Download - Derek A. Skolnik Robert L. Nigbor and John W. Wallace Specifications For Building Instrumentation
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OBJECTIVE
OBJECTIVEDetermine minimum requirements for specifications of sample rate, resolution, and time synchronization
STRATEGYQuantify the sensitivities of ground motion intensity measures and engineering response quantities to DAQ
APPROACH1. Understand how engineers use strong-motion data2. Simulate the noisy DAQ process3. Perform sensitivity analyses
(Goel & Chopra 1997)
Engineering use of Strong-Motion Response Data
Traditional – validate modeling assumptions and develop code provisions: fundamental period approximation formulas
Modern – tall building issues, structural health monitoring (SHM)
INTRODUCTION
44
55
Alternative designs citing Chap 16 of ASCE 7
NDA of 3D FEM w/ suite of motions & peer review
Exposed fundamental issues: ground motion selection, modeling guidelines, acceptance criteria
LA-TBSDC publish document for LA-DBS (2008)
INTRODUCTION
Stories Channels
10 – 20 15
20 – 30 21
30 – 50 24
> 50 30
Since 1965 LA requires accelerographs at base, mid-level, and roof
One Rincon Hill - MKA
Tall Building Construction
UCLA, LA-DBS & CSMIP update requirements
Deployment approval by peer review panel
66
INTRODUCTION
Arabdrill 19, UAE
Structural Health Monitoring (SHM)
Assess health of instrumented structures from measurements
Detect damage before reaching critical state and allow for rapid post-event assessment
– Potentially replacing expensive visual inspection which is impractical for wide spread damage in urban areas
Steel Joint Damage 1994 NorthridgeI-35W Bridge 2007
77
INTRODUCTION
Strong Motion Instrumentation Programs (SMIP)
CSMIP (CGS), ANSS & NSMP (USGS), K-net/KiK-net (Japan), Taiwan Seismology Center (CWB)
Provide real-time ShakeMaps and data for engineers and scientists to improve hazard mitigation
Since early 20th century with focus on ground monitoring
Uniform structural instrumentation specifications are lacking
650 ground170 buildings
92 ground51 buildings
762 ground133 buildings
Intensity Measures (IM)
PGA – Peak Ground Acceleration
PGV – Peak Ground Velocity
PSA – Peak Response Spectral Pseudo-Acceleration
MMI – Modified Mercalli Intensity
INTRODUCTION
Engineering Demand Parameters (EDP)
PFA – Peak Floor Acceleration
PID – Peak Interstory Drift
Advanced Engineering Analyses
SID – System Identification, Model Updating
SHM – Structural Health Monitoring
PGA – Peak Ground Acceleration
PGV – Peak Ground Velocity
PSA – Peak Response Spectral Pseudo-Acceleration
PFA – Peak Floor Acceleration
PID – Peak Interstory Drift
88
1010
Recommended Specification
ANSS(USGS 2005)
CSMIP(CGS 2007)
Sensor RangeADC Resolution
Sample Rate
±4g16bits
200sps
± 4g18bits
200sps
Sample Sync
Reference Time
Clock Stability
1% t
1.0ms
0.1ppm
0.2ms
0.5ms
1min/month
DAS SPECIFICATIONS
R (bits/g)
S (sps)
Tse (ms)
SMIP Specifications
Recommended specifications for civil structures (buildings)
Based on qualitative assessment and experience
