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Nonlinear Analysis & Performance Based Design
CALCULATED vs MEASURED
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Nonlinear Analysis & Performance Based Design
ENERGY DISSIPATION
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Nonlinear Analysis & Performance Based Design
IMPLICIT NONLINEAR BEHAVIOR
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Nonlinear Analysis & Performance Based Design
STEEL STRESS STRAIN RELATIONSHIPS
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Nonlinear Analysis & Performance Based Design
INELASTIC WORK DONE!
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Nonlinear Analysis & Performance Based Design
CAPACITY DESIGN
STRONG COLUMNS & WEAK BEAMS IN FRAMESREDUCED BEAM SECTIONS
LINK BEAMS IN ECCENTRICALLY BRACED FRAMESBUCKLING RESISTANT BRACES AS FUSES
RUBBER-LEAD BASE ISOLATORSHINGED BRIDGE COLUMNS
HINGES AT THE BASE LEVEL OF SHEAR WALLS ROCKING FOUNDATIONS
OVERDESIGNED COUPLING BEAMSOTHER SACRIFICIAL ELEMENTS
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Nonlinear Analysis & Performance Based Design
STRUCTURAL COMPONENTS
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Nonlinear Analysis & Performance Based Design
MOMENT ROTATION RELATIONSHIP
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Nonlinear Analysis & Performance Based Design
IDEALIZED MOMENT ROTATION
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Nonlinear Analysis & Performance Based Design
PERFORMANCE LEVELS
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Nonlinear Analysis & Performance Based Design
IDEALIZED FORCE DEFORMATION CURVE
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Nonlinear Analysis & Performance Based Design 17
ASCE 41 BEAM MODEL
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Nonlinear Analysis & Performance Based Design
• Linear Static Analysis• Linear Dynamic Analysis
(Response Spectrum or Time History Analysis)
• Nonlinear Static Analysis(Pushover Analysis)
• Nonlinear Dynamic Time History Analysis(NDI or FNA)
ASCE 41 ASSESSMENT OPTIONS
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ELASTIC STRENGTH DESIGN ‐ KEY STEPS
CHOSE DESIGN CODE AND EARTHQUAKE LOADSDESIGN CHECK PARAMETERS STRESS/BEAM MOMENTGET ALLOWABLE STRESSES/ULTIMATE– PHI FACTORSCALCULATE STRESSES – LOAD FACTORS (ST RS TH)
CALCULATE STRESS RATIOS
INELASTIC DEFORMATION BASED DESIGN ‐‐ KEY STEPS
CHOSE PERFORMANCE LEVEL AND DESIGN LOADS – ASCE 41DEMAND CAPACITY MEASURES – DRIFT/HINGE ROTATION/SHEAR
GET DEFORMATION AND FORCE CAPACITIESCALCULATE DEFORMATION AND FORCE DEMANDS (RS OR TH)
CALCULATE D/C RATIOS – LIMIT STATES
STRENGTH vs DEFORMATION
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Nonlinear Analysis & Performance Based Design
STRUCTURE and MEMBERS
• For a structure, F = load, D = deflection.• For a component, F depends on the component type, D is the
corresponding deformation.• The component F‐D relationships must be known. • The structure F‐D relationship is obtained by structural analysis.
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Nonlinear Analysis & Performance Based Design
FRAME COMPONENTS
• For each component type we need :Reasonably accurate nonlinear F‐D relationships.Reasonable deformation and/or strength capacities.
• We must choose realistic demand‐capacity measures, and it must be feasible to calculate the demand values.
• The best model is the simplest model that will do the job.
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Nonlinear Analysis & Performance Based Design
Force (F)
Initiallylinear
StrainHardening
Ultimatestrength
Strength lossResidual strength
Complete failure
First yield
Ductile limit
Hysteresis loop
Stiffness, strength and ductile limit mayall degrade under cyclic deformation
Deformation (D)
F-D RELATIONSHIP
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LATERALLOAD
Partially DuctileBrittle Ductile
DRIFT
DUCTILITY
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ASCE 41 - DUCTILE AND BRITTLE
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Nonlinear Analysis & Performance Based Design
FORCE AND DEFORMATION CONTROL
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Nonlinear Analysis & Performance Based Design
F
Relationship allowingfor cyclic deformation
Monotonic F-D relationship
Hysteresis loopsfrom experiment.
