Steel floor slab with closed-section rib and fabrication method of steel floor slab with closed-section rib

Abstract

To restrain occurrence of deck-penetrating cracks originated at a weld root part.SOLUTION: A steel floor slab 1 with a closed-section rib in this invention comprises a closed sectional space A surrounded with a deck plate 11 and a closed-section rib 12, and a weld part 41 where the edge face of the closed-section rib 12 and the reverse face of the deck plate 11 are welded. There is a treatment region 11a arranged on the front face of the deck plate 11 where peening treatment is applied to reduce the residual welding stress. The peening treatment is a treatment that strikes the treatment region 11a at least twice. The strike center position seen on the deck plate 11's cross section perpendicularly crossing the longitudinal direction of the deck plate 11 is located opposite to the closed-section space A in relation with a straight line L drawn on the crossing point P1 among the crossing points P1, P2 of the weld part 41 and the reverse face of the deck plate 11. The distance d from the crossing point P1 to the strike center position is double the thickness TH of the deck plate 11 or less while the strike zone width w being one eighth the thickness TH of the deck plate 11 or more.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a closed section rib steel deck in which a closed section rib is welded to the back surface of a deck plate, and a manufacturing method for a closed section rib steel deck. [Background technology]

[0002] Conventionally, steel decks have been used as decks for bridges. Steel decks are composed of flat deck plates made of steel plates, and stiffening members such as closed section ribs (also called vertical ribs) and horizontal ribs with cross-sectional shapes such as approximately U-shaped, V-shaped, circular arc-shaped, and elliptical arc-shaped. Closed section rib steel decks, in which closed section ribs and horizontal ribs are welded to the underside of the deck plate, are generally used. Such steel decks are lighter than RC decks and composite decks, and have the advantage that they can be manufactured to a certain size in a factory and then transported to the site for installation.

[0003] In such closed section rib steel decks, cracks that penetrate the deck plate (deck penetration cracks) have been found. It has become clear that deck penetration cracks occur when fatigue cracks progress from an intersection (hereinafter sometimes referred to as the weld root) located near the closed section space formed by the deck plate and closed section rib, out of two intersections between the welded part of the deck plate and the closed section rib and the underside of the deck plate. Deck penetration cracks are dangerous as they can cause the deck plate to collapse, immediately affecting traffic seriously. Therefore, there is a need to establish countermeasure technology for deck penetration cracks.

[0004] For example, the steel deck disclosed in Patent Document 1 has a plate-shaped inner reinforcement material that connects the deck plate and the closed section rib inside the closed area formed by the deck plate and the closed section rib, and suppresses fatigue cracks such as deck-penetrating cracks that propagate from the welds between the deck plate and the closed section rib.

[0005] Furthermore, the steel deck disclosed in Patent Document 2 has a groove formed on the back surface of the deck plate extending along the bridge axis direction at a position separated by a predetermined distance on the closed space side from a weld root portion formed on the closed space side at the boundary between the back surface of the deck plate and the weld metal. The steel deck disclosed in Patent Document 2 has a groove formed on the back surface of the deck plate extending along the bridge axis direction at a position separated by a predetermined distance on the closed space side from the weld root portion, thereby avoiding stress concentration near the weld root portion and preventing the occurrence of fatigue cracks such as deck-penetrating cracks that start from the weld root portion.

[0006] Furthermore, Patent Document 3 discloses a steel deck in which a treatment such as hammer peening has been applied to the back surface corresponding to a target location. In the steel deck disclosed in Patent Document 3, a treatment such as hammer peening is applied to introduce compressive residual stress into the welded portion between the deck plate and the closed cross section rib, thereby improving the fatigue performance. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-133320 A [Patent Document 2] JP 2016-205024 A [Patent Document 3] JP 2014-172043 A Summary of the Invention [Problem to be solved by the invention]

[0008] The steel deck disclosed in Patent Document 1 is configured to newly attach plate-shaped inner reinforcement members to multiple positions in the closed area formed by the deck plate and the closed cross-section rib. As a result, the overall weight of the steel deck increases, and the lightweight nature of the steel deck, which is an advantage of the steel deck, is lost. In addition, when attaching inner reinforcement members to an existing steel deck, the closed cross-section rib needs to have a hole for passing the inner reinforcement member through the inside of the closed area formed by the deck plate and the closed cross-section rib, so the work of attaching the inner reinforcement member to the existing steel deck becomes difficult.

[0009] In addition, the steel deck disclosed in Patent Document 2 requires an additional process of forming a groove on the back surface of the deck plate. As a result, the manufacturing efficiency of the steel deck decreases. In addition, by providing a groove on the back surface of the deck plate, stress concentration near the weld root can be avoided, but the groove and its surrounding area become new stress concentration points, making fatigue cracks more likely to occur in the groove and its surrounding area. As a result, there is a concern that the occurrence of deck-penetrating cracks will accompany the progression of the fatigue cracks that occur.

[0010] In addition, in the steel deck disclosed in Patent Document 3, for example, the rate of fatigue crack growth is suppressed by compressive residual stress induced in the welded portion between the deck plate and the closed cross-section rib. However, since the growth of the fatigue crack itself cannot be prevented, it is difficult to prevent the occurrence of a through-deck crack accompanying the growth of the fatigue crack.

