JP2018123563A - Design method for reinforcement structure of existing structure, and reinforcement structure of existing structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a design method for an existing structure capable of performing reinforcement treatment corresponding to the progress degree of the deterioration of the existing structure, and a reinforcement structure of the existing structure.SOLUTION: The design method for a reinforcement structure of an existing structure according to an embodiment comprises: an initial displacement calculation process to acquire a first displacement caused by a first load applied to the existing structure on the basis of a designed first curve showing the relationship between the load acting on the existing structure and the displacement; a post-deterioration load calculation process to acquire a second load for generating the first displacement on the basis of a second curve showing the relationship between the load acting on the existing structure under an assumed deterioration state and the displacement; and a reinforcement structure strength calculation process to calculate the strength of the reinforcement structure for reinforcing the existing structure on the basis of the difference between the first load and the second load.SELECTED DRAWING: Figure 30

Description

  The present invention relates to a reinforcing structure design method for reinforcing an existing structure in accordance with the degree of progress of deterioration of the existing structure, and a reinforcing structure of the existing structure.

  Among existing structures such as shield tunnels, there is a possibility that deterioration will progress due to secular change and that strength may be lowered in the future. Non-Patent Document 1 describes a method of newly providing a reinforcing segment inside an existing tunnel structure.

Takao Ochiai, Yoshitsugu Tsuburaya, Osamu Sakaida, Junichi Tanaka, “New Inner Reinforcement Method for Electric Power Tunnel Improvement Work”, 1999, Tunnel and Underground, Vol. 30, No. 1, pp. 46-52 Yukio Shioji, Yukihiro Naito, Kenichi Anan, Masahiro Otsuka, Satoshi Koizumi, “Research on Reinforcement of Shield Tunnel Aged” 2011, Proceedings of the Japan Society of Civil Engineers, F1 (Tunnel Engineering) 67 (2), pp. 62-78

Existing structures such as shield tunnels have different degrees of deterioration depending on the location and timing of construction. It is desirable to take reinforcement measures according to the degree of progress of deterioration for structures that have progressed. According to the method described in Non-Patent Document 1, a reinforcing segment is newly installed regardless of the degree of progress of deterioration of an existing tunnel structure. Therefore, in the method described in Patent Document 1, when the degree of progress of deterioration of the existing tunnel structure is small, excessive reinforcement is applied even in a state where a small amount of reinforcement is sufficient, resulting in an excessive cost. There is a risk of it. In order to appropriately reinforce, it is necessary to accurately grasp the progress of deterioration of an existing structure and take measures according to the progress of deterioration.
An object of this invention is to provide the reinforcement design method of the existing structure which can perform a reinforcement measure according to the progress degree of deterioration of the existing structure, and the reinforcement structure of an existing structure.

A 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 calculating step for obtaining a first displacement amount generated by a first load applied to the existing structure based on a first design curve indicating a relationship between a load acting on the existing structure and a displacement amount;
A post-degradation load calculation step for obtaining a second load that causes the first displacement amount based on a second curve indicating a relationship between a load acting on the existing structure in an assumed deterioration state and a displacement amount;
A reinforcing structure strength calculating 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 this configuration, the present invention obtains a second load as a virtual load applied to the existing structure in the deteriorated state from the second curve indicating the state of the existing structure in the deteriorated state, and refers to the load history. The reinforcement structure can be rationally designed.

The present invention further provides a relationship between a load acting on the existing structure after reinforcement and the displacement amount, with the second load at the first displacement amount as an initial value after the reinforcement structure is installed. A post-reinforcement curve calculation step for obtaining three curves;
A future displacement amount calculating step of calculating a future displacement amount with respect to an assumed future load based on the third curve;
May be further provided.

  With this configuration, the present invention can be designed so that the existing structure and the reinforcing structure bear the proof strength against the external force after reinforcement, and the reinforcing structure can be designed rationally.

The present invention further uses the existing structure and the reinforcing structure in which stresses generated in the main body of the existing structure and the reinforcing structure in a load state based on the future load and the future displacement amount are modeled. A stress calculation process for calculating based on the structural analysis model
May be further provided.

  With this configuration, the present invention can calculate a stress that matches the shape of a specific existing structure.

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

  With this configuration, the present invention can evaluate the safety of the reinforcing structure by determining the calculated strength of the reinforcing structure.

