My thesis in 3 Posters- Part II: Application of time series methods on long-term structural monitoring data for fatigue analysis

The second part of "My thesis in 3 Posters" is related to my studies during my secondment in Lausanne, Switzerland.  

During this period, I joined the Structural Maintenance and Safety Laboratory (MCS) of Civil Engineering depertment at EPFL.  My work in this lab was devoted to take advantage of valuable long-term monitoring data that is recorded by this lab for about two years. I have employed Time Series methods such as ARIMA to prepare a new load model for fatigue analysis while there is seasonality effect. This new model can deal with missing data, it can capture seasonality effect, and it can be used to generate fatigue loading for further analysis. 

A short abstract in addition to my poster is provided below. 

ABSTRACT: 

Structural health monitoring (SHM) can be employed to reduce uncertainties in different aspects of structural analysis such as: load modeling, crack development, corrosion rates, etc. Fatigue is one of the main degradation processes of structures that causes failure before the end of their design life. Fatigue loading is among those variables that have a great influence on uncertainty in fatigue damage assessment.

Conventional load models such as Rain-flow counting and Markov chains work under stationarity assumption, and they are unable to deal with the seasonality effect in fatigue loading. Time series methods, such as ARIMA (Auto-Regressive Integrated Moving Average), are able to deal with this effect in the data; hence, they can be helpful for fatigue load modelling. The goal of this study is to implement seasonal ARIMA to prepare a load model for long-term fatigue loading that can capture more details of the loading scenario regarding the seasonal effects in traffic loading.

Conference papers: 

▪ "Application of Time Series Methods on Long-Term Structural Monitoring Data for Fatigue Analysis", SMAR2019, 5th International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures, 27 – 29 August 2019 in Potsdam, Germany. 

**Please open the following link to be able to see the poster

https://drive.google.com/file/d/1k5exXroDYMPCeGPqsnpGoVoPlALkcMut/view?usp=sharing

Participating the SMAR 2019 with ESR4: Imane Bayan and ESR5: Bartek Sawicki

My thesis in 3 Posters- Part I: AK-SYS-T: A new approach to address time-dependent reliability using Kriging meta-modelling

Time has passed very fast and INFRASTAR is becoming THREE years old. it means it is time for all PhDs within INFRASTAR to boost their energies and finalise their results and get ready to defend their theses. As ESR number 10 of this program I am not an exception form this fact and I am getting ready to finish my PhD. During this period I have achieved invaluable experiences by working on different topics with skilled researchers and competent research centres. 

As a result, I believe I have done a very good PhD during this period and I am going to introduce the main parts of my work in posters in three different posts. 

This post is the first part of this chain and it is related to the first phase of my work in which we have developed a new time-dependent reliability method that is called AK-SYS-T. A short abstract on this work as well as some outcomes are presented afterwards.

Abstract: 

The objective of this study is to investigate system reliability methods for time-variant reliability analysis. The main challenge in time-variant reliability analysis is dealing with low probabilities of failure while computationally expensive performance functions are involved. Time-variant problems are often simplified by discretizing time intervals. This enables one to transform the initial problem to a system problem. System reliability methods can therefore be used to address time-variant reliability problems. AK-SYS is an efficient system reliability method which can be applied when costly-to-evaluate performance functions are considered. Application of this method for time-variant reliability problems is introduced in this study that is supported with two academic examples from literature.

Outcomes: 

Journal papers: 

▪ AK-SYS-T: A new time-dependent reliability method based on Kriging meta-modelling, Reliability Engineering and Systems Safety (Under review)

Conference papers: 

▪ Time variant reliability analysis based on Ak-SYS, ICASP13, 26-30 May 2019, Seoul, South Korea 

▪ Application of AK-SYS method for time-dependent reliability analysis, CFM2019, 26-30 August       2019, Brest, France
Poster session: 
 ▪ MATHIAS October 2019 by Total R&D

**Please open the following link to be able to see the poster

https://drive.google.com/file/d/1mfGJpQ7URy2cUsNfn8NdC2aKYQaf7p9M/view?usp=sharing

Presenting this poster in MATHIAS 2019 by Total R&D

Secondment at IFSTTAR

Secondments are fantastic parts of Marie Curie projects. They give us great experiences in performing research, communication, and cultural orientation.  All these experiences are achieved by working in different research centres, cooperating with experts of the field, and living in several cities and countries. 

