PI’s: J. W. Wallace, E. Taciroglu , J.P. Stewart Staff: D.H. Whang, Y. Lei, S. Keown, S. Kang
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Transcript of PI’s: J. W. Wallace, E. Taciroglu , J.P. Stewart Staff: D.H. Whang, Y. Lei, S. Keown, S. Kang
Forced Vibration Testing & Forced Vibration Testing & Analytical Modeling of aAnalytical Modeling of a
Four-story Reinforced Concrete Four-story Reinforced Concrete Frame Building Frame Building
Forced Vibration Testing & Forced Vibration Testing & Analytical Modeling of aAnalytical Modeling of a
Four-story Reinforced Concrete Four-story Reinforced Concrete Frame Building Frame Building
PI’s: J. W. Wallace, E. Taciroglu, J.P. Stewart
Staff: D.H. Whang, Y. Lei, S. Keown, S. Kang
Students: E. Yu, D. Skolnik, W. Elmer
Forced Vibration TestsForced Vibration Tests
Modal IdentificationModal Identification
Finite Element Model Updating Finite Element Model Updating
Conclusions & Outlook Conclusions & Outlook
OUTLINE
Forced Vibration Tests
Goals of forced vibration tests/studiesGoals of forced vibration tests/studies Extract dynamic properties of the structure Extract dynamic properties of the structure
experimentallyexperimentally Validate the assumptions of analyticalValidate the assumptions of analytical model model
used to predict structural responseused to predict structural response Evaluate predictive capability of analyticalEvaluate predictive capability of analytical
modelsmodels
Until now, forced vibration tests have been Until now, forced vibration tests have been performed at performed at low-level response amplitudeslow-level response amplitudes
Two kinds of shakers were used as vibration Two kinds of shakers were used as vibration sourcessources Eccentric mass shaker Eccentric mass shaker Linear shaker Linear shaker
BACKGROUND
Eccentric Mass ShakerEccentric Mass Shaker Generate harmonic forces through rotation of Generate harmonic forces through rotation of
massmass Steady state response -> frequency-response Steady state response -> frequency-response
curvecurve Generally, larger maximum load capacityGenerally, larger maximum load capacity Laborious tests; one frequency at a timeLaborious tests; one frequency at a time
Linear ShakerLinear Shaker Arbitrary forcing function (Broadband Arbitrary forcing function (Broadband
excitation) excitation) Transient response : reduce test time / more Transient response : reduce test time / more
computationcomputation Effective in System IdentificationEffective in System Identification Simulation of earthquake vibrationSimulation of earthquake vibration
BACKGROUND
Produce a high-quality dataset Produce a high-quality dataset
- Low noise - Low noise
155 dB accelerometer, 24-bit AD 155 dB accelerometer, 24-bit AD converterconverter
- High spatial density - High spatial density
Acceleration + Story Displacement + Acceleration + Story Displacement + StrainStrain
- Low / high amplitude excitation- Low / high amplitude excitation
~max 200 kip force~max 200 kip force
Test Building : 4-story RC frame buildingTest Building : 4-story RC frame building
• Damage surveyDamage survey
• nees@UCLA equipmentnees@UCLA equipment
• Instrumentation schemeInstrumentation scheme
• Test procedure Test procedure
OBJECTIVE &OVERVIEW
““Four Seasons Building”Four Seasons Building” 4-Story RC Building with penthouse 4-Story RC Building with penthouse Constructed in 1977Constructed in 1977 Damaged by the 1994 Northridge earthquakeDamaged by the 1994 Northridge earthquake Yellow Tagged (unoccupied, will be demolished)Yellow Tagged (unoccupied, will be demolished)
Western Exterior of the BuildingWestern Exterior of the Building
THE BUILDING
Located near the intersection of 101 & 405 Located near the intersection of 101 & 405 Freeway, in Sherman Oaks, California (16 km Freeway, in Sherman Oaks, California (16 km from UCLA)from UCLA)
UCLAUCLA
LOCATION
Lateral Load: Special Moment Frame Lateral Load: Special Moment Frame (Beams+Columns) around perimeter(Beams+Columns) around perimeter
Gravity Load: Post-tensioned flab slab with drop Gravity Load: Post-tensioned flab slab with drop panels + Interior columnspanels + Interior columns
Foundation: Belled Caissons + Grade beamsFoundation: Belled Caissons + Grade beams No shear wallsNo shear walls
Typical Floor PlanTypical Floor Plan
N
1 2 3 4 5 6
B
D
C
A
7
(5@30'-6")
3@9.
