JP2018024929A - Method for suppressing fatigue crack generation of steel floor slab, manufacturing method of steel floor slab and inner face pressing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device suitable for suppressing generation of fatigue crack and progress of fatigue crack in a route part of a weld bead for jointing a U rib and a deck plate.SOLUTION: In a loading process, pressure is added to a pair of side wall parts 6b and 6c from inside of a U rib 6 to let the pair of side wall parts 6b and 6c deform toward outside of the U rib 6. In a load removal process, the pressure added to the pair of side wall parts 6b and 6c in the loading process is removed. The loading process includes a rear loading process for pressing the side wall parts 6b and 6c while a press member 16 gets in contact with at least a part of a rear area Rr and a front loading process for pressing the side wall parts 6b and 6c while the press member 16 gets in contact with at least a part of a front area Rf. In the rear loading process and the front loading process, the press member 16 does not get in contact with a reference area Rb.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a method for suppressing the occurrence of fatigue cracks in a steel slab, a method for producing a steel slab in which the occurrence of fatigue cracks is suppressed, and an inner surface pressing device that presses the inner surface of a U-rib.

  Conventionally, steel decks are used in civil engineering structures such as bridges. Drawing 1 is a figure showing an example of a bridge provided with a steel deck. In FIG. 1, an X direction, a Y direction, and a Z direction orthogonal to each other are shown. The X direction indicates the length direction of the bridge 1, the Y direction indicates the width direction of the bridge 1, and the Z direction indicates the vertical direction. In the following description, the length direction of the bridge 1 is also referred to as the front-rear direction, and the width direction of the bridge 1 is also referred to as the left-right direction.

  A bridge 1 shown in FIG. 1 has a steel deck 2. FIG. 2 is a view of a part of the steel slab 2 as viewed obliquely from below. 2 also shows the X direction, the Y direction, and the Z direction, as in FIG.

  With reference to FIG. 1 and FIG. 2, the steel deck 2 includes a deck plate 3, a plurality of main girders 4 (see FIG. 1), a plurality of horizontal ribs 5, and a plurality of vertical ribs 6. Yes. The deck plate 3, the main girder 4, the lateral rib 5 and the longitudinal rib 6 are each made of steel.

  Referring to FIG. 1, deck plate 3 has a flat plate shape. The surface 3 a of the deck plate 3 is paved with a paving material 7. As the pavement material 7, for example, various materials such as asphalt or concrete can be used.

  The main girder 4 has, for example, an I shape in a cross section parallel to the YZ plane. The main girder 4 is provided so as to extend in the length direction of the bridge 1. The upper end of the main beam 4 is welded to the back surface 3b of the deck plate 3, for example.

  Referring to FIGS. 1 and 2, the lateral rib 5 has, for example, an inverted T shape in a cross section parallel to the XZ plane. The lateral rib 5 is provided so as to extend in the width direction of the bridge 1. The left and right ends of the lateral rib 5 are welded to the main girder 4, for example.

  With reference to FIG. 2, the horizontal rib 5 has a plate-like web 5a extending in the up-down direction and a plate-like flange 5b extending in the front-rear direction from the lower end of the web 5a. The upper end part of the web 5a is welded to the back surface 3b of the deck plate 3, for example.

  A plurality of recesses 5c are provided at the upper end of the web 5a. Each recess 5c is formed so as to open upward (toward the deck plate 3). Thereby, a hole for passing the vertical rib 6 is formed between the deck plate 3 and the web 5a.

  1 and 2, the vertical rib 6 is a U-rib having an open cross-sectional shape (U-shape) so that the deck plate 3 side opens. Hereinafter, the vertical rib 6 is referred to as a U-rib 6. Specifically, the U rib 6 has a bottom wall portion 6a extending in the left-right direction and a pair of side wall portions 6b, 6c extending upward from both ends in the left-right direction of the bottom wall portion 6a. The side wall portions 6b and 6c are inclined with respect to the bottom wall portion 6a so that the distance between the side wall portions 6b and 6c increases toward the front end side (the deck plate 3 side in FIG. 1). The U rib 6 is provided so as to extend in the length direction of the bridge 1 and to penetrate the lateral rib 5. The upper end portions of the side wall portions 6 b and 6 c are welded to the back surface 3 b of the deck plate 3. The outer peripheral surface of the U rib 6 is welded to the web 5 a of the lateral rib 5.

  With reference to FIG. 1, in the bridge 1 having the above-described configuration, for example, when an automobile 8 passes over the bridge 1, a fatigue crack may occur in the steel deck 2. This fatigue crack occurs, for example, at the joint 9 between the deck plate 3 and the U rib 6. Hereinafter, a mode of occurrence of fatigue cracks in the joint 9 will be described.

  FIG. 3 is an enlarged view showing the joint 9 between the deck plate 3 and the side wall 6b. As shown in FIG. 3, when the side wall portion 6 b is welded to the deck plate 3, for example, the outer portion 6 d of the front end portion of the side wall portion 6 b is joined to the deck plate 3 by the weld bead 10. Normally, the penetration amount of the weld bead 10 is based on 75% of the thickness of the U-rib, and the inner portion 6e of the tip portion of the side wall portion 6b is not joined. For this reason, a notch-shaped space 11 (hereinafter referred to as an unwelded portion 11) is formed between the deck plate 3, the weld bead 10, and the portion 6e. In such a joint 9, tensile residual stress is generated in the vicinity of the weld bead 10 due to expansion during welding and contraction after welding.

