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2024-01-16

Nonlinear structural behavior

The analysis of the deformation capacity is tied to the assumption that the model geometry has nonlinear properties. Different types of nonlinearities are possible.

Member end hinge with nonlinearity

Member ends can be assigned nonlinear hinges. Normalized hinges for steel according to FEMA 356 [1 ] with plastic criteria are particularly suitable for the pushover analysis. They describe the ratio of occurring moment to yield moment and occurring torsion to yield torsion. The working line depends on the yield point of the cross-section.

Info

The equation QCE = 0.6 Fye Aw mentioned in [1 ] (5-7) represents an approximation for the manual calculation. The program uses the exact equation QCE = Fy Aw/√3.

Alternatively, you can use joints of the type Use chart with custom acceptance criteria. Nonlinear properties can also be described in the form of a regular member end hinge by defining it as #diagram diagram .

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Before the pushover analysis, a modal analysis must be performed. This modal analysis represents a linear calculation without considering nonlinearities. It is therefore important to define the plastic hinges without fully hinged hinges for the linear calculations (see image Assigning plastic hinge according to FEMA 356 ).

Nonlinear material properties

The pushover analysis is also able to consider a nonlinear material behavior. For example, you can use the material #masonry masonry to determine the capacity curve.

You can also define custom materials using your own working lines. The material model #isotropicDamage2D3DTab Isotropic Damage is particularly suitable for this. Detailed information on this material model can be found in a technical article .

To use user-defined working lines, you need a license for the analysis add-on material behavior Nonlinear material behavior. This add-on is described in chapter Nonlinear material behavior of the RFEM manual.


References
  1. FEMA 356: Prestandard and Commentary for the Seismic Rehabilitation of Buildings. (2000). Federal Emergency Management Agency, Washington D.C.
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