In the present invention, the post-deterioration load calculating step may further determine the second curve.
A distribution curve determining step for determining a distribution curve indicating a distribution of residual amounts of a plurality of structural members constituting the existing structure;
A parameter calculation step for calculating a parameter for changing the distribution curve over time;
A structural member remaining amount estimating step that statistically estimates the remaining amount of the structural member in the future based on the distribution curve calculated with the corresponding parameter after a predetermined period of time. Good.

  With this configuration, the present invention can estimate the remaining amount of structural members that corrode due to secular change, and can estimate the load state of an existing structure that has deteriorated in the future.

The present invention further includes a design process by the above design method,
A reinforcing step of building a reinforcing structure designed in the design step, and a method of building a reinforcing structure of an existing structure may be configured.

  With this configuration, the present invention can provide a construction method for constructing a reinforcing structure for an existing structure on site.

The reinforcing structure of the existing structure according to the embodiment of the present invention is continuously arranged along the tunnel axis direction at the top end of the inner empty wall of the pipe structure and along the circumferential direction of the inner empty wall. An upper support portion arranged in a
A lower support portion arranged continuously along the tunnel axis direction at the lower end of the inner empty wall, and arranged along the circumferential direction of the inner empty wall;
A plurality of support columns arranged at predetermined intervals along the tunnel axis direction and connecting the upper support and the lower support.

  With this configuration, the present invention can construct a reinforcing structure for an existing structure.

  According to the design method of the reinforcement structure of the existing structure and the reinforcement structure of the existing structure according to the present invention, it is possible to take reinforcement measures according to the degree of progress of the deterioration of the existing structure.

It is a perspective view which shows a part of 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 showing the state of the shield tunnel reinforced with the reinforcement structure. It is a histogram which shows distribution of the thickness of the main reinforcement of the segment of the existing shield tunnel. It is a histogram which shows distribution of the thickness of the main reinforcement of the segment of the other existing shield tunnel. It is a figure which shows the parameter of the median value of the corrosion amount of a main reinforcement, the mode value, and a probability density function. It is a figure which shows the change of distribution of the probability density function shown with the parameter which changes with time. It is a graph which shows the relationship between a variable load ratio and a side 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 the shield tunnel with no deterioration, and a future tunnel. It is a graph which shows the load which a reinforcement structure bears with 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 added to a reinforcement structure. It is a graph which shows the overload burden ratio of a main reinforcement. It is a graph which shows the load history used with the design method of a reinforcement structure. It is a figure which shows the state which added the load to the structural analysis model for structural analysis. It is a figure which shows the state which added the load to the structural analysis model for structural analysis. It is a figure which shows the state which added the load to the structural analysis model for structural analysis. It is a figure which shows the state which added the load to the structural analysis model for structural analysis. It is a figure which shows the relationship between the bending moment M which arises in the segment after degradation, and a curvature. 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 verification limit value of a segment. It is a figure which shows the verification limit value of a reinforcement structure. It is a figure which shows the verification value of a segment. It is a figure which shows the verification value of a reinforcement structure. It is a figure which shows the arrangement | positioning relationship of a reinforcement structure. It is a flowchart which shows the design method of a reinforcement structure.

  Hereinafter, a reinforcement design method for 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 to be subjected to 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 segments G manufactured in advance to holes drilled by a shield machine that excavates 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 successively forming the formed rings R, and the shield tunnel 10 is completed.

  As shown in FIG. 2, the segment G is curved so as to be a part of a tunnel wall having a circular cross section. The segment G has a reinforced concrete (RC) structure in which a reinforcing bar S is covered with concrete and reinforced. The reinforcing bar S of the segment G has a main reinforcing bar S1 responsible for 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 bar (Flat Bar (FB)). The main reinforcing bar S1 is a plate-like structural member that becomes a tensile reinforcing bar. The distribution reinforcing bar S2 is a steel bar such as a deformed reinforcing bar.

  The main reinforcing bar S1 is a curved belt-like plate 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. In addition, the segment G has a large number of reinforcing bars S2 that are arranged perpendicular 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 part C. That is, the segment G is an FB segment in which the main rebar S1 is a flat bar.

  Some shield tunnels that use segment G, whose main rebar is flat steel, have been built for more than 30 years. The segment G may deteriorate due to rust and the like over time in the underground environment, resulting in a lack of strength and requiring reinforcement measures. For example, in the shield tunnel 10, there is a case where deformation or corrosion has occurred in the reinforcing bar S of the segment G, and there is a possibility that the proof stress of the entire structure of the shield tunnel 10 may be reduced in the future.