[0011] As such, there is no established technology for suppressing the progression of fatigue cracks that occur in closed section rib steel decks, so there is a growing demand for technology for suppressing the progression of fatigue cracks that occur in closed section rib steel decks.

[0012] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a closed section rib steel deck, which is formed by welding a closed section rib to the back surface of a deck plate, in which the progression of fatigue cracks originating from the weld root can be suppressed, thereby preventing the occurrence of deck-penetrating cracks that could fracture the deck plate. [Means for solving the problem]

[0013] A closed section ribbed steel deck according to one aspect is a closed section ribbed steel deck having a plate-like deck plate extending in one direction, and a closed section rib welded to the back side of the deck plate such that its extension direction is along the extension direction of the deck plate, the closed section ribbed steel deck having a closed section space surrounded by the deck plate and the closed section rib, and a welded portion where an end face of the closed section rib is welded to the back side of the deck plate with a weld metal, the surface of the deck plate is provided with a treatment area where a peening treatment is performed to relieve welding residual stress remaining in the deck plate, and the peening treatment is performed so that the center position of the impact in the peening treatment is the same position, or the amount of impact deviation is within a predetermined range. This is a process in which the area is struck at least two times, and the center position of the impact in the peening process is located on the opposite side of the closed cross-sectional space with respect to a straight line that passes through one of two intersections where the welded portion intersects with the back surface of the deck plate in a cross section of the deck plate that is perpendicular to the extension direction of the deck plate and is perpendicular to both the extension direction of the deck plate and the width direction of the deck plate, and the distance from the intersection to the center position of the impact in the peening process is not more than twice the plate thickness of the deck plate in the width direction of the deck plate, and the width of the impact in the peening process is not less than 1 / 8 of the plate thickness of the deck plate in the width direction of the deck plate.

[0014] In addition, the peening treatment preferably applies a predetermined compressive residual stress at a position a predetermined distance from the surface of the deck plate in the thickness direction of the deck plate.

[0015] In addition, it is preferable that the peening treatment is performed at multiple positions on the deck plate in the width direction of the deck plate, and the total width of the peening treatment performed at the multiple positions is 1 / 8 or more of the plate thickness t of the deck plate.

[0016] The deck plate is preferably made of fatigue-resistant steel.

[0017] According to another aspect of the manufacturing method for a closed section rib steel deck, there is provided a manufacturing method for a closed section rib steel deck having a plate-like deck plate extending in one direction and a closed section rib welded to the back side of the deck plate with its extension direction aligned with the extension direction of the deck plate, the manufacturing method comprising the steps of: welding an end face of the closed section rib to the back side of the deck plate with a weld metal in a state in which a closed section space is formed by the deck plate and the closed section rib; and performing a peening treatment on a treatment area provided on the surface of the deck plate to which the closed section rib is welded and fixed, the peening treatment being performed on the treatment area so that the center positions of the impacts in the peening treatment are the same position or the amount of impact deviation is within a predetermined range. The peening process is a process in which the area is struck at least twice, and the center position of the impact in the peening process is located on the opposite side of the closed cross-sectional space with respect to a straight line that passes through one of two intersections where the welded portion intersects with the back surface of the deck plate in a cross section of the deck plate that is perpendicular to the extension direction of the deck plate and is perpendicular to both the extension direction of the deck plate and the width direction of the deck plate, and the distance from the intersection to the center position of the impact in the peening process is not more than twice the plate thickness of the deck plate in the width direction of the deck plate, and the width of the impact in the peening process is not less than 1 / 8 of the plate thickness of the deck plate in the width direction of the deck plate. Effect of the Invention

[0018] According to the present disclosure, in a closed section rib steel deck formed by welding a closed section rib to the underside of a deck plate, the occurrence of deck-penetrating cracks that fracture the deck plate can be suppressed by suppressing the progression of fatigue cracks originating from the weld root. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic cutaway perspective view showing an example of the configuration of a closed section rib steel deck in which the present invention is implemented. [Diagram 2]FIG. 2 is a schematic front view showing the manufacturing process of a closed section rib steel deck. [Diagram 3] FIG. 4 is a partially enlarged cross-sectional view showing the vicinity of the welded portion between the deck plate and the closed cross-section rib. [Figure 4] FIG. 1 shows fatigue cracks that occur in a deck board in a conventional closed section rib steel deck, where (a) is a schematic front view and (b) is a partially enlarged view of the vicinity of a welded portion. [Diagram 5] FIG. 2 is a schematic front view showing an area where peening treatment is applied to a closed section rib steel deck. [Figure 6] FIG. 4 is a partially enlarged cross-sectional view showing the relationship between an impact tool and a deck plate in a peening process. [Figure 7] 1 is a graph showing an example of a change in the stress intensity factor range at the tip of a fatigue crack occurring in a conventional closed cross-section rib steel deck, obtained by finite element analysis. [Figure 8] 1 is a graph showing an example of a change in the stress intensity factor range at the tip of a fatigue crack occurring in a closed cross-section rib steel deck of this embodiment, obtained by finite element analysis. [Figure 9] FIG. 11 is a partially enlarged cross-sectional view showing a case where peening is performed at a plurality of positions. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An example of the configuration of a closed section rib steel deck embodying the present invention will be described with reference to the drawings. As shown in FIG. 1, the steel deck bridge 1 is composed of a closed section rib steel deck 10 and a main girder 20. Hereinafter, the closed section rib steel deck 10 may be simply referred to as a steel deck 10. The steel deck 10 is composed of a deck plate 11, a closed section rib (vertical rib) 12 that stiffens the deck plate 11, and a horizontal rib 13. When the steel deck bridge 1 is used as a road bridge, a pavement 15 such as asphalt is laid on the surface of the deck plate 11. Although not shown, the deck plate 11 is a plate-shaped member that extends along the bridge axis direction of the steel deck bridge 1, for example. Both ends of the deck plate 11 in the width direction are provided with a ground cover. Since the deck plate 11 extends along the bridge axis direction of the steel deck bridge 1, the width direction of the deck plate 11 coincides with the direction perpendicular to the bridge axis of the steel deck bridge 1.

