5. Pushover

5.1 Scia Engineer

ECtools uses the analysis model of Scia Engineer and the proposrtioning (reinforcement) results from ECtools to prepare a nonlinear analysis model for the execution of pushover analysis based on ATC 41-13 and FEMA 356.

The nonlinear analysis is performed using a dedicated Seismostruct engine which is included in the nonlinear version of ECtools.

More information on seismostruct is available here while the verification is here

The nonlinear model is prepared using 1d nonlinear finite elements and rigid links to create the cores.

The material properties are:

  • Steel with uniaxial bilinear stress-­‐strain model with kinematic strain hardening, whereby the elastic range remains constant throughout the various loading stages, and the kinematic hardening rule for the yield surface is assumed as a linear function of the increment of plastic strain.

       seismo-steel

  • Concrete Uniaxial nonlinear constant confinement model, initially programmed by Madas [1993], that follows the constitutive relationship proposed by Mander et al. [1988] and the cylic rules proposed by Martinez-­‐Rueda and Elnashai [1997].

       seismo-concl

The analysis is based on a fibber element apporach whereas:

  • each element is divided into sections

    seismo-sections

  • each section is divided into fibbers (subsections)

     seismo-fibber

  • each fibre is associated with a uniaxial stress-strain relationship

The sectional stress-strain state of beam-column elements is then obtained through the integration of the nonlinear uniaxial stress-strain response of the individual fibres

5.2 Etabs

The particular program application aims at creating an ETABS model for analyzing it using static inelastic analysis (pushover) . Specifically, based on the calculated member reinforcement resulting from the design, the member moment capacities are calculated and plastic hinge points are inserted at their ends , which follow the moment-curvature diagrams according to the relevant clauses of FEMA 356 and ATC41-13. Plastic hinge points can be inserted in beams and columns for which the required reinforcement has been calculated (i.e. jacketed sections are excluded) and at the bases of rectangular RC walls that have been modeled as linear elements. In beams, the plastic hinges are (moment-curvature diagram) applied along the 3-3 local direction (Μ3), whilst in columns and RC walls along 2-2 and 3-3 local directions (Μ2 και Μ3) without any axial load interaction.

pushover_1

The following are required in order to update the ETABS data file so as to include the plastic hinge information at the ends of linear elements :
  • Full results file : Created during design by selecting the relevant option (see section ‎2.5.3). The file name is input in the relevant field from the menu File -> Open full results file or by clicking on the   button.
  • ETABS data file : This is the text file of the form .Ε2Κ or .$ET that contains all the necessary data describing the model (mentioned also in section ‎2.5.7). The file name is input in the relevant field from the menu File -> Open ETABS data file or by clicking on the   button.

Once the previously mentioned file names are input in the relevant fields, the ETABS file can be updated to include the plastic hinges by clicking on the Update button.

In the following window, the user selects the beams and columns conforming (C = conforming) to FEMA 356 and the RC walls cantaining hidden columns. Deselected members will be considered as non-conforming (ΝC = non-conforming) or assumed to not contain any hidden columns respectively. Clicking on the square frame () next to each member name selects it as conforming or as an RC wall with hidden columns. Clicking on the cross button selects all the members in the window and the delete button deselects all. Initially, the user is prompted for the beams. Then by clicking on the Next  next button the user is prompted for the columns and lastly, again by clicking on the next Next button, for the rectangular RC wall bases that have been modelled as linear elements.

pushover_2

 

 

Once the conforming members have been selected, the user is prompted for the ETABS file name (.Ε2Κ extension) under which the updated data are to be stored. It is recommended for this file name to be different than the original one. This new file is next loaded in the ETABS environment from the menu File -> Import -> ETABS .E2K Text File in order to analyze it using static inelastic analysis.

pushover_3

 

pushover_4

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