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

  As shown in FIG. 3, the reinforcing structure 30 has a columnar body having an I-shaped cross section that is installed in a plurality in series inside the shield tunnel 10 in order to reinforce the shield tunnel 10 that is an existing structure. The reinforcing structure 30 reinforces the shield tunnel 10 whose proof strength is reduced due to corrosion of the main reinforcing bar S1 of the segment G due to deterioration over time. 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 that is formed on the floor (invert portion 12) formed at the lower portion of the shield tunnel 10, and an upper portion A plurality of support columns 31 connecting the support unit 32 and the lower support unit 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 part 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 a predetermined interval 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, the reinforcing structure 30 can be constructed with the existing equipment such as cables installed in the shield tunnel 10. The reinforcing structure 30 has a shape that can secure a space for an operator to enter and maintain cables and the like in the shield tunnel 10 even after being constructed. The reinforcing structure 30 may use, for example, an H-shaped cross section or a circular cross section in addition to a columnar body having an I-shaped cross section, and may have any shape as long as the top plate portion 11 of the shield tunnel 10 can be reinforced in accordance with the principle described later. It may be used.

  The reinforcing measure by the reinforcing structure 30 is designed such that the reinforcing structure bears the insufficient strength of the segment G caused by the deterioration. The degree of progress of degradation of segment G is evaluated based on statistical data. The degree of progress of deterioration of the segment G is mainly proportional to the remaining amount of the thickness of the main reinforcing bar S1.

  First, a statistical method used for evaluating the remaining thickness of the main reinforcing bar S1 will be described. Among the segments G included in the shield tunnel 10 to be measured, the number of segments G in which the main reinforcing bar S1 is corroded is measured. FIG. 4 and FIG. 5 show statistical data in which the thickness of the main reinforcing bar S1 of the shield tunnel 10 to be measured is associated with the number of points. As shown in the figure, the statistical data is a histogram (column graph) showing the thickness of the main reinforcing bar S1 in increments of 0.25 mm. First, a function that matches this histogram is set.

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 in which corrosion occurs with respect to the thickness (remaining amount) of the main reinforcing bar S1 is the design value (6 mm) of the thickness of the main reinforcing bar S1. Concentrated around the value. The distribution of the number of segments G with respect to the thickness of the main reinforcing bar S1 where corrosion has occurred is expressed by a probability density function distributed according to the amount of corrosion with the design value of the thickness of the main reinforcing bar S1 as a reference. This probability density function is a lognormal distribution in which the left and right distribution shapes are asymmetric. In this case, the probability density function representing the logarithmic normal distribution is defined as a function of the corrosion amount (= design value−residual amount) of the main reinforcing bar S1, for example, as in the following equation (1).

here,
m, s: probability density distribution parameter x: corrosion amount (mm)
It 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 so as to change with time, for example. First, when the parameters of the probability density distribution are expressed by the median value and the mode value of the distribution, for example, the following equation (2) is obtained.

here,
median (x): median of the histogram
mode (x): Mode value 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 calculating the parameter of the probability density distribution in the equation (2), a parameter related to time is introduced in order to take into account a temporal element that changes over time. Assuming that the corrosion amount of the main reinforcing bar S1 and the age are in a linear relationship, for example, the following formula (3) is set so that the median value and the mode of the distribution increase in proportion to the age.

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 since establishment
mode (x _t ): Estimated mode value t years from now
mode (x _p ): Current mode
m _t , _st : parameters of probability density distribution after t years.

  In the statistical data of FIG. 4, the histogram shape has a distribution close to the design plate thickness 6 mm of the main reinforcing bar S1. When the above formulas (1) and (2) are applied to the statistical data of FIG. 4 and verified, the median value of the remaining amount of the main reinforcing bar S1 is 4.90 mm (corrosion amount x = 1.10 mm). The most frequent zone is in the range of the remaining amount of 5.25 mm to 5.50 mm. As the mode value, an average value of 5.375 mm (corrosion amount x = 0.625 mm) of the mode band is adopted. When this result is applied to Equation (2), the parameters m and s of the probability density distribution are determined as m = 0.095 and s = 0.552, 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 coincides with any of the histogram shapes in FIGS. However, the above comparison is performed assuming that the peak of the distribution curve that 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 remaining 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, and mode (x _p ) = 0.625 mm. Based on these numerical values, the median value median (x _t ) and the mode value mode (x _t ) after t = 15, 25, 35 years are expressed by, for example, the following equation (4) using equation (3). Is calculated.