  Here, when the automobile 8 passes over the bridge 1, a load is applied to the deck plate 3, and the deck plate 3 bends. As a result, bending stress is generated at the boundary portion between the deck plate 3 and the weld bead 10 and the boundary portion between the side wall portion 6b and the weld bead 10, and fluctuating stresses of tension and compression are generated. Of these stresses, the tensile stress generated in the width direction of the steel slab is superimposed on the above-described residual stress, so that a large tensile stress is likely to occur at the joint 9. When the load is repeatedly applied to the deck plate 3 by passing a plurality of automobiles 8, fatigue occurs in the vicinity of the boundary portion between the deck plate 3 and the weld bead 10 and in the vicinity of the boundary portion between the side wall portion 6 b and the weld bead 10. Cracks may occur. For example, fatigue cracks occur in the toe 12 on the deck plate 3 side or the toe 13 on the side wall 6b side of the weld bead 10, or fatigue cracks occur in the root portion 14 on the deck plate 3 side. Thereby, there exists a possibility that the intensity | strength of the steel deck 2 may fall.

  By the way, in the steel deck 2, the toe 12 and the toe 13 are located outside the U rib 6. For this reason, the fatigue crack which generate | occur | produced in the toe 12 and the toe 13 is easy to be discovered by the operator at the time of the inspection of the bridge 1, etc. In this case, since the part where the fatigue crack has occurred can be repaired at an early stage, it is easy to suppress the strength reduction of the steel deck 2.

  On the other hand, since the root portion 14 is in a position that cannot be seen from the outside of the U-rib 6, it is difficult to find a fatigue crack that has occurred in the root portion 14. Even if it is found that a fatigue crack has occurred in the root portion 14, it is difficult to repair the root portion 14 from the outside of the U rib 6. For this reason, when a fatigue crack occurs in the root portion 14, it is necessary to repair the root portion 14 from the inside of the U-rib 6, and time and labor are required for repairing the fatigue crack.

  Therefore, conventionally, a technique for suppressing the occurrence of fatigue cracks in the root portion 14 has been proposed.

  For example, Patent Document 1 describes a peening method. In the method described in Patent Document 1, the surface of the deck plate is hit by a peening tool in a steel deck using a U-rib. Patent Document 1 describes that compressive residual strain can be applied to an inner portion of a U-rib by applying a hit as described above. In the method described in Patent Document 1, it is considered that by applying compressive residual stress as described above, the progress of fatigue cracks generated in the inner portion of the U rib is suppressed.

JP 2014-172043 A

  However, in the above method, since the front surface side of the deck plate is hit with a peening tool, it is difficult to give a sufficiently large compressive residual stress to the rear surface side of the deck plate. In this case, the progress of fatigue cracks or the occurrence of fatigue cracks cannot be sufficiently suppressed.

  The present invention has been made to solve such a problem, and fatigue cracks are generated in the root portion of the weld bead joining the U rib and the deck plate, and fatigue cracks are generated in the root portion. It is an object of the present invention to provide a method and an apparatus suitable for suppressing the fatigue cracks from developing in some cases.

(1) A fatigue crack generation suppressing method according to an embodiment of the present invention includes a deck plate, a lateral rib having a web having a thickness T welded to the lower surface of the deck plate, and extending through the web. A method for suppressing the occurrence of fatigue cracks in a steel slab having a pair of side wall portions welded to the deck plate and the web,
A load step of pressing the pair of side wall portions from the inside of the U-rib by a pair of pressing members so that the pair of side wall portions deform toward the outside of the U-rib;
An unloading step for removing pressure applied to the pair of side wall portions by the pair of pressing members in the loading step,
The length direction of the U rib is defined as the front-rear direction, and a reference region Rb, a rear region Rr behind the reference region Rb, and a front region Rf ahead of the reference region Rb are defined in the pair of side walls. When defined as follows,
The loading process includes a rear loading process in which the pair of pressing members presses the pair of side wall portions while contacting at least a part of the rear region Rr, and the pair of pressing members contacts at least a part of the front region Rf. And a front load step of pressing the pair of side wall portions,
In the rear load step and the front load step, the pair of pressing members press the pair of side wall portions so as not to contact the reference region Rb.
Reference region Rb: a region forward of the position of 0.5T behind the sheet thickness center line of the web and a position behind the position of 0.5T forward of the sheet thickness center line.
Back region Rr: a region rearward from the position of 0.5T behind the plate thickness center line and a front side of the position of 2.5T rearward from the plate thickness center line.
Front region Rf: a region forward of the position of 0.5 T forward from the plate thickness center line and a region rearward of the position of 2.5 T forward from the plate thickness center line.

(2) In the loading step, the pair of pressing members move in a direction perpendicular to the length direction of the U rib so as to press the pair of side wall portions,
In the unloading step, the pair of pressing members may move in a direction orthogonal to the length direction of the U rib so as to be separated from the pair of side wall portions.

(3) The loading step and the unloading step may be repeatedly performed by moving the pair of pressing members in the length direction of the U rib.

(4) A method for manufacturing a steel slab according to another embodiment of the present invention includes a deck plate, a lateral rib having a web having a thickness T welded to the lower surface of the deck plate, and penetrating the web. The method includes the step of implementing the fatigue crack generation suppression method described above on a base material that includes a U-rib that extends and has a pair of side wall portions welded to the deck plate and the web.

