I am having problems running dynamic load cases on a large model. RAM Frame will successfully solve the static wind & seismic load cases including 100/30 orthogonal load effects, but when dynamic load cases are added it gets most of the way through the analysis then crashes. I tried deleting the wind & static seismic load cases and rerunning, but it still crashes. The only way I could get the model to solve was by changing all the semirigid diiaphragms to rigid. In that case though, all of the story forces for the dynamic load cases turned out to be zero.
I am uploading the zip file 'CD_30' to the FTP site, it includes the model & some custom member tables. Do I need to simplify the model and/or uncheck the '100/30 orthogonal load cases' option to get it to run, or is something else causing the problem?
Thanks,
Jon Edens
The program is having problems with the Eigen solution. Your roof decks have little out-of-plane stiffness and this is leading to bogus deck waving mode shapes. To work around the problem, I had to increase the deck thickness and use the options to include out-of-plane stiffness for one way decks and use gravity columns/walls as springs in RAM Frame – Criteria – Diaphragm. Also, I had to increase the number of periods in the Eigen case to 27 in order to achieve 90% mass participation.
Thanks, Eric.
I increased the deck thickness from .04 in to .06 in (20 gage to 16 gage) and set the criteria to "Include out-of-plane-stiffness" and "Use gravity columns/walls as springs". After RAM Frame goes through the meshing process it gives the error "No Vertical Springs Defined for Gravity Columns because No Column Size Found. Assign Size to Gravity Columns." There's no indication which columns are missing sizes; I've reviewed RAM Modeler and verified that all gravity & lateral walls have thicknesses assigned. All gravity columns have sizes assigned in RAM Steel Column and all frame columns have sizes assigned in RAM Frame. Any idea what's causing the error?
Nevermind, I found a short column without an assigned size; apparently it was not a fatal error because the analysis still runs.
Thanks for your help!
You may need to assign a much thicker deck for analytical purposes. It really has nothing to do with the gage of the metal deck. There is little out-of-plane stiffness because the deck is being modeled with little thickness. In reality, the deck is corrugated and gravity members are present. Hence, the system is much stiffer out-of-plane that what is being represented analytically.