D
BACKBONE CURVE
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Nonlinear Analysis & Performance Based Design
HYSTERESIS LOOP MODELS
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Nonlinear Analysis & Performance Based Design
STRENGTH DEGRADATION
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Nonlinear Analysis & Performance Based Design
ASCE 41 DEFORMATION CAPACITIES
• This can be used for components of all types.• It can be used if experimental results are available.• ASCE 41 gives capacities for many different components. • For beams and columns, ASCE 41 gives capacities only for the chord
rotation model.
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Nonlinear Analysis & Performance Based Design
θi θj
Current θ
Elastic θPlastic (hinge) θ
Totalrotation
Zero length hinges
Elastic beam
Plasticrotation
Elasticrotation
Similar atthis end
Mi Mj
M or Mi j
M
θ θi j or
θ
BEAM END ROTATION MODEL
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Nonlinear Analysis & Performance Based Design
PLASTIC HINGE MODEL
• It is assumed that all inelastic deformation is concentrated in zero‐length plastic hinges.
• The deformation measure for D/C is hinge rotation.
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Nonlinear Analysis & Performance Based Design
PLASTIC ZONE MODEL
• The inelastic behavior occurs in finite length plastic zones.• Actual plastic zones usually change length, but models that have
variable lengths are too complex.• The deformation measure for D/C can be :
‐ Average curvature in plastic zone.‐ Rotation over plastic zone ( = average curvature x plastic zone length).
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Nonlinear Analysis & Performance Based Design
ASCE 41 CHORD ROTATION CAPACITIES
IO LS CPSteel Beam θp/θy = 1 θp/θy = 6 θp/θy = 8
RC BeamLow shearHigh shear
θp = 0.01θp = 0.005
θp = 0.02θp = 0.01
θp = 0.025θp = 0.02
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Nonlinear Analysis & Performance Based Design
COLUMN AXIAL‐BENDING MODEL
Mi
P
PP
P
or
V
V
Mj
MM
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STEEL COLUMN AXIAL‐BENDING
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Nonlinear Analysis & Performance Based Design
CONCRETE COLUMN AXIAL‐BENDING
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Nonlinear Analysis & Performance Based Design
NodeZero-lengthshear "hinge"Elastic beam
SHEAR HINGE MODEL
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Nonlinear Analysis & Performance Based Design
PANEL ZONE ELEMENT
• Deformation, D = spring rotation = shear strain in panel zone.• Force, F = moment in spring = moment transferred from beam to
column elements. • Also, F = (panel zone horizontal shear force) x (beam depth).
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Nonlinear Analysis & Performance Based Design
BUCKLING-RESTRAINED BRACE
The BRB element includes “isotropic” hardening.The D‐C measure is axial deformation.
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Nonlinear Analysis & Performance Based Design
BEAM/COLUMN FIBER MODEL
The cross section is represented by a number of uni‐axial fibers.The M‐ψ relationship follows from the fiber properties, areas and locations. Stress‐strain relationships reflect the effects of confinement
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Nonlinear Analysis & Performance Based Design
Steelfibers
σ
σ
ε
εConcrete
fibers
WALL FIBER MODEL
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Nonlinear Analysis & Performance Based Design
ALTERNATIVE MEASURE - STRAIN
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Nonlinear Analysis & Performance Based Design
∆ƒ
ƒ
∆ u u
1 2iteration
NEWTON – RAPHSONITERATION
∆ƒ
ƒ
∆ u u
1 2
iteration
CONSTANT STIFFNESSITERATION
3 4 56
NONLINEAR SOLUTION SCHEMES
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Nonlinear Analysis & Performance Based Design
Y
+Y
-Y
0 Radius, R
θ
CIRCULAR FREQUENCY
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Nonlinear Analysis & Performance Based Design
u.
t
ut1.
..
Slope = ut1..
t1
u
t1 t
Slope = ut1.
u
ut1..
t1 t
THE D, V & A RELATIONSHIP
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Nonlinear Analysis & Performance Based Design
UNDAMPED FREE VIBRATION
)cos(0 tuut ω=
0=+ ukum &&
mkwhere =ω
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RESPONSE MAXIMA
ut )cos(0 tu ω=
)cos(02 tu ωω−=ut&&
)sin(0 tu ωω−=ut&
max2uω−=maxu&&
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Nonlinear Analysis & Performance Based Design
BASIC DYNAMICS WITH DAMPING
guuuu &&&&& −=ω+ωξ+ 22guMKuuCuM
KuuCtuM
&&&&&
&&&
−=++
=++ 0
gu&&
M
K
C
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Nonlinear Analysis & Performance Based Design
ug..
