Drift capacity model - eesd-epfl/OpenSees GitHub Wiki

When not directly simulated by the adopted sectional models, the loss of lateral force capacity for increasing drift demand can be captures through appropriate drift models attached to the macroelement. Such models impose force-drop, prescribed by the user, after a drift criterion is attained, defined differently for flexural and shear flailure modes.

The two shear drift δ_SH and shear drift δ_FL are defined as a function of the basic displacements as:

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The drift models attached to the element can account for a drift capacity reduction with increasing axial load ratio and for a dependency on the shear span H₀. They are expressed in the general form:

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The functions f₁(σ₀/f_c) and f₂(σ₀/f_c) can be defined by the user as piecewise linear functions, including the case of a constant drift capacity for all axial load ratios. The dependency on the shear span can be accounted for β>0, or deactivated if β=0.

The loss of axial load bearing capacity is assumed to happen for a higher drift demand. The drift δ_AC defining axial load collapse is obtained by multiplication of the drift model for loss of horizontal load capacity δ_HC times a user defined factor α_AC/HC. If such factor is not imposed, the element does not model any loss of axial load bearing capacity.

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