I have an instance where ground floor is a composite steel floor so I have modeled it in RAM with a 2 ft story height. I am unable to understand that the base reactions for the load case do not sum to the loads applied (for example Wind in the X direction in this case). The story shear reported at Level 2 is 384.78 k which suddenly reverses direction with a magnitude of 1817.2 k at the ground level. The base reactions sum up to the ground floor story shear.
Can you please let me know the reason for this abrupt increase in the story shear at ground? Please refer the snip below for your reference.
Thank you.
Check our wiki on the ground level criteria for starters:
Also see:
Thanks Seth. Can you also please let me know the conditions where lateral restraint from the ground should be assumed? I have a composite floor slab at ground floor with crawl space and columns stop 4ft below ground at top of pier. It is a steel Moment Frame building.
Regards,
Hey Seth, Thanks for the links. I had a follow up question: the high story shear at ground is essentially the sum of reactions due to "rollers" at the ground level. correct?
I did the analysis of the exact same frame by hand and another analysis software to get the roller reactions and I was wondering why the addition of those did not match the ground level frame shear that RAM was reporting (roughly 25% difference).
Please let me know your insights...
Thanks,
Seth Guthrie
That's really your decision to make. The wiki on Ground Level Criteria explains about the ramifications of using it.
Thanks