2ug2..
ug1..
1
t1 t2
Time t
&&A Bt ug= + = −&& &u u u+ +2 2ξω ω
RESPONSE FROM GROUND MOTION
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Nonlinear Analysis & Performance Based Design
{ [& ] cos
[ (& )] sin }
e u B t
A u u B t B
tt d
dt t d
&ut = −
+ − − + +
−ξω
ωω
ωω ξω
ωω
ω
1 2
21 1 2 2
1
e A B t
u u A B t
A B Bt
tt d
dt t d
ut = − +
+ + − +−
+ − +
−ξω
ω
ξ
ωω
ωξω
ξω
ξ
ωω
ω
ξ
ω ω
{ [u ] cos
[& ( )] sin }
[ ]
1 2 3
1 1
2
2
2 3 2
2
1 2 1
2
DAMPED RESPONSE
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Nonlinear Analysis & Performance Based Design
SDOF DAMPED RESPONSE
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Nonlinear Analysis & Performance Based Design
RESPONSE SPECTRUM GENERATION
-0.40
-0.20
0.00
0.20
0.40
0.00 1.00 2.00 3.00 4.00 5.00 6.00TIME, SECONDS
GR
OU
ND
AC
C, g
Earthquake Record
Displacement Response Spectrum
5% damping
-4.00-2.000.002.004.00
0.00 1.00 2.00 3.00 4.00 5.00 6.00
DIS
PL,
in.
-8.00-4.000.004.008.00
0.00 1.00 2.00 3.00 4.00 5.00 6.00
DIS
PL,
in.
0
2
4
6
8
10
12
14
16
0 2 4 6 8 10PERIOD, Seconds
DIS
PLA
CEM
ENT,
inch
es
T= 0.6 sec
T= 2.0 sec
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Nonlinear Analysis & Performance Based Design
0
4
8
12
16
0 2 4 6 8 10
PERIOD, sec
DIS
PLA
CE
ME
NT,
in.
0
10
20
30
40
0 2 4 6 8 10
PERIOD, sec
VE
LOC
ITY,
in/s
ec
0.00
0.20
0.40
0.60
0.80
1.00
0 2 4 6 8 10
PERIOD, sec
AC
CE
LER
ATIO
N, g
dV SPS ω=va PSPS ω=
SPECTRAL PARAMETERS
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Nonlinear Analysis & Performance Based Design
THE ADRS SPECTRUM
ADRS Curve
Spectral Displacement, Sd
Spectral Acceleration, Sa
Period, T
Spectral Acceleration, Sa RS Curve
0.5 Second
s
1.0 Second
s
2.0 Second
s
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Nonlinear Analysis & Performance Based Design
THE ADRS SPECTRUM
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Nonlinear Analysis & Performance Based Design
ASCE 7 RESPONSE SPECTRUM
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Nonlinear Analysis & Performance Based Design
PUSHOVER
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Nonlinear Analysis & Performance Based Design
THE LINEAR PUSHOVER
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Nonlinear Analysis & Performance Based Design
EQUIVALENT LINEARIZATION
How far to push? The Target Point!
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Nonlinear Analysis & Performance Based Design
DISPLACEMENT MODIFICATION
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Nonlinear Analysis & Performance Based Design
Calculating the Target Displacement
DISPLACEMENT MODIFICATION
C0 Relates spectral to roof displacementC1 Modifier for inelastic displacementC2 Modifier for hysteresis loop shape
δ = C0C1C2SaTe2 / (4π2)
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Nonlinear Analysis & Performance Based Design
LOAD CONTROL AND DISPLACEMENT CONTROL
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Nonlinear Analysis & Performance Based Design
P-DELTA ANALYSIS
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Nonlinear Analysis & Performance Based Design
P-DELTA DEGRADES STRENGTH
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Nonlinear Analysis & Performance Based Design
STRUCTURESTRENGTH
The "over-ductility" is reduced,and is more uncertain.
P- effects may reduce the drift at which the"worst" component reaches its ductile limit.
Δ
P- effects will reduce the drift atwhich the structure loses strength.
