PUSHOVER ANALYSIS OF ASYMMETRIC THREE-DIMENSIONAL BUILDING FRAMES Author : Rui Carneiro Barros, Ricardo Almeida

The effect of higher modes of vibration on the total non-linear dynamic response of a structure is a very
important and unsolved problem. To simplify the process the static non-linear pushover analysis was proposed associ-
ated with the capacity spectrum method, utilising a load pattern proportional to the shape of the fundamental mode of
vibration of the structure. The results of the pushover analysis, with this load pattern, are very accurate for structures
that respond primarily in the fundamental mode. But when the higher modes of vibration become important for the total
response of the structure, this load pattern loses its accuracy. To minimise this problem a new multimode load pattern
is proposed based on the relative participation of each mode of vibration in the elastic response of a structure subjected
to an earthquake ground motion. This load pattern is applied to the analyses of symmetric frames as well as to stiffness
asymmetric and mass asymmetric irregular building frames, under seismic actions of distinct orientations, permitting to
draw significant conclusions.