...
In
...
addition
...
to
...
gravity
...
load,
...
should
...
initial
...
P-Delta
...
analysis
...
contain
...
notional
...
load?
...
Answer:
...
To
...
fully
...
account
...
for
...
P-Δ
...
and
...
P-δ,
...
each
...
design
...
...
...
must
...
be
...
run
...
as
...
a
...
nonlinear
...
P-Delta
...
analysis
...
which
...
includes
...
notional
...
load.
...
To
...
fully
...
account
...
for
...
P-Δ
...
in
...
buildings
...
with
...
either
...
rigid
...
or
...
semi-rigid
...
diaphragms,
...
an
...
initial
...
P-Delta
...
analysis
...
should
...
be
...
performed
...
with
...
gravity
...
load,
...
then
...
additional
...
loads
...
should
...
be
...
applied
...
linearly.
...
Justification
...
is
...
that
...
total
...
axial
...
load
...
(P)
...
at
...
each
...
story
...
level
...
remains
...
constant
...
regardless
...
of
...
lateral
...
and
...
notional
...
load.
...
For
...
subsequent
...
linear,
...
...
,
...
and
...
...
...
analyses,
...
...
automatically
...
implements
...
this
...
procedure
...
when
...
running
...
constant
...
P-Δ
...
analysis.
...
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TO DO: For the underlined portion shown below, consistency between the original and edited versions may need verification. Does initial P-Delta analysis should contain notional loads in addition to the gravity loads?To fully account for P-Δ and P-δ one needs to run each design load combination individually as a nonlinear P-Delta analysis. These load combinations should include the notional loads. However, the larger P-Δ effect is fully accounted for in buildings with rigid or semi-rigid diaphragms by first using the gravity loads to do an initial P-Delta analysis and then do analysis for other loads as linear about it. This is because the total P at each story level does not change due to any lateral loads including any notional loads. This procedure is automatically implemented in ETABS where a constant P- Δ analysis is used to perform subsequent linear, modal and response spectrum analysis. |