Guideline for ANSS Seismic Monitoring of Engineered Civil Systems, USGS Report 2005-1039
Integrated Tri-Axial Accelerograph, CGS/DGS SYSREQ 2007-TR
1111
Data Acquisition Systems (DAS)
Sampling – sample rate (sps = 1 / t)
Quantization – resolution (LSB = Range / 2 Bits)
Time stamp for synchronization of multiple channels
Sampling
Quantization
LSBt
.......110001001010
Reference Time
Sensor
DAS SPECIFICATIONS
1212
Data Acquisition Errors
Sampling – initial sampling instant and clock jitter
Quantization – Differential Non-Linearity (DNL)
2 ,iN t
1it 2it
Jitter
jx
DNL
analogdiscretedigital
1jx
it
Sampling Instant
DAS SPECIFICATIONS
2jx
1414
Baseline Earthquake Record Set
30 EQ records downloaded from PEER, NCESMD, K-Net, KiK-Net, COSMOS
Selected to capture broad nature of earthquakes
Digitally enhanced to increase resolution: resample to 2kHz, zero-pads for filtering, band-pass filter 0.1-50Hz
0 0.5 1 1.5 20
2
4
6
8
PGA (g)
Nu
mb
er
of E
Qs
0.1 0.4 1 2 5 20 5010
-6
10-4
10-2
100
Frequency (Hz)
Fo
urie
r A
mp
litu
de
(g
)
DAQ SIMULATION
1515
DAQ Simulation
Baseline Signal
S R
ADC
• Sinusoids• Earthquake ground
motions• Structural responses
Jitter and initial sampling instant
Digital Signal
Analysis AnalysisSensitivity Analysis
• IM: PGA, PGV, PSA
• EDP: PFA, PID
• SNR and Peak value
DAQ SIMULATION
10-9
10-8
10-7
10-6
10-5
80
100
120
140
160
Standard Deviation of Jitter (s)
SN
R (
dB)
sin 2X t A f t
sin 2i i
i
x A f t
t i t
Sinusoidal Signal
Sampled Signal
Clock Jitter
Independent of sample rate
Can be neglected
sin 2
,
i i
i i
x A f
N t
Jittery Sampled Signal
1616
DAQ SIMULATION
100sps
-5 -2.5 0 2.5 5-30
-25
-20
-15
-10
-5
0
PG
A E
rro
r (%
)
Sampling Instance (ms)-5 -4 -3 -2 -1 0 1 20
50
100
150
200
250
300
Log PGA Percent Error
Co
un
t (N
=3
00
0)
Initial Sampling Instant
Depends on sample rate
Biased error – always negative
analogsampled
Ep
analogsampled
Ep
20Hz
40Hz
1717
DAQ SIMULATIONE
p (%
)
Error in peak value (Ep)
100sps
10Hz
30 35 40 45 50 55 600
2
4
6
8
10
Nu
mb
er
of E
Qs
SNR (dB) Sample Rate (Hz)
Re
solu
tion
(b
its/g
)
100 200 300 400 500
8
12
16
20
24
S = [50-500] sps t=1/ S
R = [6-24] bits/g res=g /2R
200sps 12b/g
1. t0 ~ U (0,t)
2. ti = t0+ i·t
3. xi = interp(X @ ti )
4. xi =round(xi / res)·res
X = EQ record
40dB 50dB3020
1818
DAQ SIMULATION
SNR
6 9 12 15 18 21 2410
-2
10-1
100
101
102
Effective Resolution (bits/g)
PG
A E
rror
(%
)
Period (s)
PS
A E
rror
(%
)
0.03 0.1 0.4 1 2 4 810
-2
10-1
100
101
102
Intensity Measures
PGA – 100sps, 6bits/g for error less than 5%
PGV – 50sps, 8bits/g for error less than 5%
PSA – 200sps, 8bits/g for error less than 5%
14 bits/g16R = 6
200sps
500sps
100sps
12108
100sps
500sps
200sps
50sps
SENSITIVITY ANALYSIS
2020
2121
1
N
i g n ni nn
a a a
1
02
0
2 2sin
2n
n n
H
n
n H
n
n xx
H
T T
m x dx
m x dx
Baseline Building Response Set
Simulate responses to baseline EQ record set by superimposed first few modal responses
Assumptions: bounded by flexural & shear idealizations, uniform mass and stiffness, n = 5%
H
RC SW
Steel EBF
Dual System
Steel MRF .
