JP7800994B2 - Calculation method for shear strength of easily cuttable segments - Google Patents

Description

This invention relates to a method for calculating the shear strength of easily cuttable segments.

For example, after constructing a main tunnel and a ramp tunnel separately using the shield method, an underground widening section is constructed by cutting and widening a portion of the main tunnel and ramp tunnel using non-open cut construction, and the two tunnels are connected at the underground widening section. The main tunnel is an underground passage located at a great depth of, for example, 40 meters or more below ground, and a ramp tunnel is extended from this underground passage, accessible from an aboveground interchange junction, etc., and the two tunnels can be connected at the underground widening section.
In constructing this underground widening section, the main tunnel and ramp tunnel, which are spaced apart, are surrounded by, for example, a cylindrical underground structure with a relatively large cross section, and then the inside of the underground structure is excavated and the connecting section between the two tunnels is removed to construct the underground widening section. When constructing the underground structure, waterproofing treatment is carried out in the construction area of the underground structure as necessary.
One method for constructing the above-mentioned large-section underground structure is to construct an outer shell (large-section lining) by arranging multiple small-section tunnels side by side in a cylindrical shape. More specifically, multiple preceding small-section tunnels are constructed in a circular shape at intervals, and then multiple following small-section tunnels are constructed in a circular shape at those intervals while cutting out portions of the preceding small-section tunnels, and portions of the following small-section tunnels are removed to connect them to the preceding small-section tunnels. In other words, a large-section lining is formed in which the preceding and following small-section tunnels are alternately strung together, connecting the small-section tunnels. Then, main reinforcement extending circumferentially is placed in the circular connecting portions of the large-section tunnels, and fill concrete is placed, thereby constructing the underground structure, which is the large-section lining.
The preceding small-section tunnel and the following small-section tunnel that form the large-section lining are both constructed sequentially using the shield tunneling method. The preceding small-section tunnel, a portion of which is excavated by the following small-section tunnel, may be constructed using, for example, reinforced concrete (RC) segments, while the following small-section tunnel may be constructed using, for example, steel segments. Of these, it is desirable to use easy-to-cut segments that can be cut by a shield machine used to construct the following small-section tunnel for the segments that form the preceding small-section tunnel.

Patent Document 1 proposes a cutting segment using concrete as the base material and resin reinforcing bars, in which the concrete contains aggregate, the aggregate including coarse aggregate and fine aggregate, the coarse aggregate being lightweight aggregate or blast furnace slag aggregate, and the reinforcing bars being glass fiber rods with continuous threads. In this cutting segment, 0.25% to 0.5% by volume of aramid fiber is mixed into the concrete as an additive to prevent crack propagation.

According to the cutting segment described in Patent Document 1, the aramid fiber is mixed in an amount of 0.25% by volume to 0.5% by volume, thereby making it possible to prevent crack propagation.
However, it is unclear whether the incorporation of only 0.5% by volume of low-rigidity aramid fibers can effectively prevent crack propagation. Furthermore, the document does not mention any problem, such as the concentration of cracks in one location (or as few locations as possible), resulting in an increase in crack width and a decrease in the water-stopping ability of the cut segments, and it naturally does not mention any means for solving this problem. Furthermore, since it is extremely difficult to disperse cracks, reduce the crack width of each crack, and improve water-stopping ability by simply incorporating 0.5% by volume of low-rigidity aramid fibers, it is difficult to say that the characteristic configuration described in Patent Document 1 is effective in improving the crack dispersion and water-stopping ability of the cut segments.

Therefore, Patent Document 2 proposes an easy-to-cut segment that is as inexpensive to manufacture as possible and has excellent cuttability, load resistance, and water-stopping properties. Specifically, reinforcing bars made of fiber-reinforced plastic are embedded inside a base material, concrete, and steel fibers are dispersed inside the base material, with the base material concrete having a design standard strength of 42 N/ ^mm2 to 60 N/ ^mm2 , a steel fiber mixing rate of 0.3 vol% to 1.0 vol%, and an elastic modulus of the fiber-reinforced plastic being in the range of 30 kN/ ^mm2 to 120 kN/ ^mm2 .

Japanese Patent Application Laid-Open No. 2019-49191 Japanese Patent Application Laid-Open No. 2021-195812

According to the cutting segment described in Patent Document 2, it is possible to provide an easy-to-cut segment that is produced at the lowest possible cost and has excellent cutting ability, load resistance, and water-stopping properties.
The shear strength formula for concrete structures in which continuous fiber reinforcement is embedded in the concrete instead of steel bars is specified in Concrete Library 88, Design and Construction Guidelines for Concrete Structures Using Continuous Fiber Reinforcement (Draft), September 1996, Japan Society of Civil Engineers (hereinafter referred to as "Design Guidelines 1").
On the other hand, the shear strength formula for steel fiber reinforced concrete members, where concrete members are reinforced with steel fibers, is specified in Concrete Library 97, Design Guidelines for Steel Fiber Reinforced Concrete Column Members (Draft), November 1999, Japan Society of Civil Engineers (hereinafter referred to as "Design Guidelines 2").

In other words, when calculating the shear strength of an easily cuttable segment in which steel fibers are dispersed within the concrete, there is no method of calculating the shear strength of the concrete in which the steel fibers are dispersed and the shear strength of the shear reinforcement embedded in the concrete, which has a lower elastic modulus than the steel fibers (steel), and then calculating the overall shear strength of the easily cuttable segment based on these calculation results. For example, Design Guideline 1 does not take into account concrete in which steel fibers are dispersed, and only presents a calculation formula assuming the use of high-modulus carbon fiber reinforced plastic (whose elastic modulus is equivalent to that of steel bars). Design Guideline 2 makes no mention of the use of reinforcing materials such as glass fiber reinforced plastic rods, which have an extremely small elastic modulus—about one-third that of steel bars—as shear reinforcement instead of steel bars.

The purpose of this invention is to provide a method for calculating the shear strength of easily cuttable segments, which allows for a rational calculation of the shear strength of easily cuttable segments in which steel fibers are dispersed in concrete and shear reinforcement bars with a lower elastic modulus than reinforcing bars (steel materials) are used.

In order to achieve the above object, one aspect of the method for calculating the shear strength of a machinable segment according to the present invention is to:
A method for calculating the shear strength of an easily cuttable segment in which reinforcing bars made of fiber-reinforced plastic are embedded inside concrete, which is a base material, and steel fibers are dispersed inside the base material, and the reinforcing bars include main bars and shear reinforcement bars,
The shear strength of the concrete in which the steel fibers are dispersed and the shear strength of the shear reinforcement bars, which have a smaller elastic modulus than the steel fibers, are calculated separately, and the shear strength of both are added together to determine the shear strength of the easily cuttable segment.

According to this aspect, when calculating the shear strength of a cuttable segment in which shear reinforcement bars with a lower elastic modulus than the steel fibers (steel) are embedded within concrete in which steel fibers are dispersed, the shear strength of the concrete in which steel fibers are dispersed and the shear strength of the shear reinforcement bars with a lower elastic modulus than the steel fibers are calculated separately, and the shear strengths of both are added together. This allows for a rational calculation of the shear strength of the cuttable segment. The rationality of calculating the shear strength of the entire cuttable segment by adding together the shear strengths of both is based on the results of verification by the inventors.

In addition, another aspect of the method for calculating the shear strength of a machinable segment according to the present invention is as follows:
The shear strength of the easily cuttable segment: _Vu is calculated by calculating the shear strength of the concrete in which the steel fibers are dispersed: _Vc using the following formula (A), and the shear strength of the shear reinforcement: _Vs using the following formula (B), and then adding up both shear strengths.