3 m
(3@
30'-
6")
9.6 m
(31'-6")
1 2 3 4 5 6 7
2F EL 11.25' (3.43 m)
3F EL 22.75' (6.93 m)
GF : EL 0
4F EL 34.25' (10.44 m)
RF EL 47.75' (14.55 m)
PH. EL 59.58' (18.16 m)
3' (
0.9
m)
N
Section along Lone BSection along Lone B
STRUCTURAL SYSTEM
Beam : 24”x30” (Typical), 24”x36” (2nd Floor) Column : 24”x24”
Slab : 8-1/2” with 7-1/2” drop panel (typical) ; Lightweight Concrete
(3000 psi)
Interior ColumnsInterior Columns
Slab-Column connectionSlab-Column connection
Exterior ColumnsExterior Columns
Normal weight concrete (4000 psi)
STRUCTURAL MEMBERS
• Damage report (Sabol, 1994)Damage report (Sabol, 1994)
• Previous analytical studies Previous analytical studies Dovitch and Wight, 1994 Dovitch and Wight, 1994 Ascheim and Moehle, 1996 Ascheim and Moehle, 1996 Hueste and Wight, 1998 Hueste and Wight, 1998
• Analytical results were not able to Analytical results were not able to identify the amount of damage observed identify the amount of damage observed in the buildingin the building
• Effects of torsion / vertical response were Effects of torsion / vertical response were significant, orsignificant, or
• Ground motions were more severeGround motions were more severe
PREVIOUS STUDIES
Interior frameInterior frame
• Punching shear failure at slab-column Punching shear failure at slab-column connections around the perimeter of drop connections around the perimeter of drop panelpanel
Column B6 (3Column B6 (3rdrd Floor) Floor) Column B2 (2Column B2 (2ndnd Floor) Floor)
Slab dropped 0.5 ~ 0.75 in. downwardsSlab dropped 0.5 ~ 0.75 in. downwards
OBSERVED DAMAGE
Perimeter Frame Perimeter Frame
• Beam-Column joint crack with concrete Beam-Column joint crack with concrete spallingspalling
• Spalling of cover concrete at beam endSpalling of cover concrete at beam end
• Flexural cracksFlexural cracks
Spalling at beam endSpalling at beam end(Column A7 at 3F level)(Column A7 at 3F level)
Diagonal joint crackDiagonal joint crack(column A4 at 3F level)(column A4 at 3F level)
Flexural cracksFlexural cracks(column B2 at 4(column B2 at 4thth story) story)
OBSERVED DAMAGE
Non-structural MembersNon-structural Members
• Separated from adjacent structural Separated from adjacent structural membersmembers
• No structural contribution during the test No structural contribution during the test was expected, except possibly at the was expected, except possibly at the penthouse levelpenthouse level
Masonry wall at ground floorMasonry wall at ground floorPartition wall at 2Partition wall at 2ndnd story story Penthouse drywallPenthouse drywall
OBSERVED DAMAGE
(B) Slight
(T) N.A. (T) N.A.(T) N.A.(T) N.A.(T) N.A.
(T) N.A. (T) N.A.(T) N.A.(T) N.A.
1 2 3 41 2 3 4 5 6
B
D
C
A
7
(T) Slight
(T) Slight
(B) Slight
(B) Slight (B) Slight
(B) Moderate (B) Slight
(B) Slight (B) Moderate
(T) Slight (T) N.A. (T) N.A.
(T) N.A.
(T) Severe
(B) Moderate (B) Moderate
(T) Slight (T) N.E.
(B) Moderate (B) Severe
(B) Severe (B) Moderate
(B) Moderate (B) Moderate (B) Moderate
(T) N.A. (T) Moderate (T) Severe
N
T : Top faceB : Bottom faceN.A. : Not Accessible(blank) : No Damage
(T) Severe (T) Severe
(T) Severe (T) N. A.
(B) Slight (B) Slight
(T) N. A. (T) N. A.
(B) Slight (B) Slight
(B) Severe (B) Slight
(B) Severe (B) Moderate (B) N. A.