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

As shown in FIG. 7, the distribution shape of the probability density function curve has a smaller number of points (peak value of the curve) in the most frequent zone according to aging. In other words, the probability density function varies more with time. This indicates that the corrosion progresses with time and the remaining 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, the standard deviation after 35 years from the current state is 2.622 mm, and the variation is more than doubled. A future prediction of the remaining amount of one main reinforcing bar S1 per ring R is performed using the above calculation result. According to the above formulas, the mode value of the corrosion amount of the main reinforcing bar S1 after 35 years is calculated as 1.29 mm. When the standard deviation of 1σ (2.622 mm) on the corrosion side is applied to this value, the corrosion amount of the main reinforcing bar S1 is calculated to be 3.912 mm.

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

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

  When the shield tunnel 10 is constructed in a staggered arrangement of the rings R composed of a plurality of segments G, a shearing force applied from the segments G of the adjacent rings R acts on the joints between the adjacent rings R. Thereby, the deformation of the entire ring R is constrained. This is generally called an attachment effect. The bending moment is transmitted to the segment G through the joint between the rings R due to this attachment effect. Accordingly, even if the thickness of one of the two main reinforcing bars S1 in the segment G is 2.088 mm or less, the thickness of the other main reinforcing bar S1 must be larger than 2.088 mm due to the splicing effect. Thus, 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 main reinforcing bar S1 in the segment G is 2.088 mm or more is calculated. This probability is calculated by the following formula (6), for example, when selecting one or more of the two adjacent main reinforcing bars S1.

The probability is 95% or more as shown in Equation (6).

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

  Accordingly, when most corrosion occurs in the state of the future segment G, “one main reinforcing bar S1 of the two adjacent main reinforcing bars S1 disappears, and the thickness of the other main reinforcing bar S1 corrodes to at least 2 mm. It is estimated that For this reason, when considering the entire plurality of segments G of the shield tunnel 10, in the most corroded state, the remaining amount after deterioration of the thickness of the main reinforcing bar S1 is estimated to be 1 mm by taking the average of both. As described above, the remaining amount after deterioration of the thickness of the main reinforcing bar S1 can be estimated by performing the calculation related to the change in the distribution shape of the histogram.

  Next, a method for estimating the load applied to the shield tunnel 10 that changes over time will be described. In designing the reinforcing structure 30, it is necessary to set both the current load P <b> 1 applied to the shield tunnel 10 and an apparent maximum increase load due to consolidation that will occur in the future (hereinafter, maximum consolidation load Pm). . According to existing studies, it is found that the vertical earth pressure is increased 1.3 times and the lateral earth pressure is increased 0.85 times as the consolidation of the ground around the shield tunnel 10 is increased.

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

  The following existing methods are used in calculating the number of cracks. First, with respect to the top plate portion 11 of the shield tunnel 10, the tensile stress σse generated in the inner rebar main rebar S <b> 1 in the upper left and right 45 ° range is calculated. Thereafter, the crack generation stress σsw is calculated backward 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 level σse cracks and exceeds the generated stress level σsw is specified, and the length of this range is calculated. Finally, since cracks along the tunnel axis direction L due to the vertical load of the ground are generated at the position of the distribution reinforcing bar S2, the number is calculated by dividing the length of the above range by the interval of the distribution reinforcing bar S2. .

  Next, the calculated number of cracks is compared with the number of cracks of the segments actually confirmed on site. The state where both coincide with each other was taken as the current load. 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 load of consolidation that will occur in the future is estimated to increase to 1.30 times the design vertical load based on the known final predicted increase in load obtained in past experiments. As for the estimation of the current load, the estimation method based on the number of cracks is used, but the present invention 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 design method of the reinforcing structure 30 of the shield tunnel 10 will be described.

  As shown in FIG. 10, the vertical load P applied to the shield tunnel 10 and the internal air displacement amount δ in the vertical direction inside the shield tunnel 10 are correlated, and the vertical load P−internal air displacement amount δ curve is obtained. Indicated. As shown in the figure, the state of the shield tunnel 10 without deterioration at the time of design is indicated by a first design curve in which the internal air displacement amount δ increases as the vertical load P increases. Further, the future state of the shield tunnel 10 in which the future deterioration has occurred is indicated by a second curve in which the internal air displacement amount δ increases as the vertical load P increases.

