JP7064286B2 - Design method of reinforcement structure of existing structure and reinforcement structure of existing structure - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act ▲ 1 ▼ Publication date November 7, 2016 Publications Proceedings of the 26th Tunnel Engineering Research Presentation, "Study on Evaluation of Residual Reinforcement of Shield Tunnel and Reinforcement Design", Japan Society of Civil Engineers Tunnel Engineering Committee ▲ 2 ▼ Publication date January 20, 2017 Publications Electrical Review January 2017 Issue Electrical Review Co., Ltd.

The present invention relates to a method for designing a reinforcing structure for reinforcing an existing structure according to the degree of deterioration of the existing structure, and a reinforcing structure for the existing structure.

Some of the existing structures such as shield tunnels deteriorate due to aging, and there is a risk that the strength will decrease in the future. Non-Patent Document 1 describes a method of newly constructing a reinforcing segment inside an existing tunnel structure.

Takao Ochiai, Yoshita Tsuburaya, Osamu Sakata, Eiichi Tanaka, "New Inner Winding Reinforcement Method in Electricity Cable Tunnel Repair Work", 1999, Tunnel and Underground, Vol. 30, No. 1, pp. 46-52 Yukio Shioji, Yukihiro Naito, Kenichi Anan, Masahiro Otsuka, Atsushi Koizumi "Study on Reinforcement of Shield Tunnels Aged", 2011, JSCE Proceedings, F1 (Tunnel Engineering) 67 (2), pp. 62-78

Structures such as existing shield tunnels have different degrees of deterioration depending on the place and time of construction. For structures that have progressed in deterioration, it is desirable to take reinforcement measures according to the degree of progress in deterioration. According to the method described in Non-Patent Document 1, a reinforcing segment is newly established regardless of the progress of deterioration of the existing tunnel structure. Therefore, in the method described in Patent Document 1, when the degree of deterioration of the existing tunnel structure is small, excessive reinforcement is performed even when a small amount of reinforcement is sufficient, and as a result, the cost becomes excessive. There is a risk that it will end up. In order to properly reinforce, it is necessary to accurately grasp the degree of deterioration of the existing structure and take measures according to the degree of deterioration.
It is an object of the present invention to provide a method for designing reinforcement of an existing structure and a reinforcing structure for the existing structure, which can take reinforcement measures according to the degree of deterioration of the existing structure.

The method for designing a reinforcing structure of an existing structure according to an embodiment of the present invention is as follows.
An initial displacement amount calculation step for obtaining a first displacement amount generated by a first load applied to the existing structure based on a first design curve showing the relationship between the load acting on the existing structure and the displacement amount.
A post-deterioration load calculation step for obtaining a second load that causes the first displacement amount based on a second curve showing the relationship between the load acting on the existing structure in a assumed deteriorated state and the displacement amount.
The present invention includes a reinforcing structure strength calculation step of calculating the strength of the reinforcing structure for reinforcing the existing structure based on the difference between the first load and the second load.

With such a configuration, the present invention obtains a second load, which is a virtual load applied to the existing structure in the deteriorated state, from the second curve showing the state of the existing structure in the deteriorated state, and refers to the load history. And the design of the reinforcing structure can be done rationally.

The present invention further shows the relationship between the load acting on the reinforced existing structure and the displacement amount, with the second load in the first displacement amount as the initial value after the reinforcing structure is installed. 3 The post-reinforcement curve calculation process to obtain the curve and
A future displacement amount calculation process for calculating a future displacement amount with respect to an assumed future load based on the third curve, and a future displacement amount calculation process.
May be further provided.

With such a configuration, the present invention can be designed so that the proof stress against the external force after reinforcement is taken over by the existing structure and the reinforcing structure, and the reinforcing structure can be rationally designed.

The present invention further uses the existing structure and the reinforcing structure in which the stress generated in the main body of the existing structure and the reinforcing structure under the load state based on the future load and the future displacement amount is modeled. The stress calculation process that calculates based on the structural analysis model that was used,
May be further provided.

With such a configuration, the present invention can calculate the stress according to the shape of a specific existing structure.

The present invention further comprises a determination step of determining the yield strength of the reinforcing structure designed based on the calculated stress based on the response value generated with respect to the dynamic load applied to the reinforcing structure. It may be configured.

With such a configuration, the present invention can evaluate the safety of the reinforced structure by determining the calculated proof stress of the reinforced structure.

In the present invention, the post-deterioration load calculation step further determines the second curve.
A distribution curve determination step for determining a distribution curve showing the distribution of residual amounts of a plurality of structural members constituting the existing structure, and a distribution curve determination step.
A parameter calculation process for calculating parameters that change the distribution curve over time, and
Even if it is configured to further include a structural member residual amount estimation step for statistically estimating the residual amount of the structural member in the future based on the distribution curve calculated by the corresponding parameter after the lapse of a predetermined period. good.

With such a configuration, the present invention can estimate the residual amount of the structural member that corrodes due to aging, and can estimate the load state of the existing structure in a deteriorated state in the future.

The present invention further comprises a design process according to the above design method.
A method for constructing a reinforcing structure of an existing structure may be configured by comprising a reinforcing step for constructing the reinforcing structure designed in the design process.

With such a configuration, the present invention can obtain a construction method for constructing a reinforcing structure with respect to an existing structure at the site.

The reinforcing structure of the existing structure according to the embodiment of the present invention is continuously arranged along the tunnel axial direction at the top end of the inner empty wall of the pipeline structure, and is arranged along the circumferential direction of the inner empty wall. And the upper support part that is arranged
A lower support portion that is continuously arranged along the tunnel axial direction at the lower end of the inner empty wall and is arranged along the circumferential direction of the inner empty wall.
It is arranged at a predetermined interval along the tunnel axial direction, and includes a plurality of support columns for connecting the upper support portion and the lower support portion.

With such a configuration, the present invention can construct a reinforcing structure of an existing structure.

