Fiber section stiffness recorder

[dborello]

It would be useful if sections had the ability to report their stiffness to the element recorder. I am particularly interested in the fiber section.

The motivation for this request is to identify when a plastic hinge has developed. Obviously there are several methods, but noting when the section stiffness has dropped below a threshold seems like a good one.

I realize that this would require multiple outputs, but that is not unusual.

It appears easy to implement (just add a setResponse to return ks?). I would attempt to do this myself, but would spend more time setting up the development environment than actual coding.

Thanks,
Dan

[amir.bozorgmehr]

One of the best ways for realizing the development of hinges is to keep tracking the stiffness of our fiber section. I am doing so but I can not get any result not even zeros. is there anybody who has already done that?
for instance I am writing this kind of recorder:

recorder Element -file $Data/StiffnessSec1.out -time -ele 2 section 1 stiffness;

and the element is :

element nonlinearBeamColumn 2 2 3 $np 2 $IdBeamTransf;

and the fiber section is a composite beam T sections as following description:

proc Tsection { secTag MatConcrete Matsteel1 Matsteel2 b ts hr As barshift NumBar Y3 d bf tf tw {nsb 20} {nst 8} {nfdw 16} {nftw 2} {nfbf 16} {nftf 4} } {;
section fiberSec $secTag {;
set y0 [expr 0];
set y1 [expr $tf+$y0];
set y2 [expr $d-$tf+$y0];
set y3 [expr $d+$y0];
set y4 [expr $d+$hr+$y0];
set y5 [expr $d+$ts+$hr+$y0];
set z0 [expr -$b/2];
set z1 [expr -$bf/2];
set z2 [expr -$tw/2];
set z3 [expr $tw/2];
set z4 [expr $bf/2];
set z5 [expr $b/2];
# Define the four patches for concrete slab and steel section
#patch rect $matTag $numSubdivY $numSubdivZ $yI $zI $yJ $zJ
patch rect $MatConcrete $nst $nsb $y4 $z0 $y5 $z5; #slab
patch rect $Matsteel1 $nftf $nfbf $y2 $z1 $y3 $z4; #upper flange
patch rect $Matsteel1 $nfdw $nftw $y1 $z2 $y2 $z3; #web
patch rect $Matsteel1 $nftf $nfbf $y0 $z1 $y1 $z4; #lower flange
#Define reinforcing layers
layer straight $Matsteel2 $NumBar $As [expr $d+$Y3] [expr -$b/2+$barshift] [expr $d+$Y3] [expr $b/2-$barshift]; #reinfocement
};
}

do you have any idea why I am getting nothing as results of stiffness. I although checked the other codes and samples but it seems to me that this recorder is not working?!

[wuhaoshrek]

Interesting, I'm still interested on how to monitor the change of element stiffness, aiming to
track the development of plastic hinge.

amir.bozorgmehr, I did not find any stiffness recorder in the latest web-based command tutorial.