JP2004137797A - Preventive maintenance method of steel structure by ultraviolet curing type frp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the preventive maintenance method of a steel structure capable of flexibly corresponding to the shape of the steel structure. <P>SOLUTION: The generation of a crack by repeated stress is prevented and maintained by sticking a prepreg, in which reinforced fibers, through which ultraviolet rays are transmitted, are impregnated with an ultraviolet curing type resin, on the structural discontinuous section of the steel structure and curing the prepreg by an ultraviolet-light irradiaton or solar rays. A structure section excepting accessories for a bridge can be used as the steel structure. FRPs by a hand lay-up method can also be used in place of a prepreg type. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technology for preventing and maintaining fatigue fracture in a steel structure on which a repeated stress such as a load including vibration acts.
[0002]
[Prior art]
In steel structures, the existence of structural discontinuities such as welded joints, cutouts and discontinuities based on desired shapes cannot be avoided. When an external force acts on a steel structure, stress concentration occurs at such a structural discontinuity, and it is likely to be a starting point of destruction. Where a repeated load such as a load including vibration is applied, a crack may be generated due to metal fatigue, leading to breakage. Many of these fractures and fatigue failures can be avoided to a considerable extent by improving the details, increasing the toughness, and increasing the plate thickness.However, both in terms of cost and weight, There is a limit.
[0003]
With the increase in traffic volume in recent years, the repetitive load acting on a road bridge is increasing more and more in terms of the frequency and the magnitude of the load.
The inventor has previously used a carbon fiber reinforced resin plate (carbon plate) to repeatedly load test an existing steel pier (see Non-Patent Document 1) and reinforce a cracked material (Non-Patent Document 2). See). In this case, a cured carbon fiber reinforced resin plate (carbon plate) is attached to a required portion using a putty-like epoxy resin adhesive. Since the carbon fiber reinforced resin plate (carbon plate) is extremely lightweight and strong, a remarkable effect of improving the strength of the steel piers, including those having cracks, was obtained by sticking a plurality of sheets.
[0004]
[Non-patent document 1]
Japan Society of Civil Engineers 56th Annual Scientific Lecture (October 2001) IA281; p. 562-563
[Non-patent document 2]
Annual Report on Steel Structures; Volume 8 (November 2000); p. 683-688
[0005]
[Problems to be solved by the invention]
However, when a resin plate that has already been cured is used, there is a problem in that the resin plate flexibly corresponds to the shape of the steel structure.
In view of the above problems, an object of the present invention is to provide a preventive maintenance method for a steel structure that can flexibly respond to the shape of the steel structure.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention applies a prepreg obtained by impregnating an ultraviolet-curable resin to a reinforcing fiber that transmits ultraviolet light to a structural discontinuous portion of a steel structure, and cures by ultraviolet irradiation or sunlight. By doing so, the occurrence of cracks due to repeated stress is prevented and maintained. The steel structure may be a structural part other than a bridge accessory. Also, instead of the prepreg type, an FRP by a hand lay-up method can be used.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is to apply a part of the stress to the FRP body by applying an ultraviolet-curable FRP material to the surface of the steel structure by applying an ultraviolet-curable prepreg or an ultraviolet-curable FRP material by a hand lay-up method, thereby curing the steel structure. Basically, the stress concentration at the structural discontinuous portion of the steel part is relaxed, and the life extension effect is exerted on the occurrence of cracks due to metal fatigue.
An example of a structural discontinuity in a steel structure is, for example, a weld. When butt welding a thick plate with a Y-shaped groove or a L-shaped groove, a geometric discontinuity (front and back) that can be used as a contact point between the weld metal and the base material, and a microstructure such as a heat-affected zone There is a case where slag is involved in the welded portion in rare cases.
[0008]
The present invention will be described based on examples.
【Example】
A test specimen of 500 × 100 (mm) prepared by bead welding to a steel sheet of steel type SS400 having a thickness of 6 mm was prepared, and the central plate was filled to a width of 1.0 mm so as to cover the weld bead of the test specimen. A three-layer prepreg impregnated with a vinyl ester resin in which an ultraviolet curing agent (trade name: Paratar: manufactured by DSM) is added to the glass fiber of Example 1 and three layers are applied and cured by ultraviolet irradiation (GFRP). When a fatigue test was carried out by applying a tensile / compressive repetitive stress to the treated specimen in the longitudinal direction of the specimen, the results shown in FIG. 1 were obtained.