(5) An inner surface pressing device according to another embodiment of the present invention is an inner surface pressing device that is disposed and used on the inner side of the U-rib in order to carry out the fatigue crack generation suppressing method.
The main body,
A support portion for supporting the main body portion so that the main body portion can move in the length direction of the U-rib;
The pair of pressing members supported by the main body so as to be movable with respect to the main body;
A drive mechanism that moves the pair of pressing members such that the pair of pressing members presses the pair of side wall portions of the U rib toward the outside of the U rib.

  ADVANTAGE OF THE INVENTION According to this invention, in the steel deck which has a U rib and a horizontal rib, fatigue crack generation | occurrence | production and fatigue crack progress in the root part of a weld bead can be suppressed.

Drawing 1 is a figure showing an example of a bridge provided with a steel deck. FIG. 2 is a view of a part of the steel slab as viewed obliquely from below. FIG. 3 is an enlarged view showing a joint portion between the deck plate and the side wall portion. FIG. 4 is a view for explaining the basic operation of the fatigue crack generation suppressing method according to the embodiment of the present invention. FIG. 5 is a diagram for explaining a basic operation of the fatigue crack generation suppressing method according to the embodiment of the present invention. FIG. 6 is a diagram for explaining the operational effects of the basic operation of the suppression method according to the present embodiment. FIG. 7 is a plan view showing the positional relationship between the lateral rib, the pair of side wall portions, and the pair of pressing members. FIG. 8 is a plan view showing a schematic configuration of the inner surface pressing device according to the embodiment of the present invention. FIG. 9 is a diagram for explaining an example of use of the pressing device. FIG. 10 is a view showing a steel slab used in the experiment. FIG. 11 is a diagram illustrating the stress generated in the root portion after the unloading process. FIG. 12 is a diagram showing the results of a fatigue test.

  Hereinafter, embodiments of the present invention will be described in detail. In the present specification, the suppression of occurrence of fatigue cracks not only suppresses the generation of new fatigue cracks but also suppresses further expansion and expansion of existing fatigue cracks. .

(Basic operation of fatigue crack suppression method)
First, the basic operation of the fatigue crack generation suppressing method according to an embodiment of the present invention will be described. 4 and 5 are diagrams for explaining the basic operation of the fatigue crack generation suppressing method according to the embodiment of the present invention. Below, the case where the fatigue crack generation | occurrence | production suppression method (henceforth a suppression method only) based on this embodiment is applied in the steel deck 2 shown in FIGS. 1-3 is demonstrated. In the steel deck 2 to which the present invention is applied, the thickness of the deck plate 3 is, for example, 12 to 16 mm, and the thickness of the U rib 6 is, for example, 3 to 12 mm.

  In addition, the suppression method according to the present embodiment may be performed on the steel deck 2 before being used as a component of the bridge 1, or the steel deck 2 in a state of being used as a component of the bridge 1. May be implemented. Moreover, even if it implements with respect to the steel deck slab in which the main girder 4 was provided, the suppression method which concerns on this embodiment may be implemented with respect to the steel deck slab without the main girder 4 provided. Good. Below, the case where the suppression method which concerns on this embodiment is implemented with respect to the steel deck 2 before using as a component of the bridge 1 and the main girder 4 is not provided is demonstrated.

  Although illustration of the horizontal rib 5 is abbreviate | omitted in FIG. 4 and FIG. 5, the suppression method which concerns on this embodiment is implemented with respect to the steel deck 2 in the state in which the horizontal rib 5 was provided. In the following description, the direction perpendicular to the vertical direction and the length direction of the U rib 6 is defined as the width direction of the U rib 6. In FIG. 4, the left-right direction is the width direction of the U-rib 6.

  Referring to FIG. 4, in the present embodiment, for example, steel is placed on work table 15 such that deck plate 3 is down and U-rib 6 (more specifically, bottom wall 6a) is up. Place floor slab 2.

  Next, a pair of pressing members 16 are disposed in the U rib 6. The pressing member 16 has a curved surface portion 16a having a circular arc cross section. In the cross section perpendicular to the length direction of the U rib 6, the radius of curvature of the curved surface portion 16a is set to, for example, 5 to 80 mm.

  In the present embodiment, the pressing member 16 is provided so as to extend in the length direction of the U rib 6. More specifically, the length of the curved surface portion 16a in the length direction of the U rib 6 is set to 4 to 50 times the thickness t of the side wall portions 6b and 6c, for example. The curved surface portion 16a of one pressing member 16 is provided to face the inner surface of the side wall portion 6b, and the curved surface portion 16a of the other pressing member 16 is provided to face the inner surface of the side wall portion 6c. The pressing member 16 is provided so as to be movable in the left-right direction, and moves in the left-right direction when driven by a drive mechanism (not shown).

  In the present embodiment, the distance d1 between the curvature center 16b of the curved surface portion 16a and the back surface 3b of the deck plate 3 is set to, for example, 1.5 times or more, preferably 2 times or more the thickness t of the side wall portions 6b and 6c. More preferably, it is set to 3 times or more. Further, the distance d1 is set to be, for example, 7 times or less of the thickness t of the side wall portions 6b and 6c, preferably 5 times or less, and more preferably 4 times or less. The distance d1 is the length in the thickness direction of the deck plate 3 (vertical direction in FIG. 4). The thickness t is calculated as, for example, the average thickness of the side wall portions 6b and 6c.

