Risk Analysis in Bridges Railway and Fatigue Life Prediction Using AREMA Recommended Practices

Authors

Rodolfo Montoya Consultant Bridge Railway/ Montoya Alves Engenharia / Engineering / montoyaeng@gmail.com and PhD Candidate Student / Pontifícia Universidade de Rio de Janeiro – Brazil

Marcelo Botelli Experts Rail / MRS / Engineering / marcelo.botelli@mrs.com.br João Junqueira

Experts Rail / MRS / Engineering / joão.junqueira@mrs.com.br

Abstract Organizations of all types and sizes are influences and internal and external factors that make it uncertain whether achieve their goals. The effect that this uncertainty has on the organization's goals is called "risk," defined as consequence versus probability to happen to it. To ensure operational safety, all these items need to be structurally intact. Maintenance plans for each of the assets mentioned above, should follow the maintenance strategy as your risk and safety. Each railroad has a risk and maintenance strategy defined according its own characteristics. Criticality is an attribute of the equipment associated with the consequence of a failure, so that the greater the consequence of the failure of major equipment criticality thereof. Thus, the criticality is the consequence to our supply chain if the crashing equipment. Criticality is assessed on structure characteristics, obtained from the basic registration thereof. To assess the probability, we assessed the existing damage the structure, and using techniques linguistics, which were evaluated with Fuzzy Logic techniques. The Fuzzy logic allows use information with linguistic variables, so the technician can answer different levels of damage in different structural elements, each element will have an importance imposed by the matrix. Later evaluate an estimate of damage to fatigue using dynamic analysis, historical records of operation, speed, fatigue cycles in operation, serviceability, based on the AREMA standard. With the multiplication of both factors calculate the risk index, allowing you to prioritize our service preventive and corrective maintenance when necessary. Finally, we get a simple tool for prioritization of thousands of bridges in terms of risk and may have a fundamental decision-making for our technical leaders Railway.

Key Words

Bridges Risk Analysis; Prioritization; Fatigue Analysis; Time-History Analysis; Fuzzy Logic.

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Introduction

Know and adapt a prioritization technique using risk analysis focused on fatigue (probability) due the importance of the elements in stopping the process as a whole (result) and the probability of damage this unexpected stop is of great importance in current scenario cost reduction. Techniques for identifying damage to fatigue interpretation techniques technical reviews (fuzzy logic) are used to quantify the damage and the probability of collapse can prioritize estimates in an efficient and qualitatively by adapting the methodology to the found reality and problems in own and specific transport system. The technique also allows estimating the remaining life of the structure using the AREMA Standard.

Observed that there is a combination of factors that lead to this type of problem. All these cases represent a major concern for utilities or asset owners. Mitigate the risk completely represents a major investment in all stages of the structural life of the asset. However, we need to invest, but the question is how much, when and where?

Simplified Risk Analysis

Each railway has a risk and maintenance strategy defined according its own characteristics. Prioritization will be set according the risk that the equipment for this will be referred as risk for prioritizing defined in Eq1:

(1)

Effect (Criticality)

Criticality is an attribute of the equipment associated with the consequence of a failure, so that the greater the result of higher equipment failure to this criticality (Montoya, R, C). The criticality will be interpreted as consequence, which generates when this equipment to operate the system. When the information must be normalized and each feature will have a weight placed on basis of the combined importance and agreed upon by the technicians who know the rail or transport system. The sum of all weights versus the characteristics will be the value of the criticality as shown in Eq. 2

(2)

Weights are values from 0 to 1, and validated according the importance of each item for railway. The technical features are typically design or inherent to the design conditions. On Figure 2, are showing some to understand the reasoning (Junqueira, J).

Figure 2 – Assets Technical Characteristics

Probability (Structural Expert Opinion Damage)

The information technicians the railway and development of damage the bridges are valuable, so they should be considered in prioritizing techniques.

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Use linguistics techniques, which will be assessed using introductory Fuzzy logic performing the following qualitative questions obtained from visual inspection,

• Damage Permanent Way and superstructure, • Damage transitions and abutments; • Damage Bridge Bearing; • Damage inspection foundation blocks.

Linguistic variables obtained will be used in the practical experience of visual inspections to over time (CRISTANCHO, D).

Have we damaged the connections beams?

Figure 3 -Fuzzy Logic

The Fuzzy Logic was created to emulate the human logic and take certain decision though the information. Traditionally, a logical proposition has two extremes: it is either completely true or completely false. However, in fuzzy logic, a premise varies in real degree from 0 to 1, leading to partially or partially true false.

Figure 4 - Linguistic Variables Used

O assess the damage, use the following variables: normal, mild, moderate and Severe.

Always must be standardized Just as a consequence, the probability will have a value vector which in this case is a opinion vector "Av" and a weight to be an importance vector for each structural element "Cag" (Eq. 3).

(3) Probability (Structural damage focused on fatigue)

Stress concentration is defined as an increase in stress due to a change in shape or discontinuities. Fatigue cracks start at these locations. Fatigue in steel bridges starts in detail poorly designed and/or executed. Reinforcement methods for increasing the cargo capacity can have disastrous consequences if the fatigue is not correctly analyzed (AREMA).