  The vertical load P and the internal air displacement amount δ usually show a linear relationship according to the elasticity theory, but the first curve and the second curve are P / δ due to the influence of cracks or the like generated in the concrete portion C as the vertical load P increases. A situation is considered in which the slope of the slope gradually decreases from the initial slope. Since the proof strength of the shield tunnel 10 in which deterioration has occurred is reduced, the slope of the second curve is smaller than the slope 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 a state where the thickness of the main reinforcing bar S1 of the segment G is 6 mm, which is a design value, for example. The second curve shows a state in which the post-deterioration residual amount is 1 mm, for example, where the thickness of the main reinforcing bar S1 of the segment G is estimated by the method described above.

  In the first curve, the shield tunnel 10 having no deterioration at the time of design is in a state of point A where a design load P0 is applied in the vertical direction. Further, the load applied to the shield tunnel 10 increases due to the influence of an increase in consolidation of the surrounding ground as described above. It is assumed that the vertical load applied to the shield tunnel 10 in the future increases 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 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. The current load P1 is estimated using, for example, a method of estimating from the internal air displacement amount δ, a method of estimating from the number of cracks generated in the segment G, or the like. Here, the current load P1 is estimated using a method of estimating from the number of cracks.

  First, based on the first curve, a first load acting on the shield tunnel 10 that causes the shield tunnel 10 to generate the first displacement amount δ1 is obtained. When the current load P1 is applied to the shield tunnel 10 and no reinforcement measures are taken, if the corrosion of the main rebar S1 progresses, the load state of the shield tunnel 10 shows the state where the corrosion has progressed from the point B. Move to point C. 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 reinforcing method, the reinforcing structure formed in the shield tunnel 10 is designed to handle the current load. According to this design method, the current load P1 applied to the rigidity of the ring R of the shield tunnel 10 in consideration of the future corrosion state of the main reinforcing bar S1 and the rigidity of the constructed reinforcing column is generated. The cross-sectional force to be calculated is calculated.

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

  However, in this state, most of the current load is borne by the reinforcing pillars, and the segment G hardly bears the load, which may be a dangerous design for the segment G. Furthermore, there is a possibility that the reinforcing column body has an uneconomical design of bearing an excessive load.

  As shown in FIG. 12, as the corrosion of the main reinforcing bar S1 proceeds, the displacement amount δ caused by the current load P1 is changed from the displacement amount δ1 at the point B of the first curve to the displacement amount δ2 at the point C of the second curve. Increase to. Therefore, when it is desired to maintain the state of the point B even when the main reinforcing bar S1 corrodes, the current load P1 at the point B of the first curve and the point of the second curve that produces the same displacement amount as the displacement amount δ1 at the point B What is necessary is just to use the design method which bears the difference of the load with the virtual load (2nd load) Pv in F with the reinforcement structure 30. FIG.

  When the reinforcing structure 30 is formed in accordance with this design method, the first displacement amount δ1 and the second load Pv in the second curve are used as initial values, and a third relationship indicating the relationship between the load acting on the shield tunnel 10 after reinforcement and the displacement amount is shown. A curve is determined. The third curve shows a state in which the reinforcing structure 30 and the deteriorated shield tunnel 10 cooperate to bear a load applied from the outside. Accordingly, the third curve has a slope that is greater than the slope of the first curve.

  When reinforcing the shield tunnel 10, the reinforcement structure 30 is formed in the shield tunnel 10 so that no load is applied to the reinforcement structure 30 in the initial state. Then, as shown in FIG. 13, after the reinforcement structure 30 is formed, the top plate portion 11 is displaced downward as time passes, and a load is applied to the reinforcement structure 30. Then, the inner space displacement amount δ of the shield tunnel 10 is displaced from the displacement amount δ1 of the first curve point B caused by the current load P1 to the displacement amount δ3 of the third curve point G caused by the current load P1. .

  In other words, as an effect of the reinforcing structure 30, the reinforcing structure 30 is configured so that the inner displacement δ of the shield tunnel 10 in the state where the current load is applied is not the displacement δ 2 at the point C of the second curve, but the point of the third curve. The displacement amount δ3 in G can be retained.

