non linear dynamic analysis pushover

huangyhg

non linear dynamic analysis pushover
i am doing a non linear dynamic pushover analysis. i am plotting the base shear vs. the roof displacement. is it possible for the x-displacement be 'negative' with the pushover force be "positive"?? if so why is this?
if anyone has ideas, would be greatly appreciated.
thanks,
check out our whitepaper library.
pushover? bup
fe
the key word here is dynamic. if it is dynamic one or another way it will be finding displacements from vibration around the steady state. if not it would be more likely called static equivalent.
hence either from the particular excitation and state of vibration at the time (in time-history analysis), or the statistical evaluation of the same to simulate the dynamical behaviour of interest to the analysis (in response-spectra analysis), some displacements can become negative. in the response spectra variant, you must even establish criteria for the sign of the obtained displacements.
i can see a bit the bafflement in seeing displacements negative in a pushover analysis, because as i understand it was initially you were applying incremental forces statically by increments to see the effects, in steel searching plastic hinge by plastic hinge formation till the formation of a mechanism. so it was thought pushing towards one side.
in time history analysis you apply the loads in the sequence they happen and follow the effects step by step. vibration will make that time-history may show negative displacements, be it the calculation linear or not.
pushover as anyone can see is a notional concept. most of our calculations are. so that the notional concept above expounded have been generalized to include dynamical effects will involve rules mixing the advantages of dynamical analysis and pushover analysis to better mimick or predict the interesting aspects of structural behaviour, under rules very likely debatable but still there for use made by knowledgeable people and hopefully knowledgeable users.
ishvaaag
thanks for your insight.
very helpful
as i said. bup.
  
fe
fex32
i trust that you can see why you didn't get the 'very helpful' reply.
i, for one, haven't got a clue on what you're trying to say.
my guess's is backup. am i right?   
when in doubt, just take the next small step.

no no. sorry guys. i was in a weird mood last night.
in my family 'bup' is a slang word for 'i don't know'. i was hearing a lot of bup this and bup that. so i was bupping all night.
my apologies.  i was just interested in what pushover is.

fe