  Next, with reference to FIG. 4 and FIG. 5A, the pair of pressing members 16 are moved toward the outside of the U rib 6 to contact the inner surfaces of the side wall portions 6b and 6c. With reference to FIG. 4, in the present embodiment, the side walls 6 b and 6 c are inclined with respect to the deck plate 3 so that the distance between the side walls 6 b and 6 c decreases as the distance from the deck plate 3 increases. For this reason, with reference to Fig.5 (a), the contact part 17 of the curved surface part 16a of one press member 16 and the side wall part 6b is located above the curvature center 16b. Although explanation is omitted, the other pressing member 16 also contacts the side wall portion 6c in the same manner. In the following, the relationship between the side wall 6b and the one pressing member 16 will be described, but the relationship between the side wall 6c and the other pressing member 16 is the same.

  Next, as shown in FIG.5 (b), the press member 16 is moved toward the outer side of the U rib 6 (load process). Thereby, pressure is applied to the side wall portion 6b from the inside of the U rib 6. As a result, the side wall portion 6 b is deformed so as to swell toward the outside of the U-rib 6. In addition, the moving distance d2 of the pressing member 16 in the loading process is set to 0.05 to 10 mm, for example. In the present embodiment, in the loading process, for example, pressure is applied to the side wall portion 6b so that the vicinity of the root portion 14 is plastically deformed.

  Next, with reference to FIG.5 (c), the press member 16 is moved so that it may leave | separate from the side wall part 6b (unloading process). Thereby, the pressure applied to the side wall part 6b in the loading process is removed. As a result, the side wall 6b is deformed so as to return to the shape of the side wall 6b before the loading process. In the present embodiment, as described above, the vicinity of the root portion 14 is plastically deformed in the loading process. Therefore, the side wall part 6b after the unloading process does not completely return to the shape of the side wall part 6b before the loading process.

  Here, in the cross section perpendicular to the length direction of the U-rib 6, the distance in the left-right direction between the position of the side wall 6b before the loading process and the position of the side wall 6b after the unloading process is defined as the residual displacement. In the present embodiment, in a cross section perpendicular to the length direction of the U-rib 6, any position of the outer surface (or inner surface) of the side wall portion 6b before the loading process and the outer surface (or inner surface) of the side wall portion 6b after the unloading process. The distance in the left-right direction from the arbitrary position is defined as the residual displacement amount. In FIG. 5C, the residual displacement amount at a position away from the back surface 3b in the thickness direction of the deck plate 3 by the distance d1 is shown as a distance d3 (hereinafter referred to as a residual displacement amount d3). In the present embodiment, the loading process and the unloading process are performed so that the residual displacement d3 is 0.01 to 3 mm. The loading process and the unloading process may be performed once for the same part or may be performed twice or more. That is, the loading process and the unloading process may be repeatedly executed until the residual displacement d3 reaches a value in the range of 0.01 to 3 mm. Note that the target value of the residual displacement d3 is appropriately set in consideration of the shape and section modulus of the U rib 6 and suppression of out-of-plane buckling of the lateral rib 5. The residual displacement amount d3 is preferably measured with high accuracy, and the residual displacement amount d3 is preferably 0.1 mm or more. The residual displacement d3 can be measured using, for example, a dial gauge or a laser displacement meter.

(Effects of basic operation of fatigue crack suppression method)

  Hereinafter, the effect by the basic operation | movement of the suppression method which concerns on this embodiment is demonstrated. FIG. 6 is a diagram for explaining the operational effects of the basic operation of the suppression method according to the present embodiment.

  With reference to FIG. 6, as described above, in the vicinity of the root portion 14 of the weld bead 10, tensile residual stress is generated due to expansion during welding and contraction after welding. In this state, the side wall portion 6b tends to move toward the outside of the U-rib 6 by executing the above-described loading process. As a result, the weld bead 10 is pulled toward the outside of the U-rib 6, and the tensile stress near the root portion 14 temporarily increases.

  After that, by executing the unloading step, the side wall 6 b tends to move toward the inside of the U rib 6. As a result, the weld bead 10 is pressed toward the inside of the U-rib 6. That is, a so-called spring back effect occurs. Thereby, the force of a compression direction can be applied to the root part 14 vicinity. As a result, the tensile residual stress in the vicinity of the root portion 14 can be reduced, or the compressive residual stress can be generated in the vicinity of the root portion 14. Thereby, for example, even when a load is repeatedly applied to the steel deck 2, it is possible to prevent a large tensile stress from being generated in the vicinity of the root portion 14. As a result, the occurrence of fatigue cracks in the vicinity of the root portion 14 can be suppressed. In addition, when a fatigue crack has already occurred in the vicinity of the root portion 14, the tensile residual stress at the crack tip can be reduced, or the compressive residual stress can be generated at the crack tip, so the fatigue crack has progressed. Can be suppressed.

  In the present embodiment, it is not necessary to apply a force directly to the deck plate 3. Thereby, the deformation | transformation and damage of the deck plate 3 can be prevented.

  In the present embodiment, pressure is applied to the side wall portions 6b and 6c by the pressing member 16 having the curved surface portion 16a. In this case, damage to the inner surface of the U rib 6 can be suppressed.