According to this aspect, the shear strength of the easily cuttable segment: Vu can be reasonably calculated by calculating the shear strength _Vc shared by the concrete in which steel fibers are dispersed using formula (A) and the shear strength _Vs shared by the shear reinforcement bars, which have a smaller elastic modulus than the steel fibers (steel materials), using formula ₍ B). Both formulas (A) and (B) are modifications of existing formulas, with reference to the above-mentioned Design Guidelines 1 and 2.
In formula (A), the reinforcing effect of steel fiber is evaluated by κ (1.0 or more). In addition, _βp , which evaluates the dowel effect of the main reinforcement bars (main reinforcement) of the reinforcement, reflects the elastic modulus of the reinforcement made of fiber reinforced plastic (excluding high-elasticity carbon fiber reinforced plastic), which has a smaller elastic modulus than steel fiber.

In another aspect of the method for calculating the shear strength of a machinable segment according to the present invention,
The reinforcing bars are made of one of glass fiber reinforced plastic rods, aramid fiber reinforced plastic rods, and medium elasticity carbon fiber reinforced plastic rods.

According to this embodiment, the reinforcing bars are formed from rods such as glass fiber reinforced plastics (GFRP), and therefore do not contain reinforcing bars made from expensive high-elasticity carbon fiber reinforced plastics, thereby keeping production costs as low as possible, and the shear strength of the easy-to-cut segments, which have excellent machinability due to the low rigidity of the rods (elastic modulus in the range of 30 kN/ ^mm2 to 120 kN/ ^mm2 ), can be calculated.

In addition, another aspect of the method for calculating the shear strength of a machinable segment according to the present invention is as follows:
This method is characterized by applying the minimum amount of shear reinforcement specified in the 2017 Japan Society of Civil Engineers Standard Specifications for Concrete [Design Edition] without increasing the minimum amount of shear reinforcement by multiplying it by the reciprocal of the ratio of the stiffness of the reinforcement to the stiffness of the steel bar.

According to this aspect, while fiber-reinforced plastic, which has a lower elastic modulus than steel fiber, is used as shear reinforcement, the reinforcing effect of the steel fiber is appropriately evaluated. This allows the minimum shear reinforcement volume stipulated in the 2017 Japan Society of Civil Engineers Standard Specifications for Concrete [Design Edition] (hereinafter referred to as "Design Guideline 3"), in addition to the above Design Guideline 1, to be applied without increasing the minimum shear reinforcement volume by multiplying the reciprocal of the ratio of the stiffness of the reinforcing bar to the stiffness of the steel bar. This elimination of the need to increase the minimum shear reinforcement volume is based on the results of verification by the inventors.

In addition, another aspect of the method for calculating the shear strength of a machinable segment according to the present invention is as follows:
The minimum shear reinforcement amount is a reinforcement ratio of 0.15%, which is the ratio of the cross section of the shear reinforcement to the cross section of the concrete.

In this case, even though fiber-reinforced plastic, which has a lower elastic modulus than steel fiber, is used as shear reinforcement, the minimum amount of shear reinforcement is set at the reinforcement ratio of 0.15% as specified in Design Guidelines 1 and 3, thereby preventing excessive shear reinforcement.

In addition, another aspect of the method for calculating the shear strength of a machinable segment according to the present invention is as follows:
When the reinforcing bar is a glass fiber reinforced plastic rod, the ratio of the elastic modulus of the glass fiber reinforced plastic rod (60 N/mm2 ⁾ to the elastic modulus of the steel bar (200 N/mm2 ⁾ is 0.3.

According to this aspect, even if the reinforcing bars are glass fiber reinforced plastic rods and the ratio of the elastic modulus to the steel bars is 0.3, the minimum amount of shear reinforcement can be prevented by setting the reinforcing bar ratio at 0.15% as specified in Design Guidelines 1 and 3, rather than increasing the reinforcing bar ratio by an amount proportional to this ratio (dividing by 0.3) to 0.5%, thereby preventing excessive shear reinforcement.

The method for calculating the shear strength of easily cuttable segments of the present invention makes it possible to rationally calculate the shear strength of easily cuttable segments in which steel fibers are dispersed within the concrete and shear reinforcement bars with a lower elastic modulus than reinforcing bars (steel) are used.

