ASCE 7 inverted pendulum and non-building classification
ASCE 7 inverted pendulum and non-building classification
(OP)
I am designing a steel braced framed structure to support a rooftop equipment penthouse and exhaust stacks, structure is 65'overall in height in a SDC D. Believe structure will meet inverted pendulum definition. I am trying to decide most appropriate non-building structure type. Considering inverted pendulum R=2 from table ASCE 7-10 15.4-2 and would like to avoid special seismic detailing if possible. Height to width ratio of structure probably 1.5 to 2. Trying to envision how I will satisfy inverted pendulum moment analysis requirement for steel braced structure. More easy for me to envision satisfying this for say a single shaft support water tower but not a braced frame. Perhaps one could someone increase the applied shear using the in a ELF analysis to produce the desired moment envelope? Further complicating...believe I will be forced into modal analysis by a weight irregularity not sure at all how to tackle moment envelope there?






RE: ASCE 7 inverted pendulum and non-building classification
I don't see how you can classify a braced steel frame as a inverted pendulum. That's not how it is going to act.
RE: ASCE 7 inverted pendulum and non-building classification
Could you use non-building structure similar to building table 15.4-1 and the Steel OCBF with unlimited height that references AISC 360? R goes down to 1.5 but you appear to be relieved of the AISC 341 detailing requirements.
RE: ASCE 7 inverted pendulum and non-building classification
a sketch would help.....
RE: ASCE 7 inverted pendulum and non-building classification
RE: ASCE 7 inverted pendulum and non-building classification
RE: ASCE 7 inverted pendulum and non-building classification
WARose: I agree and although I would meet the 50% mass at the top now re-reading asce-7's definition of inverted pendulum I think there is more wiggle room to not to fall in that bucket as they mention and "relies on rotational restraint to the the top of the cantilevered element"..as Deker has mentioned.
azcats: Good idea...still in prelim design so don't know if an R=1.5 would overaly demanding...but certainly appears an option for me. Al thought I was planning on a knee braced portion (see sketch) which may not work with that category.
SAIL3: 1st statement was exactly my thought on how to approach although I don't know if the relative rigidity is that different. Regarding the second statement the top portion is designed by another engineer could you expand on your thoughts and a design flow path between the two engineers.
Deker: Good point and believe this is my out; although without anlayzing the top portion (which I was not planning on) hard to judge relative rigidities.
wannabeSE: Your right 65' is not the overall height (see sketch)...and I think my penthouse terminology may be in error as this is a self supported structure (see sketch).
RE: ASCE 7 inverted pendulum and non-building classification