(Implementation position of fatigue crack generation suppression method)
As described above, the suppression method according to this embodiment is performed on the steel deck 2 having the lateral ribs 5. As a result of various studies by the present inventors, by performing the suppressing method according to the present embodiment at an appropriate position around the lateral rib 5, without increasing the pressing force of the pressing member 16, It was found that the above-described springback effect can be appropriately obtained in the periphery. This will be specifically described below.

  FIG. 7 is a plan view showing the positional relationship between the lateral rib 5, the pair of side wall portions 6 b and 6 c, and the pair of pressing members 16. In the following description, the length direction of the U rib 6 is the front-rear direction.

  With reference to FIG. 7, in the present embodiment, the movement of the pair of pressing members 16 in the length direction of the U-rib 6 and the above-described loading process and unloading process are repeatedly performed intermittently. Here, in order to obtain a sufficient springback effect at a portion where the lateral ribs 5 and the U ribs 6 intersect while the present inventors are examining the method for suppressing the occurrence of fatigue cracks, It has been found that the side walls 6b, 6c must be pressed. This is because deformation of the pair of side wall portions 6b and 6c is suppressed by the lateral rib 5 at the intersecting portion.

  However, in order to press the pair of side wall portions 6b and 6c with a large force at the intersecting portion, it is necessary to drive the pair of pressing members 16 with a large force. In this case, the device for driving the pair of pressing members 16 is undesirably large.

  Therefore, in the present embodiment, as shown in FIG. 7, first, the reference region Rb, the rear region Rr, and the front region Rf are defined in the pair of side wall portions 6b and 6c. Specifically, in the pair of side wall portions 6b and 6c, the plate thickness center line C is located forward of the position P1 of 0.5T (T is the plate thickness of the web 5a) and rearward from the plate thickness center line C of the web 5a. A region behind 0.5T position P2 from the front is defined as a reference region Rb. In other words, the region intersecting the web 5a in the pair of side wall portions 6b and 6c is defined as the reference region Rb. Further, in the pair of side wall portions 6b and 6c, a region behind the plate thickness center line C is located behind the position P1 of 0.5T and behind the plate thickness center line C is located ahead of the position P3 of 2.5T. , Defined as a rear region Rr. Further, in the pair of side wall portions 6b and 6c, a region that is forward of the position P2 of 0.5T forward from the thickness center line C and rearward of the position P4 of 2.5T forward from the thickness center line C. , Defined as the front region Rf.

  In the present embodiment, the above-described loading process and unloading process are performed in the rear area Rr, and the above-described loading process and unloading process are performed in the front area Rf. In the following, the load process executed in the rear region Rr is referred to as a rear load step, and the load step executed in the front region Rf is referred to as a front load step.

  In the rear loading process, the pair of pressing members 16 press the pair of side wall portions 6b and 6c while contacting at least part of the rear region Rr. In the forward loading step, the pair of pressing members 16 press the pair of side wall portions 6b and 6c while contacting at least part of the front region Rf. However, in the rear load process and the front load process, the pair of pressing members 16 press the pair of side wall portions 6b and 6c so as not to contact the reference region Rb.

  As described above, in the present embodiment, in the rear load process and the front load process, the pair of pressing members 16 is a portion of the pair of side wall portions 6b and 6c that intersects the lateral rib 5 (that is, the reference region Rb). Do not press. In this case, the pair of side wall portions 6b and 6c can be sufficiently deformed with a small force. Thereby, in the area | region (back area | region Rr and front area | region Rf) before and behind reference | standard area | region Rb among a pair of side wall parts 6b and 6c, the effect of a spring back can fully be acquired with a small pressing force.

  In addition, since the reference region Rb is not pressed in the rear load step and the front load step, the spring back effect may not be sufficiently obtained in the reference region Rb. However, as described above, the springback effect can be sufficiently obtained in the regions before and after the reference region Rb (the rear region Rr and the front region Rf). For this reason, even if a crack occurs in the reference region Rb, the progress of the crack can be sufficiently suppressed in the rear region Rr and the front region Rf. That is, according to the present embodiment, it is possible to sufficiently suppress the occurrence of fatigue cracks or the development of fatigue cracks in the root portion 14 around the lateral rib 5 with a small pressing force.

  Note that the load process may be performed so that the reference region Rb is pressed by the pair of pressing members 16 before or after the rear load process is performed. In this case, it is not necessary to press the reference region Rb with a large force. Similarly, the load process may be performed so that the reference region Rb is pressed by the pair of pressing members 16 before or after the front load process is performed. On the other hand, it is preferable not to press the reference region Rb by the pair of pressing members 16 before or after the rear loading process is performed and before or after the front loading process is performed. This is because the labor required for the fatigue crack generation suppressing method increases.

(Description of inner surface pressing device)
Next, an inner surface pressing device used when implementing the above-described suppression method will be described. FIG. 8 is a plan view showing a schematic configuration of an inner surface pressing device (hereinafter abbreviated as a pressing device) 20 according to an embodiment of the present invention.

  Referring to FIG. 8, the pressing device 20 includes a main body 22, wheels 24 a to 24 d, axles 26 a and 26 b, drive mechanisms 28 and 30, movement amount detection units 32 a and 32 b, load detection units 34 a and 34 b, and a distance detection unit 36. , An imaging device 37, a communication unit 38, and the pair of pressing members 16 described above.