FIG. 1 is an oblique view showing an easily cuttable segment to which an example of a shear strength calculation method according to an embodiment is applied, and is a transparent view that allows the interior to be seen. FIG. 1 is a graph showing the tensile stress-strain relationship of various reinforcing bars. FIG. 1 is a perspective view of an example of a steel fiber. 1 is a schematic diagram of a test specimen used in a shear test. FIG. 1 is a graph showing the load-displacement relationship obtained by a shear test. FIG. 1 is a diagram showing the state of fracture of a test specimen in a shear test.

The following describes a method for calculating the shear strength of a machinable segment according to an embodiment, with reference to the accompanying drawings. Note that in this specification and drawings, substantially identical components may be designated by the same reference numerals, and redundant explanations may be omitted.

[Method for calculating shear strength of easily cuttable segment according to embodiment]
First, an example of a method for calculating the shear strength of a machinable segment according to an embodiment will be described with reference to Figures 1 to 3. Figure 1 is a perspective view of a machinable segment to which an example of the shear strength calculation method according to an embodiment is applied, showing the interior of the machinable segment as a visible view. Figure 2 is a graph showing the tensile stress-strain relationship of various reinforcing bars, and Figure 3 is a perspective view of an example of a steel fiber.

The machinable segment 10 designed and manufactured using the shear strength calculation method according to the embodiment has reinforcement bars 21, 22 made of fiber-reinforced plastic and a large number of dispersed steel fibers 30 inside the base material, concrete. The machinable segment 10 has a curved shape that matches the curvature of the segmented tunnel to be constructed, and has a pair of ring joint surfaces 11 and a pair of segment joint surfaces 12.

The concrete design strength of the base material is in the range of 42 N/mm ² to 60 N/mm ² , which satisfies the design standard strength of concrete to be applied to segments as specified in Design Guideline 3.

As shown in Figure 1, main reinforcement bars 21 (inner and outer main reinforcement bars) and shear reinforcement bars 22 are arranged within the base concrete material to provide tensile resistance to bending moments acting on the cuttable segment 10. Each reinforcement bar 21, 22 is made of fiber-reinforced plastic, and more specifically, is made of one of the following rods: glass fiber reinforced plastic (GFRP) rods, aramid fiber reinforced plastic (AFRP) rods, and medium-elasticity carbon fiber reinforced plastic (medium-elasticity CFRP) rods; high-elasticity carbon fiber reinforced plastic rods are not used.

As shown in Figure 2, the elastic modulus of these fiber reinforced plastics is in the range of 30 kN/ ^mm2 to 120 kN/ ^mm2 , resulting in rods with lower rigidity than steel bars, which have an elastic modulus of approximately 200 kN/ ^mm2 , or high-elasticity carbon fiber reinforced plastics, which have an elastic modulus equivalent to that of steel bars. In this way, by using reinforcing bars 21, 22 made of low-rigidity rods, the machinability of the machinable segment 10 is improved. Furthermore, by not using high-elasticity carbon fiber reinforced plastics, which are expensive materials, the manufacturing cost of the machinable segment 10 can be kept as low as possible.

However, when only the reinforcing bars 21, 22 made of rods such as glass fiber reinforced plastic are embedded in the base material, the low rigidity of the glass fiber reinforced plastic rods makes it easier for large cracks to form, which can reduce watertightness. Therefore, the easy-to-cut segment 10 is configured with a large number of steel fibers 30 dispersed within the base material. For example, the steel fibers 30 are dispersed within the base material at a mixing rate of 0.3% to 1.0% by volume.

As shown in Figure 3, the steel fibers 30 have a straight central bar 31 and one or more stepped hook members 32 at both ends of the central bar 31. By having one or more stepped hook members 32 at both ends of the straight central bar 31, the steel fibers 30 have enhanced adhesion to the base material, improving the stress-strain characteristics of the easy-to-cut segment 10, which includes reinforcing bars 21, 22 made of low-rigidity fiber-reinforced plastic. Furthermore, the cross-linking effect of the steel fibers 30 improves crack dispersion, minimizing the crack width of potential cracks and improving watertightness.