  It should be noted that the above-described method for designing the reinforcing structure 30 in FIG. 13 employs a design method for constructing the reinforcing structure 30 in the shield tunnel 10 in a state where there is no deterioration. Here, the state where there is no deterioration means a state where there is no deterioration at present but there is a possibility of deterioration in the future.

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

  However, it is realistic to determine a point that is a 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 shield tunnel 10 after reinforcement. It is difficult. Here, if it is designed that the difference between the loads of the point F and the point G of the shield tunnel 10 having no deterioration is shared by the reinforcing structure 30, the reinforcing structure 30 is compared with FIG. 11 using a general design method. It is possible to design with less load. Accordingly, a design method for constructing the reinforcing structure 30 in the shield tunnel 10 in a state in which there is no deterioration as described above by taking into consideration the difficulty of design and the economic efficiency is adopted.

  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 load Pm for consolidation is 1.30 times the design load P0 as described above. A state where the maximum load Pm of consolidation is applied in the third curve is indicated by a point H. A state where the maximum load Pm of consolidation is applied in the second curve is indicated by a point I. Therefore, comparing the cases where the reinforcement is not performed, the difference in the amount of displacement that occurs when the maximum load Pm is applied is the difference between the points H and I, and this difference can be considered as an effect of reinforcement.

  In this case, the displacement amount δm occurs at the point H where the maximum load Pm of consolidation is applied in the third curve. At the point J where the displacement amount δm is generated in the second curve, the load P2 is applied. Then, the load that the reinforcing structure 30 will bear 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 design method of the reinforcing structure 30 described above. The remaining amount of the thickness of the main reinforcing bar S1 at the time of design is set to 6 mm, and the remaining amount of the thickness of the main reinforcing bar S1 when corroded 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 sharing 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 internal displacement δ on the horizontal axis. Based on this graph, the first displacement 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.

  And the virtual load Pv of the perpendicular direction in the point F (refer FIG. 13) of the 2nd curve which produces 1st displacement amount (delta) 1 is estimated as 1.07 times the design load P0. Thereby, the load model which can rationally evaluate the load which the reinforcement structure 30 should bear by the rigidity fall of the existing shield tunnel 10 is constructed | assembled.

  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 that causes the same displacement amount as the first displacement amount δ1 = 10.9 mm at the point B. It is represented by a third curve with the point F to be used as an initial value. And in the 3rd curve of the shield tunnel 10 after reinforcement, a load course turns into a course which moves from point F to point G. That is, in the load model shown here, after the existing shield tunnel 10 bears 1.07 times the design load P0, it is reinforced and bears the current load P1 that increases to 1.13 times. .

  And in the 3rd curve of the shield tunnel 10 after reinforcement | strengthening, a load path | route becomes a path | route which moves to the point H corresponding to the maximum load Pm of consolidation which increases to 1.30 time after reinforcement from the point G. FIG. That is, in the load model shown here, after the existing shield tunnel 10 bears 1.13 times the design load P0, it bears the maximum load Pm that increases to 1.30 times in the future.

  Next, the structural analysis of the reinforcing structure 30 calculated by the design method described above 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. For the 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 to the beam, and the joint portion connecting the segments G to each other is set as a rotary spring element. And the joint part which connects the rings R comprised by the some segment G is set as a shear spring element. And the connection relationship with the ring R which the reinforcement structure 30 constructed | assembled in the shield tunnel 10 supports is set as a connection spring element. Adjacent rings R are staggered.

  As described above, the load state in the existing shield tunnel 10 includes the state of the point F where the load acts only on the shield tunnel 10 (see FIG. 16), and the point G and the point 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 the 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 interior of the structural analysis model. In this state, the reinforcing structure 30 is merely constructed in the state of the point F, and at this stage, no cross-sectional force is generated in the reinforcing structure 30 yet.

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

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

  In this structural analysis model, as a precondition, the top surface portion of the upper support portion 32 of the reinforcing structure 30 and the inner surface of the segment G in the radial direction of the ring R due to the consolidation of the ground (the current load P1 and the maximum load Pm of the consolidation). Are in close contact with each other, and the lower surface portion of the lower support portion 33 of the reinforcing structure 30 and the upper surface of the invert portion 12 are in close contact with each other. In addition, the spring value when the structural analysis model is compressed in the radial direction of the ring R is assumed to be infinite, and the spring value when tension is applied (when separated) is zero.

