JP7089105B1 - How to crush concrete around block gibber in synthetic deck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently crush concrete around a block girder in a reinforced concrete synthetic deck integrated with a steel main girder by a block girder including a U-shaped girder main body arranged in an inclined manner. offer. SOLUTION: A first impact generating agent 15 is arranged inside a ring shape formed by a base portion 9 of a block gibber 4 and a gibber main body portion 10 in a plan view, and below the gibber main body portion 10 when viewed from the bridge width direction. Will be done. The second impact generator 16 is arranged on the side opposite to the first impact generator 15 with respect to the base 9 in a plan view. The first impact generator 15 and the second impact generator 16 are detonated at the same time. At least a part of the first tensile stress wave reflected on the upper surface of the steel main girder 3 and propagating the concrete 5 toward the block gibber 4 is reflected on the upper surface of the steel main girder 3 and propagated on the block gibber 4 and then the concrete. It collides with at least a part of the second tensile stress wave propagating in the steel main girder 3 toward the steel main girder 3, overlaps and interferes with each other. [Selection diagram] Fig. 3

Description

The present invention relates to a method for crushing concrete around a block girder in a reinforced concrete synthetic deck integrated with a steel main girder by a block girder.

The synthetic deck is a reinforced concrete deck that is integrated with the steel main girder by embedding a slip stopper installed on the upper surface of the steel main girder. A block gibber may be used as a slip stopper. The block gibber, sometimes referred to as a horseshoe-shaped gibber, includes a base connected to the upper surface of the steel main girder and a U-shaped gibber body (ring streak) connected to the base at both ends.

When removing the deck and constructing a new synthetic deck on the existing steel main girder, or when dismantling a bridge, it is necessary to dismantle the synthetic deck. For example, Patent Document 1 describes a method of dismantling a concrete deck using a water jet method. In some cases, the concrete deck is manually dismantled using a tool such as a hammer drill.

Japanese Unexamined Patent Publication No. 64-48972

Crushing concrete by the water jet method takes a long time because the removal efficiency is low, it costs a lot of money to supply and treat it because it uses a large amount of water, and there are also large measures to prevent water leakage and sprinkling. There was a problem that ordinary noise (noise level at a point 3 m away was about 95 dB) was generated, which became a large scale.

In addition, crushing concrete manually using a tool such as a hammer drill tends to prolong the process because the removal efficiency is relatively low, and it is difficult to secure workers because it involves labor-intensive work. There was a problem that it was accompanied by ordinary noise (noise level at a point 10 m away was 85 to 95 dB), which was a cause of vibration damage.

In addition, when the gibber main body is installed at an angle with respect to the vertical direction when viewed from the bridge width direction, the concrete between the gibber main body and the upper surface of the steel main girder restrains the concrete in between. It was difficult to dismantle.

In view of the above background, the present invention efficiently crushes concrete around a block girder in a reinforced concrete synthetic deck integrated with a steel main girder by a block girder including an inclined girder main body. The challenge is to provide a method that can be done.

In order to solve the above problems, one aspect of the present invention is the concrete around the block gibber (4) in the reinforced concrete synthetic slab (2) integrated with the steel main girder (3) by the block gibber (4). The crushing method of (5), the portion between the girder portion (11) including the portion located on the steel main girder (3), the girder portion (11) adjacent to each other, and the bridge width. The synthetic slab (12) comprising a non-girder portion (12) including an outer portion in the bridge width direction than the girder portion (11) on the steel main girder (3) arranged at the end in the direction. From 2), a step of removing the non-girder portion (12) and a step of drilling a first charge hole (13) and a second charge hole (14) in the girder portion (11) . The step of charging the first impact generating agent (15) into the first charging hole (13) and charging the second impact generating agent (16) into the second charging hole (14), and the first. The block gibber (4) is made of steel fixed to the upper surface of the steel main girder (3), comprising one step of simultaneously detonating the impact generator (15) and the second impact generator (16). A steel gibber body portion (10) having both ends fixed to the base portion (9) so as to form a ring shape in a plan view in combination with the base portion (9) is included. The first impact generator (15) is arranged inside the ring shape in a plan view and below the gibber body portion (10) when viewed from the bridge width direction, and the second impact generator (16) is , The compression stress wave generated by the detonation of the first impact generator (15), which is arranged on the side opposite to the first impact generator (15) with respect to the base (9) in a plan view, is the steel main girder. At least a part of the first tensile stress wave (18a) generated by reflection on the upper surface of (3) and propagating in the concrete (5) toward the block gibber (4) generates the second impact. The compressive stress wave generated by the detonation of the agent (16) propagates in the block gibber (4) in the second tensile stress wave (18b) generated by being reflected on the upper surface of the steel main girder (3). The first impact generator (15) and the second impact generator (16) so as to collide with at least a part of the portion propagating toward the steel main girder (3) in the concrete (5). ) Is placed.