I have started my final secondment at IFSTTAR (The French Institute of Science and Technology for Transport, Development and Networks) in Paris in the beginning of February 2019.  The objective of my work at this institute is to study the fatigue phenomenon and crack propagation of welded details in bridges with orthotropic decks. This study has been initiated with cooperation of Cerema (Center for Studies and Expertise on Risks, the Environment, Mobility and Development).  Starting this study gives me the chance to work on the practical cases in the area of structural engineering and learning some advanced methods in finite element analysis such as XFEM in addition to learning some software like GMSH, Code-Aster, and Salome-meca. 

In the end, I hope my work during my secondment would be resourceful and I could cover a big part of our objectives by the help of my supervisors from IFSTTAR and Cerema. In the following you can see some photos of my new working environment. 

Thank you for reading this article, 

ESR10: Morteza Ahmadivala, and ESR6: Mariia Nesterova

Coffee break with supervisors at IFSTTAR

My work in a very small nutshell

In last decades maintenance optimisation of civil structures has gained increasing attention since the number of ageing structures is becoming large while available budget dedicated to maintenance is limited. Fatigue is one of the main degradation processes on steel structures that causes structural failure before the designed lifetime. Therefore, the main goal of our study is to provide an optimal maintenance planning to extend the lifetime of structures against fatigue. Structural health monitoring can help to have a better understanding of the structural condition for a better maintenance funding allocation. To reach our goal we might face different challenges in A: fatigue reliability assessment, B: application of monitoring information, and C: optimisation of maintenance strategies. Addressing these challenges can define different steps of this study. 

Within the first step, fracture mechanism and S-N curves are two regular approaches that are used to evaluate fatigue damage and provide a proper limit state for reliability analysis. Fatigue reliability can be performed within a time-independent or time-dependent framework depending on the choice of fatigue model. The challenge here is related to how to evaluate low probabilities of failure when computationally expensive performance functions are involved. Hence, we have developed an efficient methodology to perform time-dependent reliability analysis. Kriging meta-modelling is used to replace the computationally expensive performance functions while using Monte Carlo simulation. 

The second step is related to how to get benefit from monitoring information. Structural health monitoring provides us with valuable information about the current situation of civil structures. This information can be about crack development, actual loading conditions, etc. The challenge here is related to the way we employ the information coming from monitoring data. With this respect, a study has been developed on long-term monitoring data available at EPFL. Time series methods are employed to prepare a loading model for long-term monitoring data. The aim is to capture seasonality effect in traffic loading and to provide a model that gives more detail about structural fatigue loading. This load model can be used within S-N approach or fracture mechanism with some adjustments.

Finally, methods and approaches in previous steps will be combined to have a proper and updated indicator to apply maintenance actions. The desired indicator would be fatigue reliability index. The challenge in the final step can be related to the cost models for maintenance and monitoring. Therefore, an appropriate cost model will be chosen for the optimisation framework, and overall methodology will be applied on a shared object or another case study.  

Thank you very much for reading this post. 

Secondment at EPFL: such a great experience

Secondments are one of the most interesting parts of Mari Curie projects. It gives you the opportunity to work with different researchers in different companies, universities, and research centres. 

I performed my first secondment within the INFRASTAR program at EPFL. It was such a great chance for me to stay as a PhD visitor in one of the well-known engineering schools in the world and to live in Switzerland with its magnificent nature and landscapes. What I have learnt during my secondment is not only related to my work, I also learnt a lot about the Swiss culture, people, and the great international atmosphere of Lausanne. 

I joined the Structural Maintenance and Safety Laboratory (MCS) of Civil Engineering depertment at EPFL.  My work in this lab was devoted to take advantage of valuable long-term monitoring data that is recorded by this lab for about two years. It is worthy to mention that three of the shared objects within INFRASTAR are provided by MCS. Chillion viaduc is one of our shared objects and I was working on the monitoring data of this bridge. I have employed Time Series methods such as ARIMA to prepare a new load model for fatigue analysis while there is seasonality effect. This new model can deal with missing data, it can capture seasonality effect, and it can be used to generate fatigue loading for further analysis (more details about this study will be provided later).  

