JP2013002960A - Fatigue monitoring structure and steel structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fatigue monitoring structure which is capable of evaluating fatigue damage degree with high reliability and keeping the entire structure in a safe state.SOLUTION: A fatigue monitoring structure is provided with a stress concentration section formed in a structure member by providing the structure member itself of a steel structure with a notch 31 or by providing the structure member with a weld, and is preliminarily provided with a stress concentration relieving through-hole 32 of a shape causing no stress concentration on a crack progress path which is anticipated to grow from the stress concentration section.

Description

  The present invention relates to a fatigue monitoring structure of a structural member constituting a steel structure such as a ship, and a steel structure to which this fatigue monitoring structure is applied.

  In a large steel structure that is used for a long period of time such as a ship and a variable load repeatedly acts during the period of use, the occurrence of fatigue cracks is often a problem. When fatigue cracks grow in a ship, for example, there is a possibility of causing environmental pollution due to leakage of cargo loaded through the outer plate, or conversely, seawater may flow into the interior. There is also a risk of serious damage leading to massive damage. Therefore, it is of great importance that the stress generated in the structural member is measured, and the fatigue damage degree is estimated using the result, and the technology that is detected before the fatigue crack grows to a dangerous size is very important. Don't wait. For this reason, actual stress measurement may be performed in order to estimate the degree of fatigue damage after service of the steel structure.

  As for actual stress measurement, there is a technology that detects the degree of fatigue damage of a structural member by forming a wedge-shaped notch in the structural member itself of an actual steel structure and monitoring the growth of cracks generated therefrom. It has been proposed (see, for example, Patent Document 1). In this method, since the notch is provided in the actual structural member, there is a concern that the strength of the structural member may be reduced. It corresponds by attaching.

Japanese Patent Laid-Open No. 9-184792 (second page, FIG. 2)

  However, since the stress acting on the structural member itself is reduced by the amount of the reinforcing plate attached, the crack growth from the notch is significantly slower than the case without the reinforcing plate. Therefore, there is a problem that the fatigue damage degree of the entire structure may be underestimated.

  Further, since the reinforcing plate is attached only to the structural member by bolt fastening, even if the crack reaches the end of the reinforcing plate, the growth of the crack tip is not hindered and the crack continues to progress. If the state is overlooked, the crack may continue to grow and eventually break the member. In that case, although the reinforcing plate plays the role of reinforcing, the reinforcing strength is not sufficient, so the stress in other members may exceed the allowable stress, and it is difficult to keep the entire structure in a safe state There was a problem.

  The present invention has been made to solve such a problem, and enables a highly reliable evaluation of fatigue damage, and a fatigue monitoring structure capable of maintaining the entire structure in a safe state, and the fatigue monitoring structure The object is to provide a steel structure to which is applied.

  In the fatigue monitoring structure according to the present invention, the structural member itself of the steel structure is notched or a welded portion is provided on the structural member to form a stress concentration portion on the structural member, and growth is expected from the stress concentration portion. A stress concentration reducing through hole having a shape that does not concentrate stress is provided in advance on the crack propagation path.

  According to the present invention, since the stress concentration portion is provided directly on the structural member, the degree of fatigue damage can be directly monitored. Therefore, highly reliable monitoring is possible. In addition, since the through hole for stress concentration reduction was formed in advance on the crack propagation path from the stress concentration part, after the crack progressed and communicated with the through hole for stress concentration reduction, the crack did not progress any further. Can be. For this reason, it can suppress that a crack expands to another structural member, and can maintain the whole structure in a safe state.

1 is a perspective view of a part of a hull structure to which a fatigue monitoring structure according to Embodiment 1 of the present invention is applied. It is the figure which looked at FIG. 1 from the arrow A direction. FIG. 3 is an operation explanatory diagram in FIG. 2. It is a partial sectional view of the hull structure of a tanker. It is a perspective view of a part of the hull structure to which the fatigue monitoring structure according to Embodiment 2 of the present invention is applied. (A) is the figure which looked at FIG. 5 from the arrow A direction, (b) is the side view of (a), (c)-(e) is the top view of the part enclosed with the broken line of (a). It is a side view of a part of a hull structure to which a fatigue monitoring structure according to Embodiment 3 of the present invention is applied.

  An example in which the fatigue monitoring structure of the present invention is applied to a tanker hull structure will be described below.

Embodiment 1 FIG.
In the first embodiment, an embodiment in which a structural member having a fatigue monitoring structure is a longage constituting a hull structure will be described.

