Monitoring Static and Dynamic Characteristic of Tall Building Using GPS Virtual Reference Station and Seismic Sensor Data presented by TOR, Yam Khoon Assoc. Prof. School or Civil & Environmental Engineering Map Asia August 2009 Huang Liping (Dr), NTUVictor Khoo Hock Soon (Dr), SLA Kusnowidjaja Megawati (Assoc Prof), NTUGerry Ong, GPSLands (S) Pte Ltd Tor Yam Khoon (Assoc Prof), NTUTeo 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 NMEA VRS position is established VRS Source: Trimble

VRS Data FlowVRS NMEA Server uses VRS position to create corrected RTCM real-time data RTCM 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 m m Location of GPS antennas

Location of accelerometer X – A mode Y – B mode accelerometer

Combined sensor setup 5700 R701 R702 North Accelerometer X – A mode Y – B mode

High Rise building monitoring GPS receivers mounted on rooftop of the building. weatherproof housing for receivers and device servers

(63431) 5700 (North) 5700 (North) R701 (South) R701 (South) R702 (West) R702 (West) (63432) (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 SiReNT Real-Time Network Correction & Post-Process RINEX Data System Set-up for Building Movement Detection & Monitoring System

Sensors located at basement and 65 th storey Two QA700 Q-Flex accelerometers sensors with bi-axial horizontal direction are located on the 65 th storey and basement. Data collection continues from 6 th April to 13 th 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)

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 and Building 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 on the NEW Uniform Building Code (1997 UBC) T = 0.035* (280* ) 3/4 = 5.84 sec F = 1/5.84 = Hz Calculating Period Based on the OLD UBC Period = 0.1 x 66 = 6.6 sec F = 1/6.6 = Hz

Results and Analysis

A-modefrequency(Hz)B-modefrequency(Hz)T-modefrequency(Hz) A B T A B20.708T A B T A B T A-modefrequency(Hz)B-modefrequency(Hz)T-modefrequency(Hz) A10.176B10.234T A20.625B20.818T A31.406B31.641T A42.210B42.734T Modal frequency for Republic Plaza (using available data from Jan 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

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

IMF and Power Spectrum Analysis of accelerometer data IMFs Corresponding power spectrum analysis

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/ /04/2009) for R701 – 1 Hz (Rover RTK)

Observation The nature frequency of Hz is dominant for analysis of one week’s data. Comparing to the nature frequency measured by accelerometer Hz, 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) East 26 May 2009 – 10 Hz (Rover RTK) IMF (Intrinsic Mode Function) Corresponding frequencies components A2 B2 B3 A4 A3 B4

EMD (Empirical Mode Decomposition) of R701 RPB (VRS Solution) East 26 May 2009 – 10 Hz (Rover RTK) A1 B1 IMF (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 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