JP2020094847A - Deterioration prediction method for structure - Google Patents

Abstract

To provide a deterioration prediction method for structures capable of highly precisely predicting progress of deterioration of structures having a deterioration mechanism whose deterioration speed is not constant, and structures having a complicated deterioration mechanism combined with various deterioration factors.SOLUTION: A deterioration prediction method for structures comprises: a deterioration state inspection step of inspecting a deterioration state of a structure a plurality of times at time intervals; a deterioration degree evaluation step of replacing the deterioration state obtained by the deterioration state inspection step with a deterioration degree divided into a plurality of stages and evaluating a secular change of the deterioration degree; a transition rate calculation step of calculating a transition rate as a probability transferring from the secular change of the deterioration degree obtained by the deterioration evaluation step to a next-stage deterioration degree within a prescribed period for every-stage transition rate; and a deterioration prediction step of performing the deterioration prediction of the structure using the transition rate for every deterioration degree obtained by the transition rate calculation step.SELECTED DRAWING: Figure 4

Description

The present invention relates to a method of predicting deterioration of a structure.

Deterioration damage of structures decades after construction is a serious problem, and reduction of life cycle cost by appropriate maintenance of them is an important issue. Therefore, a deterioration prediction method for quantitatively evaluating the progress of deterioration of a structure has been proposed.

For example, Patent Document 1 discloses a method capable of predicting deterioration of a structure by estimating a corrosion rate of a reinforcing bar of a concrete structure caused by external salt damage due to a flying salt content or the like.

Further, Non-Patent Document 1 describes a Markov chain model (from a certain "state" as a stochastic model) when the deterioration mechanism is unknown or when the deterioration mechanism is known but modeling is difficult. Degradation prediction method that can predict the transition of the deterioration status of a structure is shown by using a statistical method that stochastically captures the transition to the next "state" at "transition rate". ..

In this deterioration prediction method, as shown in FIG. 1A, a deterioration degree indicating the degree of deterioration of a structure (for example, deterioration degree 0, 6 levels of I to V) is set in advance, and a certain deterioration degree is determined. The transition rate x is the probability that a part has moved to the next level of deterioration within a predetermined period (usually within one year), and the probability that a part with a certain deterioration level will remain at that deterioration level after one year ( 1-x). Then, using the formula shown in FIG. 1B, the rate of deterioration after t years is predicted based on the rate of deterioration in a certain year. Here, the ratio of the degree of deterioration is the ratio of the number of parts of each deterioration degree to the number of parts of the structure whose deterioration degree is to be evaluated.

JP 2012-8152 A

Technical Manual for Maintenance of Port Facilities (Coastal Technology Center, 2007)

However, the technique described in Patent Document 1 and the technique described in Non-Patent Document 1 have the following problems.

First, although the technology described in Patent Document 1 can predict deterioration of a part of a reinforcing bar in a structure, deterioration of the entire structure cannot be evaluated. Therefore, deterioration prediction of the structure is accurately evaluated. There was a problem that I could not.

On the other hand, the technique described in Non-Patent Document 1 can evaluate the deterioration of the entire structure, but since the transition rate x at all deterioration levels is defined as constant, as shown in FIG. However, there was a problem that the deterioration could not be accurately predicted and a large deviation occurred compared with the observation result of the actual structure.

For example, Fig. 3 shows the deterioration process of reinforced concrete due to salt damage, which is divided into four stages: incubation period (healthy state), development period (corrosion of reinforcing bar), acceleration period (cracking of concrete), and deterioration period (stripped concrete). Since the speed of deterioration progress differs at each stage, if the transition rate of each deterioration state is constant, the accuracy of deterioration prediction decreases.

If the deterioration cannot be predicted accurately, frequent inspections are required to formulate a repair plan, and the cost and labor burden related to the maintenance of the structure will increase. Further, there is a problem that the life cycle cost necessary for rational maintenance cannot be calculated.

The present invention has been made in view of the circumstances as described above, and a structure having a deterioration mechanism in which the deterioration rate is not constant or a structure having a complicated deterioration mechanism in which various deterioration factors are combined is used. It is an object of the present invention to provide a method for predicting deterioration of a structure, which can accurately predict the progress.