(B) Slight (T) N. A.(B) Slight
Severe : Big chunk crushed out, Floor level dropped or Reinforcements exposedModerate : Large and developed cracks, small chunk crushed out, or aggregate exposedSlight : long crack around drop panel
RoofRoof 44thth Floor Floor
22ndnd Floor Floor33rdrd Floor Floor
INTERIOR DAMAGE
1 2 3 4 5 6 7
West Perimeter Frame (Line A)West Perimeter Frame (Line A)
East Perimeter Frame (Line D)East Perimeter Frame (Line D) North Perimeter Frame (Line 7)North Perimeter Frame (Line 7)
A B C D
South Perimeter Frame (Line 1 & 2)South Perimeter Frame (Line 1 & 2)
NN EE
NN
Diagonal joint crack
Diagonal joint crack with concrete spalling
Severe concrete crushing (at beam end) /Shear crack
•Building experienced more deformation in N-S direction than E-W direction
EXTERIOR DAMAGE
Two 100-kip capacity eccentric mass shakersTwo 100-kip capacity eccentric mass shakers
15-kip capacity linear shaker15-kip capacity linear shaker
Force-Balanced Accelerometers (FBA)Force-Balanced Accelerometers (FBA)
LVDTs (DC-DC Type)LVDTs (DC-DC Type)
Concrete strain gaugesConcrete strain gauges
24-bit AD converters 24-bit AD converters
Wireless data-logging (Antelope) & Networking Wireless data-logging (Antelope) & Networking system system
National Instrument signal conditioning units National Instrument signal conditioning units (LabView)(LabView)
Mobile Command Center (MCC)Mobile Command Center (MCC)
Power generatorsPower generators
TESTING EQUIPMENT – nees@UCLA
Two 100-kip capacity shakersTwo 100-kip capacity shakers
Generate harmonic forces through rotation of Generate harmonic forces through rotation of massmass
nees@UCLA Eccentric Mass Shaker, MK-15nees@UCLA Eccentric Mass Shaker, MK-15
eccentricitymass
of a basket mass eccentricity e
m
mass
2( ) 2 sin( )eP t m t
ECCENTRIC MASS SHAKER
69 Steel bricks69 Steel bricks
Empty basket Half-full basket
Mass-eccentricity(each basket)
16786 lb-in 56620 lb-in
Limitingfrequency
5.40 Hz 2.95 Hz
Pulse MarkerPulse Marker
• Basket configurations for this studyBasket configurations for this study
• Adjustable basketAdjustable basket
Hydrostone LevelingHydrostone Leveling
ECCENTRIC MASS SHAKER
Produce force through linear motion of a moving massProduce force through linear motion of a moving mass
Moving mass (5 kip/g) + Dynamic Actuator (15 kip, Moving mass (5 kip/g) + Dynamic Actuator (15 kip, ±±15”) + 15”) + Hydraulic system (90 gpm servo-valve, 30 gpm pump, 4 Hydraulic system (90 gpm servo-valve, 30 gpm pump, 4 accumulators) + Controlleraccumulators) + Controller
Digital control : PD, LQG, adaptive ; displacement, accelerationDigital control : PD, LQG, adaptive ; displacement, acceleration Broadband excitation ; white-noise, sine-sweep, earthquake-Broadband excitation ; white-noise, sine-sweep, earthquake-
typetype
Linear ShakerLinear Shaker
Example sine-sweep forcing Example sine-sweep forcing functionfunction
LINEAR SHAKER
Linear Shaker
Eccentric Mass Shaker(South)
N
Eccentric Mass Shaker (North)Reference
Point
37.2 m (122 ft)
9.3 m (30.5 ft)
45°
SHAKER LOCATIONS
Force-balance Force-balance AccelerometerAccelerometer
DCDT (DC-DC type LVDT)DCDT (DC-DC type LVDT)
High performance 24-bit Datalogger High performance 24-bit Datalogger (Kinemetrics, Q330)(Kinemetrics, Q330)
National Instrument National Instrument Signal Conditioning Signal Conditioning Module used for Module used for concrete strain concrete strain gaugesgauges(32 ch X 3 units)(32 ch X 3 units)
Strain GaugeStrain Gauge
Synchronization using GPS timeSynchronization using GPS time
SENSORS & DATALOGGERS
Q330WAP
Yagi Antenna
WAPAntelope server
Mobile Command Center
Wireless Communication
WiredSensors
