October 4, 2018


Partial Fixity End Releases in RISA-3D


RISA-3D v17.0 now has the ability to model partial fixity member end releases. Partial fixity end releases can be utilized in RISA to model the behavior of a partially restrained or semi-rigid connection that cannot be idealized as fully fixed or pinned. Partially restrained connections are common in seismic moment frame systems and their semi-rigid rotational behavior can now be modeled in RISA-3D.

A partial fixity end release reduces the rotational stiffness at the member end joint by applying a rotational spring constant value entered by the user. RISA-3D uses the Euler-Bernoulli beam formulation to introduce this spring constant in the stiffness matrix. Partial fixity end releases can be applied in the Members Spreadsheet – Advanced tab by clicking on the red arrow in an I or J end release cell:

1 Partial Fixity 300x158 2x

Once a rotational stiffness is applied, the connection at that member’s joint will become more flexible as they are partially restrained. Graphically, the end release will show a symbol to designate that a partial fixity end release has been assigned.

2 Example Frame 300x126 2x

In the three examples above, the various frames have a beam to column connection that is either fixed, partially restrained, or pinned. The second frame beam has a rotational partial fixity member end release a stiffness of 1.0e+5 kip-in/rad in the Mz direction. There is a lateral earthquake load applied to the frame which we will compare the results for each case.

3 Example Deflected Shape 300x112 2x

After running the analysis and reviewing the deflected shape, the deflection results are as we expect. The deflected shape shows the fixed connection deflects the least while the pinned connection deflects the most. The partially restrained connection deflects somewhere in the middle to represent the semi-rigid connection using an intermediate stiffness of the partial fixity member end release.


Tags: RISA-3D Analysis

You may also be interested in

Nov 8, 2018 | Tips & Tricks
Mat Slab Overturning and Sliding Safety Factors

RISAFoundation v11.0 includes two new tabs in the Safety Factors resul...
Read More

Aug 21, 2019 | Tips & Tricks
RISA-3D v18 Sneak Peek Videos

The new release of RISA-3D is right around the corner! Check out our t...
Read More

Jul 12, 2019 | Tips & Tricks
Implementing Realistic Behavior for T/C Members in RISA-3D

Tension or Compression (T/C) Only members are commonly used in steel b...
Read More

Jun 20, 2019 | Tips & Tricks
Understanding Wall Panel Forces with Rigid Diaphragms

Rigid diaphragms represent a plane of very high rigidity and distribut...
Read More