In order to solve the above problems, the present invention has the following features.

[1] A method for predicting deterioration of a structure, comprising:
A deterioration state inspection process of inspecting the deterioration state of the structure multiple times at time intervals,
The deterioration state obtained in the deterioration state investigation step, by replacing the deterioration degree divided into a plurality of stages, the deterioration degree evaluation step of evaluating the change over time of the deterioration degree,
From the change with time of the deterioration degree obtained in the deterioration degree evaluation step, for each deterioration degree of each step, a transition rate calculation step for calculating a transition rate as a probability of moving to the next step deterioration degree within a predetermined period, ,
A deterioration prediction method for a structure, comprising: a deterioration prediction step of predicting deterioration of the structure using the transition rate for each deterioration degree obtained in the transition rate calculation step.

[2] When the degree of deterioration is classified into n+1 stages of 0 to n, when calculating the transition rate for each degree of deterioration in the transition rate calculation step and in the deterioration prediction step, deterioration prediction of the structure is performed. When performing, the method of predicting deterioration of a structure according to the above [1], wherein the following equation is used.

here,
P ₀ ′ to P _n ′: Ratio of deterioration degree from standard time t: Number of years elapsed from standard time P _{0 to} P _n : Ratio of deterioration degree after t years from standard time x _{0 to} x _n−1 : Degree of deterioration Transition rate for each i: Subscript indicating the stage of deterioration degree

In the present invention, it is possible to accurately predict the progress of deterioration of a structure having a deterioration mechanism in which the deterioration rate is not constant or a structure having a complicated deterioration mechanism in which various deterioration factors are combined.

It is a figure which shows prior art (nonpatent literature 1). It is a figure which shows the difference of the deterioration speed by a deterioration factor. It is a figure which shows progress of deterioration by salt damage. It is a figure which shows the Markov chain model in one Embodiment of this invention. It is a figure which shows the work process in one Embodiment of this invention. It is a figure which shows an example of the division of the deterioration degree in one Embodiment of this invention. It is a figure which compared the ratio of the deterioration degree in the Example of this invention.

INDUSTRIAL APPLICABILITY The present invention uses a Markov chain model, which is a statistical method that stochastically captures the transition from one “state” to the next “state” at a certain “transition rate” Is the way.

One embodiment of the present invention will be described below.

First, FIG. 4 is a Markov chain model showing the basic idea in one embodiment of the present invention.

As shown in FIG. 4, in this embodiment, the degree of deterioration divided into a plurality of stages (here, 0, 6 stages of I to V) is set in advance to indicate the degree of deterioration of the structure. .. Then, a probability (transition rate) at which a part having a certain degree of deterioration shifts to the next stage deterioration degree within a predetermined period (usually within one year) is set for each deterioration degree. That is, the respective transition rates are set to x ₀ , x ₁ to x ₄ , 0 for each of the deterioration degrees 0, I to IV, and V. Therefore, the probabilities that the parts with deterioration degrees 0, I to IV, and V have the deterioration degrees even after 1 year are 1-x ₀ , 1-x ₁ to 1-x ₄ , 1 respectively.

Thus, in this embodiment, the point that the transition rate is set for each deterioration degree is fundamentally different from the non-patent document 1 in which the transition rate is constant.

Next, FIG. 5 is a diagram showing a work process in this embodiment. As shown in FIG. 5, this embodiment has work steps (S1) to (S4).

(S1) Deterioration State Inspection Step In this deterioration state inspection step, the deterioration state of the structure is inspected a plurality of times with an interval. For example, regarding the deterioration state of each part listed in the structure as an evaluation target of deterioration, the first investigation is performed in t1 years after the completion of the structure, and a time interval (t2-t1) is set. , The second survey will be conducted two years after the completion of the structure.

Regarding the investigation method at that time, there are simple investigation methods such as visual inspection and tapping investigation, and detailed investigations such as ultrasonic flaw detection and chloride ion content investigation. Conduct an investigation using the appropriate method described in the management and inspection manual for each structure.

