Friday, 26 April 2019

Fatigue exists. It really does.


Hello everyone, long time no read.

I’d like to share with you a story on my fatigue tests. As you know, fatigue of R-UHPFC beams is the main topic of my research (if you don’t remember what this abbreviation stands for, check my previous posts!)

Do you remember that I was doing some tests in cooperation with Antoine? The first beam instrumented with his Fibre Optics we've tested back in December under quasi-static loading. This was done mostly to calibrate the future fatigue load levels.

Then, the fatigue test followed. We have started it just before Christmas (in fact, we started to run it a day before Antoine left for his holidays, and two days before I have left for mine). The plan was to run it for some three to four weeks continuously. Thanks to internet, we were controlling everything in the lab in Lausanne, while he was in Lebanon and me in Poland. That’s the real globalisation!

But, on December 27th, the localized crack under the force application point has passed through one of the fibres in the upper flange. We've become ‘blind’ from this section on. Thus, we have had to temporarily stop the test. In mid-January, when both of us were back in Lausanne, we have re-connected and re-calibrated the fibre. The test continued.

In the beginning of February, strange thing happened. The jack could not produce anymore the force we wanted. Thus, we had to remove it without touching the sensors, not to de-calibrate them. That was like a surgery on an open heart, but our technicians are experts.

The jack was sent to the company for check-up. The reason of failure was… fatigue of one of the elements inside of the piston! After reparation, which took some 3 weeks, and re-installation on the testing rig (another week of work), in the beginning of March we have picked up the test. But, after just 2 days, the jack failed again! Unfortunately, during reparation, they have made a small mistake in the assembly. This meant another month of delay for me…

Finally, in the first days of April, the jack was installed again and the test continued. After another 2 weeks, on the 15th of April, circa 8AM, the beam failed! And so, after almost 4 months and 6.5 million of cycles, we have finished the test. It took some 3 months longer than planned!
I am writing this to show that the research is not only a success story. There are many things that can go wrong. Some of them depend on us; on some we don’t have any influence. Of course, it’s us who decide how to deal with the problems… and how to manage the time not to waste it! And, trust me, during these 4 months I’ve had plenty of other topics to work on ;).
Back in 2017, when I was starting my research, one of the experts has told me: ‘the fatigue experiments are very… fatiguing’. Believe me, he was right.

Thursday, 3 January 2019

Co-operation in cooperation

Hello everyone!

As you know, thanks to INFRASTAR we can travel to the partner institutions and work there with fellow Early Stage Researchers. Now at EPFL we have a visitor from France - Antoine. He's working on crack opening measurements using distributed fibre optics strain gauges. He got some nice results with ordinary concrete, thus we have decided to put them into my beams.

We've started the preparation of common experiment in September, when he came to Lausanne to glue some of his fibres on rebars, and to cast the beams with me. I must admit, that we have prepared a massive amount of sensors for some of the beams ;)


Then, when he came to EPFL for his secondment, we've glued some more fibres onto the surface of the beams.



Some of the beams prepared in this way will be tested in static, while the others in fatigue.

Thanks to that, he'll check if his method works with UHPFRC, and I'll get more interesting data on my specimens.

So, it's a WIN-WIN situation - that's how the cooperation should look like!


Sunday, 2 December 2018

Fatigue does exist!

Hello everyone,
today just a short post as lately I am very busy in the lab.

The first proper fatigue test is running. I am still amazed with the capabilities of our machines - in the current test I load and unload my beam 5 times per second with equivalent of 16 tonnes! Still, almost 3 weeks is needed to get 10 millions of cycles. You can see the beam during the test below.



In the meantime I have proven that the fatigue does exist (do you remember this?). Here is one of the bolts from my testing rig.



After strengthening of the connection the test continued.

That's it for now, I will keep you up to date!



Sunday, 11 November 2018

Experimental campaign... finally!

Hello everyone!

Long time no hear, as I am stuck in the lab. After casting, it is time to break some beams!

