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Discovering OpenSees: Surfing the Waves of OpenSees


Modeling diaphragms in 2D models with linear and nonlinear elements

October 19th & 20th

The next seminar in the web-based "Discovering OpenSees: Surfing the waves of OpenSees" learning series will occur on October 19 & 20.  The session will be broadcast twice at times that will allow users in all time zones around the world to participate.

This session is titled “Modeling diaphragms in 2D models with linear and nonlinear elements” and will occur on October 19 at 9:00 AM Pacific Time & October 20 at 4:30 pm Pacific Time. The 1-hour session will discuss the consequences of using rigid constraints on a beam column element, and propose alternate methods for modeling the diaphragm for cases when rigid constraints are not adequate.  It will cover:

  • Introduction
  • Consequences of applying a rigid constraint on a beam-column element (demonstrated by an example)
  • Modeling a rigid diaphragm in 2D without using rigid constraints (demonstrated by an example)
  • Conclusions and summary
  • Q&A with web participants

This seminar is intended for medium and advanced users but can be of a great benefit for beginners as well.

How can I join the seminar?

Register for the seminar on October 19 at 9:00 AM Pacific Time:

Register for the seminar on October 20 at 4:30 pm Pacific Time:

Once registered, you will receive a confirmation email with instructions for joining the meeting.

More information about this seminar topic

An unintended consequence of using the Rigid Diaphragm constraint (or other constraint) on a beam column element is a result of the fact that it enforces a condition of zero axial strain on the element. For sections where the neutral axis does not shift as a consequence of bending in the beam this constraint has little effect on the axial load in the beam, e.g. elastic or steel sections. For those beams where the neutral axis does shift, i.e. Reinforced Concrete beams modeled using fiber sections under moment; the moments in an unconstrained beam will cause the beam to undergo axial deformation. To constrain this axial deformation requires axial forces, the magnitude of which can be significant.

Note: The example used for this webinar is a 2D portal frame that considers three types of elements (Elastic Beam Column Element, Displacement-Based Beam-Column Element, Force-Based Beam-Column Element) and two types of materials (concrete and steel)

For more information about this seminar, visit:

What’s next in the Discovering OpenSees Series?

The next Discovering OpenSees sessions will be on the following dates about the topics listed below.   Mark them on your calendar!

“Recorders and output in OpenSees”: November 16 at 9:00 am PT & November 17 at 4:30 pm PT

"Force-based beam-column element vs. displacement-based beam-column element": December 14 at 9:00 am PT & December 15 at 4:30 pm PT

For more information about OpenSees, visit:

The Discovering OpenSees Series is organized by the PEER Center: