JP2007332588A - U-rib steel floor slab - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a U-rib steel floor slab which is constituted by welding a U-rib to an undersurface of a deck plate, and which can accurately prevent the appearance of a deck penetrating crack penetrating the deck plate. <P>SOLUTION: A groove 13 with predetermined dimensions is preprovided on the side of the inner surface of the leading end of the U-rib 12a. The U-rib steel floor slab is manufactured by welding the U-rib 12a to the deck plate 11a from the outside of a closed-cross-section space which is formed of the deck plate 11a and the U-rib 12a. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a U-rib steel slab used for a steel bridge and formed by welding a U-rib to the lower surface of a floor plate (deck plate).

  The bridge steel slab structure has a structure in which a steel deck 10 is installed on the upper part of a bridge girder (main girder 1 and cross girder 2) as shown in FIG. The steel slab 10 employs a closed cross-section vertical rib structure (U-rib steel slab structure) in which a U-shaped vertical rib (U rib) 12 is welded to the lower surface of a floor plate (deck plate) 11 made of a steel plate. Has become the mainstream. This is because the construction is relatively high and the construction is simple. In addition, 31 in FIG. 6 is a horizontal rib, 32 is a pavement.

  However, in recent years, cracks penetrating the deck plate 11 (hereinafter referred to as deck penetration cracks) as shown in FIG. 7 have been discovered in the U-rib steel slab 10 as described above. This deck penetration crack has been found to be a fatigue crack starting from an unwelded portion between the deck plate 11 and the U rib 12 based on a field survey, a core removal survey, a UT test, and the like.

  For such deck deck cracks in steel decks, Patent Document 1 discloses a technique for improving durability by using a steel material that suppresses the occurrence or progress of fatigue cracks, but this alone is sufficient. However, more effective technology is desired.

The following Non-Patent Documents 1 and 2 are cited in [Means for Solving the Problems] and [Best Mode for Carrying Out the Invention], which will be described later.
JP 2003-183769 A Japan Road Association: Road Bridge Specification / Comment (Common / Steel Bridge), March 2002 Iki, et al .: “High-performance steel for shipbuilding-Life cycle cost reduction technology of JFE steel”, JFE Technical Report, No. 5, August 2004, p.13-18

  The present invention has been made in view of the above circumstances, and in a U-rib steel slab formed by welding a U-rib to the lower surface of a floor plate (deck plate), the occurrence of a deck penetration crack that penetrates the deck plate. An object of the present invention is to provide a U-rib steel slab that can be accurately prevented.

  The present inventors considered that it is important to suppress the occurrence of fatigue cracks in order to prevent the occurrence of deck through cracks in U-rib steel slabs, and studied the mechanism of fatigue crack occurrence. . As a result, it was clarified that fatigue cracks occur by the following mechanism.

  FIG. 4 shows the manufacturing process of the U-rib steel slab. As shown in FIG. 4 (a), as shown in FIG. 4 (b), a steel plate is formed by using a U-rib 12 formed by bending a side portion of the steel plate to the right side with respect to the width central portion of the steel plate. Therefore, the natural groove 16 opened outside the closed cross-sectional space formed by the deck plate 11 and the U rib 12 is formed on the deck plate 11. The U-rib 12 is welded to the deck plate 11 by the welding machine 19 from the outside of the closed cross-section space using the formation between the lower surface and the front end surface of the U-rib 12 with the natural groove 16 remaining. The method is common. At that time, when designed according to the road bridge specification shown as Non-Patent Document 1, as shown in FIG. 4C, the welded portion has a penetration (welded metal 20) of 75% or more of the U-rib plate thickness. Although it is ensured and welding is performed, an unwelded portion 17 of about several mm to several tens mm remains. The unwelded portion 17 is pressed against the lower surface of the deck plate 11 by welding heat shrinkage and is in a pressure-bonded state.

  Then, as shown in FIG. 5 (a), when the vehicle passes over the U-rib steel slab, as shown in FIG. 5 (b) due to the wheel load 33 of the vehicle, , A compressive stress of about the yield stress is generated in the joint surface direction between the U-rib 12 and the deck plate 11, and the tensile residual stress of the yield stress due to the thermal contraction effect around the unwelded portion 17 of the deck plate and the ring load 33 Due to the stress concentration at the weld tip 17a, the tensile stress of about the yield stress is repeated in the direction perpendicular to the joint surface of the U-rib 12 and the deck plate 11, thereby generating a fatigue crack 50, and the fatigue crack 50 becomes a deck plate. Progress in the top direction.