Wireless
DC : Data Concentration Point
WAP : Wireless Access Point
DC
Data ConcentrationPoint (DC)
Wireless Access Point (WAP)
WIRELESS DATA ACQUISITION
Power for the shakersPower for the shakers
Battery box/portable powerBattery box/portable powerPower for DAQPower for DAQ
POWER GENERATORS
• AccelerationAccelerationForce-balance type Force-balance type AccelerometerAccelerometer
• StrainStrainStrain gauges placed Strain gauges placed at top and bottom of at top and bottom of floor slabs and 3 faces floor slabs and 3 faces of columnsof columns
• InterstoryInterstory DisplacementDisplacement
DCDTs measure DCDTs measure displacement from displacement from bottom of one column bottom of one column to top of the to top of the consecutive columnconsecutive column
197 Total channels197 Total channels• 16 tri-axial + 27 uniaxial accelerometers16 tri-axial + 27 uniaxial accelerometers• 26 DCDT’s26 DCDT’s• 96 Strain gauges96 Strain gauges
INSTRUMENTATION
Vertical AccelerometerNS Accelerometer EW Accelerometer Column with strain gauge
LVDT
3u1
3v1
3u2
3v2
3u3
3v3
3u4
3v4
1 2 3 4 5 6 71u1
1v1
1w5
1w1
1w4
1v4
1w3
1v3
1w8
1w7
1w6
1u2
1v2
1w2
LVDT-NS1
LVDT-NS2LVDT-EW
Rv1
Ru1Ru4
Rv4
Rv3
Ru3
Rv2
Ru2
Pu1
N LVDT-NS2
LVDT-NS1
LVDT-EWPv1 Pv2
N
521 43 76
Rw1 Rw4
Rw3Rw2
3w1 3w4
3w33w2
Roof / Roof / Penthouse Penthouse
33rdrd floor level floor level
Ground floorGround floor Elevation (A-A)Elevation (A-A)
A A
Roof Roof LevelLevel
3F Level3F Level
GroundGround
INSTRUMENTATION PLAN
8"
8"
8"
4" 12"
24"
12"
Curtain Wall
Column Strain GaugesColumn Strain Gauges
• 3 faces for curvature 3 faces for curvature calculation in both calculation in both directionsdirections
• Along A2 & B2 Along A2 & B2 column from ground column from ground floor to roof floor floor to roof floor
• Below and above the Below and above the floor slab levelfloor slab level
S1S2S3
S4
S5
S6
S8 S10
S7 S90.25L
L=30'-6"
60"60"
42"
1 2 3
B
A
0.25L
0.25L
0.25L Floor Slab Strain Floor Slab Strain Gauges Gauges
• Top and bottom Top and bottom faces of 3faces of 3rdrd & 4 & 4thth floor floor slabslab
INSTRUMENTATION PLAN
Date Test
6/22/04 E-W translational excitation with empty basket – Run1
7/2/04 Ambient vibration measurement – Run1
7/13/04 E-W translational excitation with empty basket – Run2
Torsional excitation with empty basket – Run1
7/14/04 E-W translational excitation with half-full basket – Run1
Torsional excitation with half-full basket – Run1
7/19/04 E-W translational excitation with half-full basket – Run2
Torsional excitation with half-full basket – Run2
Ambient vibration measurement – Run2
Linear shaker sinesweep / whitenoise – Run1
7/22/04 N-S translational excitation with half-full basket – Run1
7/28/04 N-S translational excitation with empty basket – Run1
Linear shaker seismic simulation test
8/2/04 N-S translational excitation with empty basket – Run2
Linear shaker sinesweep / whitenoise – Run2
8/3/04 Ambient vibration measurement – Run3
E-W translational excitation with empty basket – Run3
TESTING SEQUENCE
Eccentric Mass Shaker Test
VIDEO CLIPS
Modal Identification
TESTING & DATA ACQUISITION
vc
Nu2 u3
v3
u4
v4
v2
u1
v1
ucrc
x
y
21 3 4 5 6 7
B
A
D
C
• Identification and updating performed with data from the linear shaker white noise excitation
• Data recorded with four tri-axial accelerometers used derive three story responses
SYSTEM IDENTIFICATION
N4SID (Numerical Algorithm for Subspace State Space System Identification)
• Discrete time domain method uses measured data directly
• Makes projections of certain subspaces generated from the input/output observations to estimate state sequence using linear algebra tools such as QRD and SVD.
