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Which tools are available for a pushover analysis?

Answer

In RFEM, it is possible to determine a pushover curve or a capacity curve and export it to Excel. The following lists the steps that have to be performed:

  1. Definition of nonlinear hinges:
    • Plastic hinge according to FEMA 356: A nonlinear hinge (elastic-plastic or rigid-plastic) with preset yield values and acceptance criteria for steel members (Chapter 5 of FEMA 356). The yield strength values depend on the member and are preset automatically. The diagram parameters are interpolated, depending on the cross-section type. The "FEMA" hinges can be customized.
    • Figure 01 - Definition of the plastic hinge according to FEMA 356.

    • Plastic hinge according to EN 1998-3: Bilinear definition of the yield curve. The bilinear hinges also have preset yield values, acceptance criteria and yield limits, but can be adjusted manually. The use of the plastic hinges has the advantage of a colored display of the hinges when evaluating the individual load steps. Thus, it is possible to quickly detect the exceeding of an acceptance criterion, for example.
    • As an alternative to the definition of a hinge, RFEM provides the "Plastic Hinge" member nonlinearity. Here, a perfectly plastic behavior can be defined; the plastic limit values must be entered manually. The advantage of this option is that the location of the created plastic hinge is found automatically.
    • Figure 02 - Definition of the plastic hinge as member nonlinearity.

  2. Definition of load schemes for nonlinear analysis: This can be done manually by entering loads into a load case, for example a uniformly distributed load over the building height.

    A load distribution similar to the mode shape distribution can be generated automatically with the RF‑DYNAM Pro - Equivalent Loads add-on module. This module determines eigenvalues and equivalent loads based on the response spectrum analysis. For each selected eigenvalue, equivalent loads are generated and exported to RFEM in load cases.

  3. Load increase in RFEM: A load increase can be defined in the calculation parameters of the load cases. The results of all load increments can be analyzed. Especially when using the "Plastic Hinges", the plasticization can be evaluated well by the colored marking of the hinges. It is important to scale the exported equivalent loads (from RF‑DYNAM Pro) so that the loads are not increased in too large increments. Figure 03 shows the load case exported from RF‑DYNAM Pro and the recommended calculation parameters.
  4. Figure 03 - Incremental Load Increase of Load Distribution Analogous to Dominant Mode Shape

  5. Calculation diagrams for creating the pushover curve: You can find them in the "Global Calculation Parameters". You can define the total seismic load on the vertical axis and the deformation in the roof plane on the horizontal axis to obtain the desired pushover curve. You can easily export the data to Excel.
  6. Figure 04 - Display of the pushover curve in the calculation diagrams.

The color display of the plastic hinges is shown in Figure 05. You can select the color scale according to the acceptance criteria or according to the defined parameters of the hinge diagram.

Figure 05 - Colored result display of the plastic hinge.

A further pushover analysis (determination of the inelastic spectrum, performance point) can then be performed, for example, in Excel.

In the download area, you can find a detailed description of these instructions within a PDF document.

Keywords

Plastic Hinges Pushover FEMA 356 Capacity curve N2 method Capacity spectrum method Acceptance criteria Dynamics

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RFEM Main Program
RFEM 5.xx

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Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

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RF-DYNAM Pro - Equivalent Loads 5.xx

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Seismic and static load analysis using the multi-modal response spectrum analysis

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