[0021] The deck plate 11 is a member that directly supports the wheel load via the pavement 15. As a floor slab, the deck plate 11 bears the bending moment and shear force between the main girders 20, and further functions as the upper flange of the main girders 20. The material of the deck plate 11 is, for example, fatigue-resistant steel. Fatigue-resistant steel is a steel material that has a slower rate of fatigue crack growth (propagation) compared to general steel materials. Below, a case where fatigue-resistant steel is used as the material of the deck plate 11 will be described, but it is also possible to use general steel materials other than fatigue-resistant steel. Note that when fatigue-resistant steel is used as the material of the deck plate 11, it is possible to more reliably obtain the effect of stopping cracks inside the deck plate 11.

[0022] For example, the threshold stress intensity factor range ΔKth for general steel is ΔKth=3-4 MPa√m, whereas the threshold stress intensity factor range ΔKth for the above-mentioned fatigue-resistant steel is ΔKth=9 MPa√m. The threshold stress intensity factor range ΔKth is the value of the stress intensity factor range ΔK at the tip of the fatigue crack when fatigue crack growth is no longer observed. Therefore, the higher the threshold stress intensity factor range ΔKth, the more difficult it is for a fatigue crack to grow.

[0023] The lower threshold stress intensity factor range ΔKth of the fatigue resistant steel should be higher than the lower threshold stress intensity factor range ΔKth (3 to 4 MPa√m) of general steel materials. Therefore, as an example, the lower threshold stress intensity factor range ΔKth of the fatigue resistant steel is preferably ΔKth≧6 MPa√m.

[0024] In addition, in consideration of improving fatigue durability, the plate thickness TH of the deck plate 11 is, for example, preferably 12 to 22 mm (preferably 12 to 16 mm). The deck plate 11 is arranged in a plane on the main girder 20, and the joints of adjacent deck plates 11 are joined by welding or high-strength bolts.

[0025] A plurality of closed cross-section ribs 12 are arranged on the underside of the deck plate 11 along the direction perpendicular to the bridge width. The multiple closed cross-section ribs 12 are members that stiffen the deck plate 11. The multiple closed cross-section ribs 12 are fixed to the underside of the deck plate 11 by welding. The closed cross-section ribs 12 are members that are arranged such that the extension direction of the closed cross-section ribs 12 coincides with the bridge axis direction of the steel deck bridge 1.

[0026] The closed cross-section rib 12 may be, for example, a Y-shaped cross-section rib, a V-shaped cross-section rib, a round cross-section rib, or a trough rib (hereinafter, sometimes referred to as a U-rib). For example, a U-rib is generally used as a closed cross-section rib used in a road bridge. The following describes a case where a U-rib is used as the closed cross-section rib 12. The material of the closed cross-section rib 12 is, for example, fatigue-resistant steel, similar to the deck plate 11. In addition, the plate thickness of the closed cross-section rib 12 is preferably set to, for example, 6 to 8 mm as a minimum thickness, taking into account corrosion and the like. In addition, the arrangement interval (interval in the direction perpendicular to the bridge axis) of the closed cross-section ribs 12 is preferably set to, for example, about 30 cm. In addition, the height of the closed cross-section rib 12 is preferably set to, for example, 240 mm.

[0027] The transverse ribs 13, like the closed cross-section ribs 12, are components that stiffen the deck plate 11 and also function as fulcrums for the closed cross-section ribs 12. The transverse ribs 13 are generally open cross-section ribs with an I-shaped cross section composed of a web and a lower flange. The transverse ribs 13 are arranged so that their longitudinal direction coincides with the direction perpendicular to the bridge axis. The transverse ribs 13 are also arranged at predetermined intervals in the bridge axis direction. Each of the transverse ribs 13 is fixed to the rear surface of the deck plate 11 by welding or the like.

[0028] Here, the arrangement interval of the transverse ribs 13 depends on the rigidity of the closed cross-section rib 12, but in fatigue design, a standard interval of 2.5 m or less is generally set. Although not shown in the figure, at the rib intersection where the closed cross-section rib 12 and the transverse rib 13 intersect, the web of the transverse rib 13 is cut out, so that the closed cross-section rib 12 penetrates the web of the transverse rib 13.