  The above is the mechanism of occurrence of fatigue cracks in the U-rib steel slab, which has been elucidated by the inventors. Based on the mechanism of occurrence, the inventors further investigated a method for suppressing the occurrence of fatigue cracks.

  As a result, in order to suppress the occurrence of fatigue cracks, by providing a groove on the inner surface side of the tip of the U rib 12 (inside the closed cross-sectional space formed by the deck plate 11 and the U rib 12), It has been found that a structure in which the restraint stress of the deck plate 11 generated due to welding heat shrinkage is less likely to be generated. That is, by providing a groove on the inner surface side of the distal end portion of the U rib 12, contact (compression deformation) between the U rib 12 and the deck plate 11 at the unwelded portion 17 as shown in FIG. This is because the tensile residual stress applied to the deck plate 11 is reduced, the unwelded portion 17 itself is almost eliminated, and the shape stress concentration is reduced. As a result, the occurrence of fatigue cracks 50 starting from the unwelded portion 17 between the deck plate 11 and the U rib 12 can be suppressed.

  On top of that, if a steel material (hereinafter referred to as fatigue resistant steel) with high fatigue durability (low fatigue crack propagation rate) is used for the deck plate 11 and the U rib 12, even if a fatigue crack occurs, The progress of the fatigue crack can be suppressed, and the fatigue crack can be prevented from penetrating the deck plate 11 (that is, the deck through crack is generated).

  Based on the above concept, the present invention has the following features.

  [1] A U-rib steel slab formed by welding a U-rib to the lower surface of a deck plate, wherein a groove is provided on the inner surface of the tip of the U-rib and welded.

  [2] The U-rib steel slab according to [1], wherein a welding method with a good back wave is used for the first layer welding.

  [3] The U-rib steel slab according to [1] or [2], wherein a steel material having a low fatigue crack propagation rate is used for the deck plate and / or the U-rib.

  In the present invention, it is possible to accurately prevent the occurrence of a deck penetration crack that penetrates the deck plate. As a result, it is possible to provide a U-rib steel slab that is lower in price and has a longer life than the conventional structure, and it is possible to avoid troubles such as traffic obstacles.

  An embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a manufacturing process of a U-rib steel slab in this embodiment. Here, as the deck plate 11 and the U rib 12, a deck plate 11a and a U rib 12a using a steel material (fatigue resistant steel) having a low fatigue crack propagation rate are used.

  First, as shown in FIG. 1 (a), a deck plate 11a and a U-rib 12a are formed using a U-rib 12a formed by bending a side portion of the steel plate to a right-angle front side with respect to the width center portion of the steel plate. By using the fact that the natural groove 16 opened outside the closed cross-sectional space is formed between the lower surface of the deck plate 11a and the front end surface of the U rib 12a, the welder 19 from the outside of the closed cross-sectional space is used. The U rib 12a is welded to the deck plate 11a.

  At this time, in this embodiment, a groove 13 having a predetermined dimension is provided in advance on the inner surface side (the inner side of the closed cross-sectional space formed by the deck plate 11a and the U rib 12a) of the tip portion of the U rib 12a. I am doing so.

  As shown in FIG. 1 (b), TIG welding is used for the first layer 21, and MAG welding, SAW welding, or the like is used for the second and subsequent layers, whereby the weld metal 20 is formed.

  In the U-rib steel slab manufactured as described above, an unwelded portion is eliminated by providing a groove on the inner surface side of the tip portion of the U-rib 12a. As a result, as shown in FIG. 4C, the U-rib and the deck plate are not crimped at the unwelded portion due to the shrinkage of the weld metal, and the shrinkage of the weld metal is absorbed by the deformation of the deck plate 11a and the U-rib 12a. The tensile residual stress is reduced, the unwelded portion itself is eliminated, and the shape stress concentration is also reduced. As a result, the occurrence of fatigue cracks starting from the unwelded portion between the deck plate and the U rib is suppressed.

  Furthermore, as the first layer welding, the occurrence of fatigue cracks is further suppressed by adopting a welding method that has few bead defects such as TIG welding or MAG welding using a flux cord wire and has a good back wave shape.

  However, even in the U-rib steel slab as described above, as shown in FIG. 2 (a), stress concentration occurs at the base of the first layer (back wave welding) 21 and the base of the deck plate 11 or the U-rib 12. Part 14. At this time, if the deck plate 11b and the U rib 12b using ordinary steel for the deck plate 11 and the U rib 12 are used, if the fatigue crack 50 is generated starting from the stress concentration portion 14, the fatigue crack is generated. It may develop and cause a deck through crack or a U-rib through crack.