According to the method for designing a reinforcing structure of an existing structure and the reinforcing structure of an existing structure according to the present invention, reinforcement measures can be taken according to the degree of progress of deterioration of the existing structure.

It is a perspective view which shows a part of the shield tunnel which concerns on embodiment. It is a perspective view which shows the structure of the segment of a shield tunnel. It is a perspective sectional view which shows the state of the shield tunnel reinforced by the reinforced structure. It is a histogram showing the distribution of the plate thickness of the main reinforcing bar of the segment of the existing shield tunnel. It is a histogram showing the distribution of the plate thickness of the main reinforcing bar of the segment of other existing shield tunnels. It is a figure which shows the parameter of the median value, the mode value, and the probability density function of the corrosion amount of a main reinforcing bar. It is a figure which shows the change of the distribution of the probability density function shown by the parameter which changes with time. It is a graph which shows the relationship between a variable load ratio and a lateral earth pressure coefficient. It is a graph which shows the relationship between the number of cracks and a variable load ratio. It is a graph which shows the load state of a shield tunnel without deterioration and a tunnel in the future. It is a graph which shows the load which a reinforcement structure bears by a general design method. It is a graph which shows the load which a reinforcement structure should bear. It is a graph which shows the effect of reinforcement by a reinforcement structure. It is a graph which shows the future load applied to a reinforcement structure. It is a graph which shows the overload ratio of a main reinforcing bar. It is a graph which shows the load history used in the design method of a reinforced structure. It is a figure which shows the state which applied the load to the structural analysis model for structural analysis. It is a figure which shows the state which applied the load to the structural analysis model for structural analysis. It is a figure which shows the state which applied the load to the structural analysis model for structural analysis. It is a figure which shows the state which applied the load to the structural analysis model for structural analysis. It is a figure which shows the relationship between the bending moment M and the curvature generated in the segment after deterioration. It is a figure which shows the specification of the reinforcement structure used for the structural analysis. It is a figure which shows the result of the numerical value obtained by the structural analysis. It is the figure which graphed the result obtained by the structural analysis. It is a figure which shows the check limit value of a segment. It is a figure which shows the check limit value of a reinforced structure. It is a figure which shows the check value of a segment. It is a figure which shows the check value of a reinforced structure. It is a figure which shows the arrangement relation of the reinforcement structure. It is a flowchart which shows the design method of a reinforced structure.

Hereinafter, a method for reinforcing and designing an existing structure according to an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the structure targeted for reinforcement measures is, for example, an existing shield tunnel 10. The shield tunnel 10 has a plurality of curved segments G. The shield tunnel 10 is constructed by sequentially fitting and connecting a segment G manufactured in advance into a hole drilled by a shield machine for excavating a tunnel having a circular cross section. At that time, a ring R in which a plurality of segments G are connected in an annular shape is formed. A tunnel wall is constructed by sequentially continuing the formed rings R, and the shield tunnel 10 is completed.

As shown in FIG. 2, the segment G is curved to be part of a tunnel wall with a circular cross section. The segment G has a reinforced concrete (RC) structure in which the reinforcing bar S is covered with concrete and reinforced. The reinforcing bar S of the segment G has a main reinforcing bar S1 that takes charge of the main load applied to the segment G and a distribution reinforcing bar S2 that distributes the load. The main reinforcing bar S1 is a strip-shaped flat steel (flat bar (FB)). The main reinforcing bar S1 is a plate-shaped structural member serving as a tensile reinforcing bar. The distribution reinforcing bar S2 is, for example, a steel rod such as a deformed reinforcing bar.

The main reinforcing bar S1 is a curved strip-shaped body having a thickness of about several mm (for example, 6 mm) and a width of about several centimeters. The segment G has, for example, two layers of a pair of main reinforcing bars S1 arranged in parallel. Further, the segment G has a large number of force distribution reinforcing bars S2 arranged orthogonally to the pair of main reinforcing bars S1. The segment G is generated by covering a reinforcing bar S composed of a plurality of main reinforcing bars S1 and a plurality of distribution reinforcing bars S2 with a concrete portion C. That is, the segment G is an FB segment in which the main reinforcing bar S1 is a flat bar.

Some shield tunnels using segment G whose main reinforcing bar is flat steel have been constructed for more than 30 years. In the underground environment, the segment G may deteriorate over time due to the occurrence of rust or the like, resulting in insufficient strength, and reinforcement measures may be required. For example, in the shield tunnel 10, there is a case where the reinforcing bar S of the segment G is deformed or corroded, and there is a possibility that the yield strength of the entire structure of the shield tunnel 10 will decrease in the future.

Here, if uniform reinforcement measures are taken for the segment G, there is a risk that the cost will increase due to excessive reinforcement, or the force will be applied to the segment G in a direction different from the direction assumed in the design. There is. Therefore, rational reinforcement measures will be taken for the existing shield tunnel 10 according to the degree of future deterioration of the segment G assumed. Specifically, a columnar reinforcing structure 30 is formed inside the shield tunnel 10 to reinforce the shield tunnel 10.

As shown in FIG. 3, the reinforcing structure 30 has a columnar body having an I-shaped cross section, which is installed in a row inside the shield tunnel 10 in order to reinforce the shield tunnel 10 which is an existing structure. The reinforcing structure 30 reinforces the shield tunnel 10 in which the main reinforcing bar S1 of the segment G is corroded due to aged deterioration and the yield strength is lowered. The reinforcing structure 30 is constructed of, for example, reinforced concrete. The reinforcing structure 30 includes an upper support portion 32 that supports the top plate portion 11 of the shield tunnel 10, a lower support portion 33 formed on a stepbed (invert portion 12) formed in the lower part of the shield tunnel 10, and an upper portion. It has a plurality of support columns 31 that connect the support portion 32 and the lower support portion 33.

The upper support portion 32 is continuously arranged along the tunnel axis L direction at the top end of the inner empty wall of the shield tunnel 10, and is arranged along the circumferential direction of the inner empty wall. The lower support portion 33 is continuously arranged along the tunnel axis L direction at the lower end of the inner empty wall of the shield tunnel 10, and is arranged along the circumferential direction of the inner empty wall. The plurality of column portions 31 are arranged at predetermined intervals between the upper support portion 32 and the lower support portion 33 along the tunnel axis L direction.