  Prior to the details of the fatigue monitoring structure, an outline of the hull structure will be described.

  FIG. 4 is a partial cross-sectional view of the hull structure of the tanker. FIG. 4 is a quotation from “2008 Summary of Damage”, Journal of the Japan Maritime Association, No. 288, 2009, page 28. The same reference numerals in all the drawings of the present specification are the same or equivalent, and this is common throughout the entire specification. Furthermore, the form of the component which appears in the whole text of this specification is an illustration to the last, and is not limited to these description.

  The hull structure 10 includes a plate member 20 such as an outer plate that forms a hull shape and an inner bottom plate that forms a double bottom, and a plurality of longages 30 that are provided longitudinally in the hull longitudinal direction with respect to the plate member 20; And a transformer 40 provided perpendicular to the longitudinal direction of the hull, and is composed of these large and small stiffeners. The longe 30 has a structure of only a web 30a without a face 30b as shown in FIG. 1 described later, in addition to a T type having a web 30a and a face 30b as shown in FIG. 5 described later. In the first embodiment, the case where the structural member having the fatigue monitoring structure is the longe 30 having only the web 30a without the face 30b will be described, and the case where the structural member is the T-type longe 30 will be described in the second embodiment. .

  FIG. 1 is a perspective view of a part of a hull structure to which a fatigue monitoring structure according to Embodiment 1 of the present invention is applied. A longi 30A for monitoring having a fatigue monitoring structure and a general longi 30B around it are shown. Show. FIG. 2 is a view of FIG. 1 viewed from the direction of arrow A. The left-right direction in FIG. 2 (the front-rear direction in FIG. 1) corresponds to the longitudinal direction of the hull. The main load direction with respect to the longi 30 (30A, 30B) corresponds to the longitudinal direction of the hull, and the main action direction of the stress with respect to the longe 30 is also the longitudinal direction of the hull.

  In the fatigue monitoring structure of the first embodiment, a slit-shaped notch 31 simulating a crack is used as a stress concentration portion at the end of the web 30a of the longe 30A opposite to the side welded and fixed to the plate member 20. Form. The notch 31 is formed so as to extend in a direction orthogonal to the main load direction with respect to the longage 30A. Then, a stress concentration reducing through hole 32 penetrating in the thickness direction of the web 30a is provided at a location where a crack from the notch 31 is predicted to progress. The through-hole 32 for reducing stress concentration preferably has a shape having a low stress concentration in the load direction. Here, the through-hole 32 has an elliptical shape having a major axis in the main load direction to the longage 30A, but is not limited to this shape.

  In this manner, the same stress as that of the longitudinal 30 </ b> B disposed in the periphery acts on the longage 30 </ b> A having the notch 31 and the stress concentration reducing through-hole 32. The stress of becomes high locally. For this reason, a crack progresses ahead of the surrounding longi 30B. By periodically monitoring the amount of crack growth, the fatigue damage degree of the structural member (Longi 30A) can be directly monitored.

  The crack that has developed from the notch 31 develops in the direction of the broken-line arrow in FIG. 2 and eventually reaches the through hole 32 for reducing stress concentration. Then, as shown by the thick line in FIG. 3, the crack communicates with the stress concentration reducing through-hole 32 and disappears, and the concentration of stress flowing into the longage 30 </ b> A is greatly reduced and the stress is greatly reduced. For this reason, the crack does not progress any more. It should be noted that fatigue cracks from the inner surface of the stress concentration reducing through hole 32 may occur if the inner surface of the stress concentration reducing through hole 32 is smoothed or a compressive residual stress is applied by a process such as peening. Since generation | occurrence | production of can be suppressed, it is still more effective.

  As described above, according to the first embodiment, the notch 31 as the stress concentration portion is provided directly in the longage 30A that is an actual structural member to be monitored for fatigue, so the fatigue damage degree is directly monitored. can do. Therefore, highly reliable monitoring is possible. In addition, since the stress concentration reducing through-hole 32 is formed by notching large on the crack propagation path from the notch 31 in advance, after the crack has progressed and communicated with the stress concentration reducing through-hole 32, No further cracks develop. For this reason, a crack does not expand to another structural member, it can suppress that it reaches the state of destruction of the whole structure, etc., and the safety of the whole structure can be maintained. As a result, there is no need for repair or reinforcement even if cracks develop.

  In addition, if the entire structure is designed so that the allowable stress in the hull structure is satisfied only with other structural parts except the structural member (Longi 30A) having a fatigue monitoring structure, the cracks in the Longi 30A reduce stress concentration. Even if the through-hole 32 is reached, there is no need to repair the Longi 30A, so no additional cost is generated.

