مهندسی عمران-زلزله(محمدجواد خسرویانی)
مهندسی عمران-زلزله(محمدجواد خسرویانی)

مهندسی عمران-زلزله(محمدجواد خسرویانی)

(درخت منطقی) Event Tress and Logic Trees in seismic risk analysis

An issue tree, also called "logic tree" or "issue map", is a graphical breakdown of a question that dissects it into its different components vertically and that progresses into details as it reads to the right.

Issue trees are useful in problem solving to identify the root causes of a problem as well as to identify its potential solutions. They also provide a reference point to see how each piece fits into the whole picture of a problem.

There are two types of issue trees: diagnostic ones and solution ones.

Diagnostic trees breakdown a "why" key question, identifying all the possible root causes for the problem. Solution tree breakdown a "how" key question, identifying all the possible alternatives to fix the problem.

To be effective, an issue tree needs to obey four basic rules:

  1. Consistently answer a “why” or a “how” question
  2. Progress from the key question to the analysis as it moves to the right
  3. Have branches that are mutually exclusive and collectively exhaustive (MECE)
  4. Use an insightful breakdown

The requirement for issue trees to be collectively exhaustive implies that divergent thinking is a critical skill.

A profitability tree is an example of an issue tree. It looks at different ways in which a company can increase its profitability. Starting from the key question on the right, it breaks it down between revenues and costs, and break these down into further details.

source: Wikipedia


Having identified the different sources of risk for an engineering system and or
activity and analysed these in respect to their chronological and causal
components logical trees may be formulated and used for the further analysis of
the overall risk as well as the risk contribution of the individual components.
In the present chapter we will consider the basic aspects of some of the most
commonly used types of logical trees, namely fault trees, event trees, cause consequence
charts and decision trees.
Fault trees and event are by far and large the most well-known and most widely
applied type of logical tree in both qualitative and quantitative risk analysis. Two
of the most important risk studies involving fault tree and event tree analysis were
the US nuclear safety study and the UK Canvey study of chemical process
industries. Even though more modern risk analysis techniques such as e.g.
Bayesian Probabilistic Nets have been developing over the last years fault trees
and event trees are still the main methods recommended for US nuclear safety
studies.
Fault trees and event trees are in many ways similar and the choice of using one
or the other or a combination of both in reality depends more on the traditions
and preferences within a given industry than the specific characteristics of the
logical tree.
A significant difference between the two types of trees is though that whereas the
fault trees take basis in deductive (looking backwards) logic the event trees are
inductive (looking forward). In practical applications a combination of fault trees
and event trees is typically used where the fault tree part of the analysis in
concerned about the representation of the sequences of failures, which may lead
to events with consequences and the event tree part of the analysis which is
concerned with the representation of the subsequent evolution of the
consequence inducing events.
The intersection between the fault tree and the event tree is in reality a matter of
preference of the engineer performing the study. Small event tree / large fault
tree and large event tree / small fault tree techniques may be applied to the same
problem to supplement each other and provide additional insight in the
performance of the considered system. Cause consequence charts incorporate significant features of fault and event
trees and are in principal just a combination of the two.
Decision trees are often seen as a special type of event tree, but may in fact bee
seen in a much wider perspective and in fact applied consistently within the
framework of decision theory provides the theoretical basis for risk analysis.

https://www.researchgate.net/profile/Simone_Barani/publication/223534256/figure/fig1/AS:305291980754944@1449798688285/Fig-1-Logic-tree-for-the-sensitivity-analysis-The-branches-connected-to-a-given-node.png

http://www.ceus-ssc.com/Pics/700px/Figure_060102-01a.jpg

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For more discussion in this subject you can see the follow link about Logic Tree and Event Tree :



هم پایه سازی شتاب نگاشت ها بر اساس Code 2800 V4.


شتاب نگاشت: به اثر انگشت زلزله یا اصطلاحا Fingerpoint زلزله شتاب نگاشت گویند که در مدت زمان رخداد برای یک پارامتر مشخص توسط شتابنگار ثبت شده است.


http://www.scielo.org.za/img/revistas/jsaice/v51n1/a03fig01.jpg


 اما به دو دلیل شتاب نگاشت ها همپایه میشود :


1- بانک اطلاعات شتاب نگاشت ها در دنیا کامل نیست چراکه زلزله ها خیلی دیر اتفاق می افتد و بشر نیز مدت زمان زیادی نیست که قادر است رکورد های زلزله را ثبت کند به همین دلیل تعداد رکوردهایی که در بانک شتاب نگاشت های دنیا ثبت شده بسیار محدود است و نمیتوان شتاب نگاشت هایی یافت که دقیقا منطبق بر پارامترهای مورد نیاز باشد در نتیجه شتاب نگاشت ها مطابق با شتاب مورد نظر همپایه میشود.


2- یکی از نقاط ضعف تحلیل تاریخچه زمانی وابستگی بسیار زیاد این تحلیل به شتاب نگاشت ورودی است و با هر شتاب نگاشت پاسخ متفاوتی بدست میاد.

به همین دلیل است که آیین نامه برای انجام تحلیل تاریخچه زمانی مقرر میدارد که بیش از یک شتاب نگاشت ( حداقل سه شتاب نگاشت ) در محاسبات استفاده شود تا حتی المقدور بتواند به پاسخ های دقیق تری دست یابد .البته برای پروژه های تحقیقاتی توصیه میشود حداقل 7 شتاب نگاشت در نظر گرفته شود حال اگر شتاب نگاشت ها همپایه نگردد با هر شتاب نگاشت پاسخ بسیار متفاوتی گرفته میشود که نتیجه گیری از تحلیل را بسیار مشکل خواهد کرد با همپایه کردن شتاب نگاشت ها در واقع پراکندگی پاسخ ها را محدودتر کرده و نتایج تقریبا با هم سازگاری بیشتری خواهد داشت البته دقت شود که با همپایه کردن شتاب نگاشت ها باز هم پراکندگی نتایج وجود خواهد داشت اما مقدار آن کمتر بوده و بهتر از قبل میتوان در خصوص پاسخ ها به جمع بندی نهایی رسید.


برای آشنایی بیشتر با نحوه همپایه سازی و مقیاس سازی شتاب نگاشت ها چندین فایل آموزشی در لینک های زیر قرار گرفته که به راحتی می توانید دانلود کنید. همچنین لینک فیلم آموزشی همپایه سازی شتاب نگاشت ها نیز قرار داده شده است:


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Source

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www.softcivil.ir

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