Since the reinforcing structure 30 is formed as a columnar body, it can be constructed with the existing equipment such as cables installed in the shield tunnel 10. The reinforcing structure 30 has a shape that allows the maintenance of cables and the like in the shield tunnel 10 by securing a space for an operator even after the structure is constructed. As the reinforcing structure 30, in addition to a columnar body having an I-shaped cross section, for example, an H-shaped cross section, a circular cross section, or the like may be used, and any shape may be used as long as the top plate portion 11 of the shield tunnel 10 can be reinforced according to the principle described later. You may use it.

The reinforcement measures by the reinforcement structure 30 are designed so that the reinforcement structure bears the shortage of the bearing capacity of the segment G caused by the deterioration. The degree of deterioration of segment G is evaluated based on statistical data. The degree of progress of deterioration of the segment G is mainly proportional to the residual amount of the thickness of the main reinforcing bar S1.

First, a statistical method used for evaluating the residual amount of the thickness of the main reinforcing bar S1 will be described. Among the segments G of the shield tunnel 10 to be measured, the number of segments G in which the main reinforcing bar S1 is corroded is measured. 4 and 5 show statistical data in which the thickness of the main reinforcing bar S1 of the shield tunnel 10 to be measured differently and the number of the locations thereof are associated with each other. As shown in the figure, the statistical data is a histogram (columnar graph) showing the thickness of the main reinforcing bar S1 in increments of 0.25 mm. First, set a function that matches this histogram.

ここで、
ｍ，ｓ：確率密度分布のパラメータ
ｘ：腐食量（ｍｍ）
である。 As shown in FIGS. 4 and 5, the distribution of the number of segments G corroded with respect to the thickness (residual amount) of the main reinforcing bar S1 is the design value (6 mm) of the thickness of the main reinforcing bar S1. Concentrated near the value. The distribution of the number of segments G with respect to each thickness of the main reinforcing bar S1 in which corrosion has occurred shall be represented by a probability density function distributed according to the amount of corrosion based on the design value of the thickness of the main reinforcing bar S1. This probability density function is a lognormal distribution with asymmetric distribution shapes on the left and right. In this case, the probability density function representing the lognormal distribution is defined as the following equation (1) as a function of the corrosion amount (= design value-residual amount) of the main reinforcing bar S1.

here,
m, s: Probability density distribution parameter x: Corrosion amount (mm)
Is.

ここで、
median(x):ヒストグラムの中央値
mode(x):ヒストグラムの最頻値
である。 The parameters m and s of the probability density distribution are set to change with time, for example. First, the parameters of the probability density distribution are expressed by the median value and the mode value of the distribution, for example, as shown in the following equation (2).

here,
median (x): Median histogram
mode (x): Mode (x): Mode of the histogram.

ここで、
t：現在からの経年数
median(x_t)：現在からt年後の推定中央値
median(x_p)：現在の中央値
T_p：新設から現在までの経年数
mode(x_t)：現在からt年後の推定最頻値
mode(x_p)：現在の最頻値
m_t，s_t：t年後の確率密度分布のパラメータ
である。 In the calculation of the parameter of the probability density distribution in the equation (2), the parameter related to time is introduced in order to take into consideration the time element that changes over time. Assuming that the amount of corrosion of the main reinforcing bar S1 and the number of years are linearly related, for example, the following equation (3) is set so that the median value and the mode value of the distribution increase in proportion to the years.

here,
t: Number of years since the present
median (x _t ): Estimated median t years from now
median (x _p ): current median
T _p : Number of years from new establishment to the present
mode (x _t ): Estimated mode from now to t years
mode (x _p ): Current mode
m _t , _st : It is a parameter of the probability density distribution after t years.

In the statistical data of FIG. 4, the histogram shape has a distribution of the main reinforcing bar S1 closer to the design plate thickness of 6 mm. When the above equations (1) and (2) are applied to the statistical data of FIG. 4 and verified, the median residual amount of the main reinforcing bar S1 is 4.90 mm (corrosion amount x = 1.10 mm). The mode zone has a residual amount in the range of 5.25 mm to 5.50 mm. As the mode, the average value of the mode band is 5.375 mm (corrosion amount x = 0.625 mm). When this result is applied to the equation (2), the parameters m and s of the probability density distribution are determined to be m = 0.095 and s = 0.752, respectively. When the determined parameters m and s are applied to the equation (1), the curve shape of the distribution curve of the probability density function substantially matches the histogram shape of either FIG. 4 or FIG. However, the above comparison is performed assuming that the peak of the distribution curve, which is the maximum occurrence probability value, corresponds to the peak of the histogram (see FIGS. 4 and 5).

Based on the above formulas (1) to (3), the future residual amount of the main reinforcing bar S1 that deteriorates with time can be set. For example, in the shield tunnel 10 33 years after completion, T _p = 33 years, median (x _p ) = 1.10 mm, mode (x _p ) = 0.625 mm. Based on these values, the median (x _t ) and mode (x _t ) at t = 15, 25, and 35 years later are calculated using Eq. (3), for example, as in Eq. (4) below. Is calculated to.

As shown in FIG. 6, both the median value and the mode value shift to the corrosion side with the passage of time, and the parameters m and s of the probability density distribution also change accordingly. Based on these numerical values, equation (1) can be used to predict the future distribution shape of the probability density function curve after t = 15, 25, 35 years.

As shown in FIG. 7, in the distribution shape of the probability density function curve, the number of points (peak value of the curve) in the mode zone decreases with the passage of time. That is, the probability density function has a large variation over time. This indicates that the corrosion progresses with the aging and the future residual amount of the main reinforcing bar S1 decreases. At this time, the corrosion side standard deviation σ indicating the variation of the histogram is determined by, for example, the following equation (5) using the parameters m and s of the probability density distribution.

