JPS61198029A - Stress distribution measuring method of structure - Google Patents

Abstract

PURPOSE:To obtain with a high accuracy the effective information for maintenance by measuring the stress of a structure by an X-ray stress measuring method, combining it with a theoretical expression, and deriving a stress distribution and its secular change. CONSTITUTION:The stress in a measuring point 1 is measured by using a stress measuring method by X rays. In this case, by measuring the stress of the measuring point in a curve 2, at the operation start time point of a pipeline system being a structure, what is called a residual stress value by which a stress history received at the time of an assembly and at the time of welding, etc. is synthesized is obtained, when manufacturing a structure element. By referring to this value as a reference, thereafter, the stress measurement after the operation is executed at a necessary period interval in this measuring point 1, and by taking a difference to the reference value, the actual stress and its secular change are calculated. By combining this derived value and a theoretical stress calculating expression, the whole image of the stress distribution is obtained. By this whole image and its secular change, an external force which becomes its cause can be estimated further, and it becomes extremely effective as maintenance information.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention measures the actual stress after operation of a structure made of metal such as steel, determines its change over time, and furthermore provides an overview of the stress distribution and its This invention relates to a method for measuring stress distribution in a structure to estimate the external force that causes it.

[Conventional technology]

Conventionally, in maintenance inspections of structures, the strain at the start of operation of the structure is measured, and using this measured value as a reference value, subsequent strain measurements at the same location after operation are performed at necessary intervals. From this measured value, the actual stress applied after operation and its change over time are determined, and the information obtained is used as maintenance information, and based on this, the content of work for periodic inspections or periodic repairs is determined. Ta. As methods for measuring this strain, a method using a strain gauge and a method using a tact gauge are adopted.

Strain measurement using a strain gauge is a commonly used measurement method in which a strain gauge (for example, a wire gauge) is attached to an element of a structure, and the strain measurement value at the time the structure starts operating is used as the standard. As a value, the strain generated after operation is measured at intervals of 18 ff for a necessary period, and the stress actually applied and its change over time are estimated from the obtained actual measurement value and reference value. However, in the case of structures, the period during which measurements are required may extend to several decades, and such long-term measurements may cause deterioration of the adhesive that attaches the strain gauge to the structure. It is difficult to maintain the accuracy of strain gauges over a long period of time due to drift in the strain gauge itself, and therefore, the estimated value of stress change over time can only be used as reference information for maintenance. I can't.

In addition, in the method using a contact gauge, contact gauge steel balls are driven into the element part of the structure at predetermined intervals, and the distance between the steel balls is actually measured at necessary intervals based on the distance between the steel balls at the time the structure starts operating. The strain, that is, the stress actually applied and its change over time, is estimated from the difference between the value and the reference value. With this method, when driving the steel balls for contact gauges, the structure will be damaged, and it cannot be applied to the element parts of the structure where stress concentration is expected. It was not possible to estimate the element part for which we wanted to know the changes over time.

[Problem that the invention seeks to solve]

The conventional methods of measuring the stress distribution of structures as described above are all indirect measurement methods, and it is difficult to maintain measurement accuracy over a long period of time. It cannot be applied to element parts, and the actual stress estimated from the actual measured value using the above measurement method and its change over time cannot be directly used as information for maintenance, and can be used as a single The problem was that it could only be used as reference information.

This invention was made to solve this problem, and it measures the elemental parts of a structure directly using the X-ray stress measurement method, determines the stress actually loaded and its change over time, and calculates the accuracy. The purpose is to make it possible to obtain information for high-quality maintenance.

[Means for solving problems]

The method for measuring stress distribution of a structure according to the present invention is as follows. Using the stress measurement method, the stress at the start of operation is directly measured and used as a reference value.Afterwards, stress measurements at the same location after operation are performed at necessary intervals, and the actual stress and its changes over time are calculated from the reference value. In addition to providing information for maintenance, the system also allows us to use theoretical formulas to estimate the overall picture of stress distribution and the external forces that cause it.