Δ
DRIFT
P-DELTA EFFECTS ON F-D CURVES
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Nonlinear Analysis & Performance Based Design
THE FAST NONLINEAR ANALYSIS METHOD (FNA)
NON LINEAR FRAME AND SHEAR WALL HINGESBASE ISOLATORS (RUBBER & FRICTION)
STRUCTURAL DAMPERSSTRUCTURAL UPLIFT
STRUCTURAL POUNDINGBUCKLING RESTRAINED BRACES
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RITZ VECTORS
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FNA KEY POINT
The Ritz modes generated by the nonlinear deformation loads are used to modify the basic structural modes whenever the nonlinear elements go nonlinear.
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Nonlinear Analysis & Performance Based Design
CREATING HISTORIES TO MATCH A SPECTRUM
FREQUENCY CONTENTS OF EARTHQUAKES
FOURIER TRANSFORMS
ARTIFICIAL EARTHQUAKES
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ARTIFICIAL EARTHQUAKES
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Nonlinear Analysis & Performance Based Design71
MESH REFINEMENT
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Nonlinear Analysis & Performance Based Design72
This is for a coupling beam. A slender pier is similar.
APPROXIMATING BENDING BEHAVIOR
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Nonlinear Analysis & Performance Based Design73
ACCURACY OF MESH REFINEMENT
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Nonlinear Analysis & Performance Based Design74
PIER / SPANDREL MODELS
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Nonlinear Analysis & Performance Based Design75
STRAIN & ROTATION MEASURES
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Nonlinear Analysis & Performance Based Design76
Compare calculated strains and rotations for the 3 cases.
STRAIN CONCENTRATION STUDY
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Nonlinear Analysis & Performance Based Design77
The strain over the story height is insensitive to the number of elements. Also, the rotation over the story height is insensitive to the number of elements.
Therefore these are good choices for D/C measures.
No. of elems
Roof drift
Strain in bottom element
Strain over story height
Rotation over story height
1 2.32% 2.39% 2.39% 1.99%
2 2.32% 3.66% 2.36% 1.97%
3 2.32% 4.17% 2.35% 1.96%
STRAIN CONCENTRATION STUDY
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Nonlinear Analysis & Performance Based Design
DISCONTINUOUS SHEAR WALLS
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Nonlinear Analysis & Performance Based Design79
PIER AND SPANDREL FIBER MODELS
Vertical and horizontal fiber models
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Nonlinear Analysis & Performance Based Design 80
RAYLEIGH DAMPING
• The αM dampers connect the masses to the ground. They exert external damping forces. Units of α are 1/T.
• The βK dampers act in parallel with the elements. They exert internal damping forces. Units of β are T.
• The damping matrix is C = αM + βK.
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Nonlinear Analysis & Performance Based Design 81
• For linear analysis, the coefficients α and β can be chosen to give essentially constant damping over a range of mode periods, as shown.
• A possible method is as follows :Choose TB = 0.9 times the first mode period.Choose TA = 0.2 times the first mode period.Calculate α and β to give 5% damping at these two values.
• The damping ratio is essentially constant in the first few modes.• The damping ratio is higher for the higher modes.
RAYLEIGH DAMPING
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Nonlinear Analysis & Performance Based Design
KuuC &tuM && =++ 0
Kuu& ++ = 0(α M + β K )
u&& + CM
u&M
u+ K = 02uu& =ω+ωξ+ 2 0 ωξ2 M = C
ω2ξ = α + βω2
ω2ξ = CM 2
= CM
MK =
2C
MK 2 MKα M + β K=
tuM &&
u&& ;
2 MK
RAYLEIGH DAMPING
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Nonlinear Analysis & Performance Based Design
Higher Modes (high ω) = βLower Modes (low ω) = α
To get ζ from α & β for any ω MK=
To get α & β from two values of ζ1& ζ
2
; Τ 2πω=
ζ1
= α2ω
1
+ β ω12
ζ2
= α2ω
2
+ β ω22
Solve for α & β
RAYLEIGH DAMPING
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Nonlinear Analysis & Performance Based Design
DAMPING COEFFICIENT FROM HYSTERESIS
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Nonlinear Analysis & Performance Based Design
DAMPING COEFFICIENT FROM HYSTERESIS
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Nonlinear Analysis & Performance Based Design
A BIG THANK YOU!!!
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