Using equation (5), the current standard deviation is 1.272 mm, and the standard deviation 35 years after the current state is 2.622 mm, and the variation is more than doubled. Using the above calculation results, the future prediction of the residual amount of one main reinforcing bar S1 per ring R in the future is performed. According to each of the above equations, it is calculated that the mode of the corrosion amount of the main reinforcing bar S1 after 35 years is 1.29 mm. When the standard deviation of 1σ on the corroded side (2.622 mm) is applied to this value, the amount of corrosion of the main reinforcing bar S1 is calculated to be 3.912 mm.

Here, the design value of the thickness of the main reinforcing bar S1 from 6 mm to 3.912 mm corroded 2.088 mm is adopted as the residual amount after deterioration of the thickness of the main reinforcing bar S1 at one place in the future. At this time, from the nature of the lognormal distribution curve, the probability that the residual amount of the thickness of one main reinforcing bar S1 to be investigated in the future is 2.088 mm or more is calculated to be 87%.

Here, the reason why the corrosion amount that minimizes the residual amount of the thickness of the main reinforcing bar S1 is not adopted is that there is a property peculiar to the structure of the shield tunnel 10. The shield tunnel 10 is located at a depth of, for example, 10 m or more underground, and the ground supports the structure. Therefore, the shield tunnel 10 becomes a high-order statically indeterminate structure, and even if there is a local cross-sectional loss of the main reinforcing bar S1, it does not collapse immediately. Further, the adjacent rings R in the shield tunnel 10 are installed in a staggered arrangement in which the seams between the adjacent segments G appear alternately in the ring R (see FIG. 1).

When the shield tunnel 10 is constructed by arranging the rings R composed of a plurality of segments G in a staggered manner, a shearing force applied from the segments G of the adjacent rings R acts on the joints between the adjacent rings R. As a result, the deformation of the entire ring R is constrained. This is commonly referred to as the collusion effect. Then, due to this splicing effect, the bending moment is transmitted to the segment G via the joint between the rings R. Therefore, even if the thickness of one of the two main reinforcing bars S1 in the segment G is 2.088 mm or less due to the splicing effect, the thickness of the other main reinforcing bar S1 should be larger than 2.088 mm. For example, the structural system of the shield tunnel 10 is maintained.

上記確率は、式（６）に示されるように、９５％以上となる。 Here, the probability that the thickness of one of the main reinforcing bars S1 in the segment G is 2.088 mm or more is calculated. This probability is calculated by, for example, the following equation (6), assuming that one or more of the two adjacent main reinforcing bars S1 are selected.

The above probability is 95% or more as shown in the equation (6).

Therefore, the reliability that the thickness of at least one of the main reinforcing bars S1 remains 2.088 mm or more is 95% or more. To simplify the numerical value to the safe side, it is estimated that the residual amount of the thickness of the main reinforcing bar S1 of the segment G whose deterioration has progressed in the future is 2 mm by the above calculation. That is, it is estimated that even if one of the two adjacent main reinforcing bars S1 disappears, the thickness of the other main reinforcing bar S1 has a residual amount of at least 2 mm.

Therefore, in the case of the most corrosion in the state of the segment G in the future, "one of the two adjacent main reinforcing bars S1 has disappeared, and the thickness of the other main reinforcing bar S1 has been corroded to at least 2 mm. It is estimated that "if". Therefore, in the most corroded situation when considering the entire plurality of segments G of the shield tunnel 10, the residual amount after deterioration of the thickness of the main reinforcing bar S1 is estimated to be 1 mm on average of both. As described above, the residual amount after deterioration of the thickness of the main reinforcing bar S1 can be estimated by performing the calculation regarding the change in the distribution shape of the histogram.

Next, a method of estimating the load applied to the shield tunnel 10 that changes with time will be described. In designing the reinforcement structure 30, it is necessary to set both the current load P1 applied to the shield tunnel 10 and the apparent maximum increase load due to consolidation (hereinafter referred to as the maximum consolidation load Pm) that will occur in the future. .. According to existing studies, it has been found that the vertical earth pressure increases 1.3 times and the lateral earth pressure 0.85 times as the consolidation of the ground around the shield tunnel 10 increases.

Therefore, assuming that the initial lateral earth pressure coefficient is 0.80 at the time of tunnel design from this result, the relationship between the variable load ratio α and the lateral earth pressure coefficient λ shown in FIG. 8 can be obtained. Here, the variable load ratio α means the ratio of the sum of the design vertical load and the variable load in the vertical direction to the design vertical load (Non-Patent Document 2). By the way, as the current load estimation method, for example, a method of estimating from the amount of internal air displacement, a method of estimating from the number of cracks, or the like can be used. Here, a method of estimating from the number of cracks in Non-Patent Document 2 is adopted. In order to calculate the number of cracks generated in the segment G, the structural calculation by the beam spring model calculation method linked with the load is performed.

The following existing method is used to calculate the number of cracks. First, for the top plate portion 11 of the shield tunnel 10, the tensile stress degree σse generated in the main reinforcing bar S1 on the inner air side is calculated in a range of 45 ° above and to the left and right. Then, the crack generation stress degree σsw is calculated back from the crack width w = 0.1 mm that can be observed in the field using the crack width calculation formula. Then, a range in which the tensile stress degree σse exceeds the cracked generated stress degree σsw is specified, and the length of this range is calculated. Finally, since cracks along the tunnel axial direction L due to the vertical load of the ground occur at the position of the distribution reinforcing bars S2, the number is calculated by dividing the length in the above range at the intervals of the distribution reinforcing bars S2. ..

Next, the calculated number of cracks is compared with the number of cracks in the segment actually confirmed in the field. The current load was defined as the state in which the two match. As shown in FIG. 9, as a result of this examination, the current load is estimated to be 1.13 times the design vertical load. In addition, the maximum consolidation load that will occur in the future is estimated to increase up to 1.30 times the design vertical load, based on the known final predicted load increase values obtained in past experiments. For the estimation of the current load, the estimation method based on the number of cracks was used, but the estimation is not limited to this, and any other method including actual measurement may be used as long as the current load can be estimated.