[0029] The main girder 20 is a member that is spanned between the abutments and piers and bears the bending moment and shear force between the spans. The main girder 20 is generally a member with an I-shaped cross section consisting of a web and upper and lower flanges. The deck plate 11 may also serve as the upper flange of the main girder 20. Furthermore, the main girder 20 may be an open cross-section main girder in which I-shaped cross-section members are arranged at predetermined intervals, or a closed cross-section main girder in the shape of a box girder. Although not shown in the figure, vertical stiffeners that stiffen the web of the main girder 20 are welded to the main girder 20 as necessary.

[0030] As shown in Figures 5 and 6, a treatment area 11a is provided on the surface of the above-mentioned deck plate 11. The treatment area 11a is an area that is subjected to a peening process after the closed cross-section rib 12 is welded and fixed to the back side of the deck plate 11. An example of the peening process is a hammer peening process in which a striking tool 45 strikes the base material (in this case, the deck plate 11) at least two times. The hammer peening process imparts compressive residual stress to the deck plate 11. By imparting compressive residual stress to the deck plate 11, the effect of tensile residual stress generated in the welded portion 41 on the deck plate 11 is mitigated.

[0031] Here, the shape of the impact surface of the impact tool 45 used in the hammer peening process is, for example, a 4 mm × 5 mm rectangle with rounded corners and chamfered corners. Note that the shape of the impact surface of the impact tool 45 does not need to be limited to a rounded rectangle, and may be any appropriate shape, such as a square, a circle, an ellipse, or the like.

[0032] Next, a manufacturing method of the closed section rib steel deck 10 will be described. As shown in FIG. 2(a), the closed section rib 12 is formed, for example, by bending the width end portions 31b, 31c of the width center portion 31a of the steel plate 31 to just before a right angle by plate bending processing. The end faces of the width end portions 31b, 31c of the steel plate 31 have a rectangular cross section. Therefore, as shown in FIG. 2(b), when the deck plate 11 and the closed section rib 12 form a closed section space A, a natural groove 35 that opens to the outside of the closed section space A is formed between the back surface of the deck plate 11 and both end portions (width end portions 31b, 31c) of the closed section rib 12. Using this natural groove 35, the deck plate 11 and the closed section rib 12 are welded from the outside of the closed section space A by using a welding machine 36. After the deck plate 11 and the closed section rib 12 are welded, a peening process is performed on the treatment area 11a (see FIG. 5) provided on the surface of the deck plate 11.

[0033] As shown in Figure 3, regarding the welding between the deck plate 11 and the closed section rib 12, the Highway Bridge Specifications state that it is necessary to ensure a penetration of thickness T (75% or more of the thickness of the closed section rib 12) relative to the plate thickness t of the closed section rib 12.

[0034] Furthermore, when the deck plate 11 and the closed cross section rib 12 are welded together, a welded portion 41 is present between the deck plate 11 and the closed cross section rib 12, where the deck plate 11 and the closed cross section rib 12 are welded together by the weld metal. Furthermore, an unwelded portion 42 of, for example, several mm to several tens of mm is present between the welded portion 41 and the closed cross section space A.

[0035] Of the intersections P1, P2 between the above-mentioned welded portion 41 and the underside of the deck plate 11, the intersection P1 located on the closed cross-sectional space A side is a portion called a weld root portion. In the steel deck 10, fatigue cracks that cause deck-penetrating cracks will occur starting from the weld root portion P1.

[0036] Here, we will explain fatigue cracks that occur in conventional closed section rib steel decks. As shown in Figures 4(a) and 4(b), when a vehicle passes over the closed section rib steel deck 100, the wheel load F of the vehicle generates compressive stress of about the yield stress in the weld root P1' of the unwelded portion 115 in the direction of the joint surface between the closed section rib 112 and the deck plate 111. In addition, tensile residual stress of about the yield stress generated by the thermal contraction effect around the unwelded portion 115 of the deck plate 111 and stress concentration at the tip of the unwelded portion 115 due to the wheel load F repeatedly acts on the direction perpendicular to the joint surface direction between the closed section rib 112 and the deck plate 111. As a result, a fatigue crack 120 is generated starting from the weld root P1'.

[0037] When the deck plate 111 and the closed cross-section rib 112 are welded together, heat from the welding is transferred to each of the deck plate 111 and the closed cross-section rib 112. As the heat from the welding is transferred to each of the deck plate 111 and the closed cross-section rib 112, the corresponding portions of the deck plate 111 and the closed cross-section rib 112 harden and appear as heat-affected zones (HAZ). Therefore, as shown in FIG. 4(b), when the deck plate 111 and the closed cross-section rib 112 are welded together at the welded portion (e.g., position X1), from the center side, the welded portion (welded metal) 116, the heat-affected zones (HAZ) 117a, 117b, and the base material (deck plate 111 and closed cross-section rib 112) appear.

[0038] Here, the tensile strengths of the deck plate 111, the welded portion 116, and the heat-affected portion 117a are different from each other. Therefore, when the above-mentioned wheel load F acts on the deck plate 111, the fatigue crack 120 starting from the weld root portion P1' does not grow linearly in a direction perpendicular to the maximum principal stress direction (i.e., in a direction perpendicular to the bridge axis), but grows while curving toward the surface of the deck plate 111 (see FIG. 4(b)).