Here, it is preferable to use high performance steel fiber (HPSF) as the steel fiber 30, which has a high tensile strength of about 1800 N/ ^mm2 . The stepped hook material 32 of the steel fiber 30 in the illustrated example has a substantially Z-shape, but stepped hook materials of various shapes and forms can be used, such as a multi-stage stepped hook material with two or more substantially Z-shapes. Furthermore, while the central rod 31 of the steel fiber 30 in the illustrated example is linear, it may also be zigzag, wavy, curved, or other shapes.

By setting the mixing rate of steel fibers 30 to, for example, a range of 0.3% to 1.0% by volume, it is possible to ensure both manufacturability when manufacturing segments at concrete plants and the segment reinforcement effect of the steel fibers.

In addition, by mixing steel fibers 30 into the base material, the machinable segment 10 is prevented from becoming a segment in which brittle bending compression failure or shear failure occurs first.

In addition, reinforcing bars 20 made of rods such as glass fiber reinforced plastic are embedded within the base concrete, and a predetermined amount of steel fibers 30 are dispersed within, resulting in an easily cuttable segment with superior M-φ characteristics compared to those of ordinary RC segments and high load-bearing capacity.

In addition, in the easily machinable segment 10, a large number of steel fibers 30 are dispersed within the base material, which improves crack dispersion due to the bridging effect of the steel fibers 30, effectively suppressing the crack width of any cracks that do occur.

Returning to Figure 1, the machinable segment 10 has a tenon groove 13 on one ring joint surface 11 and a tenon 14 on the other ring joint surface 11. In the illustrated example, three tenon grooves 13 are provided on one ring joint surface 11, and three tenons 14 are provided on the other ring joint surface 11 at positions corresponding to the three tenon grooves 13. Therefore, the three tenons 14 of one machinable segment 10 to be joined engage with the three tenons 13 of the other machinable segment 10, respectively. Note that the number of tenons 13 and tenons 14 provided on the ring joint surfaces 11 is not limited to the illustrated example.

For example, a butt joint is applied to the segment joint surface 12. As shown in Figure 1, a butt joint is formed by inserting and screwing a resin assembly diagonal bolt 25, also made of resin, into one of the machinable segments 10 from the other machinable segment 10, into the resin assembly insert 26. Furthermore, multiple (three in the illustrated example) partial tenon joints can be applied to the ring joint surface 11, and bending moments at the segment joint surface 12 can be effectively transmitted to the adjacent machinable segment 10 via the engagement structure of the tenons 14 and tenon grooves 13 on the ring joint surface 11. Note that various types of joints other than butt joints can also be applied to segment joints.

In addition to the tenon-type joint shown in the illustration, various types of joints may be used as ring joints, including one-touch joints. For example, in a one-touch joint, the ring joint is formed by, for example, pushing a male joint provided on the ring joint surface of one segment into a female joint provided on the ring joint surface of the other segment. When using this type of ring joint on an easily machinable segment, it is recommended that both the female joint and the male joint be made of an easily machinable resin.

Next, we will explain an example of a method for calculating the shear strength of the easily cuttable segment 10 shown in Figure 1.

In the shear strength calculation method according to the embodiment, the shear strength _Vc shared by the concrete in which the steel fibers 30 are dispersed is calculated using the following formula (A), and the shear strength _Vs shared by the shear reinforcement 22 is calculated using the following formula (B), and the shear strengths of both are added together to calculate the shear strength _Vu of the easily cuttable segment 10.

Here, formula (A) is a modified version of the existing formula described in Design Guidelines 1 and 2 with reference to these guidelines, and formula (B) is a modified version of the existing formula described here with reference to Design Guidelines 1. In formula (A), the reinforcing effect of steel fibers 30 dispersed in concrete is evaluated by κ (1.0 or more). Furthermore, β _p , which evaluates the dowel effect of the main reinforcement bars 21, reflects the elastic modulus of reinforcing bars made of fiber-reinforced plastic (e.g., GFRP), which has a smaller elastic modulus than steel fibers.