RC MRF
Flexural Bldg Shear Bldg
SENSITIVITY ANALYSIS
2222
0 10 20 30 40 50 600
1
2
3
4
5
6
7
Number of Stories
Fun
dam
enta
l Per
iod
(s)
FlexuralShear
(Goel and Chopra 1997-98, Naeim 1998)
Fundamental Period
Depends on building structure and height... sort of
Based on real data from instrumented buildings
Empirical conventions in code (ASCE 7) are lower bounds
0.68 0.11
0.46 0.03s
f
T N
T N
ASCE 7-05 S12.8.2.1
xa t nT C h
Steel MRF
SENSITIVITY ANALYSIS
2323
Simulation Digitizing Processing
Structure Type:Flexural/Shear S R
N ADCAA
Ag
AA
N: No of StoriesS: Sample RateR: Resolution
Ag : Ground AccelerationAA: Absolute AccelerationRA: Relative AccelerationRD: Relative Displacement
LEGEND
High-pass Filter
Double Integrate
Fc
SNR
RD
RA = AA – Ag
RD
SENSITIVITY ANALYSIS
Newmark Integration
-50
0
50
-10
0
10
-5
0
5
-5
0
5
0 10 20 30 40 50 60 70-5
0
5
Time(s)
Dis
plac
emen
t (in
)
No correctionSNR = -31dB
Detrend SNR = -16.3dB
Fc = 0.01HzSNR = -8.9dB
Fc = 0.1HzSNR = 20.5dB
Fc = 1.0HzSNR = 1.25dB
SENSITIVITY ANALYSIS
2424
Optimizing Frequency Cutoff
High-pass 4th order acausal digital Butterworth filter
A single floor of a 10-story bldg to one earthquake
Resolution is important which corroborates Boore’s (2003) findings of ADC quantization being a source of numerical drifts
0 0.2 0.4 0.6 0.8 1-60
-40
-20
0
20
40
60
Fc (Hz)
SN
R (
dB
)
Flexural
0 0.1 0.2 0.3 0.4 0.5-40
-20
0
20
40
60
Fc (Hz)
SN
R (
dB
)
Shear
100sps 200sps500sps
8b/g 12b/g 14b/g 18b/g
100sps 200sps 500sps
8b/g 12b/g 14b/g 18b/g
Shear: fn = [1.5, 9.3, 26] Hz Flexural: fn = [0.4, 1.2, 1.9] Hz
SENSITIVITY ANALYSIS
2525
2626
Engineering Demand Parameters
PFA – 100sps, 8b/g for error less than 5%
PID – 100sps, 14b/g for error less than 5%
8 201816141210 bits/g
Stories (s)
PID
Err
or (
%)
3 6 9 12 15 18 2010
-2
10-1
100
101
102
Stories (s)
PID
Err
or (
%)
3 10 20 30 40 50 6010
-2
10-1
100
101
102
Stories (s)
PF
A E
rror
(%)
3 6 9 12 15 18 2010
-2
10-1
100
101
102
Stories (s)
PF
A E
rror
(%)
3 10 20 30 40 50 6010
-2
10-1
100
101
102
Flexural
Shear
SENSITIVITY ANALYSIS
200sps
500sps
100sps
2727
Time Synchronization Error
Sync errors are additional to digitizing error
PID – 200sps, 16b/g and sync to 1.0ms for total error < 5%
3 6 9 12 15 18 2010
-2
10-1
100
101
102
Stories (s)
PID
Err
or (
%)
Flexural
3 10 20 30 40 50 6010
-2
10-1
100
101
102
Stories (s)
PID
Err
or (
%)
Shear
10ms
1.0ms
0.1ms
SENSITIVITY ANALYSIS
10ms
1.0ms
0.1ms
2929
SpecificationANSS
(USGS 2005)CSMIP
(CGS 2007)Recommend(Skolnik 2009)
RangeADC Resolution
Sample Rate
±4g16bits200Hz
±4g18bits200Hz
±4g20bits200Hz
Sample SyncReference Time
0.05ms1.0ms
0.2ms0.5ms
1.0ms
Potential Improvements
Other specifications – frequency response, dynamic range, cross-axis sensitivity, sensor layout
Improved simulations – non-uniform stiffness; vary damping ratios, combo flex-shear shapes, non-linear responses
Other engineering analyses – system identification
CONCLUSIONS