JP2009046931A - Repair method for steel material by carbon fiber reinforced plastic board and repaired steel material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a permanent repair method for the fatigue crack of a steel structure by using a carbon fiber reinforced plastic board (CFRP board). <P>SOLUTION: A stop hole 5 is formed at the tip end of the fatigue crack 4 introduced into a steel material 1, the carbon fiber reinforced plastic board (CFRP board) 6 is stuck to cover the stop hole 5, and a CFRP board 7 is stuck to cover the crack 4. So that a higher effect is obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to repair of steel materials such as steel bridges, and relates to a method for repairing fatigue cracks easily and effectively.

  In recent years, many damages have been reported to each member of a steel bridge due to fatigue, corrosion, and the like due to vibrations, shocks, and the like accompanying an increase in the size of a vehicle and an increase in traffic. Moreover, in order to cope with an increase in load, many steel bridges require reinforcement. Once a fatigue crack occurs in a steel member, the crack gradually progresses and the main member may break. In particular, it is known that many cracks are concentrated at the welded joint of the steel plate.

  In order to suppress such crack growth, an emergency repair method in which a stop hole is formed at the crack tip is generally implemented. By forming such a stop hole, the stress concentration at the crack tip is relaxed, so that the progress of the crack can be temporarily stopped. However, since this stop hole is only an emergency measure, it is necessary to repair and reinforce it further to suppress crack growth.

  Conventionally, a method of attaching by attaching a steel plate using a high-strength bolt or welding a steel plate using this stop hole has been mainly performed. For example, in Patent Document 1, when repairing a crack generated at the end of an out-of-plane gusset portion, a stop hole is opened at the tip of the crack and tightened with a high-strength bolt with a specially shaped washer (plate material) interposed. The construction method is disclosed. Further, in Patent Document 2, the plate material is harder than the base material, and a plate material in which teeth are formed in a direction in which compressive stress can be applied to the tensile load acting on the base material is interposed, and a stop hole is formed. A method is disclosed in which a compressive force at the center is applied to reliably stop the growth of fatigue cracks.

  However, such repair / reinforcement is often a narrow part where the joints of the members are complex and the workability is extremely poor in both high-strength bolted joints and welded joints. was there. In addition, a material harder than the base material as in Patent Document 2 is heavier in weight and further increases in weight when combined with a fastening bolt, so there is room for improvement in terms of workability and portability. Therefore, a simple and efficient construction method is desired.

  In response to such a request, Patent Document 3 was discovered by attaching a fiber-reinforced synthetic resin sheet that can be easily carried to a crack generated in a portion where a repeated stress acts on a steel structure. A method for delaying crack growth is disclosed. Here, a method has been proposed in which an uncured prepreg sheet is applied to a steel structure and then cured by irradiation with heat or ultraviolet rays. In the Examples, a glass fiber reinforced synthetic resin prepreg is pasted and the delay rate of crack propagation is measured. It is disclosed that the crack growth rate is reduced to about 1/3 as compared with the case where a reinforcing sheet is not attached.

  However, this method merely suppresses the crack growth rate, and is implemented as a bridge until permanent repair. The permanent repair itself must be relied on the conventional method. In addition, in order to cure the prepreg, it is necessary to irradiate heat and ultraviolet rays, and there is a possibility that a sufficient effect cannot be obtained particularly in a narrow portion. In addition, the sheet is excellent in workability on site because of its high flexibility. However, since the sheet has a small amount of fibers per sheet, it needs to be laminated considerably in order to ensure sufficient rigidity.

  As a simple method for suppressing the progress of a crack generated from the toe portion of a so-called out-of-plane gusset portion in which the gusset plate is turned and welded out of the plane of the steel base material, the present inventors A repair method using a carbon fiber reinforced resin plate (hereinafter referred to as a CFRP plate) is proposed (Patent Document 4). According to this method, a CFRP plate molded in a U-shape can be stuck along the bead shape of the out-of-plane gusset, and the crack growth rate can be effectively delayed.

However, even with such a method, the progress of cracks cannot be stopped completely, and a more effective repair method that can be expected as a permanent countermeasure is desired.
Japanese Patent Laid-Open No. 10-168817 JP 2004-176254 A Japanese Patent Application Laid-Open No. 2004-211338 JP 2006-57352 A

  Therefore, an object of the present invention is to provide a simpler and more effective repair method for fatigue cracks introduced into steel materials.

  In order to solve the above problems, the present invention provides a stop hole at the tip of a fatigue crack introduced into a steel material, and covers the stop hole so that at least a carbon fiber reinforced resin plate ( The present invention relates to a method for repairing a steel material characterized in that a CFRP plate is attached.

