Hello Professor,

I believe that concrete will not fail as you indicated if it is subjected to a total stress equals to the average triaxial state of stresses. At that point, there will be only change in the volume (similar to a concrete tube at the bottom of the sea). However, once a distortion stress is added (the normal case since we use a passive confinement) a change in the shape will be obtained and that is the point which the concrete can release some of the confined stresses by initiating even unseen microcracks. Therefore, the confinement process is a function of the lateral stiffness.

Thanks

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When I still worked in Newton Paiva Universitary Center, a group of students which I advised in their called 'conclusion of engineering course' work, developed two models for a simple experimental test.

A tube of 2 inch diamenter with thickness of 2 mm of steel was filled by self compacting concrete and only a 1/4 inch round bar (6 mm) was put inside in its center.

One model had a rectangular plate welded as a foot, another was only the tube. Both tubes were compressed untill buckling; It was amazzing to see that steel and concrete work already together and the final deformed shape showed no difference in the final load nor any visible demage to the concrete. The foot had not change their behavior or final load.

It really seemed like it was only one material working at all.

I would like so much to continue this work and also publish my conculsions, but afterwards, the crises of the Brazilian Educational system, when pres. DILMA ROUSSEFF took off more than 10 billion from the financial program for students scholarship (called here FIES).

My university closed 4 of the 6 classes where I was teaching (steel structures and general mechanics). More than 50 people in the staff has lost their job.

I tried once again to enter in a Federal University, where we can do research in Brazil, like Ouro Preto. I submitted to a contest where I afford only the 3rd place and some irregularities were claimed, the contest was cancelled, then it went to Justice and it is still there. I already gave up to try to be a TEACHER again in Brazil.

(Edited: I wrote "researcher" before. I am researching by myself with my own time, dedication, efforts, money and skill. If this will give me any future? I don't know, but now I only think about the things I just did and that deserves to be published before someone takes out this contributions from me. It is not a question of pride or vanity, or even to reach some top place. I guess that my contributions can open new trends for research. Who is better qualified to present it, in a clear way? Did my followers already understand what this is about? So I feel that this task belongs to me and I feel glad to do it).

Nevertheless, I was very happy with the work developed by my team, it was very simple of course, but surely showed us that steel tube filled with concrete is a very promising idea.

I would like to say that if the dimensions of concrete and steel tube are small, the confinement can already succeed. If somebody would like to go ahead in this research, make yourself at home. Thank you.