According to this aspect, the first tensile stress wave and the second tensile stress wave collide with each other in the restraint region sandwiched between the upper surface of the steel main girder in the deck and the gibber main body of the block gibber, so that the time is short. Can crush the concrete in the restraint area with.

In the above embodiment, in a plan view, the distance from the center of the second impact generator (16) to the base (9) is 60 mm or less, and the steel main is from the lower end of the second impact generator (16). The distance of the girder (3) to the upper surface is preferably 60 mm or less.

According to this aspect, the compressive stress wave generated by the detonation of the second impact generator is reflected on the upper surface of the steel main girder to generate the second tensile stress wave, and this second tensile stress wave is transmitted to the block gibber. Since it becomes easy, the crushing of the concrete in the restraint area becomes remarkable.

In the above aspect, the first impact generator (15) may be arranged substantially at the center of the ring shape in a plan view. Here, the "substantially center" means that the case where the first charge hole is deviated from the center by the amount necessary for drilling the first charge hole while avoiding the reinforcing bar is included.

According to this aspect, since the first tensile stress wave collides with the second tensile stress wave in the restraint region at the stage where the damping is small, the crushing of the restraint region becomes remarkable.

In the above embodiment, a plurality of the block gibber (4) are arranged so as to form a row along the bridge axis direction, and for each of the block gibber (4), the first impact generator (15) and the block gibber (15) are arranged. A pair of the second impact generator (16) is arranged so as to face each other in the bridge axis direction, and the first impact generator (15) is the first impact generator (15) in a plan view. ) To the second impact generating agent (16) adjacent to the base (9), and adjacent to the first impact generating agent (15) without sandwiching the base (9). The distance (L2) to the second impact generator (16) is arranged so as to be offset from the center in the bridge axis direction of the ring shape in a direction close to each other, and the detonating steps are in the same row in common with each other. It may include simultaneously detonating a plurality of the first impact generating agent (15) and the second impact generating agent (16) arranged along the same.

According to this aspect, since the distance between the first impact generator and the second impact generator adjacent to each other is arranged so as to be evenly close to each other, the first impact generator and the second impact generator adjacent to each other are arranged so as to be evenly close to each other. 2 The concrete between the impact generator and the concrete is easily crushed.

According to the above aspects, a method capable of efficiently crushing concrete around a block girder in a reinforced concrete synthetic deck integrated with a steel main girder by a block girder including an inclined girder main body is provided. Can be provided.

A perspective view showing the upper part of a bridge including a synthetic deck to which the method according to the embodiment is applied. Top view of the synthetic deck in the middle of applying the method according to the embodiment Partial cross-sectional front view of the synthetic deck in the middle of applying the method according to the embodiment (view from the bridge width direction) A: Cross-sectional view taken along line AA in FIG. 2, B: Cross-sectional view taken along line BB in FIG. Explanatory drawing of a synthetic deck to which the method according to the embodiment is applied (partial cross-sectional front view) Diagram for explaining the reason why concrete is crushed by the method according to the embodiment (partial cross-sectional front view, hatching for showing concrete cross-section omitted) Photograph of the specimen to which the method according to the embodiment is applied Photograph when concrete is partially removed from the specimen to which the method according to the embodiment is applied.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of the upper part of the bridge 1 to which the method according to the embodiment is applied, and shows a state in which the deck 2 is partially removed. The bridge 1 includes a steel main girder 3 including H-shaped steel supported at the lower part (not shown) so as to extend in the direction of the bridge axis, and a reinforced concrete deck 2 supported by the steel main girder 3. Be prepared.

