Derek A. Skolnik Robert L. Nigbor and John W. Wallace Specifications For Building Instrumentation.

Derek A. Skolnik

Robert L. Nigbor and John W. Wallace

Specifications For Building Instrumentation

22

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

33

Introduction

DAS Specifications

DAQ Simulation

Sensitivity Studies

Conclusions

OUTLINE

(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



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

99

Introduction

DAS Specifications

DAQ Simulation

Sensitivity Studies

Conclusions

OUTLINE

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

1313

Introduction

DAS Specifications

DAQ Simulation

Sensitivity Studies

Conclusions

OUTLINE

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

1919

Introduction

DAS Specifications

DAQ Simulation

Sensitivity Analysis

Conclusions

OUTLINE

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


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


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


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


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


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


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


10ms

1.0ms

0.1ms

2828

Introduction

DAS Specifications

DAQ Simulation

Sensitivity Analysis

Conclusions

OUTLINE

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

3030

Support provided by NSF CENS and nees@UCLA

Future Publications

BSSA: A quantitative basis for strong-motion instrumentation (12/09)

EQS: A quantitative basis for building instrumentation

Derek A. Skolnik Robert L. Nigbor and John W. Wallace Specifications For Building Instrumentation.

Documents