The reinforcing structure 30 is designed based on the estimated current load and the maximum consolidation load. The design method of the reinforcing structure 30 is performed in consideration of deterioration of the shield tunnel 10. Hereinafter, a method of designing the reinforcing structure 30 of the shield tunnel 10 will be described.

As shown in FIG. 10, there is a correlation between the vertical load P applied to the shield tunnel 10 and the amount of internal air displacement δ in the vertical direction inside the shield tunnel 10, and the vertical load P-internal air displacement amount δ curve. Shown. As shown in the figure, the state of the shield tunnel 10 without deterioration at the time of design is shown by the first design curve in which the amount of internal displacement δ increases as the vertical load P increases. Further, the state of the shield tunnel 10 in the future, which is deteriorated in the future, is indicated by the second curve in which the amount of internal displacement δ increases as the vertical load P increases.

The vertical load P and the amount of internal displacement δ usually show a linear relationship according to the elastic theory, but the first curve and the second curve are P / δ due to the influence of cracks and the like that occur in the concrete portion C as the vertical load P increases. The situation where the gradient of is gradually lowered from the initial gradient is taken into consideration. Since the shield tunnel 10 in which the deterioration has occurred has a reduced yield strength, the gradient of the second curve is smaller than the gradient of the first curve.

Here, the shield tunnel 10 without deterioration refers to a tunnel without corrosion of the main reinforcing bar S1. The first curve shows, for example, a state where the thickness of the main reinforcing bar S1 of the segment G is 6 mm, which is the design value. The second curve shows, for example, a state in which the thickness of the main reinforcing bar S1 of the segment G is estimated by the method described above, and the residual amount after deterioration is 1 mm.

In the first curve, the shield tunnel 10 which has not deteriorated at the time of design is in the state of the point A where the design load P0 is applied in the vertical direction. Further, the load applied to the shield tunnel 10 increases due to the influence of the increase in consolidation of the surrounding ground condition as described above. The vertical load applied to the shield tunnel 10 in the future shall increase up to 1.30 times the design load P0 as described above.

Therefore, the vertical load applied to the shield tunnel 10 increases from the design load P0 to the current load (first load) P1, and shifts to the state of the point B that causes the first displacement amount δ1. The current load P1 is 1.13 times the design load according to the above estimation method. For the estimation of the current load P1, for example, a method of estimating from the amount of internal displacement δ, a method of estimating from the number of cracks generated in the segment G, and the like are used. Here, the current load P1 is estimated using a method of estimating from the number of cracks.

First, based on the first curve, the first load acting on the shield tunnel 10 that causes the first displacement amount δ1 in the shield tunnel 10 is obtained. If reinforcement measures are not taken while the current load P1 is applied to the shield tunnel 10, if the corrosion of the main reinforcing bar S1 progresses, the load state of the shield tunnel 10 is the second curve indicating the state where the corrosion has progressed from the point B. It shifts to the point C of. At this time, the internal displacement amount δ increases from the first displacement amount δ1 to the second displacement amount δ2.

According to a general reinforcement method, the reinforcement structure formed in the shield tunnel 10 is designed to bear the current load. According to this design method, it is generated by the current load P1 applied to the rigidity of the ring R of the shield tunnel 10 in consideration of the future corrosion condition of the main reinforcing bar S1 and the rigidity of the constructed reinforcing column. The section force to be used is calculated.

As shown in FIG. 11, a P-δ curve of a vertical load P and an internal displacement amount δ showing the relationship between the shield tunnel 10 after deterioration and the reinforcing structure in a general reinforcing method is drawn. The reinforced shield tunnel 10 to which the current load P1 is applied is in the state of point D. At this time, the load borne only by the shield tunnel 10 is the load in the state of the point E. Therefore, according to this design method, the segment G bears the load up to the point E, and the reinforcing prism bears the difference between the loads at the points D and E.

However, in this state, the reinforcing column bears most of the current load, and the segment G bears almost no load, which may result in a dangerous design for the segment G. Further, the reinforcing column may be uneconomically designed to bear an excessive load.

As shown in FIG. 12, as the corrosion of the main reinforcing bar S1 progresses, the displacement amount δ generated by the current load P1 is from the displacement amount δ1 at the point B on the first curve to the displacement amount δ2 at the point C on the second curve. Increases to. Therefore, if it is desired to maintain the state of the point B even if the main reinforcing bar S1 is corroded, the current load P1 at the point B of the first curve and the point of the second curve that causes the same displacement as the displacement amount δ1 at the point B. A design method may be used in which the reinforcing structure 30 bears the difference in load from the virtual load (second load) Pv in F.

When the reinforcing structure 30 is formed according to this design method, the relationship between the load acting on the shield tunnel 10 after reinforcement and the displacement amount is shown with the first displacement amount δ1 and the second load Pv in the second curve as initial values. A curve is required. The third curve shows a state in which the reinforcing structure 30 and the deteriorated shield tunnel 10 cooperate with each other to bear a load applied from the outside. Therefore, the third curve has a gradient larger than the gradient of the first curve.

When reinforcing the shield tunnel 10, the reinforcing structure 30 is formed in the shield tunnel 10 so as not to apply a load to the reinforcing structure 30 in the initial state. Then, as shown in FIG. 13, after the reinforcing structure 30 is formed, the top plate portion 11 is displaced downward with the passage of time, and a load is applied to the reinforcing structure 30. Then, the internal displacement amount δ of the shield tunnel 10 is displaced from the displacement amount δ1 at the point B of the first curve caused by the current load P1 to the displacement amount δ3 at the point G of the third curve caused by the current load P1. ..

That is, as an effect of the reinforcing structure 30, in the reinforcing structure 30, the internal empty displacement amount δ of the shield tunnel 10 under the current load is not the displacement amount δ2 at the point C of the second curve, but the point of the third curve. It can be fixed by the displacement amount δ3 in G.