As shown in FIGS. 2 and 3, a block gibber 4 is fixed to the upper surface of the upper flange 3a of the steel main girder 3 by welding or the like as a slip prevention. The concrete 5 of the deck 2 embeds the block gibber 4, so that the deck 2 is a synthetic deck integrated with the steel main girder 3. The deck 2 has a vertical bar 6 extending in the direction of the bridge axis, a horizontal bar 7 extending in the width direction of the bridge, and reinforcing bars arranged so as to surround one block gibber 4 in pairs in a plan view. 8 and concrete 5 in which a block gibber 4, a vertical bar 6, a horizontal bar 7 and a reinforcing bar 8 are embedded are included.

The block gibber 4 is a steel base 9 fixed to the upper surface of the upper flange 3a of the steel main girder 3 by welding or the like, and a U-shaped steel gibber body whose both ends are fixed to the base 9 by welding or the like. Includes part 10. The base 9 extends in the width direction of the bridge to form a block shape or a plate shape. Both ends of the base 9 may be curved so as to face the bridge axis direction. The gibber body 10 includes U-shaped steel rods whose ends are separated from each other in the bridge width direction, is inclined in the vertical direction when viewed from the bridge width direction, and is combined with the base 9 in a plan view. It forms a ring shape. A plurality of block gibber 4s are arranged on each steel main girder 3 so as to be arranged in a row along the bridge axis direction.

When dismantling the deck 2, first, as shown in FIG. 1, the girder portion 11 having a width slightly wider than both ends in the width direction of the steel main girder 3 remains on the steel main girder 3. The non-digit portion 12 is removed. The non-girder portion 12 is outside the bridge width direction from the portion between the two girder portions 11 adjacent to each other and the girder portion 11 on the steel main girder 3 arranged at the end in the bridge width direction. Including parts.

With respect to the floor slab 2, in order to remove the non-girder portion 12, the worker supports the non-girder portion 12 with a temporary member (not shown), and the worker uses a cutting device such as a concrete cutter (not shown). ) Is used to cut the boundary between the non-girder portion 12 and the girder portion 11 up and down along the bridge axis direction. Further, the worker should divide the deck 2 into a weight that can be unloaded by a crane (not shown) and a weight and a size that can be carried by a transportation machine such as a truck (not shown), if necessary. , The deck 2 is cut up and down along the bridge width direction using a cutting device. The worker lifts the divided non-girder portion 12 with a crane, puts it on a transport machine, and carries it out.

Next, as shown in FIGS. 2 to 4, the worker can use the first charge hole 13 and the first charge hole 13 based on the positions of the block gibber 4, the vertical bar 6, the horizontal bar 7, and the reinforcing bar 8 that have been investigated in advance. The second charge hole 14 is drilled. After that, the worker charges the first impact generating agent 15 into the first charging hole 13 and the second impact generating agent 16 into the second charging hole 14.

The positions of the block gibber 4, the vertical bar 6, the horizontal bar 7, and the reinforcing bar 8 can be grasped based on the bar arrangement diagram of the deck 2. If necessary, the worker grasps these positions by using a reinforcing bar probe or the like.

The first charge hole 13 and the second charge hole 14 are drilled downward from the upper surface of the deck 2. One first charge hole 13 and one second charge hole 14 are drilled for one block gibber 4. In a plan view, the first charge hole 13 is provided inside the ring shape formed by the base portion 9 and the gibber body portion 10, and the second charge hole 14 is the first charge hole 13 with respect to the base portion 9. Is provided on the opposite side of the bridge axis direction. If the arrangements of the first impact generating agent 15 and the second impact generating agent 16 satisfy predetermined conditions, the first charge hole 13 and the second charge hole 14 are inclined in the vertical direction. Also, holes may be drilled from the side surface of the girder portion 11. Further, the drilling of the first charge hole 13 and the second charge hole 14, and the charge of the first impact generator 15 and the second impact generator 16 are made of the non-girder portion 12 (see FIG. 1). You may go before the removal. If there are vertical bars 6, horizontal bars 7 or reinforcing bars 8 at positions suitable for the first charge hole 13 and the second charge hole 14, the worker cuts these reinforcing bars and cuts the first charge hole 13 and the first charge hole 13. The second charge hole 14 may be provided, and if the positions of the first impact generator 15 and the second impact generator 16 satisfy the predetermined conditions described later, the first charge is displaced from these reinforcing bars. A hole 13 and a second charge hole 14 may be provided.