• Identifies system matrices from estimated states based on a linear least squares solution
• Can be applied to systems subjected to known or unknown excitation
• Well implemented in MATLAB’s System Identification Toolbox
1k k k
k k k
X X u
y X u
A B
C D
2
Re 2
sign Re
i i
i i i
i i i
f
f
C C
u: input force applied with linear shaker
y: output measured floor responses
SYSTEM IDENTIFICATION
Stability Tolerances
• f ≤ 1.5%
• ≤ 5%
• MAC ≥ 98%
Stability Plot
EW NS Tor
2
( , )T
A B
T TA A B B
MAC A B
SYSTEM IDENTIFICATION
EW NS Tor
Frequencies and Damping Ratios
For Amb
Mode Forced
f (Hz) (%)Ambient
f (Hz) (%)Ambient /
Forced
1 EW 0.88 5.6 1.09 3.4 1.24 0.61
2 NS 0.94 6.9 1.25 3.1 1.33 0.45
3 Tor 1.26 6.0 1.55 2.1 1.23 0.35
4 EW 2.73 5.6 3.23 3.0 1.18 0.54
5 NS 2.94 7.7 3.63 3.1 1.23 0.40
6 Tor 3.44 6.1 4.16 2.1 1.21 0.34
7 Mix 4.54 13.5 - - - -
Ks1 Ks2
Ambient vibration > linear shaker test > EMS testAmbient vibration > linear shaker test > EMS test
=> Stiffness degradation of structural member => Stiffness degradation of structural member
(contribution of nonstructural elements is negligible ; damage (contribution of nonstructural elements is negligible ; damage survey)survey)
3 ~ 4% frequency drop in ambient vibration after EMS test3 ~ 4% frequency drop in ambient vibration after EMS test
due to the high amplitude vibrations during Half-full basket due to the high amplitude vibrations during Half-full basket testingtesting
=> degradation of (cladding / Foundation & soil / structural => degradation of (cladding / Foundation & soil / structural member) ??member) ??
Larger frequency drop in Larger frequency drop in N-S direction => effect of N-S direction => effect of damagedamage
DISCUSSION
Finite Element Model Updating
FINITE ELEMENT MODELING
Modeling Assumptions
• Lumped Mass
• Rigid Diaphragms
• Classical Damping
From Core Tests
• n =140pcf, l = 115pcf
• Ecn = 4028ksi, Ecl = 2517ksi
Effective Stiffness (FEMA 356 , FEMA 356 , Paulay&Priestley, “Effective Paulay&Priestley, “Effective Beam Method”Beam Method”)
• Columns: 0.5EcnIg
• Beams: 0.42EcnIg
• Slabs: 0.4EclIg
N
FINITE ELEMENT MODELING
Mode FE SID FE / SID
1 EW 0.92 0.88 1.05
2 NS 1.12 0.94 1.19
3 Tor 1.35 1.26 1.07
4 EW 2.6 2.73 0.95
5 NS 2.94 2.94 1.00
6 Tor 3.53 3.44 1.03
Natural Frequencies (Hz)
EW NS Tor
FINITE ELEMENT MODELING
FRF - NS direction
2( )
H( ) x( ) / ( )
i
f
B M C K
MODEL UPDATING
x( ) x( ) x( ) ( )t t t L f t M C K
2 x( ) ( )i L f M C K
( )H( ) L B
2 K M
Sensitivity-Based Updating Procedure using Frequency Response Function (FRF) and Modal Frequencies
MODEL UPDATING1 2p [ , , , ]T
kp p p
0
0
0
p p
0
p p
(p, )H( ) L (p , )H( )
(p)Ω (p )
F
M
pp
pp
BB
Error residuals
dp
dF F F
M M M
C
C
ε L (p, )H( )
ε Ω (p)
F
M
B
Parameter Vector
Non-linear functions of p
Linearize with a first-order Taylor series expansion
MODEL UPDATING
0p p p plb ub
2
pMin p d W C W
lim1 cor(C ,C ) , if cor(C ,C ) i j i j i jp p c
such that
and
Objective Function
MODEL UPDATING
Parameter(s) associated with Bounds Initial Values
Mass of 2F
85 % - 115 %
65.0 (kips sec2/ft)