It should be noted that the design method of the reinforcing structure 30 of FIG. 13 described above employs a design method of constructing the reinforcing structure 30 in the shield tunnel 10 in a state where there is no deterioration. Here, the state without deterioration means a state in which there is no deterioration at present, but there is a possibility of deterioration in the future.

When designing strictly in consideration of the load borne by the reinforcing structure 30, ideally, the reinforcing structure 30 should be designed in the load state at the time when the shield tunnel 10 becomes the limit with respect to the external force. This is because the load borne by the reinforcing structure 30 can be designed to be the smallest, and the design becomes economical.

However, it is realistic to determine the limit to the external force between the load state at the point F of the future shield tunnel 10 in FIG. 13 and the load state at the point G of the reinforced shield tunnel 10. It is difficult. Here, if the difference between the loads of the points F and the points G of the shield tunnel 10 without deterioration is designed to be shared by the reinforcing structure 30, the reinforcing structure 30 is compared with FIG. 11 which uses a general design method. It can be designed with less load. Therefore, a design method is adopted in which the reinforcing structure 30 is constructed in the shield tunnel 10 in a state where there is no deterioration as described above by weighing the difficulty of the design and the economic efficiency.

As shown in FIG. 14, the load applied to the shield tunnel 10 in the future increases due to consolidation and reaches a maximum value. At this time, the maximum consolidation load Pm is 1.30 times the design load P0 as described above. The state in which the maximum consolidation load Pm is applied in the third curve is indicated by the point H. The state in which the maximum consolidation load Pm is applied in the second curve is indicated by the point I. Therefore, comparing the case without reinforcement, the difference in the amount of displacement that occurs when the maximum load Pm is applied is the difference between points H and I, and this difference can be considered to be the effect of reinforcement.

In this case, the displacement amount δm is generated at the point H in the state where the maximum consolidation load Pm is applied on the third curve. At the point J where the displacement amount δm is generated on the second curve, the load P2 is applied. Then, the load to be borne by the reinforcing structure 30 in the future is the difference between the maximum load Pm at the point H and the load P2 at the point J.

The reinforcing structure 30 is specifically designed based on the above-mentioned design method of the reinforcing structure 30. The remaining amount of the thickness of the main reinforcing bar S1 at the time of design is 6 mm, and the remaining amount of the thickness of the main reinforcing bar S1 in the case of corrosion in the future is set to 1 mm based on the above estimation method.

As shown in FIG. 15, when the structural calculation is performed based on these values, a P-δ curve showing the load-bearing ratio of both is obtained. However, in this P-δ curve, the variable load ratio α is taken on the vertical axis with respect to the amount of internal air displacement δ on the horizontal axis. Based on this graph, the first displacement amount δ1 at the point B (see FIG. 13) of the first curve caused by the current load P1 (1.13 times the design load P0) is estimated to be 10.9 mm.

Then, the virtual load Pv in the vertical direction at the point F (see FIG. 13) of the second curve that causes the first displacement amount δ1 is estimated to be 1.07 times the design load P0. As a result, a load model capable of reasonably evaluating the load to be borne by the reinforcing structure 30 due to the decrease in rigidity of the existing shield tunnel 10 is constructed.

As shown in FIG. 16, the P-δ curve of the shield tunnel 10 after reinforcement corresponds to the virtual load Pv in the second curve, which causes the same displacement as the first displacement amount δ1 = 10.9 mm at the point B. It is represented by a third curve with the point F as the initial value. Then, in the third curve of the shield tunnel 10 after reinforcement, the load path is a path that shifts from the point F to the point G. That is, in the load model shown here, the existing shield tunnel 10 bears 1.07 times the design load P0, and then bears the current load P1 which is reinforced and increases up to 1.13 times. ..

Then, in the third curve of the shield tunnel 10 after reinforcement, the load path is a path that shifts from the point G to the point H corresponding to the maximum consolidation load Pm that increases up to 1.30 times after reinforcement. That is, in the load model shown here, the existing shield tunnel 10 bears 1.13 times the design load P0 and then bears the maximum load Pm that will increase up to 1.30 times in the future.

Next, the structural analysis of the reinforcing structure 30 calculated by the above-mentioned design method is performed, and the suitability of the design of the reinforcing structure 30 is determined. A structural analysis model is constructed by tracking the load model described above. This structural analysis model is a composite model in which the existing shield tunnel 10 and the reinforcing structure 30 cooperate with each other. For structural analysis, for example, a known beam spring model is used.

As shown in FIGS. 17 to 20, in the beam spring model, the segment G is set as a beam, and the joint portion connecting the segments G to each other is set as a rotary spring element. The joint portion connecting the rings R composed of the plurality of segments G to each other is set as a shear spring element. Then, the connection relationship with the ring R supported by the reinforcing structure 30 constructed in the shield tunnel 10 is set as a connection spring element. Adjacent rings R are staggered together.

As described above, the load states in the existing shield tunnel 10 are the state of the point F where the load acts only on the shield tunnel 10 (see FIG. 16), and the points G and H where the load acts on the shield tunnel 10 after reinforcement. There are two states (see FIG. 16).

As shown in FIG. 17, a virtual load Pv (1.07 times the design load P0) corresponding to the state of the point F is added to the structural analysis model in which adjacent rings R are staggered. Then, the cross-sectional force generated in the cross-section of the segment G is calculated.

As shown in FIG. 18, the reinforcing structure 30 is constructed in the inner space of the structural analysis model. In this state, only the reinforcing structure 30 is constructed in the state of the point F, and at this stage, the cross-sectional force is not yet generated in the reinforcing structure 30.

As shown in FIG. 19, after the construction of the reinforcing structure 30 is completed, the load applied to the structural analysis model is increased up to the current load P1 (1.13 times the design load P0) corresponding to the state of the point G. As the load increases, a cross-sectional force is also generated in the reinforcing structure 30.