The first impact generator 15 and the second impact generator 16 are charged to the bottoms of the first charge hole 13 and the second charge hole 14. The first impact generating agent 15 is arranged inside the ring shape formed by the base portion 9 and the gibber main body portion 10 in a plan view, and is arranged below the gibber main body portion 10 when viewed from the bridge width direction.

In a plan view, the distance from the center of the second impact generator 16 to the base 9 is 60 mm or less, and it is preferable that the second impact generator 16 is arranged as close to the base 9 as possible. Therefore, the distance from the second impact generator 16 to the base 9 is shorter than the distance from the first impact generator 15 to the base 9. The value of 60 mm or less was identified based on the experimental results. The distance from the lower end of the second impact generator 16 to the upper surface of the upper flange 3a of the steel main girder 3 is 60 mm or less. In the illustrated embodiment, the distance from the lower end of the first impact generating agent 15 to the upper surface of the upper flange 3a of the steel main girder 3 and from the lower end of the second impact generating agent 16 to the upper surface of the upper flange 3a of the steel main girder 3. Distances are equal to each other. Therefore, the depths of the first charge hole 13 and the second charge hole 14 can be made common to each other, and the drilling depths of the first charge hole 13 and the second charge hole 14 are reversed. You can prevent the construction mistake of making it.

In order to separate the deck 2 from the steel main girder 3, it is important to crush the restraint region A (see FIG. 5) sandwiched between the upper flange 3a of the steel main girder 3 and the gibber body 10 in the concrete 5. Will be. When emphasizing the crushing of the restraint region A, it is desirable that the first impact generating agent 15 is arranged substantially in the center of the ring shape formed by the base portion 9 and the gibber body portion 10 in a plan view. Here, the "substantially center" means that the case where the first charge hole 13 is deviated from the center by the amount necessary for drilling the first charge hole 13 while avoiding the vertical bar 6, the horizontal bar 7, or the reinforcing bar 8 is also included. do.

Further, when emphasizing the crushing of the portions of the concrete 5 between the adjacent block gibber 4, the first impact generating agent 15 and the second impact generating agent 16 are arranged so as to be as evenly spaced as possible. Will be done. That is, each of the first impact generators 15 has a second impact adjacent to the base 9 with the base 9 in between, rather than the center in the bridge axis direction of the ring shape formed by the base 9 and the gibber body 10 in a plan view. The distance L1 to the generator 16 and the distance L2 from itself to the adjacent second impact generator 16 without sandwiching the base 9 are arranged so as to be offset from each other in the direction of approaching each other. In the illustrated example, the first impact generator 15 is arranged at a position farther from the base 9 than the center in the bridge axis direction of the ring shape formed by the base 9 and the gibber body 10 in a plan view. As a result, the distance between the first impact generator 15 and the second impact generator 16 is set to be evenly close to each other. In a plan view, the distance between the bases 9 of two block gibber 4s adjacent to each other is L, the distance between the first impact generator 15 and the second impact generator 16 adjacent to each other across the base 9 is L1, and the base 9 When the distance between the first impact generating agent 15 and the second impact generating agent 16 adjacent to each other is L2, 0.4L ≦ L1 ≦ 0.6L and 0.4L ≦ L2 ≦ 0.6L. It is preferable, and it is more preferable that L1 ≈ L2.

When a block gibber 4 with standard dimensions (width: 180 mm or more and 250 mm or less, height: 180 mm or more and 220 mm or less) is used, the first impact generator 15 and the second impact generator 16 are the steel main girder 3. It is preferable to apply an impact within a range of 60 mm or less from the upper surface of the upper flange 3a with a maximum pressure of 1.8 GPa or more and 2.4 GPa or less and a maximum pressure arrival time of 25 microseconds or more and 35 microseconds or less. Examples of the types of the first impact generator 15 and the second impact generator 16 satisfying such conditions include a nitromethane-based impact generator and an impact generator containing a mixture of aluminum powder and metal oxide powder. .. It is preferable that the types of agents used in the first impact generator 15 and the second impact generator 16 are the same as each other.

Next, the worker simultaneously detonates a plurality of first impact generating agents 15 and a plurality of second impact generating agents 16 arranged so as to be substantially aligned in the direction of the bridge axis. As a result, the concrete 5 of the deck 2, particularly the restraint area A (see FIG. 5) is crushed. The worker removes the crushed concrete 5, the vertical bar 6, the horizontal bar 7, and the reinforcing bar 8.

