Yield moment note

[GiorgosCham]

Hi, in the following section there's a steel hollow circular section of 51cm diameter and 0.5cm thickness and filled with C25/35 concrete material. The yield moment produced from this composite section is way less that the one calculated by hand caclulations. It seems that the module is not taking into account the steel members contribution.


is there an explanation for this?

[robbievanleeuwen]

The yield moment occurs when any fibre in the cross-section reaches the yield stress - please see the theory. The moment stated here is most likely when the concrete reaches the yield stress (thus still a low stress in your steel section). As stated in the documentation, sectionproperties uses linear-elastic theory. If you are after non-linear analysis (and perhaps not a yield moment, but a plastic moment?), please see concreteproperties.

[GiorgosCham]

Hence, for this geometry the concrete section will yield before the steel does -> this is the yield moment! The steel is not being neglected, it just hasn't yielded when the concrete reaches its yield stress

that's not supported from theory..theory says the following:

So in other words in a reinforced concrete section,which is a composite section cause it contains 2 materials,..yield moment always takes into account yielding of steel rebar..show me where in theory of reinforced concrete design structures it says that yield moment is the moment capacity captured at the lowest yielding point of the section..the link you are directing me to is not proving that..

I'm not sure how you expect to obtain the "true" yield moment for this section from a linear-elastic analysis, i.e. where the steel is yielding (unless you somehow have concrete that can take huge tensile stresses!)

This is like asking me how do to obtain the yield moment of a reinforced concrete section..the answer according to literature is by assuming concrete has cracked and steel yielding. There's nothing nonLinear about it. By the way in the yielding point of the material curve we are in the elasto-plastic region not plastic..it's different..maybe there's smth I am not getting here but at the end of the day..yielding moment that sectionproperties produces is severely lower than the one described by literature and code standards..

[robbievanleeuwen]

Hi @GiorgosCham, again I am trying to tell you that sectionproperties is not the tool for analysing the yielding of reinforced concrete. sectionproperties is material agnostic, it analyses geometry, shapes and the like. It doesn't know what steel is, it doesn't know what concrete is. Just because you name a material 'concrete' doesn't mean it will know to apply special rules like ignoring tensile strength.

show me where in theory of reinforced concrete design structures it says that yield moment is the moment capacity captured at the lowest yielding point of the section..the link you are directing me to is not proving that..

I never said this, I explained how sectionproperties works and why you are getting certain output. You are giving it two materials with two yield strengths, and it is giving you a yield moment based on this - as described in the documentation all materials are linear-elastic (have the same linear behaviour in both tension and compression). Again, sectionproperties is not a concrete analysis program. You need to understand how the program is working and what it is doing (hint - read the docs). Rubbish in -> rubbish out.

This is like asking me how do to obtain the yield moment of a reinforced concrete section..the answer according to literature is by assuming concrete has cracked and steel yielding. There's nothing nonLinear about it.

You've just described non-linear behaviour, i.e. concrete having different properties in compression and tension. Here's a plot of moment-curvature of a simple reinforced concrete section BEFORE yielding - extremely non-linear:

Please take the time to understand the software you are using. sectionproperties is an open-source project and I contribute my time here for free. I am happy to help debug errors and potential bugs, however like other open-source projects, I expect that users take the time to read the documentation prior to asking questions.

[GiorgosCham]

I dont know where you're getting your theory from ..but the cracking of concrete happens all the wayyy down there..

and is always neglected by all codes and standards in design practise cause it happens very fast..so as u can see up to yielding of section we are considering linear behavior..that's why we use 1st order equations like the ones I pasted above to find yielding moment..right?

look I am not trying to downgrade your script..as I ve said in the past this is the best open source section designer I ve seen in a while..but if your script has the option of producing yield moment information..then there's no excuse for the yield moment to be so far off the real value..meaning the value calculated by hand calculations based on code and literature..

[robbievanleeuwen]

I dont know where you're getting your theory from ..but the cracking of concrete happens all the wayyy down there..

Peer reviewed literature... (not screenshots from linkedin posts or random excel plots - this is an extremely low and atypical cracking moment so this is extremely misleading, I suggest you start with a google image search for 'reinforced concrete moment curvature' to get some more realistic diagrams and then maybe look into the theory of why this is the case). I don't think there's any point continuing this conversation - you're not responding to anything I'm saying or what is documented about how sectionproperties works.

is always neglected by all codes and standards in design practise

What? Citation? I guess tension stiffening isn't a thing.

then there's no excuse for the yield moment to be so far off the real value

No excuse?? I don't appreciate the tone of this, I put a lot of work into making sectionproperties free and accessible for all and it is doing exactly what it says it does. The output of your analysis match exactly what I expect given you asked sectionproperties to conduct a linear yield analysis. If this is your attitude towards thoroughly documented, tested, validated and published (https://joss.theoj.org/papers/10.21105/joss.06105) open-source software, then I suggest this community is probably not for you.

[GiorgosCham]

What? Citation?
Are you seriously debading with me that Mcr and My is the same thing?

file:///C:/Users/User/Downloads/extended%20abstract%20L56562.pdf
Go to your script and change my to mcr..its misleading
Code does not accept Mcr as the beggining of nonlinear region.
Peer reviewed literature
where show me .. show me code or RC literature supporting the start of nonlinear region happens after cracking..concrete tensile strength is neglegible and this is the case with all codes..
I don't appreciate the tone of this
I am trying to point out as politely as possible the error so that u change and impove an otherwise soild script..
thoroughly documented, tested, validated and published (https://joss.theoj.org/papers/10.21105/joss.06105)
What exaclty is the "Journal of Open -source Software" ..I don't know them..