[0009]
According to FIG. 1, in the unreinforced test specimen, as indicated by a circle, a straight line connecting points of about 5 × 10 ⁵ repetitions at 190 MPa and about 1.4 × 10 ⁶ repetitions at 150 MPa. In the GFRP material reinforced test specimens indicated by a triangle, the number of repetitions was 1.7 × 10 ⁶ at 190 MPa, the number of repetitions was about 2.0 × 10 ⁶ at 185 MPa, and 5.0 × 10 at 165 MPa. Since it did not break even with the number of repetitions of ⁶ times, it increased to 178 MPa at that stage, indicating that it was broken by a total of about 9.1 × 10 ⁶ times of repetition.
From both straight lines shown in FIG. 1, when a large repetitive external force of, for example, 178 MPa is applied, the life is increased from about 5.3 × 10 ⁶ repetitions to 7.0 × 10 ⁶ repetitions depending on the presence or absence of the reinforcing material. Is about 13 times longer.
Not only welds, but also structural discontinuities in steel structures, for example, around the entrance of manholes for bridge inspection, notches, corners of structures, misplaced parts, etc. Extension can be expected.
[0010]
As the reinforcing fiber material for the prepreg in the present invention, it is necessary that the material is transparent so that the ultraviolet rays can be sufficiently transmitted to the inside when irradiating the ultraviolet rays, and outside the glass fibers, acrylic fibers, transparent polyester fibers, and polyethylene. Fiber, nylon fiber and the like.
In addition, these fibers are used in a weaving form such as a cloth woven by an appropriate method such as a plain weave or a twill weave, a roving cloth, or a form processed into a chopped strand mat, a unidirectional UD cloth, triaxial and multiaxial. You.
Examples of the resin material for impregnating the reinforcing fibers for prepreg include vinyl ester resin, unsaturated polyester resin, acrylic resin, polyamide resin, epoxy resin and the like.
As the ultraviolet curing agent added to the ultraviolet curing resin, an ultraviolet curing agent that absorbs ultraviolet rays having a wavelength range of 365 to 410 is usually used. Examples of the light source include an ultraviolet fluorescent lamp, a high-pressure mercury lamp, and a metal halide lamp, and the light source may be cured using sunlight. The curing time is 5 to 30 minutes, depending on the illuminance of ultraviolet rays, the thickness of the prepreg, and the thickness of the coating.
[0011]
The reinforcing body may be one that has been cured in advance, but the impregnated resin is uncured or semi-cured so that the reinforcing body can respond to and apply to minute irregularities in the structure. It is preferable to use one. By completely curing after application, the resin can be cured and simultaneously bonded and joined to the steel structure without using an additional adhesive.
Although the prepreg-type FRP has been mainly described above, the FRP body applied in the present invention may be formed by a hand lay-up method.
The reinforcing body of the present invention can be advantageously applied to a part having a planar structure such as a girder part of a steel bridge, but is not limited thereto, and includes a pier (rectangular section, circular section, etc.) section, a water pipe, a gas pipe, and the like. It can also be applied to pipes, pipelines, etc.
When an ultraviolet-curable prepreg using a unidirectional UD cloth is used as a reinforcing fiber that transmits ultraviolet light, the prepreg is applied at right angles to a crack direction due to assumed repeated stress, and exhibits a life-prolonging effect by bonding.
[0012]
【The invention's effect】
According to the present invention, since it is affixed to a required part in the form of an uncured or semi-cured prepreg, it can flexibly respond to the shape of the surface of the steel structure, effectively preventing cracking of the steel structure and the like. Preventive maintenance can be performed.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between repeated tensile and compressive stress and fatigue fracture with and without glass fiber reinforced resin reinforcement.

Claims (3)

Prevents the occurrence of cracks due to repeated stress by applying a prepreg made by impregnating a UV-curable resin to a reinforcing fiber that transmits UV rays to a structural discontinuity of a steel structure and curing it by UV irradiation or sunlight. A preventive maintenance method for steel structures characterized by performing maintenance. The preventive maintenance method for a steel structure according to claim 1, wherein the steel structure is a structural part other than an accessory of a bridge. After applying the hand-lay-up method to the reinforcing fiber that transmits ultraviolet light together with the ultraviolet curable resin to which an ultraviolet curing agent has been added, and curing by ultraviolet irradiation or sunlight, it is possible to prevent and maintain the occurrence of cracks due to repeated stress. Characteristic preventive maintenance method for steel structures.

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