[0039] Therefore, in this embodiment, fatigue-resistant steel is used as the material for the deck plate 11, and after the deck plate 11 and the closed cross-section rib 12 are welded together using a welding machine 36, a peening treatment is performed on the treatment area 11a provided on the surface of the deck plate 11. As a result, the growth of a fatigue crack that originates from the weld root P is stopped before it reaches the surface of the deck plate 11.

[0040] As described above, the processing area 11a provided on the surface of the deck plate 11 is subjected to the peening process. First, the details of the processing area 11a provided on the surface of the deck plate 11 will be described. As shown in Figs. 5 and 6, the processing area 11a is set as an area on the surface of the deck plate 11, for example, on the outer side of the vertical line L passing through the weld root portion P in the direction perpendicular to the bridge axis of the deck plate 11 (i.e., when the vertical line L is used as a reference, the area is on the opposite side of the closed cross-sectional space A with respect to the vertical line L), and is included in the range of the distance W from the weld root portion P. Here, the weld root portion P1 refers to the intersection point P1 located on the closed cross-sectional space A side of the two intersection points where the welded portion 41 and the back surface of the deck plate 11 intersect when the closed cross-sectional rib 12 is welded to the back surface of the deck plate 11 (see Fig. 6). As described above, the closed cross-section rib 12 welded and fixed to the deck plate 11 is formed by bending the width end portions 31b, 31c of the steel plate 31, and therefore the closed cross-section rib 12 is welded to the deck plate 11 at two locations, the width end portions 31b, 31c of the steel plate 31. In other words, the above-mentioned treatment regions 11a are provided corresponding to the welded locations (reference symbols X1 and X2 in FIG. 5) at both ends of the closed cross-section rib 12. The peening treatment is performed on these treatment regions 11a.

[0041] The peening process is carried out so as to satisfy the following conditions A to C. Condition A: As shown in Figure 6, in the direction perpendicular to the bridge axis, the distance d from a straight line L passing through the weld root portion P1 to a straight line Lc passing through the center of the impact tool 45 is, for example, less than twice the plate thickness TH of the deck plate 11 (more preferably, less than 1.5 times the plate thickness TH). Condition B: As shown in FIG. 6, the width w of the impact by the impact tool 45 in the direction perpendicular to the bridge axis (synonymous with the width of the impact tool 45) is 1 / 8 or more (more preferably 1 / 4 or more) of the plate thickness TH of the deck plate 11. Condition C: Strikes are performed at least two times (more preferably four times or more) so that the center position of the strike in the peening process is the same position or the amount of deviation of the strike in the peening process is within a predetermined range.

[0042] (Regarding condition A) As described above, the peening process involves striking the surface of the deck plate 11 with the striking tool 45. The striking of the striking tool 45 imparts compressive residual stress to the deck plate 11. At this time, the distance d from the weld root P1 to the line Lc passing through the center of the striking tool 45 is set within a range that includes the trajectory of a fatigue crack propagating inside the deck plate 11 in the direction perpendicular to the bridge axis.

[0043] According to this, the compressive residual pressure applied to the deck plate 11 by performing the peening process acts to counteract the tensile residual pressure generated in the welded portion 41. As a result, the slowing down of the growth rate of the fatigue crack propagating inside the deck plate 11 is faster than when the peening process is not performed. The slowing down of the fatigue crack growth rate leads to a decrease in the stress intensity factor range ΔK at the tip of the fatigue crack. Therefore, when the peening process is performed, the stress intensity factor range ΔK at the tip of the fatigue crack is reduced to the lower threshold stress intensity factor range ΔKth before the fatigue crack reaches the surface of the deck plate 11. As a result, the fatigue crack stops growing before it reaches the surface of the deck plate 11.

[0044] On the other hand, if the distance d is set to a value exceeding twice the plate thickness TH of the deck plate 11, it is assumed that the position where the peening process is performed in the direction perpendicular to the bridge axis is shifted from the region where the fatigue crack grows. In this case, the compressive residual pressure applied to the deck plate 11 may not be able to cancel the tensile residual pressure generated in the welded portion 41. As a result, as in the case where the peening process is not performed, there is a risk that the fatigue crack will reach the surface of the deck plate 11 before the stress intensity factor range ΔK at the tip of the fatigue crack decreases to the lower threshold stress intensity factor range ΔKth. Therefore, if the distance d is set to a value exceeding twice the plate thickness TH of the deck plate 11, the fatigue crack may reach the surface of the deck plate 11 and cause a deck-penetrating crack.

[0045] (Regarding condition B) As described above, when the peening process is performed, compressive residual stress is imparted to the deck plate 11. At this time, by setting the width w of the impact by the impact tool 45 in the direction perpendicular to the bridge axis to 1 / 8 or more (more preferably 1 / 4 or more) of the plate thickness TH of the deck plate 11, it is possible to impart a desired compressive residual stress to the deck plate 11 during the peening process. By imparting compressive residual stress to the deck plate 11, the influence of tensile residual stress generated by welding the deck plate 11 to the closed cross-section rib 12 is reduced. As a result, before the fatigue crack reaches the surface of the deck plate 11, the stress intensity factor range ΔK at the tip of the fatigue crack decreases to the lower threshold stress intensity factor range ΔKth, and the growth of the fatigue crack is stopped.