When a new synthetic deck slab is to be installed on the existing steel main girder 3 with cast-in-place concrete after the existing floor slab 2 is removed, the worker may use the existing block gibber 4 as a slip stopper. The block gibber 4 may be cut to provide a new slip stopper. Further, when a new synthetic deck is provided on the existing steel main girder 3 with a precast concrete member, the worker cuts the existing block girder 4 and installs the precast concrete member on the steel main girder 3. , A slip stopper is provided in the box punch hole that penetrates in the vertical direction provided in the precast concrete member, and concrete is filled in the box punch hole (not shown).

FIG. 6 schematically shows how the maximum pressure portion or the earliest portion of the shock wave (stress wave) due to the detonation of the first impact generator 15 and the second impact generator 16 propagates. The reason why the concrete 5 of the deck 2 is crushed will be described with reference to FIG. As shown in FIG. 6A, the compressive stress wave 17 generated by the detonation of the first impact generator 15 and the second impact generator 16 is reflected on the upper surface of the upper flange 3a of the steel main girder 3 and the tensile stress. Converted to wave 18. As shown in FIG. 6B, the tensile stress wave 18 propagates inside the concrete 5 and inside the block gibber 4. The tensile stress wave 18 propagating in the concrete 5 propagates while being attenuated upward substantially parallel to the upper surface of the upper flange 3a. In general, a wave propagating in a metal propagates faster with little attenuation than a wave propagating in a concrete 5. Therefore, the tensile stress wave 18 propagating in the block gibber 4 propagates faster than the tensile stress wave 18 propagating in the concrete 5 with almost no attenuation, and the propagation point becomes a new wave source for concrete. 5 It also propagates inside.

The first tensile stress wave 18a caused by the first impact generator 15 becomes the main wave source of the tensile stress wave 18 from the upper surface of the upper flange 3a toward the gibber main body 10 of the block gibber 4 above the upper surface. The second tensile stress wave 18b caused by the second impact generator 16 becomes the main wave source of the tensile stress wave 18 propagating in the block gibber 4. At least a part of the first tensile stress wave 18a reflected on the upper surface of the upper flange 3a and propagating in the concrete 5 toward the block gibber 4 propagates in the block gibber 4, and then in the concrete 5 the steel main girder 3 It collides with at least a part of the second tensile stress wave 18b propagating toward the upper flange 3a. Due to this collision, a tensile force is applied to the concrete 5, and the concrete 5 is crushed. Further, the first tensile stress wave 18a and the second tensile stress wave 18b overlap each other and interfere with each other to form a complicated propagation path of the tensile stress wave 18, so that the concrete 5 is finely crushed. Since the collision, overlap, and interference between the first tensile stress wave 18a and the second tensile stress wave 18b occur mainly in the restraint region A (see FIG. 5), the concrete 5 in the restraint region A can be crushed in a short time.

Therefore, the first impact generator 15 and the second impact generator 16 are arranged so that the first tensile stress wave 18a and the second tensile stress wave 18b collide with each other. It is a predetermined condition regarding the arrangement of the impact generator 15 and the second impact generator 16. Further, in a plan view, the distance from the center of the second impact generating agent 16 to the base 9 is 50 mm or less, and the distance from the lower end of the second impact generating agent 16 to the upper surface of the upper flange 3a of the steel main girder 3 is 60 mm or less. As a result, the crushing of the concrete 5 in the restraint area A becomes remarkable.

Further, when the first impact generator 15 is arranged substantially in the center of the ring shape formed by the base portion 9 and the gibber body portion 10 in a plan view, the first tensile stress wave 18a is at a stage where the damping is small. Since it collides with the second tensile stress wave 18b in the restraint region A (see FIG. 5), the crushing of the restraint region A becomes remarkable. Further, the concrete 5 other than the restraint area A remains as a relatively large lump. Since the deck 2 is separated from the steel main girder 3 by crushing the restraint region A, the parts other than the restraint region A and the portion in the vicinity thereof in the deck 2 can be easily separated from the steel main girder 3 by using a crane (not shown) or the like. Can be removed. On the other hand, a plurality of first impact generators 15 and second impact generators 16 arranged so as to be arranged in a row in a plan view are spaced apart from each other by adjacent first impact generators 15 and second impact generators 16. When the concrete 5 is arranged so as to be as close to each other as possible, the portion between the block gibber 4 in the concrete 5 is likely to be crushed.

