Drift capacity model definition - eesd-epfl/OpenSees GitHub Wiki
Two shear models can be attached to the macroelement to model the loss, or the reduction, of the lateral strength for increasing drift demand. they apply independent drift criteria for shear and for flexural failure.
The drift model can be specified in the form of a piecewise linear function of the axial load ratio, and can account for a dependency on the shear span (see the formulation for details). Such functions are imposed through the corner coordinates pairs, and can contain an unlimited number of branches.
-driftShear $sigma0_fc_1 $du_1 $sigma0_fc_2 $du_2 ... $beta <$fcLt>
-driftFlexure $sigma0_fc_1 $du_1 $sigma0_fc_2 $du_2 ... $beta <$fcLt>
Where:
| sigma0_fc_1, sigma0_fc_2, ... | Axial load ratio of points 1,2,.. defining the drift model |
| du_1, du_2, ... | Drift corresponding to the axial load ratios sigma0/fc_1, sigma0/fc_2, ... |
| fcLt | product of the compressive strength fc times the section area A=Lt. Must be omitted in all cases, except when the flags "fiberSectionShearModel1d", or "custom" are used. |
| beta | Parameter β as defined here. |
The axial load ratio/drift capacity relations should be defined for the whole domain [0,1] of the axial load ratio. If incomplete relations are given, a constant drift capacity is assumed for the remaining part of the domain, equal to the closest given value. As an example, a drift model as the one in the figure, fitted on a sample of 35 drift capacities obtained from shear and compression tests on stone masonry walls of irregular/slightly regular typologies (see Vanin et al., 2017 for details), can be imposed as:
-driftShear 0.0 0.015 0.3 0.003 1.0 -driftFlexure 0.0 0.015 0.3 0.003 1.0
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Such model, which is given as an example and is not meant to be extended directly to other masonry typologies, is defined imposing β=1 and a function in the form:
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A constant drift capacity for all axial load ratios is obtained through the simpler definition, if only one parameter is given:
-driftShear $driftS $beta -driftFlexure $driftF $beta
The loss of axial load bearing capacity can be modelled as well through a drift criterion. It is assumed that the drift criterion governing the axial collapse can be obtained multiplying the drift criterion related to the loss of lateral force capacity by a factor αACHC defined as:
-AxialCollapseRatio $alphaAC_HC
If no factor is specified, the element maintains its axial load bearing capacity for any imposed drift. As a standard option, after attainement of the drift criteria defining the loss of lateral or axial load bearing capacity, the response of the element in the corresponding directions is cancelled. The user can however impose a factor for multiplying the resisting forces, to model a partial force reduction:
-failureFactor $failureFactor
If the flags "failureFactorFlexure" or "failureFactorShear" are used, different factors can be specified for shear and flexural failure.
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