ETABS Enveloped Base Reactions
ETABS Enveloped Base Reactions
(OP)
Hello,
I am curious how other engineers are obtaining base reaction output for foundation designs. As far as I can tell, ETABS will not provide you with an enveloped base reaction and only considers live load reduction in the design phase. What I have done is isolated my joints at the base level and exported the joint reactions by load case to excel. I was also able to export the live load reduction factors to excel from ETABS. I then did my own load combinations (including the live load reduction factors) in excel, then enveloped these combinations using the "min" and "max" functions from excel. I feel like with a program as advanced as ETABS there has got to be an easier way. I am new to the program and just wondering if there is a feature that I am missing.
Thanks!
I am curious how other engineers are obtaining base reaction output for foundation designs. As far as I can tell, ETABS will not provide you with an enveloped base reaction and only considers live load reduction in the design phase. What I have done is isolated my joints at the base level and exported the joint reactions by load case to excel. I was also able to export the live load reduction factors to excel from ETABS. I then did my own load combinations (including the live load reduction factors) in excel, then enveloped these combinations using the "min" and "max" functions from excel. I feel like with a program as advanced as ETABS there has got to be an easier way. I am new to the program and just wondering if there is a feature that I am missing.
Thanks!






RE: ETABS Enveloped Base Reactions
RE: ETABS Enveloped Base Reactions
I typically will reduce live loads in Excel later. I'm using Excel anyways to post-process the analysis results into something that is actually readable, so it's typically not a big deal. I won't run it individually for each supporting element, but will do a couple rough hand checks to get an idea of general live load reduction levels. Since I'm typically doing heavier concrete structures where live load reduction of 40 vs. 50 vs. 60 doesn't make a huge difference, I'll usually take a little bit less of a reduction than my rough hand calculations resulted in. Just for a bit of wiggle room. Lighter steel structures would of course need a little bit more attention to detail. Also have to watch out for areas where you either can't reduce or can't take the full reduction like heavy loads or parking.
Workarounds for ETABS would be to do exactly what I do but with custom load combinations instead. You could also try running design with your allowable combinations and just look at the axial design load in columns. Doesn't help as much for walls or braced frames, but is a start anyways.
RE: ETABS Enveloped Base Reactions