Monitoring Static and Dynamic Characteristic of Tall Building Using GPS Virtual Reference Station and Seismic Sensor Data

presented by

TOR, Yam KhoonAssoc. Prof.School or Civil & Environmental Engineering

Map Asia 200920 August 2009

Huang Liping (Dr) , NTU Victor Khoo Hock Soon (Dr), SLA

Kusnowidjaja Megawati (Assoc Prof), NTU Gerry Ong, GPSLands (S) Pte Ltd

Tor Yam Khoon (Assoc Prof), NTU Teo Swee Tiong, GPSLands (S) Pte Ltd

Contents

• SiRENT• GPS and Accelerometer Setup• Natural Frequency of Building• Results and Analysis

– Accelerometer– 1-Hz GPS– 10-Hz GPS

• Conclusions

Singapore Satellite Positioning Reference Network (SiReNT )

SSEK-Senoko

SNTU-NTU SLOY-Loyang

SNYP-

Nanyang Poly

SKEP-Keppel

Club

Apparent Advantages of Virtual Reference System (VRS) Network

• Significantly reduces systematic errors (ionospheric and tropospheric delay)

• Extended operating range with improved initialization and accuracy

• Increased productivity

• Less investment for the user

• Eliminates needs to establish local reference station

Source: Trimble

VRS Data Flow

Reference station data

streams back to the

server via leased lines

or LAN/WAN

Source: Trimble

VRS Data Flow

Roving receiver sends its

position back to the server

NMEANMEA

VRS position is

established

VRSVRS

Source: Trimble

VRS Data Flow

VRSVRS

NMEANMEA

Server uses VRS position

to create corrected

RTCM real-time data

RTCMRTCM

Rover surveys as in

normal RTK – but

getting VRS data as if from a nearby reference

station

Source: Trimble

GPS and Accelerometer Setup

20.629m

20.445m

29.211m

Location of GPS antennas

Location of accelerometer

X – A m

ode

Y – B mode

accelerometer

Combined sensor setup

5700

R701

R702

North

Accelerometer

X – A m

odeY – B mode

High Rise building monitoring

GPS receivers mounted on rooftop

of the building.

weatherproof housing

for receivers and device

servers

192.168.1.21

(63431)

5700

(North)

5700

(North)

R701

(South)

R701

(South)

R702

(West)

R702

(West)

192.168.1.22

(63432)

192.168.1.23

(63433)

Port 1 – 9011

Port 2 – 9012

Port 3 – 9013

Port 1 – 9021

Port 2 – 9022

Port 3 – 9023

Port 1 – 9031

Port 2 – 9032

Port 3 – 9033

RG213

RG58

RS232

RJ45

Port 1 – RT17

Port 2 – Configuration

Port 3 – NMEA/CMR

Internet

Processing

Server

Processing

Server

SiReNTSiReNT

Real-Time Network

Correction

&

Post-Process RINEX Data

System Set-up for

Building

Movement Detection &

Monitoring System

System Set-up for

Building

Movement Detection &

Monitoring System

Sensors located at basement and 65th storey

Two QA700 Q-Flex accelerometers sensors with bi-axial horizontal direction are located on the

65th

storey and basement. Data collection continues from 6th

April to 13th

April at sampling

frequency at 100 Hz. Totally one week’s data was collected.

GPS Vs Accelerometer

• The purpose of the accelerometer system is to capture structural response due to wind loading and during occasional events such as long-distant earthquake

• The seismic sensor system can only record the dynamic performance of the structure instead of tracking dynamic and static performance at the same time as GPS

Differential processing (for displacement data by GPS)

Differential processing (for displacement data by GPS)

Velocity

Velocity differential from GPS data

Velocity integrated from seismic sensor data

Displacement

GPS data

Displacement integrated from seismic sensor data

Natural Frequency of Building

Natural Frequency

• When a body freely executes a to-and fro motion about some fixed point it is in oscillation

• The time required to make one full oscillation is the natural frequency of the body in seconds

Modes of Vibration

• Structures can Have More than one Mode of Vibration

• 1st , 2nd , 3rd , 4th , etc.• Lowest Frequency is 1st Mode• Frequency increases with each subsequent mode

of vibration

Modes of Vibration

1st 2nd 3rd

Natural Frequency andBuilding Design

• Design Buildings OUTSIDE their Natural Frequency … Otherwise they are Subject to Collapse

• General Rule …– Short Buildings are Stiff and Have High Natural

Frequencies– Tall Buildings have Low Natural Frequencies

Calculating Period Based onthe NEW Uniform Building Code (1997 UBC)

T = 0.035* (280*3.28084)3/4

= 5.84 secF = 1/5.84 = 0.1712 Hz

Calculating Period Based onthe OLD UBC

Period = 0.1 x 66 = 6.6 secF = 1/6.6 = 0.1515 Hz

Results and Analysis

A-mode frequency(Hz) B-mode frequency(Hz) T-mode frequency(Hz)

