Why the elasticity modulus are inconsistency?

[YoungXu]

Dr. Aschellenberg
I saw the OpenSees and OpenFresco examples of PortalFrame, why the elasticity modulus of uniaxialMaterial Steel02 is not equal with the elasticity modulus of expElement? Could you tell me the reason? Thank you!

uniaxialMaterial Steel02 1 1.5 2.8 0.01 18.5 0.925 0.15 0.0 1.0 0.0 1.0
expElement beamColumn 1 3 1 1 -site 1 -initStif 1310.8 0 0 0 11.2 -280.0 0 -280.0 9333.3333

[aschellenberg]

The initial stiffness matrix for the experimental beam column element in the cantilever basic system (see OpenFresco command language manual on the OpenFresco website) is given by:
kinit = [EA/L, 0, 0; 0, 12EI/L^3, -6EI/L^2; 0, -6EI/L^2, 4EI/L]

The columns in the PortalFrame example have a length of L = 50 in. Now when we simulate the columns which behave like cantilevers that are fixed at the top and free to rotate at the bottom using a uniaxial material the stiffness of the cantilever is given by 3EI/L^3 which we determined from tests to be 2.8 kip/in. This is why the uniaxial material has its stiffness set to 2.8 kip/in.

Given the above we can calculate EI = 2.8 L^3/3 = 116'667. From that we get 12EI/L^3 = 11.2, -6EI/L^2 = 280 and 4EI/L = 9333

[YoungXu]

Thank you very much! Dr.! And, so the Fy=1.5 is not from the test?