  Even in the tangential direction of the ring R, if a compressive force is applied, the shear resistance increases, so that the spring value when the structural analysis model is compressed is equivalent to infinity, and the tension works, similarly to the spring value in the radial direction. In this case, the spring value is assumed to be zero.

  As shown in FIG. 21, M− indicates 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 space side of the segment G becomes 1 mm due to corrosion. The Φ relationship is used. Here, the M-Φ relationship used for the calculation depends on the axial force in the reinforcing bar arrangement direction of the main reinforcing bar S1 of the segment G, and the M-Φ relationship in the case where the axial force is 400 kN is shown as a typical case. Yes. In addition, since corrosion is recognized only in the main rebar S1 on the inner surface side of the tunnel at present, the main rebar S1 on the outer surface side of the tunnel is not corroded.

  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. For example, a trilinear model is adopted for a model of a shear spring that connects the rings R to each other based on a known method. In addition, since the corrosion of the joint part is lighter than that of the main rebar S1 at present, the rotation spring characteristics are not changed.

  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 each item set based on the above preconditions and the like. . 23 and 24 show 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 consolidated load Pm, the axial force generated in the segment G hardly changes from 440 kN to 442 kN.

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

  That is, when the variable load ratio α increases from 1.13 to 1.30, 15% or more, and the lateral earth pressure coefficient λ decreases from 0.80, 0.67, 15% or more, the vertical earth pressure and the side 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.

  FIG. 24 shows the calculation results for the ring R and the reinforcing structure 30 for the bending moment diagram and the axial force diagram, respectively, according to the 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 change little, 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 in accordance with the corrosion of the main reinforcing bar S1 of the segment G in the stress state where the current load P1 is applied. The situation where M occurs is reproduced. As described above, the stress generated in each of the segment G and the reinforcing structure 30 can be appropriately calculated by building the structural analysis model that tracks the load model and designing the reinforcing column.

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 proof stress of the reinforcing structure 30 designed based on the stress calculated by the above method is determined. The yield strength of the reinforcing structure 30 is determined by structural verification based on the known equation (7). By the structural verification, the proof strength of the reinforcing structure 30 is determined from a response value based on a dynamic generated sectional force generated in the reinforcing structure 30 and a limit value determined by a predetermined structural verification item. That is, the proof stress of the designed reinforcing structure is determined based on a response value generated with respect to a dynamic load applied to the reinforcing structure 30.

here,
S _d : Response value
R _d : Limit value γ _i : Structural coefficient (= 1.0)
It is.

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

  Hereinafter, the installation interval 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 support columns 31 are arranged along the tunnel axis L in the shield tunnel 10. Each support column 31 is arranged such that the center position of the support column 31 in the direction along the tunnel axis L is the position of the joint U between the rings R of the shield tunnel 10. When a vertical load is applied to the shield tunnel 10, a shear surface T that forms 45 degrees in the segment G of the upper support portion 32 and the top plate portion 11 is generated by the axial force generated in the cross section of the support column portion 31.

  When a vertical load is applied to the shield tunnel 10, the installation interval D of the column portions 31 is determined so that the intersection of the shear surfaces T generated by the adjacent column portions 31 is in the segment G. Thereby, the width W in the direction along the tunnel axis L of the support column 31 is determined. And the width | variety of the direction orthogonal to the tunnel axis | shaft of the support | pillar part 31 is also determined based on the stress which generate | occur | produces in the reinforcement structure 30 calculated by said design method. A force in an unexpected direction is prevented from being applied to the segment G, and a safe design for the segment G can be achieved.

  Next, the flow of the design method of the reinforcing structure 30 will be described with reference to FIG. A first displacement amount δ1 caused by a known current load P1 is obtained based on a first design curve indicating the load state of the shield tunnel 10 without deterioration (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, a virtual load (second load) that causes the first displacement 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 the reinforcement structure 30 is installed, a third curve indicating the relationship between the load acting on the shield tunnel 10 after reinforcement and the displacement amount is obtained using the second load at the first displacement amount as an initial value (S103).

  Based on the third curve, a future displacement amount with respect to an 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 occurs is calculated based on a structural analysis model in which the shield tunnel 10 and the reinforcing structure 30 are modeled by a beam and a spring ( S105). The proof stress of the reinforcing structure 30 designed based on the calculated stress is determined based on a response value generated with respect to a dynamic load applied to the reinforcing structure 30 (S106).