  Further, by applying a CFRP plate on the crack so as to cover the crack, a higher effect can be obtained, and it is preferable to attach an independent CFRP plate on the stop hole and on the crack.

  According to the present invention, when the crack growth prevention by the stop hole and the reinforcement method by the CFRP plate are combined, a synergistic effect more than expected by simply combining these is recognized. Reinforcement effective for suppression can be achieved by a very simple method.

  Although the CFRP plate used in the present invention has a specific gravity of about 1/5 that of steel, the tensile strength is about 6 times that of steel, and can be easily carried. Since it is a simple method of applying and sticking, it is easy to repair narrow portions.

  The steel material to be repaired in the present invention can be applied to any steel material as long as a crack has occurred. However, in the following description, the gusset is perpendicular to the side surface of the steel material as the base material. A description will be given of a so-called out-of-plane gusset welded with a plate, in which a fatigue crack is generated in the weld due to repeated stress. In such an out-of-plane gusset, a fatigue crack is likely to occur from the toe portion of the fillet welded portion of the gusset, and if left as it is, the crack progresses and the base material is broken.

  First, a stop hole is formed in the steel material in which a crack is found, as in the conventional method. The shape dimension of the stop hole is not particularly limited, and may be appropriately adjusted according to the steel material to be repaired and the crack condition. Usually, a hole with a diameter of about 25 mm is drilled, and deburring or mirror finishing in a stop hole is performed with a grinder or the like. Further, after such polishing, it is preferable to perform rust prevention treatment in order to suppress the generation of rust.

  In the present invention, after the stop hole is formed in this way, a CFRP plate is attached so as to cover the stop hole. Usually, it is preferable that the CFRP plate is attached so that the longitudinal direction of the CFRP plate is in a direction perpendicular to the extension line of the crack whose progress is prevented by the stop hole. A part of the side surface in the longitudinal direction of the CFRP plate may be on the crack.

  Further, in the present invention, a higher effect can be obtained by covering the crack and reinforcing it with a CFRP plate so as to prevent the crack from expanding.

  In addition, the CFRP plate on the stop hole is laminated to prevent the peeling of the CFRP plate covering the entire crack, and the outer side of the stop hole is used to cope with the reoccurrence and propagation of the crack from the stop hole tip. A CFRP plate can also be affixed to the crack undeveloped part.

  In the case of a steel material having an out-of-plane gusset portion, as shown in FIG. 1 of Patent Document 4, the affixing position of the CFRP plate covering the crack is the both side surfaces and the toe end portion (longitudinal tip portion) of the gusset plate. It is preferable to laminate and paste so as to cover.

  CFRP plates with different U-shaped slit widths and slit lengths are used in layers, and the CFRP plates in each layer are stacked on top so that they are in close contact with the weld bead. Is preferably used. Alternatively, a prepreg sheet having different U-shaped slit widths and slit lengths may be laminated in advance to obtain a laminated body, and a laminated CFRP plate integrally molded by pressurizing and heating to cure the resin can be obtained. Alternatively, a laminate is obtained by simply laminating a plurality of prepreg sheets, and after obtaining a laminated CFRP plate integrally formed by pressurizing and heating to cure the resin, it is cut into a shape along the weld bead shape. An opening may be formed.

The CFRP plate used in the present invention is, for example, a standard product (S type) 1.52 × 10 ⁵ N / mm ² or more, a medium elastic product in a tensile test method of carbon fiber reinforced resin according to JIS K7073. A material having a tensile modulus of 1.96 × 10 ⁵ N / mm ² or more is used for (M type), and 2.94 × 10 ⁵ N / mm ² or more is used for a highly elastic product (H type).

  In particular, the CFRP plate is preferably formed by so-called pultrusion, in which a predetermined amount of carbon fiber is continuously fed from a creel stand, drawn, and cured with a mold heated through a resin bath. Also, prepreg sheets in which fibers aligned in one direction are impregnated with resin are laminated in the same direction as required to obtain the desired strength, and this laminate is pressed and heated to cure the resin. Can also be obtained.

  A room-temperature curable adhesive is used for attaching such a CFRP plate. In general, since the matrix resin of the CFRP plate is an epoxy resin, a preferable result is easily obtained when an epoxy adhesive is used. The adhesive strength of such an adhesive is not particularly limited, as long as the attached CFRP plate does not easily peel off. Moreover, the adhesive which protrudes after CFRP board sticking can be easily removed by wiping off before hardening.