As shown in FIG. 20, the structural analysis model is used from the current load P1 (1.13 times the design load P0) to the maximum consolidation load Pm (1.30 times the design load P0) corresponding to the state of the point H. Increase the applied load and calculate the cross-sectional force of each member. In addition, in FIGS. 18 to 20, for the sake of clarity, the ring R of the segment G and the reinforcing structure 30 are described apart from each other, but in the actual calculation, they are in close contact with each other as described later. There is. That is, the spring value of the ground contact surface between the shield tunnel 10 and the reinforcing structure 30 is set separately in the radial direction and the tangential direction of the ring R.

In this structural analysis model, as a prerequisite, the top surface of the upper support portion 32 of the reinforcing structure 30 and the inner air surface of the segment G in the radial direction of the ring R due to the consolidation of the ground (current load P1 and maximum consolidation load Pm). It is assumed that the lower surface portion of the lower support portion 33 of the reinforcing structure 30 and the upper surface portion of the invert portion 12 are in close contact with each other. Further, it is assumed that the spring value when the structural analysis model is compressed in the radial direction of the ring R corresponds to infinity, and the spring value when tension works (when it separates) becomes 0.

Even in the tangential direction of the ring R, the shear resistance increases when a compressive force acts. Therefore, as with the spring value in the radial direction, the spring value when the structural analysis model is compressed is equivalent to infinity, and tension works. In this case, the spring value is assumed to be 0.

As shown in FIG. 21, M- showing the relationship between the bending moment M applied to the segment G and the changing curvature Φ when the thickness of the main reinforcing bar S1 on the inner air side of the segment G becomes 1 mm due to corrosion. The Φ relationship is used. Here, the M-Φ relationship used in the calculation depends on the axial force in the reinforcing bar arrangement direction of the main reinforcing bar S1 of the segment G, and as a typical case, the M-Φ relationship when the axial force is 400 kN is shown. There is. Further, since only the main reinforcing bar S1 on the inner surface side of the tunnel is currently corroded, it is assumed that the main reinforcing bar S1 on the outer surface side of the tunnel does not corrode.

A known method is used for the model of the rotary spring showing the joint portion of the segment G. However, since 35 years have passed since the completion of the shield tunnel 10 and the fastening force of the joint portion cannot be expected, the spring value after the joint portion is separated is adopted. As for the model of the shear spring that connects the rings R to each other, for example, a trilinear model is adopted based on a known method. Since the corrosion of the joint portion is lighter than that of the main reinforcing bar S1 at present, it is assumed that the characteristics of the rotary spring do not change.

As shown in FIG. 22, the stress generated in the existing shield tunnel 10 and the reinforcing structure 30 is calculated according to the load state based on the structural analysis model using the specifications set based on the above preconditions and the like. .. 23 and 24 are analysis results analyzed based on the structural analysis model. As shown in FIG. 23, when the load value increases from the current load P1 to the maximum consolidation load Pm, the axial force generated in the segment G hardly changes from 440 kN to 442 kN.

After that, the axial force generated in the cross section of the support column 31 of the reinforcing structure 30 greatly changes from 75.9 kN to 300 kN. This analysis result reproduces the load history (see FIG. 16) that the reinforcing structure 30 functions effectively as the load increases. Further, the bending moment M of the ring R also changes from 63.8 kNm to 70.2 kNm, and the increase rate is about 10%.

That is, when the variable load ratio α increases by 15% or more from 1.13 to 1.30 and the lateral earth pressure coefficient λ decreases by 15% or more from 0.80 to 0.67, the vertical earth pressure and lateral earth pressure. Despite the deterioration of the earth pressure balance, the reinforcing structure 30 bears a load and suppresses an increase in the cross-sectional force generated in the segment G.

In FIG. 24, calculation results are shown for the ring R and the reinforcing structure 30 for the bending moment diagram and the axial force diagram according to the above load history. As shown in the figure, the bending moment M and the axial force generated in the ring R of the shield tunnel 10 do not change much, whereas the bending moment M and the axial force of the reinforcing structure 30 both increase as the load increases.

In particular, as shown in FIG. 24A, according to the structural analysis model, the bending moment is applied to the upper support portion 32 of the reinforcing structure 30 due to the corrosion of the main reinforcing bar S1 of the segment G under the stress state in which the current load P1 is applied. The situation where M is occurring is reproduced. As described above, by constructing a structural analysis model that tracks the load model and designing the reinforcing prism, the stress generated in each of the segment G and the reinforcing structure 30 can be appropriately calculated.

ここで、
S_d：応答値
R_d：限界値
γ_i：構造物係数(=1.0)
である。 Next, the yield strength of the reinforcing structure 30 designed based on the stress calculated by the above method is determined. The proof stress of the reinforced structure 30 is determined by structural inspection based on the known formula (7). By the structural inspection, the yield strength of the reinforcing structure 30 is determined from the response value based on the dynamically generated cross-sectional force generated in the reinforcing structure 30 and the limit value determined by the predetermined structural inspection item. That is, the yield strength of the designed reinforcing structure is determined based on the response value generated with respect to the dynamic load applied to the reinforcing structure 30.

here,
S _d : Response value
R _d : Limit value γ _i : Structure coefficient (= 1.0)
Is.

The limit value is determined by the yield stress value for the current load P1 and the ultimate cross-sectional yield strength for the maximum consolidation load Pm. The determined limit values are shown in FIGS. 25 and 26. The verification of the response value with respect to the limit value is as shown in FIGS. 27 and 28, and the values are all 1.0 or less in the segment G and the reinforcing structure 30, and it is determined that the load bearing performance is satisfied. In the above-mentioned reinforcement design, inspection during an earthquake was also carried out, and it was confirmed that both the existing shield tunnel 10 and the reinforcement structure 30 satisfy the load bearing performance against the level 1 earthquake motion and the level 2 earthquake motion.