On the other hand, in formula (B), the minimum shear reinforcement mass of the shear reinforcement 22 is determined by applying the minimum shear reinforcement mass specified in Design Guidelines 1 and 3 without increasing the minimum shear reinforcement mass by multiplying it by the reciprocal of the ratio of the stiffness of the shear reinforcement 22 to the stiffness of the steel bars.

Specifically, when the stiffness of GFRP reinforcement is one-third that of rebar, as specified in Design Guideline 1, the minimum shear reinforcement amount of 0.15% specified in Design Guideline 3 is increased in accordance with the stiffness ratio to the rebar. Since the elastic modulus of rebar is 200 N/ ^mm2 , the elastic modulus of GFRP rod is 60 N/ ^mm2 , and the stiffness ratio of GFRP to rebar is 0.3, the minimum shear reinforcement amount should essentially be increased by 1/0.3 from 0.15% specified in Design Guideline 3, to 0.5%.

However, if the shear reinforcement volume exceeds 0.5%, the shear reinforcement will be arranged too densely, which will not only increase the manufacturing costs of the easy-to-cut segments, but will also cause problems such as reduced flowability of concrete during manufacturing, which directly affects the quality of the easy-to-cut segments.

The inventors conducted verification tests, detailed below, and confirmed that even when GFRP or other rods with approximately one-third the rigidity of ordinary steel bars are used as shear reinforcement, sufficient shear strength can be achieved with an appropriate amount of shear reinforcement without increasing the amount of shear reinforcement according to its rigidity (elastic modulus). Therefore, in the shear strength calculation method according to this embodiment, even when shear reinforcement is made of fiber-reinforced plastic, which has lower rigidity than steel bars (steel), the minimum shear reinforcement amount is set to 0.15%, as specified in Design Guideline 3.

This method for calculating the shear strength of easily cuttable segments allows for a reasonable calculation of the shear strength of easily cuttable segments in which steel fibers 30 are dispersed in concrete and shear reinforcement bars with a lower elastic modulus than reinforcing bars (steel) are used, by properly evaluating the reinforcing effect of the steel fibers 30 dispersed in the concrete and properly evaluating the dowel effect of the main reinforcement bars 21.

[Shear test and results]
Next, we will explain the shear tests and their results conducted by the present inventors with reference to Figures 4 to 6. The purpose of this shear test is to verify the validity of calculating the shear strength of easily cuttable segments, in which fiber-reinforced plastic (GFRP) reinforcing bars are embedded in a concrete matrix containing dispersed steel fibers, by modifying and combining the shear strength calculation formulas described in the previous Design Guidelines 1, 2, and 3. Furthermore, the purpose of this shear test is to verify the validity of not requiring an increase in the minimum shear reinforcement amount even when the shear reinforcement amount is below the minimum shear reinforcement amount of 0.15% specified in the Design Guidelines 1 and 3.

<Test Overview>
Figure 4 shows a schematic diagram of the specimen used in the shear test. As shown in Figure 4, the specimen was a beam member with a square cross section of 250 mm on each side and a length of 1600 mm. A vertical linear load was applied to the beam until failure occurred at a single point in the center. The shear span ratio was 2.8, and five GFRP reinforcement bars (φ25 × 5) were placed as main reinforcement to ensure that shear failure occurred first.

In this shear test, CASE 1 was conducted in which no shear reinforcement was placed to confirm the shear strength ( _Vc) borne by the concrete, and CASE 2 was conducted in which a shear reinforcement ratio of 0.2% (GFRP reinforcement φ8 @ 95 mm) was placed to confirm the shear strength (Vs ₎ borne by the shear reinforcement. The test cases are shown in Table 1 below, and the materials used are shown in Table 2 below.

<Test Results>
The load-displacement relationship obtained from the test is shown in Figure 5, and a comparison of the test results and design values is shown in the following Table 3. Furthermore, the fracture state of the test specimen is shown in Figure 6.