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Figure 5 - Elements with high stress concentration

Following the described technique will determine a fatigue index that estimates the remaining life and the level of fatigue that the structure is solicited the loading cycles, allowing you to prioritization. Estimated Useful Life fatigue and fatigue index Determination

The proposal is based on AREMA standard, the models used and finite element analysis has been developed by the author using a program called Cartool Fatigue (Montoya, A. C), the same can be studied all purposes dynamic and fatigue using finite element.

Model analysis using Matrix and/or Finite Element

Programs were developed able to calculate elements bars, frames and area to assess the different structural configurations of elements and connections. This module of the program Cartool (MONTOYA, R. C) allows dynamic and stories time record evaluation, getting strains and stresses for any section at any point.

Figure 6 - Structural Model of a bridge using finite elements and characteristics of the vehicles

Distances wheel base of locomotives, wagons and axle load, care for the distribution of loads on beams is very important for this analysis.

Count cycles using Rainflow

The passage of the compositions on a particular bridge causes variations stress the various structural elements that may be represented by diagrams stress versus time (σ-t). Based on these diagrams it is possible through rainflow counting methods, to obtain the number of stress cycles to which the element is subjected in correspondence with certain stress amplitude classes. As result of this counting, it is possible to obtain a frequency histogram of stress amplitude spectrum also called stress or tension ranges, and which are the basis for analysis of the fatigue (Alfonso D). Stress amplitudes are defined as the difference between a local maximum and a local minimum stress Eq. 5.

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Figure 7 - Counting cycles Rainflow

Cumulative criterion Palmgren-Miner

Palmgren and Miner assumed the possibility linear accumulation relative to each stress amplitude classes damage. The nonlinear behavior in damage accumulation relates to the fact of different stress range of classes present different weights in the evaluation of the damage (AFONSO, D).

Figure 8 - Damage accumulation of rules

(4)

Therefore, the damage related to small amplitude stress cycles is distinct from damages associated with large amplitude stress cycle, due the former are responsible for the initiation of cracks while the latter being linked to its development. However, the ease of applying the Miner's rule, and the good results obtained by it compared with results from experimental testing have led to the hypothesis linear accumulation of damage is accepted (Alfonso D). The criterion breaks when resorting to damage accumulation method when D is greater than 1.0 their fissure (Eq. 4) when less can be calculated how many years remaining to exist. This index is also used as when less than 1 priority, will be a way to prioritize the damage in the structure for different bridges. As can be estimated remaining fatigue life.

Damage interpretation model AREMA

Rating by AREMA Method using some proposed changes (AREMA). ● Local Dynamics Assessment where there is the possibility of rupture fatigue, use the actual

dimensions of vehicles, actual shipments and amounts of operation in trains since the construction of the bridge,

● is evaluated for different times passing each axis and saved a tension record over time, ● the stress differences are evaluated in the registry and used to count rainflow cycles, may

parameterize in Eq 5 frequency stress; ● chose type of second AREMA detail for the coefficient an and Sr, it allows to calculate the

number of cycles for this stress level. Using Figure 9,

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Figure 9 - Connections and constant values A, second AREMA

● calculate the "SRE", Equation 6 and Equation 7, which is the applied stress range best

correlated with the Miner's rule, where Ni is the number of cycles for a range of tensions, Sri acting of my record stress;

(5) (6) (7

● calculate the accumulated damage using the cumulative criteria of Palmgren-Miner

multiplying by Eq coefficient 8 and Equation 9;

(8)

(9)

Where, "Nciclos" is the number of cycles to reach the "Sfrat" of the tables of AREMA and "ni" are the cycles of the cycle count got.

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Figure 10 - Tensions records and histogram of charge cycles

The index "Dd" will be our priority to our system and to estimate the life (EVU) we should use Eq 10 and Eq 11.

AS = Current Year construction (10)

or (11)

Prioritization using risk analysis focused on Fatigue

Prioritization will be set according the risk that the equipment concerned, when for working in the production chain, defined it as follows, Eq.12:

(12)

The percentage should be agreed between the technicians of the rail in function of the tool reliability, for example, when newly established, the technical opinion is more important than the number, or percentage a is greater than B.

Conclusions and Main results using priorization techniques

The frequency of inspections will largely depend on the expertise and experiences from the technician, for it was recommended conduct a brief survey on the different standards and railways. Each railroad will have to decide the frequency that best suit the scene, conditions and economic partner’s interests. The figure 11, showing a new vision of all bridge railway, later the fatigue analysis and visual inspection damage, we can see different pathologies and solution for each railway.

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Figure 11 – View Static Prioritization all Bridge later Fatigue Analysis

We can use tablets can feed with standardized field information, constantly updating the program and improving the investment continuously, showing in Figure 12.

Figure 12 – Tablets information standardization

Using the prioritization techniques was achieved more effective management of railway assets, minimizing risks and properly planning resources. References Montoya, A. C; et al - Vale Infrastructure Guide. 2011.

CRISTANCHO, D - Systems Inference Fuzzy.2013

AREMA- Manual for Railway Engineering-.

MONTOYA, R. C Cartool fatigue. 2009.

AFONSO, D - Check the Bridges Fatigue Steel Railway. 2007.

NBR 9452 - Procedure for inspections of bridges and concrete viaducts-.

ARMY TM 5-600 and AIR FORCE AFJPAM 32-1088.

Junqueira, J; BOTELLI M; et AL - Infrastructure Procedure MRS. 2015.

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