[Effect]

In this invention, the stress in the element parts of the structure is directly measured using the X-ray stress measurement method, so the stress actually applied, including the residual stress at the start of operation, can be measured for a long period of time after operation. , calculate aging changes with high precision and provide highly accurate maintenance information. Furthermore, by using the actual stress and the calculated stress distribution based on the theoretical formula, it is possible to estimate the overall picture of the stress distribution and the external force that causes it, and to provide more specific maintenance information.

〔Example〕

FIG. 1 is a diagram showing a piping system showing an embodiment to which the stress distribution measuring method according to the present invention is applied. In the figure, (1
) is a measurement point, and (2) is a bent pipe on the ground, and the center of the neutral axis on its side is selected as measurement point (1). (3)
is a horizontal pipe, (4) is a vertical pipe rising from underground, (5) is the ground, (6) is the building into which the horizontal pipe (3) is drawn, (force is the load due to the ground law, etc., and (8) is underground The load (
7), a bending moment is applied to the bent pipe (2) by the horizontal pipe (3) and vertical pipe (4) restrained by the building (6), and this bending moment causes the largest circumference at the measurement point (1). Generates directional stress.

The stress at this measurement point (1) is measured using an X-ray stress measurement method. This measurement method is based on stress
The distribution of lattice strain is measured by detecting the amount of movement of the diffraction line of I, and the stress value is determined using the elasticity theory formula. When the stress at measurement point (1) is measured at the start of operation of the piping system, which is a structure, the so-called residual stress value, which is a composite of the stress history experienced during manufacturing, assembly, welding, etc. of the structural elements, is obtained. can get. Using this value as a reference, stress measurements after operation are subsequently performed at this measurement point (1) at necessary time intervals, and the actual stress and its secular change are calculated by taking the difference from the reference value. By combining this determined value with a theoretical stress calculation formula, an overall picture of the stress distribution can be obtained.

In the bent pipe (2) of the example, if the outside diameter of the pipe, the plate thickness 2, the bending radius, etc. are known, and the moment can be estimated, the bent pipe (2)
The stress distribution state can be calculated using Kalman's third approximation formula as shown in FIG. Conversely, if the stress at a certain point is known, that is, it can be measured, the outer diameter of the pipe, the plate thickness, and the bending radius are known, so the stress and moment in the circumferential direction can be calculated based on Kalman's sixth approximation formula. It becomes possible to estimate the distribution of The results obtained in this manner are shown in FIG. 2, where a distribution curve is drawn based on the actual stress at measurement point (1).

In this way, we can accurately measure the actual stress during operation using the X-ray stress measurement method, estimate the overall picture of the stress distribution using the theoretical formula for stress calculation, and use this overall picture and its changes over time to estimate the external force that causes it. can be further estimated, making it extremely effective as maintenance information.

〔Effect of the invention〕

As explained above, this invention measures the stress in a structure using the X-ray stress measurement method, and calculates the stress distribution and its changes over time using a theoretical formula and a combination of valleys and valleys, thereby providing effective information for maintenance. can be provided with high precision.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a piping system according to an embodiment of the present invention, and FIG. 2 is a circumferential stress distribution diagram of a curved pipe determined by Kalman's sixth approximation formula. In the figure, (1) is the measurement point, (2) is the curved pipe, (3) is the horizontal pipe, (4) is the vertical pipe, (5) is the building, (force is the load due to the ground law, etc.) (8) is an underground pipe.

Claims (1)

[Claims] In a structure, the stress at the start of operation is measured using the X-ray stress measurement method, this is used as a reference value, and thereafter the stress after operation is measured at the same location at necessary intervals, and the difference from the above reference value is calculated. The actual stress and its change over time are calculated and used as information for maintenance, and the overall picture of the stress distribution and the external force that causes it are estimated from the above actual stress and the stress distribution obtained from the theoretical formula. A method for measuring stress distribution in structures.