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It appears to me that heavy vehicle garage demands in IBC 2012/2015 are substantially higher than IBC 2009. Beginning with IBC 2012, section 1607.7.3 Heavy Vehicle Garages references "the jurisdiction having authority", which is typically AASHTO with local amendments. IBC 2009 had Table 1607.6...

I'm not familiar with that feature in ETABS, but this is a RAM project so it doesn't apply in this case.

Yes and yes. Although we don't use RAM exclusively. We typically use ETABS for systems using 2-way slabs and RAM for everything else, unless there's something requiring nonlinear behavior or a sequence analysis.

Sure. I took the subgrade floor plate as a standalone FEM. I restrained the perimeter and then imposed lateral displacements in two orthogonal directions at the core-floor interface parallel to the walls. The reactions gave me a target spring value. Back in the full model, I could add beams at...

Update: I blanked the mass at grade and below (well, actually set it to 1 k-s^2/ft) and assigned those three diaphragms (Level 1, B1, and B2) as rigid. Then I disconnected the core nodes from the diaphragm and reconnected them using custom beams that provide restraint similar to considering...

That's my sense as well, and I'm a little embarrassed that I hadn't that done already. I've used that solution for other problems in the past. It appears I may have uncovered a bug with the software, because using the over-write for story mass is not affecting my modal participation at all. I've...

I didn't turn off the mass. For the software I'm using, it would be pretty easy to do. That might be the easiest solution. Anyone see any issues with that?

WARose, No consideration of soil-structure interaction. The perimeter foundation wall is idealized (perhaps poorly) as a shear wall.

KootK, I agree regarding your point about diaphragm flexibility. As to the others: 1. Separate models would work, but I would rather not maintain 2 models. Transferring the reactions from walls above to walls below will also be cumbersome. Still, it's a valid approach. 2. My structure doesn't...

KootK, do you mean delete it? I still need to design the walls, etc. below grade.

I am having problems getting more than 90% modal mass participation in my response spectrum analysis. The structure consists of 2 framed levels below grade, a large 3 story podium above grade, and then three towers extending up from the podium for a total of 21 stories (including basement)...

To get rid of vertical modes, make sure you define mass source to include lateral mass only. Go to define/mass source, and select the check box.

I am trying to track story shear for individual frames for a steel braced frame system. I tried using pier labels, but ETABS only allows labels to be assigned to vertical frame members or area elements (works great for moment frames and concrete shear walls). The only other option I see is to...

I think there is more to this. I have also had columns and braces that span stories. Sometimes they break and sometime they don't. I'd like to know why.

We use both ETABS and RAM, and our office designs concrete and steel buildings anywhere from 1 to 60 stories. RAM can be much more productive because it makes a distinction between gravity and lateral members, and only models lateral members as finite element. Everything else is simple beam...