  Therefore, as shown in FIG. 2 (b), even when a fatigue crack 50 is generated starting from the stress concentration portion 14 by using the deck plate 11a and the U rib 12a using fatigue resistant steel, The progress of fatigue cracks can be suppressed, and the occurrence of deck penetration cracks and U-rib penetration cracks can be prevented.

  Here, the fatigue-resistant steel refers to, for example, AFD (anti-fatigue damage) steel (registered trademark: manufactured by JFE Steel) described in Non-Patent Document 2.

  In order to confirm the effect of using fatigue resistant steel for the deck plate, the thickness of the deck plate 11 is 12 mm for ordinary steel and fatigue resistant steel having the chemical composition shown in Table 1 and the microstructure shown in Table 2. The repeated stress range was set to 134 MPa, and the crack propagation rate was evaluated when a semi-elliptical fatigue crack having a depth of 2 mm and a length of 10 mm occurred in the deck plate 11 from the stress concentration portion 14.

  As a result, the normally used crack propagation rate equation (1) of the normal steel plate and the crack propagation rate equation (2) of the fatigue resistant steel plate shown in FIG. 3 were obtained.

da / dN = 8.04 × 10 ^-12 (ΔK) ^3.09 ： Normal steel (1)
da / dN = 4.02 × 10 ^-12 (ΔK) ^3.09 : Fatigue resistant steel (2)
Here, da / dN is the crack propagation rate (m / cycle), and ΔK is the stress intensity factor range (MPa · m ^1/2 ).

  Under the above conditions, the fatigue crack propagation analysis based on the Japan Welding Association standard WES2805, the number of repetitions required for the above-mentioned fatigue crack to grow to 80% of the plate thickness is 264,650 times for normal steel plate, fatigue resistant steel plate 529,300 times, and by using fatigue resistant steel, it is possible to obtain a fatigue crack growth life twice that of using ordinary steel and to delay the crack penetration through the deck plate.

  Similarly, even when a fatigue crack occurs in the U rib 12 from the stress concentration portion 14, by using a fatigue resistant steel for the U rib 12, it is possible to obtain a fatigue crack growth life that is twice that in the case of using ordinary steel. It is possible to delay the U-rib penetration of the crack.

  In some cases, fatigue resistant steel may be used for either the deck plate 11 or the U rib 12 based on the stress state of the stress concentration portion 14.

  Further, fatigue resistant steel may be used for a part of the deck plate 11 or a part of the plurality of U ribs 12 based on the wheel load distribution of the passing vehicle.

  Thus, in this embodiment, it is possible to accurately prevent the occurrence of a deck penetration crack that penetrates the deck plate and a U rib penetration crack that penetrates the U rib. As a result, it is possible to provide a U-rib steel slab that is lower in price and has a longer life than the conventional structure, and it is possible to avoid troubles such as traffic obstacles.

It is a figure which shows the manufacturing process of the U rib steel deck in one Embodiment of this invention. It is a figure which shows the stress concentration part in one Embodiment of this invention. It is the figure which compared the crack propagation rate of normal steel and the crack propagation rate of fatigue-resistant steel. It is a figure which shows the manufacturing process of the conventional U rib steel deck. It is a figure which shows the fatigue crack generation mechanism in the conventional U rib steel deck. It is a figure which shows the structure of steel bridges. It is a figure which shows the deck penetration crack in a U rib steel deck.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main girder 2 Cross girder 10 U rib steel deck 11 Deck plate 11a Fatigue-resistant steel deck plate 11b Normal steel deck plate 12 U rib 12a Fatigue-resistant steel U rib 12b Normal steel U rib 13 Groove 14 Stress concentration Part 16 Natural groove 17 Unwelded part 17a End part of unwelded part 19 Welding machine 20 Weld metal 21 First layer 22 Second layer and beyond 31 Lateral rib 32 Pavement 33 Wheel load 50 Fatigue crack

Claims (3)

  A U-rib steel slab formed by welding a U-rib to the lower surface of a deck plate, wherein a groove is provided on the inner surface of the tip of the U-rib and welded.   The U-rib steel slab according to claim 1, wherein a welding method with a good back wave is used for the first layer welding.   The U-rib steel slab according to claim 1 or 2, wherein a steel material having a low fatigue crack propagation rate is used for the deck plate or / and the U-rib.

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