By setting the maximum pressure of the shock wave of the first impact generator 15 and the second impact generator 16 to the above numerical range, the concrete 5 of the deck 2 can be crushed while preventing the steel main girder 3 from being damaged. ..

7 and 8 show photographs of specimens to which the above embodiment is applied. In the embodiment, the plurality of first impact generating agents 15 and the second impact generating agents 16 arranged so as to be arranged in a row have a distance between the first impact generating agent 15 and the second impact generating agent 16 adjacent to each other. They were arranged so as to be as close to each other as possible (see FIGS. 2 to 5 for the portion indicated by the reference numeral, and the same applies hereinafter).

FIG. 7 shows the state immediately after the detonation of the first impact generating agent 15 and the second impact generating agent 16. Even in the region between the block gibber 4, the concrete 5 is cracked along the vertical bar 6 and the reinforcing bar 8.

FIG. 8 shows after removing the concrete 5 in the portion other than the vicinity of the block gibber 4, and the vertical bars 6, the horizontal bars 7, and the reinforcing bars 8. The concrete 5 in the restraint area A was crushed more finely than the other parts.

Although the description of the specific embodiment is completed above, the present invention is not limited to the above-described embodiment or modification, and can be widely modified. The above embodiment may be applied not only to the replacement work of the synthetic deck but also to the demolition work of the bridge.

2: Floor slab 3: Steel main girder 4: Block gibber 5: Concrete 9: Base 10: Jibel body 13: 1st charge hole 14: 2nd charge hole 15: 1st impact generator 16: 2nd impact Generator 18a: 1st tensile stress wave 18b: 2nd tensile stress wave A: Restraint region

Claims (4)

A method for crushing concrete around the block girder in a reinforced concrete synthetic deck integrated with a steel main girder by a block girder.
From the girder portion on the steel main girder arranged at the girder portion including the portion located on the steel main girder, the portion between the girder upper portions adjacent to each other, and the end portion in the bridge width direction. The step of removing the non-girder portion from the synthetic deck including the non-girder portion including the outer portion in the width direction of the bridge.
A step of drilling a first charge hole and a second charge hole in the girder portion ,
The step of charging the first impact generator into the first charge hole and charging the second impact generator into the second charge hole, and the step of charging the second impact generator.
A step of simultaneously detonating the first impact generating agent and the second impact generating agent is provided.
The block gibber has a steel base fixed to the upper surface of the steel main girder and a steel gibber body in which both ends are fixed to the base so as to form a ring shape in a plan view in combination with the base. Including the part
The first impact generating agent is arranged inside the ring shape in a plan view and below the gibber body portion when viewed from the bridge width direction, and the second impact generating agent is arranged with respect to the base portion in a plan view. Is placed on the opposite side of the first impact generator.
At least a part of the first tensile stress wave generated by the compression stress wave generated by the detonation of the first impact generating agent reflected on the upper surface of the steel main girder and propagating in the concrete toward the block gibber. However, after the compressive stress wave generated by the detonation of the second impact generator propagates in the block gibber in the second tensile stress wave generated by being reflected on the upper surface of the steel main girder, the inside of the concrete. The method in which the first impact generator and the second impact generator are arranged so as to collide with at least a part of the portion propagating toward the steel main girder. Claimed that the distance from the center of the second impact generating agent to the base is 60 mm or less and the distance from the lower end of the second impact generating agent to the upper surface of the steel main girder is 60 mm or less in a plan view. Item 1. The method according to Item 1. The method according to claim 1 or 2, wherein the first impact generator is arranged substantially in the center of the ring shape in a plan view. A plurality of the block gibber are arranged so as to form a row along the direction of the bridge axis.
For each of the block gibber, the first impact generator and the second impact generator are arranged in pairs so as to face each other in the direction of the bridge axis.
In a plan view, the first impact generating agent has a distance from the first impact generating agent to the second impact generating agent adjacent to the base and without sandwiching the base from the first impact generating agent. It is arranged so as to be offset from the center of the ring shape in the bridge axis direction in a direction in which the distance to the adjacent second impact generator is close to each other.
The method according to claim 1 or 2, wherein the detonating step comprises simultaneously detonating a plurality of the first impact generating agents and the second impact generating agents arranged along the same row.

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