Hereinafter, the installation intervals D of the plurality of column portions 31 in the shield tunnel 10 of the reinforcing structure 30 designed by the above design method will be described. As shown in FIG. 29, the plurality of column portions 31 are arranged in the shield tunnel 10 along the tunnel axis L. Each strut portion 31 is arranged so that the position of the center of the strut portion 31 in the direction along the tunnel axis L is the position of the seam U between the rings R of the shield tunnel 10. When a vertical load is applied to the shield tunnel 10, the axial force generated in the cross section of the support column 31 creates a shear surface T that forms 45 degrees in the segment G of the upper support portion 32 and the top plate portion 11.

When a vertical load is applied to the shield tunnel 10, the installation interval D of the strut portions 31 is determined so that the intersections of the shear surfaces T generated by the adjacent strut portions 31 are within the segment G. As a result, the width W in the direction along the tunnel axis L of the support column 31 is determined. Then, the width in the direction orthogonal to the tunnel axis of the support column 31 is also determined based on the stress generated in the reinforcing structure 30 calculated by the above design method. It is possible to prevent a force in an unexpected direction from being applied to the segment G, and the design can be made safe with respect to the segment G.

Next, the flow of the design method of the reinforcing structure 30 will be described with reference to FIG. Based on the first design curve showing the load state of the shield tunnel 10 without deterioration, the first displacement amount δ1 caused by the known current load P1 is obtained (S100). Based on the second curve showing the relationship between the load acting on the shield tunnel 10 in the assumed deteriorated state and the displacement amount, a virtual load (second load) that causes the first displacement amount δ1 is obtained (S101). The strength of the reinforcing structure 30 is obtained based on the difference between the first load and the second load (S102). After installing the reinforcing structure 30, the second load in the first displacement amount is set as an initial value, and a third curve showing the relationship between the load acting on the shield tunnel 10 after reinforcement and the displacement amount is obtained (S103).

Based on the third curve, the amount of future displacement with respect to the assumed future load is calculated (S104). The stress generated in the main body of the shield tunnel 10 and the reinforcing structure 30 when a future displacement amount occurs is calculated based on a structural analysis model modeled by constructing the shield tunnel 10 and the reinforcing structure 30 with beams and springs (). S105). The yield strength of the reinforcing structure 30 designed based on the calculated stress is determined based on the response value generated to the dynamic load applied to the reinforcing structure 30 (S106).

As described above, according to the design method of the reinforcing structure 30, reinforcement measures can be taken according to the progress of deterioration of the existing structure. That is, according to the design method of the reinforcing structure 30, the load borne by the reinforcing structure 30 can be reasonably set by tracking the load history of the load applied to the shield tunnel 10. Then, according to the design method of the reinforcing structure 30, the specifications of the reinforcing structure 30 can be rationally set based on the load borne by the set reinforcing structure 30, and excessive design can be reduced. Further, according to the design method of the reinforcing structure 30, the safety of the reinforcing structure 30 can be evaluated by determining the proof stress of the reinforcing structure 30 based on the set specifications of the reinforcing structure 30.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and variations thereof are included in the scope of the invention described in the claims and the equivalent scope thereof, as are included in the scope and gist of the invention.

For example, in the above embodiment, the reinforcing structure 30 of the existing shield tunnel 10 has been exemplified, but the design method of the reinforcing structure can be applied to the reinforcement of other existing structures. For example, the existing structure may be another reinforced concrete structure under load. In addition, the above method for designing a reinforcing structure may be applied to any existing structure that may deteriorate in the future. In that case, after calculating the load history, the above structural analysis model may be constructed according to the shape of another existing structure to perform stress calculation. Further, although the main reinforcing bar S1 used in the above-mentioned method for estimating the residual amount of the main reinforcing bar S1 exemplifies a flat bar, the above-mentioned estimation method may be applied to reinforcing bars having other shapes.

10 Shield tunnel 11 Top plate part 12 Invert part 30 Reinforcing structure 31 Strut part 32 Upper support part 33 Lower support part C Concrete part G Segment R Ring S Reinforcing bar S1 Main reinforcing bar S2 Distribution reinforcing bar

Claims (5)

It is a method of designing a reinforced structure of an existing structure that is in a deteriorated state.
An initial displacement amount calculation step for obtaining a first displacement amount generated by a first load applied to the existing structure based on a first design curve showing the relationship between the load acting on the existing structure and the displacement amount.
A post-deterioration load calculation step for obtaining a second load that causes the first displacement amount based on a second curve showing the relationship between the load acting on the existing structure in a assumed deteriorated state and the displacement amount.
A reinforcing structure strength calculation step for calculating the strength of the reinforcing structure for reinforcing the existing structure based on the difference between the first load and the second load .
After installing the reinforcing structure, the second load in the first displacement amount is set as an initial value, and after reinforcement, a third curve showing the relationship between the load acting on the existing structure after reinforcement and the displacement amount is obtained. Curve calculation process and
A future displacement amount calculation step for calculating a future displacement amount with respect to an assumed future load based on the third curve is provided.
How to design a reinforced structure for an existing structure. Based on a structural analysis model using the existing structure and the reinforcing structure, which models the stress generated in the main body of the existing structure and the reinforcing structure in the load state based on the future load and the future displacement amount. And the stress calculation process
Further prepare,
The method for designing a reinforced structure of an existing structure according to claim 1 . Further comprising a determination step of determining the yield strength of the reinforcing structure designed based on the calculated stress based on the response value generated with respect to the dynamic load applied to the reinforcing structure.
The method for designing a reinforcing structure of an existing structure according to claim 2 . The post-deterioration load calculation step is for determining the second curve.
A distribution curve determination step for determining a distribution curve showing the distribution of residual amounts of a plurality of structural members constituting the existing structure, and a distribution curve determination step.
A parameter calculation process for calculating parameters that change the distribution curve over time, and
Further comprising a structural member residual amount estimation step of statistically estimating the residual amount of the structural member in the future based on the distribution curve calculated by the corresponding parameter after the lapse of a predetermined period.
The method for designing a reinforcing structure of an existing structure according to any one of claims 1 to 3 . The design process according to the design method according to any one of claims 1 to 4 .
A reinforcement process for constructing a reinforcement structure designed in the design process is provided.
How to build a reinforced structure for an existing structure.

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