  In the first embodiment, an example of the slit-shaped notch 31 that simulates a crack is given as the stress concentration portion. However, the shape of the notch 31 is not limited to the slit shape, and the stress concentration reducing through hole 32 side. It is good also as a triangular shape which has a vertex in. Further, the stress concentration portion is not limited to the notch 31, and a path from the end of the longe 30 </ b> A to the stress concentration reducing through hole 32 may be intentionally cut, and the cut portion may be butted and welded to form the stress concentration portion. . Even when the stress concentrating portion has these configurations, the same effect as that obtained when the notch 31 is formed can be obtained.

Embodiment 2. FIG.
In the first embodiment, the structural member having the fatigue monitoring structure is the longi 30A constituting the hull structure, and in particular, the longi 30A does not have the face 30b. In the second embodiment, a T-type Longi 30A is used.

FIG. 5 is a perspective view of a part of a hull structure to which the fatigue monitoring structure according to the second embodiment of the present invention is applied. The T-shaped longe 30A provided with the fatigue monitoring structure and the surrounding T-shaped longi 30B. Is shown. 6A is a view of FIG. 5 viewed from the direction of arrow A, FIG. 6B is a side view of FIG. 6A, and FIGS. 6C to 6E are broken lines of FIG. 6A. It is a top view of the part enclosed by.
The longe 30A is formed in a T-shape by welding a face 30b extending in the longitudinal direction of the hull substantially perpendicularly to the web 30a at one end of a web 30a provided longitudinally in the longitudinal direction of the hull. The plate member 20 is welded and fixed. In the face 30b, slit-shaped notches 31a simulating cracks are formed as stress concentration portions.

  The notch 31a is formed so as to extend in the direction orthogonal to the main load direction with respect to the face 30b in the face 30b. Further, the notch 31a may be a central portion in a direction perpendicular to the load direction in the face 30b as shown in FIG. 6C, or the load direction in the face 30b as shown in FIG. 6D. You may provide in the edge part of the orthogonal direction. Further, as in the first embodiment, the stress concentration portion may be formed by butt welding the faces 30b as in the weld portion 31b of FIG. 6E instead of the notch 31a.

  A stress concentration reducing notch 32a is formed at one end of the web 30a so as to straddle the portion of the face 30b where the notch 31a is formed. The notch 32a for reducing stress concentration is formed in a rectangular shape extending from one end side to the other end side of the web 30a here, but is limited to this shape as long as the stress concentration is low in the load direction. Absent.

  In the fatigue monitoring structure configured as described above, as shown by broken line arrows in FIGS. 6C and 6D, cracks progress in the direction of cutting the face 30b from the notch 31a, and finally, The face 30b is broken. As a result, the stress of the fatigue monitoring structure is shared only by the web 30a. Therefore, when the notch 32a for reducing stress concentration is not provided, the web 30a is cracked from the portion of the web 30a that faces the broken portion of the face 30b. However, in this example, the stress concentration reducing notch 32a is provided in advance in the crack propagation portion so as not to concentrate the stress in the load direction, so that the stress inflow and the stress concentration are reduced as in the first embodiment. The web 30a does not crack.

  Note that the face 30b of the longe 30A having the fatigue monitoring structure is higher than the face 30b of the longe 30B that is not provided with the notch 32a for reducing stress concentration because the web 30a to be welded to the surface is cut away. Stress acts. For this reason, the difference in stress in the face 30b from the longi 30B in the longi 30A may be corrected by calculation, and the structural calculation of the entire structure may be performed with the corrected stress. It may be thicker than the face 30b of the longi 30B, and the same stress as the face 30b of the longi 30B may act on the longi 30A.

  As described above, also in the second embodiment, the same effect as in the first embodiment can be obtained. As in the first embodiment, if the inner surface of the stress concentration reducing notch 32a is smoothed or a compressive residual stress is applied by processing such as peening, the notch 31a Since the occurrence of fatigue cracks from the inner surface can be suppressed, it is more effective.

  In addition, if the entire structure is designed so that the allowable stress in the hull structure is satisfied with only the other structural parts except the structural member (Longi 30A) having a fatigue monitoring structure, even if the face 30b breaks, There is no need for repairs, so no additional costs are incurred.

Embodiment 3 FIG.
In the third embodiment, an embodiment in which a structural member having a fatigue monitoring structure is a bracket disposed between the longitudinal 30 and the transformer 40 will be described.