  In the present embodiment, the main body 22 houses drive mechanisms 28 and 30, movement amount detection units 32 a and 32 b, load detection units 34 a and 34 b, a distance detection unit 36, and a communication unit 38. The wheels 24a and 24b are rotatably supported by the main body 22 through the axle 26a. The wheels 24c and 24d are rotatably supported by the main body 22 through the axle 26b. In the present embodiment, the wheels 24a to 24d include magnets. In the present embodiment, the wheels 24 a to 24 d and the axles 26 a and 26 b correspond to a support portion that supports the main body portion 22.

  The drive mechanism 28 includes, for example, an electric motor, and rotationally drives the wheels 24a and 24b via the axle 26a. Thereby, the pressing device 20 moves. In the following, as shown in FIG. 8, the direction in which the pressing device 20 moves is referred to as the front-rear direction. Further, the left-right direction is defined based on the front-rear direction.

  The pair of pressing members 16 are supported by the main body 22 so as to be movable in the left-right direction at the center in the front-rear direction of the main body 22. For example, the drive mechanism 30 moves the pair of pressing members 16 in the left-right direction by hydraulic pressure.

  The movement amount detection unit 32 a detects the movement amount of one pressing member 16, and the movement amount detection unit 32 b detects the movement amount of the other pressing member 16. The detection results of the movement amount detection units 32 a and 32 b are output to the distance detection unit 36. As the movement amount detection units 32a and 32b, for example, a known displacement sensor can be used. Therefore, detailed description of the movement amount detection units 32a and 32b is omitted.

  The load detection unit 34 a detects a load applied to one pressing member 16, and the load detection unit 34 b detects a load applied to the other pressing member 16. The detection results of the load detectors 34 a and 34 b are output to the distance detector 36. In addition, as load detection part 34a, 34b, a well-known load sensor can be used, for example. Therefore, detailed description of the load detection units 34a and 34b is omitted.

  As will be described later, the distance detection unit 36 detects the residual displacement amounts of the side wall portions 6b and 6c of the U rib 6 based on the detection results of the movement amount detection units 32a and 32b and the load detection units 34a and 34b. The detection result of the distance detection unit 36 is output to the communication unit 38.

  The imaging device 37 images the inside of the U rib 6 and outputs image data to the communication unit 38. The communication unit 38 transmits / receives data to / from a remote operation device (not shown).

  In the present embodiment, for example, the operator of the pressing device 20 can operate the pressing device 20 via the remote operation device. In the present embodiment, for example, a control signal for controlling the drive mechanisms 28 and 30 is output from the remote operation device based on the operation of the operator, and the control signal is received by the communication unit 38. The communication unit 38 outputs the received control signal to the drive mechanisms 28 and 30. Thereby, the drive mechanisms 28 and 30 are controlled. Further, the detection result of the distance detection unit 36 is transmitted to the remote operation device via the communication unit 38. Thereby, the operator of the pressing device 20 can control the pressing device 20 with reference to the detection result of the distance detection unit 36 transmitted to the remote control device. Further, the image data inside the U-rib 6 photographed by the photographing device 37 is transmitted to the remote control device via the communication unit 38. The operator can grasp the position of the lateral rib 5 with reference to the image data. Thereby, the above-mentioned front load process and back load process can be performed in an appropriate position. Although detailed explanation is omitted, for example, the relationship between the position of the lateral rib 5 in the U rib 6 and the movement distance of the pressing device 20 is stored in the pressing device 20 in advance, and the pressing device 20 is predetermined. You may make it perform the above-mentioned front load process and back load process when moving to this position.

  FIG. 9 is a diagram for explaining an example of use of the pressing device 20. With reference to FIG. 9, when using the pressing device 20, the pressing device 20 is disposed inside the U-rib 6. As described above, in the present embodiment, the wheels 24a to 24d include magnets. Therefore, the wheels 24a to 24d can be attached to the back surface 3b of the deck plate 3 by magnetic force in a state where the deck plate 3 is on and the bottom wall portion 6a is on the bottom. For example, the wheels 24 a to 24 d can be attached to the back surface 3 b of the deck plate 3 in a state where the steel deck 2 (see FIG. 1) is used as a constituent member of the bridge 1 (see FIG. 1). As described above, the pressing device 20 can move in the front-rear direction. Thereby, the pressing device 20 can move in the length direction of the U-rib 6 inside the U-rib 6.

  After arrange | positioning the press apparatus 20 as mentioned above, a pair of press member 16 is moved to the left-right direction, and the above-mentioned load process and unloading process are performed. Thereafter, the pressing device 20 is advanced to execute the loading process and the unloading process. By repeating the above operation, the above loading process and unloading process can be performed over the entire length of the U-rib 6.

  In the pressing device 20, the residual displacement amount of the side wall portion can be detected as follows. In the following, the method for detecting the residual displacement amount of the side wall portion 6b will be described, but the method for detecting the residual displacement amount of the side wall portion 6c is also the same.

  Referring to FIG. 9, first, in the loading process, the curved surface portion 16a contacts the side wall portion 6b by moving the pressing member 16 from the reference position (zero point) to the side wall portion 6b side. When the curved surface portion 16a contacts the side wall portion 6b, the load applied to the pressing member 16 increases. For this reason, the distance detection part 36 can detect that the curved surface part 16a contacted the side wall part 6b based on the detection result of the load detection part 34a. Moreover, the distance detection part 36 detects the movement amount (movement amount from a reference position) of the pressing member 16 when the curved surface part 16a contacts the side wall part 6b based on the detection result of the movement amount detection part 32a. Can do. Hereinafter, the movement amount of the pressing member 16 when the curved surface portion 16a contacts the side wall portion 6b is referred to as a first movement amount.

