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A feasibility study of building structural deformation monitoring using Global Positioning System (GPS), terrestrial surveying technique (TST) and crack gauge measurement (CGM)

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A feasibility study of building structural deformation monitoring using Global Positioning System (GPS), terrestrial surveying technique (TST) and crack gauge measurement (CGM)
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    A Feasibility Study of Building Structural Deformation Monitoring Using Global Positioning System (GPS), Terrestrial Surveying Technique (TST) and Crack Gauge Measurement   (CGM). Mat Rahim Ibrahim 1  , Jasmee Jaafar 1 , Zahrullaili Yahya 2 & Abd. Manan Samad 1  Pixelgrammetry & Al-Idrisi Research Group (  Pi_ALiRG ) 1 Faculty of Architecture, Planning and Surveying 2 Faculty of Civil Engineering Universiti Teknologi MARA (UiTM) Malaysia, 40450 Shah Alam, Selangor, MALAYSIA. Email: dr_abdmanansamad@ieee.org  Abstract-   Deformation of engineering structures is often monitored in order to ensure that the structure is exhibiting safe deformation behaviour. The deformation of high-rise building can be monitored using geodetic surveys and geotechnical/structural measurements. Geodetic surveys include conventional (terrestrial) and satellite (Global Positioning System); wherelse geotechnical/structural measurements detect either by using leasers, tiltmeters, joint-meters and micrometers. This research will discuss the capability of monitoring high and low-rise building structure using geodetic surveys (conventional and satellite) and geotechnical measurement (crack width measurement). Two buildings namely the Twin Tower of Science and Technology Complex and Innovation Centre Building of University Technology MARA (UiTM), Selangor, Malaysia are chosen for the research study. UiTM Twin Tower represents high-rise building, five control points were been established around the building in the monitoring work. Innovation Centre was monitored using nine monitored points. The monitoring exercises are carried out at four (4) different epochs. The Terrestrial and Global Positioning System (GPS) dataset in the monitoring exercise are process and analysed using the intersection technique and Trimble Geomantic Survey (TGO) software. Generally the monitored points for the Twin Tower Building experience movements within 1 mm to 10 mm. For Innovation Centre Building monitored points seem to shift between 1 mm to 9 mm. Detection of movement for both building’s structure seems to be within the allowable tolerance. It is shown that monitoring building structure using the techniques adopted in this study has significant advantages and disadvantages.   I.   I  NTRODUCTION  The measuring techniques and instrumentation for monitoring structural deformation have traditionally been categorised into two groups, namely (USACE, 2002); A)   Geodetic surveys, including conventional (terrestrial surveys), satellite Global Positioning System (GPS),  photogrammetric and special techniques (interferometer, hydrostatic leveling and alignment), and B)   Geotechnical measurement of local deformations using lasers, tilt meters, accelerometer and micrometers. Geodetic surveys comprises of observation through a network of points interconnected by bearing and distance measurements which are sufficient for the statistical evaluation of quality and detection of errors (USACE, 2002). The most popular techniques in geodetic surveys are terrestrial surveys and Global Positioning System (GPS). Terrestrial surveying methods, such as precision triangulation of traversing and geodetic leveling has been established since 1940’s for monitoring big structures such as dams (Casaca, 2002). A terrestrial survey is a technique where a total station or electronic distance measurements (EDM) are used to observe the monitored points on a structure relative to a stable control stations. Coordinates of monitored points can be determined using intersection method as discussed by Allan (1997), Ahmad (1987), E-Mok (1990), Ismakum (1994) and Amin (1996). GPS survey technique on the other hand also monitors the movement of monitored points relative to a stable control stations (USACE, 2003). Recent studies have