[0046] If the width w of the impact by the impact tool 45 is set to less than 1 / 8 of the plate thickness t of the deck plate 11, it is difficult to impart a predetermined compressive residual stress to the deck plate 11. Therefore, even if a peening process is performed, it is difficult to affect the growth of a fatigue crack that originates from the weld root portion P1. As a result, if the width w of the impact tool 45 is set to less than 1 / 8 of the plate thickness t of the deck plate 11, the fatigue crack will grow to the surface of the deck plate 11, increasing the possibility of a through-deck crack occurring.

[0047] (Regarding condition C) As described above, compressive residual stress is applied to the deck plate 11 by the peening process. At this time, the impact is performed at least twice (more preferably four times or more) so that the center position of the impact in the peening process is the same position or the impact deviation amount in the peening process is within a predetermined range. By performing the impact at least twice, it is possible to apply a predetermined compressive residual stress to the deck plate 11. By applying the compressive residual stress to the deck plate 11, the influence of the tensile residual stress generated by welding the deck plate 11 and the closed cross-section rib 12 is reduced. As a result, before the fatigue crack reaches the surface of the deck plate 11, the stress intensity factor range ΔK at the tip of the fatigue crack is reduced to the lower threshold stress intensity factor range ΔKth, and the growth of the fatigue crack is stopped. Note that the "predetermined range" in condition C is, for example, a deviation amount of the impact surface when the impact tool 45 hits the deck plate 11 is within 25%.

[0048] On the other hand, with a peening process in which a specific position on the surface of the deck plate 11 is struck once with an impact tool 45, it is difficult to impart a specific compressive residual stress to the deck plate 11. Therefore, even if a peening process is performed, it is difficult to affect the growth of a fatigue crack that originates from the weld root P1. As a result, the fatigue crack will grow to the surface of the deck plate 11, increasing the possibility of a through-deck crack occurring.

[0049] The above-mentioned peening treatment is preferably carried out so as to impart a compressive residual stress of −50 MPa or more to a position that is 2 mm or more deep from the surface of the deck plate 11, for example.

[0050] For example, if compressive residual stress is applied to a position less than 2 mm deep from the surface of the deck plate 11, it is possible to stop the progression of the above-mentioned fatigue crack. However, because the thickness (residual thickness) from the surface of the deck plate 11 to the tip of the fatigue crack is thin, there is a risk that the fatigue crack will progress and cause a through-deck crack due to factors other than the repeated application of the wheel load F. Also, for example, if a compressive residual stress of less than -50 MPa is applied, it is difficult to reduce the stress intensity factor range ΔK at the tip of the fatigue crack to the lower threshold stress intensity factor range ΔKth, and there is a risk that the progression of the fatigue crack cannot be stopped.

[0051] Finally, the results of finite element analysis for the conventional closed section rib steel deck 100 and the closed section rib steel deck 10 of this embodiment will be explained using Figures 7 and 8. In the finite element analysis, the deck plate thickness was set to 16 mm. In Figures 7 and 8, the horizontal axis shows the crack depth in the thickness direction of the deck plate, and the vertical axis shows the stress intensity factor range ΔK at the crack tip. Here, the crack depth in the thickness direction of the deck plate is set to 0 on the back side of the deck plate and 16 mm on the front side of the deck plate.

[0052] In a conventional closed cross-section ribbed steel deck 100, when a wheel load F is repeatedly applied to the surface of the deck plate 111, a fatigue crack is generated starting from the weld root part P1'. The fatigue crack that is generated starting from the weld root part P1' progresses in the order of the welded part 116 and the heat-affected part 117a.

[0053] As shown in FIG. 7, as the fatigue crack propagates in the thickness direction of the deck plate 111, the stress intensity factor range ΔK1 at the crack tip increases. Then, when the fatigue crack propagates to the boundary between the heat-affected zone 117a and the deck plate 111, the stress intensity factor range ΔK1 at the crack tip reaches a maximum value. Note that, as the fatigue crack propagates from the heat-affected zone 117a to the deck plate 111, the stress intensity factor range ΔK1 at the fatigue crack tip gradually decreases. Accordingly, the propagation speed of the fatigue crack slows down. However, before the stress intensity factor range ΔK1 at the crack tip reaches the lower limit stress intensity factor range ΔK1th, the crack depth of the fatigue crack in the thickness direction of the deck plate 111 reaches the thickness of the deck plate 111 (in other words, the surface of the deck plate 111).

[0054] On the other hand, in the closed section ribbed steel deck 10 of this embodiment, as in the conventional closed section ribbed steel deck 100, as the fatigue crack propagates in the thickness direction of the deck plate 11, the stress intensity factor range ΔK2 at the crack tip increases. As shown in FIG. 8, when the fatigue crack propagates to the boundary between the heat-affected zone (HAZ) and the deck plate 111, the stress intensity factor range ΔK2 at the crack tip reaches a maximum value. Then, when the fatigue crack propagates from the heat-affected zone to the deck plate 11, the stress intensity factor range ΔK2 at the fatigue crack tip decreases. Accordingly, the fatigue crack propagation speed slows down. In the closed section ribbed steel deck 10 of this embodiment, the stress intensity factor range ΔK2 at the fatigue crack tip decreases compared to the stress intensity factor range ΔK2 at the fatigue crack tip propagating in the conventional closed section ribbed steel deck 100.