(S2) Deterioration Degree Evaluation Step In this deterioration degree evaluation step, the deterioration state obtained in the deterioration state inspection step is replaced with the deterioration degree divided into a plurality of stages to evaluate the change with time of the deterioration degree.

That is, the degree of deterioration of each part in the t1 year is evaluated from the deterioration state investigation result of each part in the t1 year (first time), and each deterioration state investigation result of each part in the t2 year (second time) is evaluated. The degree of deterioration of the part at the second year t is evaluated.

It should be noted that the deterioration level has an evaluation standard determined by each structure. For example, FIG. 6 is an example of the degree of deterioration used in a port structure. The degree of deterioration is evaluated in 6 grades, with the three indicators of corrosion of reinforcing bars, cracking of concrete, and peeling of concrete. The degree of deterioration is best "0" indicating the completed state, and is set up to "V" according to the deterioration thereafter. Here, the source of FIG. 6 is "Portal Technology Research Institute, Ministry of Transport, Manual for Maintenance and Repair of Port Structures, June 1999, Research Center for Coastal Development Technology".

(S3) Transition rate calculation step From the change with time of the deterioration degree obtained in the deterioration degree evaluation step, to the deterioration degree of the next step within a predetermined period (usually within one year) for each deterioration degree of each step The transition rate as the probability of transition is calculated.

For example, the transition rates x ₀ , x _{1 to} x ₄ (, 0) are calculated for each of the deterioration degrees 0 and I to IV (, V). In that case, the equation (1) described later is used.

(S4) Deterioration Prediction Step In this deterioration prediction step, deterioration prediction of the structure is performed using the transition rate for each deterioration degree obtained in the transition rate calculation step.

For example, using the deterioration rates 0, I to IV, and the transition rates x ₀ , x _{1 to} x ₄ , and 0 for each V, the deterioration rate after t years is calculated based on the deterioration rate in a certain year. Predict. In that case, the equation (1) described later is used. Here, the ratio of the degree of deterioration is the ratio of the number of parts of each deterioration degree to the number of parts of the structure whose deterioration degree is to be evaluated.

Here, the formula (1) used in the transition rate calculation step (S3) and the deterioration prediction step (S4) is shown.

here,
P ₀ ′ to P ₅ ′: Ratio of deterioration degree at reference time t: Number of years elapsed from reference time P _{0 to} P ₅ : Ratio of deterioration degree after t years from reference time x _{0 to} x ₄ : For each deterioration degree Transition rate

The equation (1), the number of years elapsed t as 1 year, based on the ratio P _{0 '~P} 5' degradation of the reference time, the ratio P ₀ to P ₅ of the deterioration rate after one year from the reference time It means that the rate of deterioration after t years from the reference time is calculated by repeating the calculation for t times in sequence.

Therefore, in the above (S3) transition rate calculation step, when calculating the transition rates x ₀ , x _{1 to} x ₄ for each of the deterioration degrees 0 and I to IV using the equation (1), the “reference time Substituting the deterioration rate according to the survey result in the t1 year into the deterioration rate ratio P ₀ ′ to P ₅ ′”, and in the “ratio of the deterioration degree after t years from the reference time”, the survey in the t2 year The substitution rates x ₀ and x _{1 to} x ₄ can be back-calculated by substituting the rate of deterioration according to the result. When performing the back calculation, it is preferable to use the approximation by the least square method.

Next, in the deterioration prediction step (S4), when predicting the deterioration state (ratio of deterioration degrees) of a desired year using the equation (1), “transition rate for each deterioration degree (x ₀ , x _{1 to} x ₄ )”, the value calculated back in (S3) above is substituted, and the “deterioration rate P ₀ ′ to P ₅ ′ at the reference time” is replaced with the rate of deterioration based on the survey result in the t2 year By substituting, it is possible to calculate the ratio of the degree of deterioration in the year in which t years have passed since the second year t2.

