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Anal zin withPAnal zin withPDeltaDelta
Presenter:Presenter: DeborahPenko,P.E.DeborahPenko,P.E.
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Wh ?
y
When?
How?
PPDelta?Delta?
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Definition:
Destabilizin momente ualtotheforceof ravit multi liedb the
horizontaldisplacementastructureundergoesasaresultofalateral
displacement.
P (ForceofGravity) x Delta (HorizontalDisplacement)
WhatisPWhatisPDeltaEffect?DeltaEffect?
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Step1:Modeldeflects
P*=V*LV= P*
LStep2:Secondaryshearforce(V)calculated
Step4:Iterateuntilthemodelconverges
WhatisPWhatisPDeltainRISA?DeltainRISA?
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Pd Little
P
Delta
:
curvatureoftheelement
RISAImplementation:
AddIntermediateJointstotheelement
WhatislittlePWhatislittlePDelta?Delta?
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u yu y
o o y y o
SecondOrderAnalysis(P ,P )
ACI2008&ACI2012
. .
ElasticSecondOrderAnalysis(10.10.4)
MomentMagnification(10.10.5)
ForeignCodes(CSA,etc.)
Why?Why?
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NoPDelta
2.Design
Lateral
System
e ta
3.FinalDesign
PDelta
When?When?
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P DeltaDeflection
LittlePDelta:
1.166
1.7951.807 1.809
De ection:1.226in
3%Increase
.
1 2 3 4 5
StrongAxisBending %Change
Deflection
1stIteration: 1.021in
AISC14th Edition:
FinalDeflection:2.342in
2ndIteration: 1.166in 14.20%
3rdIteration: 1.186in 53.95%
4thIteration: 1.189in 0.67%
5thIteration: 1.19in 0.11%
96%Increase
PPDeltaExampleDeltaExample
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Deflection
65.432
99.439
9.848
23.22
.
1 2 3 4 5
WeakAxisBending %Change
Deflection
1stIteration: 9.848in
2ndIteration: 23.22in 135.78%3rdIteration: 41.22in 77.52%
4thIteration: 65.432in 58.74%
5thIteration: 99.439in 51.97%
PPDeltaExampleDeltaExample
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ThePDeltaeffect increasestheflexuralstiffnessofmembersintension
CompressionOnlyCompressionOnly
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HowdowegetpastaPDelta
Divergence?
1. TurnoffPDelta
.
3. Review Deflection
4. ReviewDesignResults
How?How?
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Instabilities
Inadequatelysizedmembers
Tension/Compression
Only
Members
StiffnessAdjustment(DirectAnalysismethod)
ModelErrors
CommonPCommonPDeltaProblemsDeltaProblems
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Letsreviewsomeexamples!
CommonPCommonPDeltaProblemsDeltaProblems
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Questions?
Pleaseletusknowifyouhavequestions.
Wewillanswerasmanyquestionsastimepermitsduringthe
webinar.
Oncethe
webinar
is
closed,
we
will
post
all
Q&As
to
our
. .
Forfurtherinformation,contactusat:[email protected]
Presenter:Presenter: DeborahPenko,P.E.DeborahPenko,P.E.