FIG. 7 is a partial side view of the hull structure to which the fatigue monitoring structure according to Embodiment 3 of the present invention is applied.
In the fatigue monitoring structure of the third embodiment, a slit-shaped notch 31c simulating a crack is provided as a stress concentration portion on the end face of the bracket 50 that reinforces the space between the face 30b of the T-shaped longe 30 and the transformer 40. A notch 32c for reducing stress concentration is provided at a location where crack growth from the notch 31c is predicted. The notch 32c for reducing stress concentration is a so-called scallop, and the scallop is used as a notch in the fatigue monitoring structure. The shape of the stress concentration reducing notch 32c is preferably a shape having a low stress concentration with respect to the load direction, and FIG. 7 shows an example of a sector shape having a central angle of 90 degrees. However, the shape is not limited to this shape. Absent. Note that the longage 30 of the third embodiment has a configuration that is not provided with a slit or a notch for reducing stress concentration like the longage 30B of FIG.

  Also in the third embodiment, the same effect as that of the first embodiment can be obtained. Moreover, although the example of the slit-shaped notch 31c simulating a crack is given as the stress concentration portion, the shape of the notch 31c is not limited to the slit shape, and is a triangular shape having a vertex on the stress concentration reducing notch 32c side. Also good. Further, the stress concentration portion is not limited to the notch 31c, and a path from the end portion of the bracket 50 to the stress concentration reduction notch 32c may be intentionally cut, and the cut portion may be butt welded to form the stress concentration portion. . Even when the stress concentrating portion has these configurations, the same effect as that obtained when the notch 31c is formed can be obtained.

  Similarly to the first embodiment, if the inner surface of the stress concentration reducing notch 32c is smoothed or a compressive residual stress is applied by a process such as peening, the stress concentration reducing notch 32 Since generation | occurrence | production of the fatigue crack from the inner surface of 32c can be suppressed, it is still more effective.

  In addition, if the entire structure is designed so that the allowable stress in the hull structure is satisfied with only the other structural parts except the structural member (bracket 50) having a fatigue monitoring structure, even if the bracket 50 breaks, There is no need for repairs, so no additional costs are incurred.

  In the first to third embodiments, the example of the hull structure is described as the steel structure to which the fatigue monitoring structure is applied. However, the steel structure is not limited to the hull structure and may be a bridge, an elevated road, or the like.

  10 hull structure, 20 plate member, 30 longe, 30A longe, 30B longe, 30a web, 30b face, 31 notch, 31a notch, 31b welded part, 31c notch, 32 through hole for reducing stress concentration, 32a stress concentration Notch for reduction, 32c Notch for stress concentration reduction, 40 transformer, 50 bracket.

Claims (7)

  The structural member itself of the steel structure is provided with a notch or a welded portion is formed on the structural member to form a stress concentration portion on the structural member, and on the crack propagation path where growth is expected from the stress concentration portion, A fatigue monitoring structure characterized in that a stress concentration reducing through hole having a shape that does not concentrate stress is provided in advance.   2. The fatigue monitoring structure according to claim 1, wherein the steel structure is a hull structure having a longe longitudinally extending in a longitudinal direction of the hull, and the structural member is the longi.   The longe is formed by a web, and the notch of the stress concentration portion is a slit formed at an end of the web so as to extend in a direction orthogonal to a main load direction with respect to the web, and the stress The fatigue monitoring structure according to claim 2, wherein the concentration reducing through hole has a shape that does not concentrate stress in the load direction.   The longe is formed in a T shape with a face fixed substantially perpendicularly to an end of a web, and the notch of the stress concentration portion extends in a direction perpendicular to a main load direction with respect to the face. It is a slit provided in the face, and the through hole for stress concentration reduction is a notch provided in an end portion on the face side of the web so as to straddle the stress concentration portion of the face. The fatigue monitoring structure according to claim 2.   The steel structure includes a longe having a face substantially fixed to an end portion of a web and formed in a T shape, a transformer provided perpendicular to the longitudinal direction of the hull, the face of the longe, and the The fatigue monitoring structure according to claim 1, wherein the structure is a hull structure having a bracket for reinforcing between the transformers, and the structural member is the bracket.   6. The fatigue monitoring structure according to claim 5, wherein the notch of the stress concentration portion is a slit provided at an end portion of the bracket, and the scallop of the bracket is the through hole for reducing stress concentration.   A steel structure having the fatigue monitoring structure according to any one of claims 1 to 6.

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