A1 0.1709 B1 0.1953 T1 0.5127

A2 0.6592 B2 0.708 T2 1.1963

A3 1.4404 B3 1.6357 T3 2.124

A4 2.2705 B4 2.7832 T4 3.2959

A-mode frequency(Hz) B-mode frequency(Hz) T-mode frequency(Hz)

A1 0.176 B1 0.234 T1 0.469

A2 0.625 B2 0.818 T2 1.093

A3 1.406 B3 1.641 T3 1.956

A4 2.210 B4 2.734 T4 3.203

Modal frequency for Republic Plaza

(using available data from Jan. 2007 to Dec. 2007)

Modal frequency for Republic Plaza

(using GPS R701 – VRS Solution, East, 26 May 2009 ) – 10 Hz

Accelerometer

Seismic sensor data and corresponding power spectrum analysis with high-pass filter from 0.1 Hz (00:00:00-00:59:59 9 April, 2009) – 100Hz

0.1709

0.1953

2.78322.27051.6357

0.708

Empirical mode decomposition (EMD)

• EMD is a method of breaking down a signal without leaving the time domain

• Using the EMD method, any complicated data set can be decomposed into a finite and often small number of components, which is a collection of Intrinsic mode functions (IMF).

• An IMF represents a generally simple oscillatory mode as a counterpart to the simple harmonic function.

IMF and Power Spectrum Analysis of accelerometer data

IMFs Corresponding power spectrum analysis

2.27052.7832

IMF and Power Spectrum Analysis of accelerometer data

IMFs Corresponding power spectrum analysis

2.27051.6357

1.4404

0.708

0.6592

0.1709

0.1953

1 Hz GPS

Displacements of R701 (VRS Solution)27 May 2009 – 1 Hz

North

East

Displacements of R702 (VRS Solution) 27 May 2009 – 1 Hz (Rover RTK)

North

East

Displacements of R701 (Non-VRS Solution) 28 May 2009 – 1 Hz (Rover RTK)

North

East

Displacements of R702 (Non-VRS Solution) 28 May 2009 – 1 Hz (Rover RTK)

North

East

Power Spectrum of R701 (VRS Solution) 27 May 2009 – 1 Hz (Rover RTK)

North

East

Power Spectrum of R701 (Non-VRS Solution) 28 May 2009 – 1 Hz (Rover RTK)

North

East

Power Spectrum of a week of data (05/04/2009-12/04/2009) for R701 – 1 Hz (Rover RTK)

Observation

• The nature frequency of 0.1758 Hz is dominant for analysis of one week’s data. Comparing to the nature frequency measured by accelerometer 0.1709 Hz, 0.0049 Hz differences exist. Though GPS monitoring of displacement (using 1 Hz data) is somewhat noisy, it can record natural dynamic characteristic of slender engineering like high-rise buildings.

10 Hz GPS

Displacements of R701 & R702 (VRS Solution) 26 May 2009 – 10 Hz (Rover RTK)

East

Displacements of R701 & R702 (VRS Solution) 26 May 2009 – 10 Hz (Rover RTK)

North

Displacements of R701 & R702 (Non-VRS Solution) 27 May 2009 – 10 Hz (Rover RTK)

East

Displacements of R701 & R702 (Non-VRS Solution) 27 May 2009 – 10 Hz (Rover RTK)

North

Displacements of R701 & R702 (Non-VRS Solution) 27 May 2009 – 10 Hz (Rover RTK)

North

Power Spectrum Analysis of R701 & R702 (VRS Solution) 26 May 2009 – 10 Hz (Rover RTK)

East

Power Spectrum Analysis of R701 & R702 (VRS Solution) 26 May 2009 – 10 Hz (Rover RTK)

North

EMD (Empirical Mode Decomposition) of R701 RPB (VRS Solution) East26 May 2009 – 10 Hz (Rover RTK)

IMF (Intrinsic Mode Function) Corresponding frequencies components

A2

B2 B3 A4A3

B4

EMD (Empirical Mode Decomposition) of R701 RPB (VRS Solution) East26 May 2009 – 10 Hz (Rover RTK)

A1

B1

B1IMF (Intrinsic Mode Function) Corresponding frequencies components

Power Spectrum Analysis – 1 Hz GPS data

• If sampling R701 (VRS Solution) - North, 26 May 2009 data at 1 Hz, the first mode of the structure is at 0.1836 Hz.

Conclusions

• Accelerometer is capable to measure sway vibration response, but cannot detect the permanent changes in buildings induced by wind or due to environment temperature changes. GPS system data can give information for dynamic + static performance

• If only minor tremors occurred like under ambient vibration condition, the amplitude of response displacement might be covered by GPS noise. While GPS data may show possibility in higher amplitude acceleration induced by wind or long-distance earthquake

Consclusion

• 10-Hz GPS is better in detecting the natural frequency of the tall and slender building than the 1-Hz GPS

• VRS solution is acceptable