  As described above, according to the design method of the reinforcing structure 30, it is possible to take a reinforcing measure according to the degree of 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 set rationally by tracking the load history of the load applied to the shield tunnel 10. And according to the design method of the reinforcement structure 30, the specification of the reinforcement structure 30 can be set rationally based on the load which the set reinforcement structure 30 bears, and an excessive design can be reduced. Furthermore, according to the design method of the reinforcing structure 30, the safety of the reinforcing structure 30 can be evaluated by determining the strength of the reinforcing structure 30 based on the set specifications of the reinforcing structure 30.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  For example, in the above-described embodiment, the reinforcing structure 30 of the existing shield tunnel 10 has been illustrated, but the above-described reinforcing structure design method can be applied to the reinforcement of other existing structures. For example, the existing structure may be another reinforced concrete structure in a loaded state. In addition, the above-described reinforcing structure design method may be applied to any existing structure that may be deteriorated in the future. In that case, after calculating the load history, the above structural analysis model may be constructed in accordance with the shape of another existing structure to perform stress calculation. Moreover, although the main reinforcing bar S1 used for the estimation method of the remaining amount of the main reinforcing bar S1 is a flat bar, the above estimating method may be applied to reinforcing bars of other shapes.

DESCRIPTION OF SYMBOLS 10 Shield tunnel 11 Top plate part 12 Invert part 30 Reinforcement structure 31 Support | pillar part 32 Upper support part 33 Lower support part C Concrete part G Segment R Ring S Reinforcement S1 Main reinforcement S2 Power distribution reinforcement

Claims (7)

A method for designing a reinforcing structure of an existing structure,
An initial displacement amount calculating step for obtaining a first displacement amount generated by a first load applied to the existing structure based on a first design curve indicating a relationship between a load acting on the existing structure and a displacement amount;
A post-degradation load calculation step for obtaining a second load that causes the first displacement amount based on a second curve indicating a relationship between a load acting on the existing structure in an assumed deterioration state and a displacement amount;
A reinforcing structure strength calculating step of calculating the strength of a reinforcing structure for reinforcing the existing structure based on the difference between the first load and the second load.
Design method for reinforcement structure of existing structures. After the reinforcement structure is installed, the second load at the first displacement amount is used as an initial value, and a third curve indicating the relationship between the load acting on the existing structure after reinforcement and the displacement amount is obtained after reinforcement. Curve calculation process;
A future displacement amount calculating step of calculating a future displacement amount with respect to an assumed future load based on the third curve;
Further comprising
The design method of the reinforcement structure of the existing structure of Claim 1. Based on a structural analysis model using the existing structure and the reinforcing structure in which stresses generated in the main body of the existing structure and the reinforcing structure in a load state based on the future load and the future displacement amount are modeled. A stress calculation process for calculating
Further comprising
The design method of the reinforcement structure of the existing structure of Claim 2. A determination step of determining the yield strength of the reinforcing structure designed based on the calculated stress based on a response value generated with respect to a dynamic load applied to the reinforcing structure,
The design method of the reinforcement structure of the existing structure of Claim 3. In the post-deterioration load calculating step, in order to determine the second curve,
A distribution curve determining step for determining a distribution curve indicating a distribution of residual amounts of a plurality of structural members constituting the existing structure;
A parameter calculation step for calculating a parameter for changing the distribution curve over time;
A structural member remaining amount estimating step that statistically estimates the remaining amount of the future structural member based on the distribution curve calculated with the corresponding parameter after a predetermined period of time;
The design method of the reinforcement structure of the existing structure of any one of Claim 1 to 4. A design process by the design method according to any one of claims 1 to 5,
A reinforcement step of constructing a reinforcement structure designed in the design step,
A method of constructing a reinforcement structure for existing structures. An upper support portion arranged continuously along the tunnel axis direction at the top end of the inner empty wall of the pipe structure, and arranged along the circumferential direction of the inner empty wall;
A lower support portion arranged continuously along the tunnel axis direction at the lower end of the inner empty wall, and arranged along the circumferential direction of the inner empty wall;
A plurality of struts arranged at predetermined intervals along the tunnel axis direction and connecting the upper support part and the lower support part;
Reinforcement structure for existing structures.

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