I am attempting to use the Joint Code check functionality of RAM Frame, and am a bit confused about implemenation, so any help would be appreciated.
From my readings of the Frame anlysis, and steel post-processor manuals/technical manuals, I though I had deduced the following:
1-Ignoring rigid end zones (in the frame/general criteria) would ignore panel zone deformation, and therefore frame stability has not been considered so AISC360-05 eqn. J10-9 would be used for panel zone shear
2a-Including effects at 0% reduction would not consider deformation and be in the same insctance as ignoring the effects.
2b-Including effects at 100% would consider deformation, and therefore J10-11 should be used.
This does not appear to be the correct understanding however, as situations 1 and 2b produce the same effect. Does anyone have any more info about this code interpretation?
Thanks.
I would like to add that AISC would generally say that rigid end zones should not be used in the analysis of steel frames.
www.aisc.org/.../f2da0d72-c80d-4c04-9726-c905d349615e.pdf
Not positive on Eric's original reference, but check this post too: there is a link at the bottom for NEHRP Seismic Design Technical Brief No. 2 which has similar recommendations.
So if I'm understanding your link correctly, Bentley's recommendation and RAM Frame's default behavior is to ignore rigid end zones, correct? This would then have the program using using the higher column panel zone shear strengths in the RAM Frame joint check but at the cost of having more drift, correct? When I check my drift, with REZ ignored, it did come out higher (with the 413k PZS capacity in the attached screenshot). Then when I checked it with REZ and no reduction, my drift on my little 1 bay test frame was about 20% less (and with the 321k PZS capacity in the screenshot). So that seems to match up.
As far as which option was selected in RAM Frame, this information is then not brought into the RAM Connection module, and the user needs to check or uncheck the "Frame stability considered in analysis" option to match their REZ setting in RAM Frame (or possibly differently to explore effects of changing that, I suppose?). Having it unchecked by default in RAM Connection is the more conservative route, but I just want to make sure I'm understanding the interplay correctly. If I've already taken the hit on drift, then I might as well take advantage of the extra strength coming from that when I check it in RAM Connection. Whereas, if I'm doing delegated connection design for someone else, using RAM Connection as a standalone program, I would keep that unchecked in Connection unless I confirmed with them that they had not used REZ in their model. Am I understanding this functionality correctly? One thing I'm still a little unclear about is the following NEHRP verbiage in section 5.4.3 of the 2016 2nd edition: "If the effect of panel zone deformations on frame stability is considered (see Section 4.2.1), AISC 360 §J10.6 permits an increase in the design shear strength beyond the level associated with global shear yielding of the panel zone. In this instance, Equations J10-11 and J10-12 may be used rather than Equations J10-9 and J10-10. If panel zones are explicitly modeled in the analysis, it is permissible to use these equations. However, as explained in Section 4.2.1, this is not common."NEHRP section 4.2.1 that was referenced above says: "Most designers model moment frames with fully restrained connections using line representations of beams and columns, with the lines intersecting at dimensionless nodes. This accounts in an approximate manner for flexibility inherent in the panel zone. It is also possible to explicitly model panel zones using any of several 4-node scissor or 8-node quadrilateral elements. When this is done, AISC 360 §J10.6 permits consideration of increased strength for the panel zones. However, the benefits of doing this when fully restrained connections are employed are typically small; thus, this is not typically done. Some analysis software permits specification of a rigid end offset to simulate stiffness of the panel zone and to simplify calculation of forces at the column face. This is not an appropriate method to represent panel zones and often results in unconservative estimates of frame stiffness and underestimation of design drift." [underlining mine]That makes it sound like RAM is not justified in using the higher capacity shear equations because RAM Frame is using centerline modeling. Or are you doing the explicit modeling internally?
Yes, we are now recommending that user ignore rigid end zones, using centerline analysis for the greatest flexibility in the model. We do not explicitly model the joint using 8-node quadrilateral elements.
My reading of NEHPR 4.2.1 is that if an explicit joint is modeled or centerline analysis is done, either way you can use AISC 360-05 Eq J10-11 (and J10-12).
Elastic panel zone deformation contributions to story drift can be accounted for by either explicit modeling of panel zone shear behavior [we don’t do this] or by adjusting the lengths of beams and columns in a manner that accounts implicitly for the contributions of panel zone deformations to drift [this is accomplished using centerline analysis].
Ram Connection is not getting the information from Ram Frame about whether a rigid end zone was considered or not. The check box for “Frame stability considered in analysis” is unchecked initially, and it needs to be checked for models with no REZ used in the analysis so that the Connection program will also use J10-11.
I’ll log an enhancement for that workflow to be automated (it involves a change in the data exposed through Ram DataAccess and an update for Ram Connection).