  Next, in the unloading step, the curved surface portion 16a is separated from the side wall portion 6b by moving the pressing member 16 to the main body portion 22 side. When the curved surface portion 16a is separated from the side wall portion 6b, the load applied to the pressing member 16 is reduced. For this reason, the distance detection part 36 can detect that the curved surface part 16a left | separated from the side wall part 6b based on the detection result of the load detection part 34a. Moreover, the distance detection part 36 can detect the movement amount of the pressing member 16 when the curved surface part 16a leaves | separates from the side wall part 6b based on the detection result of the movement amount detection part 32a. Hereinafter, the movement amount (movement amount from the reference position) of the pressing member 16 when the curved surface portion 16a is separated from the side wall portion 6b is referred to as a second movement amount.

  Finally, the distance detection unit 36 obtains the difference between the first movement amount and the second movement amount detected as described above. Thereby, the distance detection part 36 is a distance (in this embodiment, the direction parallel to the back surface 3b of the deck plate 3) of the position of the side wall part 6b before the said loading process, and the position of the side wall part 6b after the said unloading process. Can be detected. That is, in the present embodiment, the distance detection unit 36 can determine the residual displacement amount of the side wall portion 6b by calculating the difference between the first movement amount and the second movement amount detected as described above. . Specifically, the distance detection unit 36 can obtain the residual displacement amount of the side wall portion 6b by subtracting the first movement amount from the second movement amount.

(Method of manufacturing steel slab)
The above-described method for suppressing the occurrence of fatigue cracks can also be used when manufacturing a steel deck. Specifically, first, a base material having a configuration in which a lateral rib and a U-rib are welded to a deck plate is prepared. As a base material, the steel deck 2 (refer FIG. 2) before implementing the above-mentioned suppression method can be used, for example. Therefore, a base material can be manufactured by the well-known manufacturing method utilized when manufacturing the conventional steel deck. After preparing a base material, the above-mentioned fatigue crack generation suppression method is implemented with respect to the base material. Thereby, it is possible to manufacture a steel slab in which generation and progress of fatigue cracks are suppressed.

(Study based on simulation)
Hereinafter, the effects of the present invention will be described together with simulation results by FEM analysis using a computer. In the simulation, an FEM analysis model was created assuming a steel slab of the size and shape shown in FIG. 10 (hereinafter referred to as a virtual steel slab). The virtual steel deck shown in FIG. 10 has a configuration in which three U ribs are welded to a plate material corresponding to a deck plate. Moreover, in the virtual steel deck, it was set as the structure which welded the plate | board material (thickness: 9 mm) equivalent to the web of a horizontal rib to the center part in the length direction of a U rib. The unit of the dimension shown in FIG. 10 is “mm”.

  In the FEM analysis, a 1/4 symmetric model of the virtual steel deck shown in FIG. 10 was used as an analysis model, and analysis was performed using an 8-node hexahedral element. SM490B data was used for the stress-strain relationship of the steel used. The Young's modulus was 206 GPa, the Poisson's ratio was 0.3, and the hardening rule was isotropic hardening.

  In the FEM analysis, an analysis model corresponding to the above-described pair of pressing members 16 was further created, and a loading process and an unloading process were performed on the side wall portion of the U rib. The curvature radius of the curved surface portion (see the curved surface portion 16a in FIG. 4) of the pressing member was 35 mm, and the length (the length in the length direction of the U rib) was 50 mm. In the FEM analysis, the distance between the sheet thickness center line of the web of the lateral rib and the pressing member (refer to the distance L in FIG. 7) is changed stepwise to perform the loading process and the unloading process. And the residual stress of the root part after the unloading process was calculated. The pushing amount of the pressing member during the loading process was 1.2 mm. Table 1 below shows analysis conditions and analysis results (indentation load). As described above, in the analysis model, the web thickness (see thickness T in FIG. 7) is 9 mm. The distances L of 3 to 5 correspond to 0.5T (4.5 mm), 1.0T (9.0 mm), and 1.5T (13.5 mm), respectively. Therefore, analysis no. The load process in 3-5 is corresponded to the above-mentioned front load process. On the other hand, analysis no. In 1 and 2, in the loading process, the pressing member presses a region within 0.5 T forward from the plate thickness center line of the web. That is, analysis no. In 1 and 2, the pressing member presses the reference region of the side wall (see the reference region Rb in FIG. 7).

  As shown in Table 1, the analysis no. Compared with 1 and 2, the analysis No. which does not press the reference area. In 3-6, the indentation load was fully reduced. From this result, it can be seen that according to the suppression method according to the embodiment of the present invention, the pair of side wall portions can be deformed with a small force.

  FIG. 11 is a diagram illustrating the stress generated in the root portion 14 after the unloading process. In FIG. 11, the vertical axis indicates the stress generated in the width direction of the U-rib, the positive value indicates the tensile stress, and the negative value indicates the compressive stress. In FIG. 11, the horizontal axis indicates the distance from the thickness center line of the web in the length direction of the U rib. As shown in FIG. 3 to 6, since the amount of deformation of the side wall portion decreases in a portion intersecting with the lateral rib (reference region: region within 4.5 mm from the web thickness center line of the web), it is sufficient in the vicinity of the intersecting portion. Compressive stress is not generated. However, a sufficient compressive stress could be generated at a position about 20 mm away from the web thickness center line. In particular, the analysis No. in which the loading process corresponding to the forward loading process of the above-described embodiment was performed. In 3-5, the area | region where a tensile residual stress generate | occur | produced was able to be narrowed sufficiently. Thereby, even if a fatigue crack occurs in the root portion around the lateral rib, it can be seen that the progress of the fatigue crack can be sufficiently suppressed by the compressive stress.

  In the example, the virtual steel slab shown in FIG. 10 was created, and the fatigue life was measured by performing the above-described loading process and unloading process. The pressing position of the pair of side wall portions by the pressing member is the same as the analysis No. described above. The same position as in FIG. The radius of curvature of the pressing surface of the pressing member was 35 mm, and the loading process was performed using a hydraulic jack. The pressing amount of the pair of pressing members was 1.8 mm, and the residual displacement amount of the side wall portion was about 1.1 mm. Further, as a comparative example, the fatigue life was measured for the virtual steel slab shown in FIG. 10 without performing the above-described loading process and unloading process. In the fatigue test, a 200 x 200 mm rubber plate (40 mm thick) that assumes a single tire of a large vehicle is installed on the top surface of the deck plate (more specifically, above the center of the U-rib), and an axial load is loaded. did. Also, in the fatigue test, a strain gauge (gauge length: 1 mm) is attached to the bottom surface of the deck plate at a position 5 mm from the intersection with the U rib (position inside the U rib: 2 locations) to determine the strain amplitude during loading. It was measured. For the determination of the fatigue life, the number of repetitions when the strain amplitude decreased by 10% after the start of loading of the axial load was used. FIG. 12 shows the results of the fatigue test.

  From the results shown in FIG. 12, it can be seen that the fatigue life is sufficiently improved in the virtual steel deck slab subjected to the loading process and the unloading process according to the embodiment of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, in a steel deck, fatigue crack generation | occurrence | production and fatigue crack progress in the root part of the weld bead which joins a U rib and a deck plate can be suppressed, suppressing a deformation | transformation of a deck plate. Therefore, this invention can be utilized suitably for fatigue crack generation | occurrence | production suppression of the steel deck which comprises a bridge etc.

1 Bridge 2 Steel Floor Slab 3 Deck Plate 4 Main Girder 5 Horizontal Rib 6 U Rib (Vertical Rib)
7 Pavement Material 8 Automobile 9 Joint Part 10 Weld Bead 11 Non-welded Part 12, 13 Toe 14 Route Part 16 Pressing Member

Claims (5)

A deck plate, a transverse rib having a web having a thickness T welded to the lower surface of the deck plate, a U-rib extending through the web and having a pair of side wall portions welded to the deck plate and the web; A method for suppressing the occurrence of fatigue cracks in a steel slab having
A load step of pressing the pair of side wall portions from the inside of the U-rib by a pair of pressing members so that the pair of side wall portions deform toward the outside of the U-rib;
An unloading step for removing pressure applied to the pair of side wall portions by the pair of pressing members in the loading step,
The length direction of the U rib is defined as the front-rear direction, and a reference region Rb, a rear region Rr behind the reference region Rb, and a front region Rf ahead of the reference region Rb are defined in the pair of side walls. When defined as follows,
The loading process includes a rear loading process in which the pair of pressing members presses the pair of side wall portions while contacting at least a part of the rear region Rr, and the pair of pressing members contacts at least a part of the front region Rf. And a front load step of pressing the pair of side wall portions,
In the rear load step and the front load step, the pair of pressing members press the pair of side wall portions so as not to contact the reference region Rb.
Reference region Rb: a region forward of the position of 0.5T behind the sheet thickness center line of the web and a position behind the position of 0.5T forward of the sheet thickness center line.
Back region Rr: a region rearward from the position of 0.5T behind the plate thickness center line and a front side of the position of 2.5T rearward from the plate thickness center line.
Front region Rf: a region forward of the position of 0.5 T forward from the plate thickness center line and a region rearward of the position of 2.5 T forward from the plate thickness center line. In the loading step, the pair of pressing members move in a direction perpendicular to the length direction of the U rib so as to press the pair of side wall portions,
2. The method for suppressing the occurrence of fatigue cracks according to claim 1, wherein in the unloading step, the pair of pressing members move in a direction orthogonal to the length direction of the U rib so as to be separated from the pair of side wall portions.   The fatigue crack generation suppressing method according to claim 1 or 2, wherein the loading step and the unloading step are repeatedly executed by moving the pair of pressing members in the length direction of the U-rib.   A deck plate, a transverse rib having a web having a thickness T welded to the lower surface of the deck plate, a U-rib extending through the web and having a pair of side wall portions welded to the deck plate and the web; The manufacturing method of the steel slab including the process of implementing the fatigue crack generation | occurrence | production suppression method in any one of Claim 1 to 3 with respect to the base material provided with these. In order to carry out the fatigue crack occurrence suppressing method according to any one of claims 1 to 3, an inner surface pressing device used by being arranged inside the U-rib,
The main body,
A support portion for supporting the main body portion so that the main body portion can move in the length direction of the U-rib;
The pair of pressing members supported by the main body so as to be movable with respect to the main body;
An inner surface pressing device comprising: a drive mechanism that moves the pair of pressing members such that the pair of pressing members presses the pair of side wall portions of the U rib toward the outside of the U rib.

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