demonstrated the possibility of using GPS technology to monitor structure deformations and can be found in Ogaja et al (2001), Duth & Hyzuk (1997), Hudnut (1998) and Manetti & Knecht (2001). On the other hand, geotechnical measurements generally  been used for detecting relative deformation within deformable object and its surroundings. Geotechnical measurements provide localised information without any check unless it is compared with other independent measurements (USACE, 2002). Geotechnical instruments are easy to operate for continuous monitoring compared to geodetic surveys. However, with the technological progress in the last few years, the differences between the two 2010 6th International Colloquium on Signal Processing & Its Applications (CSPA)96978-1-4244-7122-5/10/$26.00 ©2010 IEEE    monitored technique seems negligible compared to twenty years ago (USACE, 2002). The equipments frequently use for geotechnical measurements are tilt meters, accelerometer and micrometers. Crack width measurements using micrometers was chosen in this research based on its advantage such as, the instrument is easy to operate and the reading can be obtained to the nearest 0.01mm (USACE, 2002). II.   O BJECTIVE  Main objectives of this research study are: 1.   To study and identify most suitable points on the  building structure and most suitable control points surrounding the structure for the building structural monitoring purposes. 2.   To study and explore the appropriate technique using GPS survey, Terrestrial and Geotechnical measurement approach towards the building structural monitoring purposes. 3.   To evaluate, validate and analyse the gathered dataset based on the building structural monitoring. III.   M ETHODOLOGY  This research study investigates the capability of three techniques in monitoring structural deformations. These techniques are; i)   GPS survey using rapid static technique, ii)   Terrestrial survey using intersection technique and iii)   Crack width measurements using Digital Movement Gauge. The monitored buildings structures are the UiTM Twin Tower of Science and Technology Complex and the UiTM Innovation Centre Building. The UiTM Twin Tower is situated at west side of the UiTM campus area. The building consists of two towers, the north and south tower. South tower was chosen since it is considered to be a new building and officially occupied in the year 2004 with height of twenty stories. The UiTM Innovation Centre building is located near the second entrance of Universiti Teknologi MARA, Shah Alam and was occupied in 1996. This building seems to be experiencing defects, such as crack due to settlement. In order to achieve the objectives of this research study, the outlines of the general methodology for this research study is as shown in Figure 1.0. Literature ReviewConclusion and RecommendationData AnalysisMonitoring TechniquesLiterature ReviewConclusion and RecommendationData Analysis   Monitoring Techniques  Figure 1.0: General Methodology Flow Chart.  A. Accuracy Requirements. Accuracy for each monitored point is directly related to the maximum expected displacement. As an example, ± 200 mm displacement is allowed for building duration of 50 years under normal structure operating conditions (Bennetts et al  . 1995). Accuracy requirements are computed by quating the maximum allowable positioning error to some  portion of the total magnitude of movement that is expected at each point. Specifically, the positioning accuracy (at the 95% probability level) should be equal to one fourth (0.25 x 200/50) of allowable displacement (USACE, 2002). Therefore the accuracy achieved by GPS (± 1 mm) and total station (± 1 mm, 1”) can be used and suitable to monitor structural deformation of high-rise building.  B. Monitoring Survey Design Monitoring survey design begins whenever the intention to monitor the healthy of the building structure was decided (USACE, 2002). Survey design involve in determining the techniques of surveying (Figure 2.0) in achieving the objective and accuracy required. Design of control station networks and monitored points are planed and set-up at the selected position. Figure 2.0 shows the flows of the monitoring techniques . Innovation CentreTerrestrialSurveyGPSSurveyControl PointsFirst Order DGPS(Rapid Static)Crack Width DGPS(Rapid Static)Monitoring of Building StructureSouth Tower IntersectionControl Monitoring Innovation CentreTerrestrialSurveyGPSSurveyControl PointsFirst Order DGPS(Rapid Static)Crack Width DGPS(Rapid Static)   Monitoring of Building StructureSouth Tower IntersectionControl Monitoring Figure 2.0: Monitoring of Building Structure Flowchart. 