Why does not the period change even though shear is included

[emrekizilarslan]

Hi all,

I added "section aggregator" in order to add shear stiffness to the stiffness matrix. however, the period did not change. I did not see any problem with running but i feel like the period should change once the section aggregator is added. Thank you for answer in advance...


here is the part of the section aggregator in my code:

## For wall section

set G_shear [expr 11200.0*$ksi];

set matShearTagWall 3001;
uniaxialMaterial Elastic $matShearTagWall [expr $G_shear*$AgWall];
set matShearTagCB 3002;
uniaxialMaterial Elastic $matShearTagCB [expr $G_shear*$AgCB];

set secWallTag 123;
set secWall2Tag 124;
section Aggregator $secWallTag $matShearTagWall Vy -section $secWallTag_PM;
section Aggregator $secWall2Tag $matShearTagWall Vy -section $secWall2Tag_PM;

## For CB section
set secCBTag 1023;
set secCB2Tag 1024;
section Aggregator $secCBTag $matShearTagCB Vy -section $secCBTag_PM;
section Aggregator $secCB2Tag $matShearTagCB Vy -section $secCB2Tag_PM;

[selimgunay]

It should change at least slightly. Just to check you can multiply G by 10000 and see if there is any difference

[emrekizilarslan]

Hi Selim,

I also tried that but the period did not change. I am sure that after adding the combined shear stiffness to cross section, I am assigning that combined cross-section to elements used (100% sure). i am guessing i cannot add because of either

- type of element (dispBeamColumn), or
- I am adding force-disp. relation for shear to stress-strain for flexural.

Am i right?

[fmk]

sorry .. shear aggregator does not work with disp based elemnets, only forced based include shear defo effects if provided in the section.

[emrekizilarslan]

Thank you so much for your reply. is there a way to include the shear stiffness externally to fiber model then? i would really appreciate if there is. i cannot use "Flexure-Shear Interaction Displacement-Based Beam-Column Element" as it does not allow to use "P-delta" geometric transfer, which i will need to use.

[fmk]

you cannot use with disp beam element, your only choice is to switch to forcebeam element .. or put element in parallel with a force beam element with negligably small elastic section (can't be too small as has to invert it) and the shear aggregator you are using.

[emrekizilarslan]

Thank you again. I will try that.