Thursday, February 13, 2020

¿Cómo evaluar la capacidad de puentes de hormigón existentes?

I recently published a paper titled "¿Cómo evaluar la capacidad de puentes de hormigón existentes?" in the III Congreso Iberamericano de Ingenieria Civil.

In this paper, I give some ideas for the integral management and maintenance of existing concrete bridges in Ecuador. The abstract of the paper is:
Después de la expansión de la red vial del país, la comunidad de ingenieros civiles y el gobierno tienen un número mayor de puentes existentes a manejar. En el futuro, esos puentes necesitaran mantenimiento y adopciones a los cambios en términos de las cargas vivas. En ese artículo vamos a ver como en Europa y América del Norte se está evaluando la capacidad de puentes de hormigón existentes. Típicamente, la evaluación es primero analítico, y después, dependiendo de la necesidad, experimental. En caso de concluir que no hay capacidad suficiente, diseñamos un refuerzo estructural para el puente. Revisaremos diferentes métodos de cálculo, inspección, pruebas de carga, y reforzamiento para puentes de hormigón existentes.

You can find the slides of the presentation here:

Tuesday, February 11, 2020

ANN-Based Fatigue Strength of Concrete under Compression

Miguel Abambres and I worked on the development of an ANN-based expression for the fatigue strenght of concrete under compression - using Miguel's algorithm and my database of fatigue tests. I'm quite pleased that the resulting model only takes 3 input values, so it's as easy to use as most code equations, yet much more accurate.

You can access the paper (Open Access) which is published in Materials here.

The abstract is:
When concrete is subjected to cycles of compression, its strength is lower than the statically determined concrete compressive strength. This reduction is typically expressed as a function of the number of cycles. In this work, we study the reduced capacity as a function of a given number of cycles by means of artificial neural networks. We used an input database with 203 datapoints gathered from the literature. To find the optimal neural network, 14 features of neural networks were studied and varied, resulting in the optimal neural net. This proposed model resulted in a maximum relative error of 5.1% and a mean relative error of 1.2% for the 203 datapoints. The proposed model resulted in a better prediction (mean tested to predicted value = 1.00 with a coefficient of variation 1.7%) as compared to the existing code expressions. The model we developed can thus be used for the design and the assessment of concrete structures and provides a more accurate assessment and design than the existing methods.

Thursday, February 6, 2020

PhD Talk for AcademicTransfer: How to find time for reading when you have a faculty position

This post is part of the series PhD Talk for AcademicTransfer: posts written for the Dutch academic career network AcademicTransfer, your go-to resource for all research positions in the Netherlands.

These posts are sponsored by AcademicTransfer, and tailored to those of you interested in pursuing a research position in the Netherlands.

If these posts raise your interest in working as a researcher in the Netherlands, even better - and feel free to fire away any questions you might have on this topic!

During your PhD, you read a lot - or at least, you've read what you need to read to be able to write your literature review. Then, you get a faculty position, and before you know, you are juggling writing proposals, carrying out new research, writing the papers from your PhD, teaching, supervising students, service tasks and much more. It's easy to let reading slip to the side when you have a faculty position.

Here are a few different approaches to find time for reading:

1. Schedule it
To make sure you stay up to date, reading consistently is important. The best way to make sure you make time for reading, is to put it on your calendar. Set aside two blocks of time of 1,5 hours during the week to read up on the literature in your field. Remember that reading sparks creativity - you may come up with your next proposal idea by reading something new. This approach works very well when you use a weekly template.

2. Subscribe to print journals
If you receive a print journal in the mail, you will at least flip through it. And then maybe you will read something that catches your attention, before you place the journal on your shelves.

3. Set an alert for digital journals
If you don't want to start accumulating paper in your office, or if the journal of your choice is only digital, subscribe to a newsletter so that you receive a notification when new articles are available. Skim the headlines, click on the interesting ones, download the articles, and read them quickly before deleting the email.

4. Binge read for a project
If you need to start a new topic, a bit of binging is OK. I used to caution against binging at all times, but I've seen for myself that sometimes it is necessary to dive into a new project - especially for short-term projects in a field not directly related to yours. Better set aside a few big chunks of time (say, blocks of 3 hours every day, since I don't think anybody can read an entire day) and get up to speed.

5. Write a review paper
If you really want to delve into the literature on a new topic, challenge yourself to write a review article. So far, I've published a review article on shear in slabs, fatigue in concrete under compression, load testing of bridges, and shear in steel fiber reinforced concrete. Reviews are not a waste of time - they are the best way to go really deep into the topic.

6. Review papers and serve as editor
A lot of my reading these days is in the form of reviewing papers or as journal editor. As a reviewer, I read deeply and critically, so it certainly improves my reading and understanding of a topic. As an editor, I read quickly to see if the work fulfills the requirements to be sent to review, and then together with the review reports to make an editorial decision.

7. Join a challenge

Join a #365papers challenge to motivate yourself to read a paper every day
. While I think 365 days may be too much (you need your holidays too, it may be motivating to join an challenge, and it can be helpful to build the habit of reading daily or at least a few times a week.

Tuesday, February 4, 2020

Primer on Bridge Load Testing

Within the TRB AFF 40 Standing Committee on Testing and Evaluation of Transportation Structures, we have finalized and published the Circular: Primer on Bridge Load Testing.

It took us nearly four years and many conference calls and discussions, but you can find the result online.

A short description is as follows:

Load testing of bridges to assess bridge performance has been in practice since at least 1891 in Switzerland. In times when engineering models were not as accurate and available as today, a critical step in the construction of a bridge was to load test prior to opening or during the opening ceremony of the bridge. Several bridges, including ones in Serbia, Switzerland, and France, collapsed during such load tests.

While advanced calculation methods are available to determine the ultimate capacity of existing structures, load testing provides a useful alternative for such cases where current calculation methods, for one reason or another, cannot provide satisfactory answers to performance questions on existing bridges.

AASHTO’s Manual for Bridge Evaluation and the 1998 Manual for Bridge Rating Through Load Testing have been generally used as a guidance to load testing. This TRB E-Circular, TR Circular E-C257: Primer on Bridge Load Testing, provides significant updates to the existing documents to reflect the current state of the practice on bridge load testing. It covers the preparation, execution, and analysis of load tests, including diagnostic and proof tests. If effectively used, these methods can extend the useful life of existing bridges in a cost-effective fashion.

Tuesday, January 28, 2020

PhD Defenses around the World: a Defense in Argentina

Today, I have the pleasure of inviting Maria Belen Sathicq to tell us about PhD defenses in Argentina. Maria Belen is an Argentinean biologist, living and working in Italy. She got a B.Sc. degree in Biology, from the Universidad Nacional de La Plata (Buenos Aires, Argentina), and a PhD from the same University, specialized in water quality assessment. Herthesis was about the use of different populations of phytoplankton to assess changes in the water quality of a coastal system under high anthropogenic pressure. Currently she holds an AXA postdoctoral fellowship and works at the IRSA (Istituto di Ricerca sulle Acque, sede Verbania). Her project ENEAS aims to understand the role of microplastics in the spread of antibiotic resistant bacteria in the Tyrrhenian Sea.
She is starting in the Citizen Science world, but already considers herself a fan,and is a feminist

A PhD defense in Argentina is, as in most countries, a big event. To reach to this stage, first you have to enroll in a PhD program and carry it on for almost five years. Fortunately, thanks to educational policies, in my country doing a PhD in a public University is free of charge, that gives the opportunity to those who cannot afford a tutoring fee. My PhD was about water quality in the big Estuary of Rio de la Plata, using phytoplankton as an indicator tool, so it required a lot of field work (extensive and intensive) and microscope time, and of course, after that, a management of large quantities of data.

Once you carry on your investigation and have your results, it is time to write it down, a manuscript that ends up being as big as a book. This book goes to three specialist in your field (not necessarily from your own University, or even your own Country), and they act as reviewers of your work. Once you have all these three feedbacks (usually this takes a couple of months), you are ready for the oral and public defense of your thesis.

The thesis defense is in an auditorium, usually full with your family, friends and coworkers. I remember mine was a very hot day and I was (of course) super nervous. The director of the PhD of my University lead me to the auditorium, still empty, and left me there for a few minutes to organize my presentation. The same specialists that reviewed the thesis work, this day also act like the reviewing panel. With them and all the public present I started my dissertation. The two or three first slides I felt like I was speaking with squeaky robot voice, but then I remembered that this work had been my routine for the last 4 years, and I had really enjoyed it, so I relaxed a little and continued for 40 minutes presenting my thesis.

At the end of the presentation, the panel asks you questions, sometimes about what they already mentioned on the previous review stage, or something that has caught their attention, or even about your future scientific plans; and when they finish, they leave to a separate office to discuss your final score. After a few (endless) minutes they come back with the final certificate and they read it for all the audience. My final score was 10/10 so I was absolutely happy, and for the next moment, when I had to make the public acknowledgements, I was already crying of joy. These acknowledgements are usually also written in the first pages of the thesis, and they are for all the people who supported you throughout the process, not only academic but also personally.

The most common thing is that your tutor gives you a bouquet of flowers, independently if you are a boy or a girl, and my tutor (Dr. Nora Gomez) gave me a beautiful and very big one! For the celebration, the University building has a Hall with a very big table and your family and friends bring some things to eat and some champagne to make a congratulation toast, so you can share a very good moment with all of them and mark it as the end of your path as a PhD student.

Thursday, January 23, 2020

ANN-Based Shear Capacity of Steel Fiber-Reinforced Concrete Beams without Stirrups

For the year 2019, Miguel Abambres and I won a Collaboration Grant from USFQ. The first paper from this collaboration is titled "ANN-Based Shear Capacity of Steel Fiber-Reinforced Concrete Beams without Stirrups". It's open access and published in the journal fibers. You can read the paper here.

The abstract is:
Comparing experimental results of the shear capacity of steel fiber-reinforced concrete (SFRC) beams without stirrups to the capacity predicted using current design equations and other available formulations shows that predicting the shear capacity of SFRC beams without mild steel shear reinforcement is still difficult. The reason for this difficulty is the complex mechanics of the problem, where the steel fibers affect the different shear-carrying mechanisms. Since this problem is still not fully understood, we propose the use of artificial intelligence (AI) to derive an expression based on the available experimental data. We used a database of 430 datapoints obtained from the literature. The outcome is an artificial neural network-based expression to predict the shear capacity of SFRC beams without shear reinforcement. For this purpose, many thousands of artificial neural network (ANN) models were generated, based on 475 distinct combinations of 15 typical ANN features. The proposed “optimal” model results in maximum and mean relative errors of 0.0% for the 430 datapoints. The proposed model results in a better prediction (mean Vtest/VANN = 1.00 with a coefficient of variation 1 × 10−15) as compared to the existing code expressions and other available empirical expressions, with the model by Kwak et al. giving a mean value of Vtest/Vpred = 1.01 and a coefficient of variation of 27 %. Until mechanics-based models are available for predicting the shear capacity of SFRC beams without shear reinforcement, the proposed model thus offers an attractive solution for estimating the shear capacity of SFRC beams without shear reinforcement. With this approach, designers who may be reluctant to use SFRC because of the large uncertainties and poor predictions of experiments, may feel more confident using the material for structural design.