-strength concrete.

Therefore, in the graph of FIG. 10, the alignment showing the relationship between the aperture ratio R and the proof stress ratio (Vd'/ Vd) is located at the position including all the plots of Cases 1 to 5, that is, below these plots. Α and β are determined, and the reduction ratio D is set. By doing so, at least, the shear strength Vd'standing on the safe side can be set with respect to the member thickness of the shaft main body 2, the shear reinforcing bar ratio, the compressive strength of concrete, and the number of defective portions 3.

The broken line shown in the graph of FIG. 10 is α = 1, β = 0, and when α and β are set in the range of at least α ≦ 1 and β ≧ 0, the shear strength Vd'of the shaft body 2 having the defect portion 3 is set. It will be possible to carry out a safe seismic performance check. When α = 1 and β = 0 are adopted, from the mathematical formulas (3) and (4), the shear strength Vd'of the shaft body 2 having the defective portion 3 is calculated by the following mathematical formula (5) as the aperture ratio R. Can be estimated by substituting.
Vd'= (1-R) x Vd ... (5)

In the conventional seismic design method, the above-mentioned mathematical formula (2) is applied mutatis mutandis when calculating the shear strength Vd'of the shaft body 2 having one defective portion 3. In this case, the portion of the shaft body 2 where the defect 3 is present (when viewed from the plan view of the shaft body 2, the range of 45 degrees in the radial direction from the axis of the shaft body 2 including the defect 3 (FIG. 5 (FIG. 5). b))) is not treated as a shear transfer member. Therefore, when the shearing force Vc in charge of concrete is set by the mathematical formula (6), the abdominal width bw is halved for calculation.
Vc = (τ _al b _w z) ・ ・ ・ ・ (6)
τ _al : Short-term allowable shear stress of concrete
b _w : Width of the abdomen of the member cross section
z = d / 1.15
: Distance from the point of action of total compressive stress to the center of gravity of the tensile reinforcing bar cross section

Then, since the quantity of the shear force Vc that the concrete is responsible for is underestimated, if the required shear strength Vd'is to be secured without changing the member thickness of the shaft body 2, the shear force Vs that the shear reinforcing bar is responsible for is increased. There was no choice but to make the shear reinforcements overcrowded, which was uneconomical.

However, in the earthquake design method of this implementation, since the shear force Vd'is secured in the entire shaft body 2, the shear force Vc in charge of concrete can be appropriately evaluated without underestimating, which is compared with the conventional seismic design method. Therefore, the shearing force Vs of the shear reinforcing bar can be reduced. This makes it possible to reduce the amount of reinforcement of the shear reinforcing bars and design a rational and economical design.

The method for designing a shaft at the time of an earthquake of the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention.

For example, in the present embodiment, a cylinder is adopted as the cross-sectional shape of the shaft main body 2, but the present invention is not necessarily limited to this, and any cylindrical body such as a square cylinder may be used.

Further, the shape of the defect portion 3 is not necessarily limited to a circular hole shape, and may be any shape such as a horseshoe shape as long as it is closed. Further, if the position of the defective portion 3 is near the lower end portion of the shaft main body 2, one defective portion 3 is provided in the vertical shaft main body 2 such as a so-called one-sided opening, or two defective portions 3 such as double-sided openings are provided in the vertical shaft main body. Either of the cases where the two are provided facing the same depth may be used.

In addition, in the present embodiment, the response value of the entire plan view cross section of the shaft main body 2 without the defective portion 3 is calculated in <STEP 1>, but the response value is not necessarily limited to this. For example, the response value of the entire vertical cross section corresponding to the aperture ratio R of the shaft main body 2 having the defective portion 3 may be calculated and the cross-sectional force may be used for the seismic performance verification of <STEP 3>.

1 Shaft 1a Shaft 2 Shaft body 3 Missing part

Claims (2)

It is a method of designing a shaft at the time of an earthquake to construct a shaft with a defect in the main body of the shaft in the ground.
The process of two-dimensionally modeling the vertical direction of the shaft body as a vertical beam with equivalent rigidity and calculating the response value at the time of an earthquake.
The process of estimating the shear strength of the shaft body and
It has a step of comparing the estimated shear strength with the response value to evaluate seismic performance.
The shear strength of the shaft body is calculated based on the short side of the shaft body and the maximum length of the defect in the direction parallel to the short side on the elevation view of the shaft body. However, at the time of an earthquake in the shaft, it is estimated based on a reduction rate preset corresponding to the aperture ratio and the shear strength of the entire plan view cross section in a state where the shaft body has no defect. Design method. The method for designing a shaft at the time of an earthquake according to claim 1.
The reduction rate is
The ratio of the shear strength in the state of having the defect to the state without the defect in the shaft body is defined as the yield strength ratio, and a plurality of the proof stress ratios are calculated by changing the aperture ratio.
A method for designing a shaft at the time of an earthquake, which is set from the relationship between the aperture ratio and the proof stress ratio.

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