[0055] In addition, the material of the deck plate 11 of the closed cross-section rib steel deck 10 in this embodiment is fatigue-resistant steel, and its lower threshold stress intensity factor range ΔKth2 is higher than that of general steel materials. Therefore, when a fatigue crack propagates inside the deck plate 11, the stress intensity factor range ΔK2 at its tip is likely to decrease, and also to decrease to the lower threshold stress intensity factor range ΔKth2. As a result, the stress intensity factor range ΔK2 at the crack tip decreases to the lower limit stress intensity factor range ΔKth, making it possible to stop the propagation of the fatigue crack before the crack depth in the thickness direction of the deck plate 11 reaches the plate thickness TH of the deck plate 11.

[0056] In this embodiment, a case is described in which one impact tool 45 is used when performing the peening process on the processing area 11a of the deck plate 11. When one impact tool 45 is used, for example, it is possible to perform the peening process while shifting the impact tool 45 in the bridge axis direction at a first position perpendicular to the bridge axis, and then perform the peening process at a second position shifted a certain amount from the first position while shifting it in the bridge axis direction. The shift amount from the first position to the second position may be such that the processing area by the impact tool 45 at the first position and the processing area by the impact tool at the second position overlap.

[0057] Also, instead of shifting the impact tool 45 from the first position to the second position in the treatment area 11a of the deck plate 11, a hammer peening treatment may be performed in which two impact tools 45a, 45b are simultaneously struck as shown in Fig. 9. In this case, it is preferable that the sum of the width w1 of the impact tool 45a and the width w2 of the impact tool 45b in the direction perpendicular to the bridge axis is set to 1 / 8 or more (more preferably 1 / 4 or more) of the plate thickness TH of the deck plate 11.

[0058] In this embodiment, the tip faces of the width end portions 31b, 31c of the steel plate 31, which form the closed cross-section rib 12, have a rectangular cross section. However, for example, the tip faces of the width end portions 31b, 31c may be chamfered.

[0059] In this embodiment, the welding method between the deck plate 11 and the closed cross-section rib 12 is not particularly limited, but the occurrence of fatigue cracks can be suppressed by adopting a welding method with fewer bead defects, such as TIG (Tungsten Inert Gas) welding or MAG (Metal Active Gas) welding using flux cord wire.

[0060] In the present embodiment, a fatigue-resistant steel with a slow crack growth rate is used as the material for the deck plate 11 and the closed cross-section rib 12. An example of the fatigue-resistant steel is AFD (Anti-fatigue Damage) steel (registered trademark: manufactured by JFE Steel Corporation). By using such fatigue-resistant steel, it is possible to suppress the occurrence of deck-penetrating cracks.

[0061] <Summary of the invention> According to the closed section ribbed steel deck of the present invention, there is provided a closed section ribbed steel deck 10 having a plate-shaped deck plate 11 extending in one direction, and a closed section rib 12 welded to the back side of the deck plate 11 with its extension direction aligned with the extension direction of the deck plate 11, the closed section ribbed steel deck 10 having a closed section space A surrounded by the deck plate 11 and the closed section rib 12, and a welded portion 41 where an end face of the closed section rib 12 and the back side of the deck plate 11 are welded with a weld metal, and a treatment area 11a is provided on the surface of the deck plate 11 where a peening treatment is performed to relieve welding residual stress remaining in the deck plate 11, and the peening treatment is performed by narrowing the treatment area 11a so that the center position of the impact in the peening treatment is the same position, or the amount of impact deviation is within a predetermined range. The peening process is a process in which impacts are applied at least two times, and the center position of the impact in the peening process is located on the opposite side of the closed cross-sectional space A with respect to a straight line L that passes through intersection P1 located on the closed cross-sectional space A side of two intersections P1, P2 where the welded portion 41 intersects with the back surface of the deck plate 11 in a cross-section of the deck plate 11 perpendicular to the extension direction of the deck plate 11 and is perpendicular to both the extension direction of the deck plate 11 and the width direction of the deck plate 11, and the distance d from intersection P1 to the center position of the impact in the peening process is not more than twice the plate thickness TH of the deck plate 11 in the width direction of the deck plate 11, and the width w of the impact in the peening process is not less than 1 / 8 of the plate thickness TH of the deck plate 11 in the width direction of the deck plate 11.

[0062] According to this, the compressive residual pressure applied to the deck plate 11 by performing the peening treatment acts to counteract the tensile residual pressure generated in the welded portion 41. The rate at which a fatigue crack propagates inside the deck plate 11 decreases is faster than when the peening treatment is not performed. Therefore, the stress intensity factor range ΔK at the tip of a fatigue crack propagating inside the deck plate 11 is more likely to decrease to the lower limit stress intensity factor range ΔKth, and the propagation of the fatigue crack stops before it reaches the surface of the deck plate 11, making it possible to obtain a so-called crack arrest effect.