In the above, the case where the deterioration degree is classified into 6 stages of “0” to “5” has been described, but the deterioration degree is divided into n+1 stages of “0” to “n”. In this case, the following equation (2) may be used instead of the above equation (1).

here,
P ₀ ′ to P _n ′: Ratio of deterioration degree from standard time t: Number of years elapsed from standard time P _{0 to} P _n : Ratio of deterioration degree after t years from standard time x _{0 to} x _n−1 : Degree of deterioration Transition rate for each i: Subscript indicating the stage of deterioration degree

In this way, in this embodiment, it is possible to accurately predict the progress of deterioration of a structure having a deterioration mechanism in which the deterioration rate is not constant or a structure having a complicated deterioration mechanism in which various deterioration factors are combined. You can As a result, future repair costs can be calculated, and there is also an effect that life cycle costs can be calculated and compared. Furthermore, since it is possible to reduce the number of times the observation survey of the target object is performed by performing the deterioration prediction, it is possible to reduce the survey cost.

As an example of the present invention, the deterioration state (ratio of deterioration degree) of a harbor concrete structure was predicted. The deterioration degree used was that shown in FIG. Therefore, the degree of deterioration is set to 0 and 6 stages of I to V.

At that time, as an example of the present invention, deterioration prediction was performed based on the above-described embodiment of the present invention. Specifically, the first deterioration state investigation was conducted in 2002, the second deterioration state investigation was conducted in 2014, and the deterioration degrees 0, I to IV(, V ), the respective transition rates x ₀ , x _{1 to} x ₄ (, 0) were calculated. Table 1 shows the calculated transition rates x ₀ and x _{1 to} x ₄ . Then, the transition rates x ₀ , x _{1 to} x ₄ (, 0) were substituted into the equation (1) to predict the deterioration state (rate of deterioration degree) in 2017.

On the other hand, as a comparative example, deterioration prediction was performed by the method described in Non-Patent Document 1. Specifically, the transition rate x was calculated using only the deterioration state survey conducted in 2014. Table 2 shows the calculated transition rate x. Then, the transition rate x was substituted into the equation of FIG. 1B to predict the deterioration state (rate of deterioration degree) in 2017.

Then, in order to confirm the accuracy of the deterioration prediction of the present invention example and the comparative example, the deterioration state is investigated again in 2017, and the investigation result (measured value) and the deterioration prediction result (the present invention example, the comparative example) are compared. A comparison was made.

Table 3 shows the results of comparison between the examples of the present invention and the comparative examples with the measured values. Further, a graph comparing the comparative example with the measured value is shown in FIG. 7A, and a graph comparing the example of the present invention with the measured value is shown in FIG. 7B.

As a result, in the comparative example, the difference (average) from the measured value was 7.7%, whereas in the example of the present invention, the difference (average) from the measured value was 1.6%, which is extremely high. It was confirmed that the deterioration can be predicted with good accuracy.

Claims (2)

A method for predicting deterioration of a structure,
A deterioration state inspection process of inspecting the deterioration state of the structure multiple times at time intervals,
The deterioration state obtained in the deterioration state investigation step, by replacing the deterioration degree divided into a plurality of stages, the deterioration degree evaluation step of evaluating the change over time of the deterioration degree,
From the change with time of the deterioration degree obtained in the deterioration degree evaluation step, for each deterioration degree of each step, a transition rate calculation step for calculating a transition rate as a probability of moving to the next step deterioration degree within a predetermined period, ,
A deterioration prediction method for a structure, comprising: a deterioration prediction step of predicting deterioration of the structure using the transition rate for each deterioration degree obtained in the transition rate calculation step. When the degree of deterioration is divided into n+1 stages of 0 to n, when calculating the transition rate for each degree of deterioration in the transition rate calculating step and when performing deterioration prediction of the structure in the deterioration prediction step. The method for predicting deterioration of a structure according to claim 1, wherein the following equation is used for:

here,
P ₀ ′ to P _n ′: Ratio of deterioration degree from standard time t: Number of years elapsed from standard time P _{0 to} P _n : Ratio of deterioration degree after t years from standard time x _{0 to} x _n−1 : Degree of deterioration Transition rate for each i: Subscript indicating the stage of deterioration degree

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