  Prior to the application of the CFRP plate, the surface of the steel material to be applied is peeled off or the exposed surface of the steel material is coupled with an adhesion improver such as a silane coupling agent or a titanate coupling agent. Processing is also effective.

  In the case of an out-of-plane gusset structure, the shape of the weld bead is also adjusted by grinding with a grinder or the like, or conversely, the shape of the CFRP plate weld bead contact portion is polished to match the shape of the weld bead. By doing, the adhesiveness of a weld bead part and a CFRP board can also be made more favorable.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited only to these Examples.

<Preparation of test piece>
As shown in FIG. 1, a gusset plate 2 (JIS SM400A, 100 × 9 × 140 mm) is turned and welded to both sides of a central portion of a steel plate base material 1 (JIS SM400A, 250 × 9 × 1030 mm (central portion width: 300 mm)). Then, a bead portion 3 was formed to prepare a test piece.

  Table 1 shows the mechanical properties of the steel plate, CFRP plate and epoxy resin adhesive. Regarding the test method, first, after the crack 4 was propagated from the toe of the test piece to about 33 mm by a fatigue test, the three cases as shown in FIGS. Tests and fatigue tests were conducted and their repair effects were compared. Specifically, repairs were performed as follows.

(A) SH: Repaired only with stop hole 5 (φ25) (Fig. 2)
(B) SHS: After repairing the stop hole 5 (φ25), repaired with a single-layer CFRP plate 6 immediately above the stop hole 5 (FIG. 3)
(C) SHMS: After the stop hole 5 (φ25) is constructed, a single layer CFRP plate 6 is repaired with a laminated CFRP plate 7 (five layers) so as to be in close contact with the bead shape immediately above the stop hole 5 (FIG. 4). )

All experimental series are shown in Table 2. In the fatigue test, an electrohydraulic servo actuator with a capacity of 750 kN was used, the loading speed was 2 Hz, and the stress range Δσ _n of the test piece was 100 MPa. In addition, the strain gauge was stuck on the surface of the steel plate and CFRP board on the progress of a crack, and the stress was measured. In addition, a clip-type displacement meter was installed to measure the crack opening displacement.

<Static loading test results>
First, FIG. 5 shows the strain distribution of the steel plate on the crack growth at the time of loading of Δσ _n = 100 MPa (ΔP = 250 kN). As shown in the figure, in the case of SH repaired only with stop holes, the maximum stress is about five times the uniform tensile stress Δσ _n . Furthermore, it turns out that the maximum stress of a steel plate can be reduced by using a stop hole and a CFRP board together. It can also be seen that the effect of reducing the stress of SHMS is high, and the maximum stress is reduced by about 50% as compared with SH repaired only with stop holes.

  Next, FIG. 6 shows the stress distribution on the CFRP plate. From the figure, it can be seen that the stress generated in the CFRP plate in SHS is large, but in SHMS, the acting stress is effectively shared in the laminated portion, so that the stress burden in the single layer portion is reduced. Thus, in SHMS, it can be seen that the stress of the steel sheet is effectively reduced by the laminated part and the CFRP plate of the single layer part. Therefore, it is expected that the fatigue strength is also increased.

  FIG. 7 shows the opening displacement of each series. From the figure, when comparing the stop hole before construction (when the crack length is 33 mm) and after construction (corresponding to the crack length of 50 mm), the opening displacement after construction becomes large. It can be seen that the effect of reducing the opening displacement at the center position is small in SHS. On the other hand, in SHMS, since it is covered with a CFRP plate, it is not possible to measure the opening displacement. However, judging from the effect of reducing the stress of the steel plate, it is easy for the opening displacement to be further reduced compared to SHS. Can be guessed.

<Fatigue test results>
FIG. 8 shows an S-Np diagram. Here, Np is the number of repetitions (remaining life) from after repair (corresponding to a crack length of 50 mm) to full fracture. First, the remaining life of SH is 1.6 times that of N without repair. It can be seen that SHMS has a remaining life of 80 times or more and a sufficient repair effect.

  In SHMS, the laminated CFRP plate on one side peeled off when Np reached about 470,000 times, and the other laminated CFRP plate peeled off at about 4.3 million times. However, even when Np reaches about 5.565 million times, no separation of the CFRP plate in the single layer part and reoccurrence of cracks from the edge of the stop hole have been confirmed. That is, it can be understood that the repair effect in the state is high even though the state is in the SHS state.

