Question about Bilin Material

[jamshidiha]

Hi

I need to use the Bilin model in OpenSees to model special steel moment resisting frames. Therefore, I studied the following papar about the parameters of this model:

Lignos, D.G., and Krawinkler, H. (2011). “Deterioration modeling of steel components in support of collapse prediction of steel moment frames under earthquake loading”, Journal of Structural Engineering, ASCE, Vol. 137 (11), 1291-1302.
link: opensees.berkeley.edu/wiki/images/c/ce/BilinMaterialOpenSees.pdf

and also the Opensees example entitled “Pushover Analysis of 2-story moment frame (concentrated plasticity)". I have a problem, the values of some parameters of the Bilin material presented in this example are not consistent with those obtained using Equations (7) and (8) in the aforementioned paper. For example, The value of theta_pc_Plus in rotational spring of first floor. I would be so grateful if any one can help me to find what the problem is.

Section W24x131

Fy=55ksi

L=180 in

d=24.5 in

bf=12.9 in

tf=.96 in

h/tw=35.6

Lb/ry=50

The value of th-pcP (theta_pc_Plus) in the OpenSees example (Pushover Analysis of 2-story moment frame (concentrated plasticity)) is:

th-pcP=0.3

while the value of Th-pcP obtained using Equation (7) is:

th-pcP=0.152

and the value of Th-pcP obtained using Equation (8) is:

th-pcP=0.136

Thank you very much.

Best regards.