In both Case 1 and Case 2, the failure mode was shear failure due to the opening of diagonal cracks. Furthermore, the maximum load in the test exceeded both the design value and the value calculated based on the actual strength (safety factor of 1.0). The reason the value exceeded the calculated value based on the actual strength is thought to be because the reinforcing effect κ of the mixed steel fibers was 1.0 or greater.

Here, the difference in maximum load between CASE 1 and CASE 2 was 39 kN. This is equivalent to the calculated shear reinforcement load of 44 kN (312 - 268 = 44 in Table 3), confirming that the reinforcing effect of the GFRP shear reinforcement can be appropriately evaluated. Furthermore, due to the inclusion of steel fibers, no brittle fracture was observed even after the maximum load was reached.

Through this shear test, it was confirmed that the shear strength calculation formula, which adds together formulas (A) and (B), an appropriately modified version of the shear strength calculation formulas set out in Design Guidelines 1 and 2, can be applied to easily cuttable segments in which GFRP reinforcement is used as the main reinforcement and shear reinforcement and steel fibers are dispersed within the concrete, both in cases where no shear reinforcement is placed and in cases where 0.2% shear reinforcement is placed.

Furthermore, it was confirmed that the minimum shear reinforcement content of 0.15% based on Design Guidelines 1 and 3 can be applied to the 0.15% specified in Design Guideline 3 without increasing it depending on the stiffness ratio between GFRP and steel bars.

Note that other embodiments may be possible in which other components are combined with the configurations described in the above embodiments, and the present invention is in no way limited to the configurations shown here. In this regard, changes can be made without departing from the spirit of the present invention, and can be determined appropriately depending on the application form.

10: Easy-to-cut segment 11: Ring joint surface 12: Segment joint surface 13: Mortise groove 14: Mortise 20: Reinforcement 21: Reinforcement (main reinforcement)
22: Reinforcement (shear reinforcement)
25: Assembly diagonal bolt 26: Assembly insert 30: Steel fiber 31: Central rod 32: Stepped hook material

Claims (4)

A method for calculating the shear strength of an easily cuttable segment in which reinforcing bars made of fiber-reinforced plastic are embedded inside concrete, which is a base material, and steel fibers are dispersed inside the base material, and the reinforcing bars include main bars and shear reinforcement bars,
The shear strength of the concrete in which the steel fibers are dispersed and the shear strength of the shear reinforcement, which has a smaller elastic modulus than the steel fibers, are calculated separately, and the shear strengths of both are added together to determine the shear strength of the easily cuttable segment ;
The reinforcing bar is formed of any one of a glass fiber reinforced plastic rod, an aramid fiber reinforced plastic rod, and a medium elasticity carbon fiber reinforced plastic rod ;
A method for calculating the shear strength of an easily cuttable segment, characterized by applying the minimum amount of shear reinforcement specified in the Standard Specifications for Concrete [Design Edition] established by the Japan Society of Civil Engineers in 2017, without increasing the minimum amount of shear reinforcement by multiplying it by the reciprocal of the ratio of the stiffness of the reinforcement to the stiffness of the steel bar. 2. The method for calculating the shear strength of a cuttable segment according to claim 1, characterized in that the shear strength _Vc shared by the concrete in which the steel fibers are dispersed is calculated by the following formula (A), the shear strength _Vs shared by the shear reinforcement is calculated by the following formula (B), and the shear strengths of the cuttable segment _Vu are calculated by adding up both shear strengths.
A method for calculating the shear strength of an easily cuttable segment as described in claim 1 or 2 , characterized in that the minimum amount of shear reinforcement is a reinforcement ratio of 0.15%, which is the ratio of the cross-section of the shear reinforcement to the cross-section of the concrete. A method for calculating the shear strength of an easily cuttable segment as described in claim ³ , characterized in that when the reinforcing bar is a glass fiber reinforced plastic rod, the ratio of the elastic modulus of the glass fiber reinforced plastic rod: 60 N/ ^mm2 to the elastic modulus of the steel bar : 200 N/mm2 is 0.3.