convergence problem

[saeedeh]

hi

i have a simple model of a concrete cantilever concrete beam under cyclic load, the material i used is Concrete01WithSITC and ReinforcingSteel, and the fiber section, when i use beamWithHing element and one forceBeamColumn element it converges ,as we know we should use more than one element for DBEs but when i use more than one element it can not converge, and when i use nonlinearBeamColumn again it can not converge, the length of beam is 1.25 meter.
if i use 2 number of integration point for nonlineraBeamColumn it converges! and if i change the material with concrete01 and steel02 it converge again, is there any problem with Concrete01WithSITC and ReinforcingSteel material? how they effect the convergence of problem? is 2 integration point ok for nonlinearBeamColumn?

thank you

[fmk]

neither the beamWithHinges or the forceBeamColumn is a displacement based element, so only 1 should be used .. if you have more than 1 you can get problems.

while there is nothing wrong with either that I know off, they are complicated (especially the Reinforcing Steel) .. in my experience complicated materials do not result in models that converge well when put in larger problems as there is so too much going on.

[saeedeh]

thanks a lot for answering
yeah sorry, i mean "dispBeamColumn" instead of "forceBeamColumn in my previous message, and i used more than one element for just dispBeamColumn, and one element for nonlinearBeamColumn and BeamWithHing as you said, thanks

so its better not to use Reinforcing Steel yeah?

i have a question about material Conceret01WitSITC, in the opensees manual you find the script as :

uniaxialMaterial Concrete01WithSITC $matTag $fpc $epsc0 $fpcu $epsU <$endStrainSITC>

but i know it should get some other parameters too and i use it as an example that i have like this:

uniaxialMaterial Concrete01WithSITC 1 $fc_uncf $epsc0_uncf $fu_uncf $epsU_uncf 0.02 0.2 0.03

but i dont know what are " 0.02 0.2 0.03" these 3 numbers, and when i change them it has effects in convergence, whoud you pleas explain these ultra parameters?

[fmk]

only the first of those 3 numbes is looked at (read the manual). the code does this:

else if (Tstrain >= CendStrainSITC) {
Tstress = 0.0;
Ttangent = 0.0;
Tindex = 5;
}
so basically when strain is greater than that value specified, the stress and tangent returned by the material are 0. note that a tensile strain is positive.