Apart from work, this period was a great opportunity for me to enjoy the nature of Switzerland. What is very interesting in Switzerland is that one can make a plan to visit any place in the country during a weekend, however, there are plenty of beautiful places out there. Another thing that sounds even more interesting in this small country is that they have four official languages and when you visit different regions you will see the diversity of the languages and cultures. 

In conclusion, I would say that my secondment at EPFL was a great incident for me. I could get benefit of the invaluable experiences of researchers at MCS lab. Also, I could add the experience of living in Switzerland in my memory besides all other beautiful experiences that I had in another countries. 

Thank you for reading this article, 

Chillion Viaduc

A trip with MCS members to visit a newly constructed pedestrianise bridge with UHPFRC that is a new material developed at MCS.  

Training weeks are full of adventures and experiences

I would like to write about interesting training weeks that we had so far within INFRASTAR. 

We had our Third training week recently at Aalborg University, Denmark, and we performed the previous ones at EPFL (Lausanne, Switzerland) and BAM (Berlin, Germany). 

Apart from the lessons that I have received during our training weeks in different areas of engineering and career development, having the opportunity to visit different labs, structures, materials, and advance technologies in civil engineering domain, gave a me a great insight and experience about what I am currently doing. 

We had our first training week in BAM, Berlin, which is the Federal Institute for Materials Research and Testing in Germany. During this training week, we visited their testing laboratory for concrete structures. They are developing some new tools and methods of none-destructive testing for concrete structures, and we had the chance to get familiar and work with some of their sensors during our visit. 

During the second training week in EPFL (École polytechnique fédérale de Lausanne), we had the chance to get familiar with a new type of material for construction that is a relative of concrete with different properties and it is called UHPFRC (Ultra-High Performance Fibre Reinforced Concrete). We also visited some structures that have already been built using this new type of concrete. 

Finally, we have visited a testing wind farm in Aalborg within our third training week in Aalborg University. Since I was always interested in renewable energy and sustainable development, It was the most amazing experience for me among all visits that I have had so far. We could learn about the recent technologies in the area of wind energy and see some of them working in the wind farm. 

In the end I would like to thank my program (INFRASTAR) that has provided us this amazing training in different and interesting places. 

Thanks a lot for reading this post, 

Training week 1, BAM 

Training week 2, EPFL

Training week 3, Aalborg

What is better than having another Marie Curie PhD at your office?

 I would like to devote this post to my colleague Barbara Heitner who is a PhD in TRUSS ITN under Marie Curie actions.

When you want to start a new career particularly when you need to move to another country, in the beginning, you always need some people to assist you with different issues to be able to stand on your own. Apart from the other great members of Phimeca, I would like to admit that I am so lucky to have Barbara as my colleague who has started her PhD one year before me in Phimeca and paved most of the roads before me. Not only for my research and work issues, she is also a great help to tackle personal problems.

With respect to the work, when your work situation and contract is different than other colleagues in the company you may go through different administrative procedure than others and in some cases it might be very boring and time consuming. As Barbara has already started her work before me as Marie Curie PhD at Phimeca, it made my recruitment procedure much easier and more straightforward. Also, it is always a great change when you start working in a company after university and it is not so easy for many people to easily get used to the new environment. It is much easier to adapt to work in a company when there is someone else in the workplace who has the same situation as yours.

In the other hand, since my research project and Barbara's are in the same domain, when I am facing different questions, she is the first person who hears them. Thank to the Phimeca's research team and Barbara, I could make a great progress in structural reliability analysis, probabilistic modelling, and programming in Python.

Apart from being colleagues Barbara is a great friend too. I appreciate her helps regarding my personal life as well. She made it easier for me to get used to live in  Clermont-Ferrand, France. Sometimes when I needed a company to discuss about different topics and maybe having a drink in the evening she was always there.

Since the next two weeks will be our final weeks that we spend together in Phimeca, by this post I would like to appreciate her help and support and I want to say that I was so lucky and glad to have her as my colleague.


Thank you very much for reading this post.

Me and Barbara after preparing the Christmas tree for 2018 in Phimeca