Moment Releases On horizontal beams
Moment Releases On horizontal beams
(OP)
Good Morning All,
I have always been told to release my horizontal simple shear connection members with in the My and MZ for Staadpro. However a clients staad just has the Mz released.
Number one is this correct?
Number two, where can I find documentation regarding this?
I have always been told to release my horizontal simple shear connection members with in the My and MZ for Staadpro. However a clients staad just has the Mz released.
Number one is this correct?
Number two, where can I find documentation regarding this?






RE: Moment Releases On horizontal beams
RE: Moment Releases On horizontal beams
RE: Moment Releases On horizontal beams
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Moment Releases On horizontal beams
RE: Moment Releases On horizontal beams
The short answer to your questions is "no".
If it's a typical shear connection then I'd release both the my and mz. As for bracing; did they properly set the unbraced length to the length of beam in Staad? Is there actually any weak-axis moment on the beam? Are there any items that could potentially be bracing the compression flange of the beam (such as metal decking)? Some pictures or details showing these beams will greatly help us tailor our responses to your question.
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Moment Releases On horizontal beams
BA
RE: Moment Releases On horizontal beams
The easiest way to check whether the model is handling the loads in the assumed manner is to print member end forces (or turn on the member force diagrams in the GUI) and see if any members are picking up (or delivering) unintended load to other members. If they are, then this is your justification to the other engineer (ex. Beam XXX looks like it is currently transferring significant torsion to column XX, did you intend to release My for that member or are you planning on somehow transferring that force through the connection..) That should go over a little better than a blanket statement on mow member ends are supposed to be modeled.
At the end of the day it does not matter so much just how it is modeled so long as there are simple clear load paths and connections to resist the applied forces, and the model matches the detailing in the drawings.
Regarding the "instabilities" do a search of Bentley's forums and help files. In many cases this is actually a member that is technically able to rotate about some axis but may not be loaded in a way that induces the rotation (i.e. a simple span beam loaded in the vertical direction with Mx released on both ends will give a instability warning due to the fact that it is modeled like it is free to twist - While this is technically correct, the minimal torsional resistance from a standard shear connection is adequate to maintain stability so long as there are no loads that induce torsion.)
RE: Moment Releases On horizontal beams
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Moment Releases On horizontal beams
BA
RE: Moment Releases On horizontal beams
The instabilities and zero stiffness warnings are there because you either aren't planning your beams out properly or because you require bracing.
RE: Moment Releases On horizontal beams
Thank you for your comments. I understand the purpose and meaning of the zero stiffness warnings and potential instabilities. But this does not always mean that bracing is needed or that the beams are not "planned out" properly. You may want to do some additional reading on the topic.
These warnings are generally resolvable (with some thought) and may point to potential problems in a model, but they do not necessarily mean that there is a problem. See the following FAQ for additional information
http://communities.bentley.com/products/structural...
The point of my original post was simply that the designer must understand the load paths through the structure and ensure that the model is behaving as expected and detail the joints accordingly. While paying attention to potential instabilities and warnings is part of this process, it it not the whole game...
RE: Moment Releases On horizontal beams
RE: Moment Releases On horizontal beams