So far, I have tested three beams statically. I did it to get their resistance, which will help in calibration of my fatigue tests. One of the tested R-UHPFRC beams below, with visible huge force-redistribution steel beam on top of it.



I've got one unexpected shear failure... Which opened a whole new research branch on influence of vibrations during casting on the fibre orientation in beam! The project is ongoing.


And, when I say I BREAK the beams, I really mean it. The one below is broken for sure ;)

Thanks to its fibres, the UHPFRC is very ductile. Here, you can see a time-lapse video of the post-peak load. This means, that the beam has already reached its maximum resistance and now can be considered as damaged, but there is still a lot of capability of deflection and load support. 
Just imagine, that you can see through the beam while there is still a load of around 25 tonnes on it! (so, weight of 15 cars...) 



Stay tuned to see more pictures from another tests! Coming when I'll only find some time to upload them...






Thursday, 9 August 2018

Casting campaign

Hello everyone!

In the last post I was informing you about preparation of the casting campaign.
Now, my own small factory is fully operational, including:


Mixing,


casting... with use of external vibrators!


curing for 7 days in formworks,



demoulding, labeling,


...and finally moving to the storage area.

In July I have reached efficiency of  3 beams per week, which is a good result.

Unfortunately, I am not that good in taking videos with my cell phone... or maybe this post was just optimised for your mobiles? ;)

Now, the beams are awaiting for my test setup to be ready. This should happen within a week or two.
So, stay tuned!

Saturday, 2 June 2018

Step by step towards experimental campaign

Hello everyone!

One important part of my PhD research within INFRASTAR is an experimental campaign on R-UHPFRC beams (Reinforced Ultra High Performance Fibre Reinforced Cementitious composite).

This complex name stands for combination of UHPFRC and reinforcement bars, as known from reinforced concrete. I will not spoil the fun and reveal all the details for now - wait for it ;)

Currently I am getting step by step closer to the experiments themselves. But, there is a long way behind me already.

The origin of campaign takes back to the end of last year, when I was getting ready for my candidacy exam (read here) and I had to come up with ideas. I have decided to look at the problem of steel reinforcement and UHPFRC long term behaviour. This topic is relevant, as more and more structures are built every year, and it largely still hasn't been explored.

Since the beginning of 2018, fight for materials started. Finally, UHPFRC and reinforcement arrived to EPFL around May.





Then, there was time for material testing,

strain gauges gluing,

formwork preparation,

and the trial casting!

It even fitted the support that our technician fabricated for me!

For now, I have casted just the trial beam. But once I know the system works, I will start an extensive casting campaign this month! And, the first tests in July.

I will let you know!

Wednesday, 4 April 2018

Art of engineering

Hello everyone,

Lately, I've been taking part in 1st INFRASTAR implementation day (more info here). It was held by BASt (Federal Highway Research Institute) near Cologne, Germany.

Once there, I took a chance to walk the city and its riverbank. They have couple of road and railway bridges over there. This brought some thoughts to my mind.

According to the European codes, the design service life of a bridge is around 100 years. During that time, the traffic and the demands that we, a society, impose on a structure can change considerably. Just think of how the road traffic changed between 1918 and now!

One of the common cases, especially in case of bridges within the city limits, is need of widening of a bridge to accommodate higher number of cars, trains etc. But, this must be done not only under economical, but also under architectural constraints.

One of ways to widen the bridge is to add new, parallel structure. This strategy was used in two cases in Cologne.

In case of the railway bridge, a new structure was built next to existing one. Same material (steel) and type of structure was used, so that it is difficult to say the difference from the distance. But, closer look, reveals the progress that happened in civil engineering during the time.



Another case is a road-pedestrian bridge. Here, two different material were used (concrete and steel) but, to keep the nice look and compatibility, the box-girders were formed in similar way.

These two cases show, that an engineer needs to think of aesthetics, as well!

Fatigue exists. It really does.

Hello everyone, long time no read. I’d like to share with you a story on my fatigue tests. As you know, fatigue of R-UHPFC beams is th...