Purpose of Nonlinear Static Pushover
Analysis?
The purpose of pushover
analysis is to evaluate the expected performance of structural systems by
estimating performance of a structural system by estimating its strength and
deformation demands in design earthquakes by means of static inelastic
analysis, and comparing these demands to available capacities at the
performance levels of interest. The evaluation is based on an assessment of
important performance parameters, including global drift, interstory drift,
inelastic element deformations (either absolute or normalized with respect to
a yield value), deformations between elements, and element connection forces
(for elements and connections that cannot sustain inelastic deformations), The
inelastic static pushover analysis can be viewed as a method for predicting
seismic force and deformation demands, which accounts in an approximate manner
for the redistribution of internal forces that no longer can be resisted
within the elastic range of structural behavior.
The pushover is expected to provide information on many response
characteristics that cannot be obtained from an elastic static or dynamic
analysis. The following are the examples of such response characteristics:
• The realistic force demands on potentially brittle
elements, such as axial force demands on columns, force demands on brace
connections, moment demands on beam to column connections, shear force demands
in deep reinforced concrete spandrel beams, shear force demands in
unreinforced masonry wall piers, etc.
• Estimates of the deformations demands for elements that have to form
inelastically in order to dissipate the energy imparted to the structure.
• Consequences of the strength deterioration of individual elements on
behavior of structural system.
• Consequences of the strength detoriation of the individual elements on the
behaviour of the structural system.
• Identification of the critical regions in which the deformation demands are
expected to be high and that have to become the focus through detailing.
• Identification of the strength discontinuities in plan elevation that will
lead to changes in the dynamic characteristics in elastic range.
• Estimates of the interstory drifts that account for strength or stiffness
discontinuities and that may be used to control the damages and to evaluate
PDelta effects.
• Verification of the completeness and adequacy of load path, considering all
the elements of the structural system, all the connections, the stiff
nonstructural elements of significant strength, and the foundation system.
The last item is the most relevant one as the analytical model incorporates
all elements, whether structural or non structural, that contribute
significantly to the lateral load distribution. Load transfer through across
the connections through the ductile elements can be checked with realistic
forces; the effects of stiff partialheight infill walls on shear forces in
columns can be evaluated; and the maximum overturning moment in walls, which
is often limited by the uplift capacity of foundation elements can be
estimated.
These benefits come at the cost of the additional analysis effort, associated
with incorporating all important elements, modeling their inelastic
loaddeformation characteristics, and executing incremental inelastic
analysis, preferably with three dimensional analytical models.
Target Displacement