Mass of 3F & 4F 64.7 (kips sec2/ft)
Mass of RF 62.1 (kips sec2/ft)
Mass of PH 50 % - 150 % 7.6 (kips sec2/ft)
Radius of gyration of 2F & 3F
75 % - 135 %
64.2 (ft)
Radius of gyration of 4F 64.0 (ft)
Radius of gyration of RF 57.5 (ft)
Radius of gyration of PH 26.7 (ft)
Column Stiffness at 2F - RF
35 % - 150 %
0.5Ecn Ig
Column Stiffness at PH0.75Ecn Ig, (NS)
2.5Ecn Ig (EW)
Slab Stiffness at 2F - RF 0.4Ecl Ig,
Slab Stiffness at PH0.6Ecl Ig (NS)
2.0Ecl Ig (EW)
Beam Stiffness at 2F - RF 0.42Ecn Ig
Damping ratios 2.5 % - 20 % 5 %
Dimensionless Parameters
• 10 Mass
• 52 Stiffness
• 9 Damping
MODEL UPDATINGRatios of Initial Mass 2F 3F 4F RF PH
Translational Mass 94% 97% 104% 105% 97%
Radius of gyration 102% 104% 97% 102% 104%
Stiffness Factors 2F 3F 4F RF PH
NS Interior, North & South Frame Columns 0.40 0.48 0.32 0.45 0.73
NS of East Frame Columns 0.36 0.41 0.22 0.49 -
NS of West Frame Columns 0.45 0.39 0.26 0.46 -
EW of Interior, East & West Frame Columns 0.46 0.62 0.49 0.42 2.20
EW of North Frame Columns 0.49 0.52 0.59 0.49 -
EW of South Frame Columns 0.52 0.56 0.34 0.46 -
East Frame Girders 0.45 0.23 0.38 0.41 -
West Frame Girders 0.42 0.17 0.39 0.40 -
South Frame Girders 0.49 0.32 0.36 0.39 -
North Frame Girders 0.43 0.57 0.43 0.42 -
Slab NS 0.43 0.19 0.36 0.40 0.58
Slab EW 0.44 0.36 0.35 0.37 1.86
Damping Ratios
7th 8th 9th 10th 11th 12th 13th 14th 15th
9.6% 15.9% 7.3% 15.5% 2.5% 8.8% 8.8% 5.4% 13.5%
MODEL UPDATINGRatios of Initial Mass 2F 3F 4F RF PH
Translational Mass 94% 97% 104% 105% 97%
Radius of gyration 102% 104% 97% 102% 104%
Stiffness Factors 2F 3F 4F RF PH
NS Interior, North & South Frame Columns 0.40 0.48 0.32 0.45 0.73
NS of East Frame Columns 0.36 0.41 0.22 0.49 -
NS of West Frame Columns 0.45 0.39 0.26 0.46 -
EW of Interior, East & West Frame Columns 0.46 0.62 0.49 0.42 2.20
EW of North Frame Columns 0.49 0.52 0.59 0.49 -
EW of South Frame Columns 0.52 0.56 0.34 0.46 -
East Frame Girders 0.45 0.23 0.38 0.41 -
West Frame Girders 0.42 0.17 0.39 0.40 -
South Frame Girders 0.49 0.32 0.36 0.39 -
North Frame Girders 0.43 0.57 0.43 0.42 -
Slab NS 0.43 0.19 0.36 0.40 0.58
Slab EW 0.44 0.36 0.35 0.37 1.86
Damping Ratios
7th 8th 9th 10th 11th 12th 13th 14th 15th
9.6% 15.9% 7.3% 15.5% 2.5% 8.8% 8.8% 5.4% 13.5%
MODEL UPDATING
Mode Initial Updated SID
1 EW 0.92 0.90 0.88
2 NS 1.12 0.97 0.94
3 Tor 1.35 1.25 1.26
4 EW 2.6 2.72 2.73
5 NS 2.94 2.93 2.94
6 Tor 3.53 3.44 3.44
Natural Frequencies (Hz)
EW NS Tor
MODEL UPDATING
FRF - NS direction
MODEL UPDATING
2nd Floor
3rd Floor
4th Floor
Roof
Penthouse
Predicted and Measured NS response to 0.5 - 5 Hz linear shaker sine sweep
Conclusions & Outlook
CONCLUSIONS
• Identified modal properties of the first seven modes using N4SID
• Frequencies identified from ambient vibrations represent a stiffer structure than that identified from white noise excitation
• FE model is updated using a modal- FRF-sensitivity based method
• Frequencies, mode shapes, and FRF of the updated model compare well with those identified
• Predicted acceleration response of the updated model compares quite well with the measured data