  In Patent Document 4, a case is examined in which repair is performed using a laminated CFRP plate that is in close contact with and adhered to the center of the gusset without forming a stop hole. Although the test piece width is different, the evaluation is based on the remaining width excluding the crack length, which is almost the same, and is shown as a comparative example for reference. In the comparative example, the number of repetitions is about 2.6 million times in the stress range of 100 MPa. On the other hand, in the case of SHMS, it can be understood that the life expectancy is greatly extended by greatly exceeding the number of times that can be predicted by simply combining the effects of the case of Patent Document 4 (comparative example) and SH. .

  In addition, in SHMS, when a laminated CFRP plate bonded to the center of a gusset and a stop hole are used in combination, although the effect of reducing the stress concentration at the edge of the stop hole is high, the displacement of the opening increases due to the construction of the stop hole. It is thought that the board became easy to peel off. In order to prevent the peeling of the CFRP plate covering the entire crack and to deal with the reoccurrence and propagation of the crack from the tip of the stop hole, as shown in FIG. If a CFRP plate is affixed to the outside of the stop hole, more effective repair can be realized and it can be expected as a permanent repair method.

  Further, as shown in FIG. 10, a repairing method is conceivable in which only the crack 4 is covered with the laminated CFRP plate 7 without covering the stop hole 5. This method is also more effective than repairing only stop holes. In this case, there is a concern that the peeling of the CFRP plate as seen in SHMS becomes more prominent, but a high repair effect can be expected by improving the adhesive and the bonding method.

It is a figure explaining the outline | summary of the test body used for the test, (a) shows a top view, (b) shows a side view. It is a partial top view of the test body (SH) repaired only with the conventional stop hole (phi25). It is a partial top view of the test body (SHS) repaired with the single layer CFRP board directly on the stop hole after construction of the stop hole (φ25). It is a partial top view of the test body (SHMS) which repaired the crack top with the lamination | stacking CFRP board with the single layer CFRP board directly on the stop hole after construction of a stop hole (phi25). It is a figure which shows the strain distribution of the steel plate on the crack growth at the time of loading of (DELTA) (sigma) _n = 100MPa ((DELTA) P = 250kN). It is a figure which shows the stress distribution on a CFRP board. It is a figure which shows the opening displacement of each series implemented in the Example. The S-Np diagram of the relationship between the stress range and the number of repetitions Np from after repair to fracture is shown. It is a partial top view explaining the form which repairs the upper part of a stop hole and the crack upper part with a laminated CFRP board after construction of a stop hole (phi 25), and repairs the outer side of a stop hole with a single layer CFRP board. It is a partial top view explaining the form which repairs only a crack top with a laminated CFRP board after construction of a stop hole (phi 25).

Explanation of symbols

1 Base material 2 Gusset plate 3 Weld bead 4 Crack 5 Stop hole 6 Single layer CFRP plate 7 Multilayer CFRP plate 8 Multilayer CFRP plate

Claims (8)

  A repair of a steel material characterized by opening a stop hole at the tip of a fatigue crack generated in the steel material and covering the stop hole with at least a carbon fiber reinforced resin plate affixed on the steel material Method.   The method for repairing a steel material according to claim 1, wherein a carbon fiber reinforced resin plate is attached so as to cover the crack so as to suppress expansion of a fatigue crack generated in the steel material.   The steel material according to claim 2, wherein the carbon fiber reinforced resin plate and the carbon fiber reinforced resin plate to be applied to cover the crack and the carbon fiber reinforced resin plate to be applied to cover the stop hole are obtained by attaching independent carbon fiber reinforced resin plates. Repair method.   The steel material has an out-of-plane gusset structure in which a gusset plate is turned and welded to the outside of the steel base material, covers a fatigue crack generated at the end of the gusset plate, and adheres closely to the weld bead. 4. A substantially U-shaped carbon fiber reinforced resin plate and another carbon fiber reinforced resin plate affixed so as to cover a stop hole provided at the crack tip. Repair method for steel materials.   The method for repairing a steel material according to any one of claims 1 to 4, wherein a carbon fiber reinforced resin plate is also attached to a crack undeveloped portion outside the stop hole.   6. The carbon fiber reinforced resin plate attached to cover the stop hole and the carbon fiber reinforced resin plate attached to the crack undeveloped portion are obtained by attaching independent carbon fiber resin plates to each other. Repair method for steel materials.   A method for repairing a steel material, comprising: forming a stop hole at a tip portion of a fatigue crack generated in a steel material, and attaching a carbon fiber reinforced resin plate to cover only the crack.   A steel material repaired by the repair method according to claim 1.

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