[0063] Moreover, the peening process applies a predetermined compressive residual stress to the deck plate 11 at a position a predetermined distance from the surface of the deck plate 11 in the thickness direction of the deck plate 11.

[0064] According to this, the compressive residual stress applied to the deck plate 11 by performing the peening process acts to counteract the tensile residual stress occurring in the welded portion 41. As a result, the growth of a fatigue crack that originates from the weld root portion P1 can be stopped before it reaches the surface of the deck plate 11.

[0065] In addition, it is preferable that the peening treatment is performed at multiple positions on the deck plate 11 in the direction perpendicular to the bridge axis, and the total width of the peening treatment performed at the multiple positions in the direction perpendicular to the bridge axis is 1 / 8 or more of the plate thickness t of the deck plate 11.

[0066] According to this, by performing the peening treatment, a predetermined compressive residual pressure is reliably applied to the deck plate 11, thereby preventing the residual tensile pressure generated in the welded part 41 from acting on the deck plate 11. As a result, even if the wheel load F is repeatedly applied to the deck plate 11, the stress intensity factor range ΔK at the tip of the fatigue crack is reduced to the lower threshold stress intensity factor range ΔKth before the tip of the fatigue crack propagates on the surface of the deck plate 11, and the propagation of the fatigue crack is stopped. [Explanation of symbols]

[0067] 1 Steel slab bridge 10. Closed section rib steel deck 11 Deck plate 11a Processing area 12 Closed section rib 13 Horizontal ribs 15. Pavement 20 Main digit 31 Steel plate 31a Width center part 31b,31c Width end part 35 Natural groove 36 Welding Machine 41 Welded area 42 Unwelded area 45, 45a, 45b Impact tools 100 Conventional closed section rib steel deck 111 Deck plate 112 Closed Section Rib 115 Unwelded area 116 Welded area 117a,117b Heat affected zone (HAZ) 120 Fatigue cracks A closed section space P1 Weld root (intersection)

Claims

1. A closed section rib steel deck having a plate-shaped deck plate extending in one direction and a closed section rib welded to the back side of the deck plate such that the extension direction of the closed section rib is aligned with the extension direction of the deck plate. The closed section rib steel deck is A closed cross-sectional space surrounded by the deck plate and the closed cross-sectional rib; a welded portion in which an end face of the closed cross-section rib and a back surface of the deck plate are welded by a weld metal; having A treatment area is provided on a surface of the deck plate, where a peening treatment is performed to relieve welding residual stress remaining in the deck plate, the peening process is a process of striking the treatment region at least two times so that the center positions of the strikes in the peening process are the same position or the amount of deviation of the strikes is within a predetermined range; a center position of the impact in the peening process is located on the opposite side of the closed cross-sectional space with respect to a straight line that passes through one of two intersections at which the welded portion intersects with the rear surface of the deck plate in a cross section of the deck plate perpendicular to the extension direction of the deck plate and is perpendicular to each of the extension direction of the deck plate and the width direction of the deck plate, and is located on the opposite side of the closed cross-sectional space with respect to the straight line, a distance from the intersection to a center position of the impact in the peening process is equal to or less than twice the plate thickness of the deck plate in a width direction of the deck plate, The width of the impact in the peening process is 1 / 8 or more of the plate thickness of the deck plate in the width direction of the deck plate. A closed section rib steel deck characterized by the above.

2. The peening process applies a predetermined compressive residual stress to the deck plate at a position a predetermined distance from the surface of the deck plate in the thickness direction of the deck plate.

2. The closed section rib steel deck according to claim 1 .

3. The peening process is performed at a plurality of positions of the deck plate in a width direction of the deck plate, The total width of the peening process performed at the multiple positions is equal to or greater than 1 / 8 of the plate thickness t of the deck plate.

3. The closed section rib steel deck according to claim 1 or 2.

4. The material of the deck plate is fatigue resistant steel.

2. The closed section rib steel deck according to claim 1 .

5. A manufacturing method of a closed section rib steel deck having a plate-shaped deck plate extending in one direction and a closed section rib welded to the back side of the deck plate such that the extension direction of the closed section rib is the same as the extension direction of the deck plate, a step of welding an end surface of the closed cross-section rib and a back surface of the deck plate with a weld metal in a state in which a closed cross-section space is formed by the deck plate and the closed cross-section rib; a step of performing a peening treatment on a treatment area provided on a surface of the deck plate to which the closed cross-section rib is welded and fixed; having the peening process is a process of striking the treatment region at least two times so that the center position of the strike in the peening process is the same position or the amount of deviation of the strike is within a predetermined range, a center position of the impact in the peening process is located on the opposite side of the closed cross-sectional space with respect to a straight line that passes through one of two intersections at which the welded portion intersects with the rear surface of the deck plate in a cross section of the deck plate perpendicular to the extension direction of the deck plate and is perpendicular to each of the extension direction of the deck plate and the width direction of the deck plate, and is located on the opposite side of the closed cross-sectional space with respect to the straight line, a distance from the intersection to a center position of the impact in the peening process is equal to or less than twice the plate thickness of the deck plate in a width direction of the deck plate, The width of the impact in the peening process is 1 / 8 or more of the plate thickness of the deck plate in the width direction of the deck plate. A manufacturing method for closed section rib steel deck plate characterized by the above.

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