2010 6th International Colloquium on Signal Processing & Its Applications (CSPA)97    C. Design of Reference Networks Each control stations in the reference network are inter-visible to maximum number of structural monitoring points (placed on the structure). Control stations are established at a distance from the monitored structure at strategic location (USACE, 1990). Controls stations as shown in Figure 3.0 are constructed from steel pipe (1 m long and 20 cm diameter) with cast-in-situ concrete . The steel pipe for the control station is inserted into the earth with 10 cm heights above ground surface (USACE, 1990). There are five main control station constructed around the study area. The main control stations are indicated by CS 1, CS 2, CS 3, CS 4 and CS 5. Every control stations have a reference station (RS) as shown in Figure 4.0. SoilSteel pipe(L = 1m, d = 20 cm) Tripod legPlumb-bob Concrete(1 x 1 x 1) feet   SoilSteel pipe(L = 1m, d = 20 cm) Tripod legPlumb-bob Concrete(1 x 1 x 1) feet   SoilSteel pipe(L = 1m, d = 20 cm) Tripod legPlumb-bob Concrete(1 x 1 x 1) feet  Figure 3.0: Control station specification. Centre CS 5CS 4CS 1CS 2CS 5CS 4CS 1CS 2CS 5CS 4CS 1CS 2 RS 4RS 3RS 5RS 2RS 1 Innovation Centre CS 5CS 4CS 1CS 2CS 5CS 4CS 1CS 2CS 5CS 4CS 1CS 2CS 3 RS 4RS 3RS 5RS 2RS 1 South TowerInnovation LEGENDLEGENDLEGENDReference StationLEGENDLEGENDLEGENDGPS survey network Traverse lineGPS survey network Traverse lineGPS survey network Traverse lineGPS survey network Traverse lineGPS survey network Traverse lineGPS survey network Traverse lineReference StationControl StationControl Station StationNorth TowerCentre CS 5CS 4CS 1CS 2CS 5CS 4CS 1CS 2CS 5CS 4CS 1CS 2 RS 4RS 3RS 5RS 2RS 1 Innovatio   n Centre CS 5CS 4CS 1CS 2CS 5CS 4CS 1CS 2CS 5CS 4CS 1CS 2CS 3 RS 4RS 3RS 5RS 2RS 1 South TowerInnovation LEGENDLEGENDLEGENDReference StationLEGENDLEGENDLEGENDGPS survey network Traverse lineGPS survey network Traverse lineGPS survey network Traverse lineGPS survey network Traverse lineGPS survey network Traverse lineGPS survey network Traverse lineReference StationControl StationControl StationControl StationControl Station StationNorth Tower  Figure 4.0: Control station network by GPS Survey and first class traverse. The steel pipe for the control station is inserted into the earth with 10 cm heights above ground surface (USACE, 1990). There are five main control station constructed around the study area. The main control stations are indicated by CS 1, CS 2, CS 3, CS 4 and CS 5. Every control stations have a reference station (RS) as shown in Figure 4.0. Figure 4.0 shows the location of control stations and its reference stations. GPS survey technique is adopted to establish the coordinates of the control stations. Terrestrial survey of first class order (DSMM, 2003) is used to establish the coordinates of the reference network. The stability of the control stations are check by these two techniques to ensure the ± 5 mm tolerance in horizontal movement is achievable (USACE, 2002, DeLoach, 1989 and Cooper, 1987).  D. Monitored Points Locations of monitored points are at South Tower and Innovation Centre building. Figure 5.0 shows the monitored  points located at the roof top of the South Tower building. The locations are selected based from the requirements discussed by USACE Publications (USACE, 2002 and 1990), DeLoach (1989), Duth (1997) and Carpinteri (2006).   South Tower  ABCDEF  A, B, C, D, E and F: Monitored Points   South Tower  ABCDEF  A, B, C, D, E and F: Monitored Points South Tower  ABCDEF  A, B, C, D, E and F: Monitored Points  Figure 5.0: Position of    monitored points at roof top of the South Tower building Monitored points are set-up by inserting a steel bolt or concrete nail into the roof slab. Figure 6.0 shows the cross-section of monitored point where GPS antenna or reflector (prism) will be setup during observation. The coordinates of the monitored points are calculated and analyse by GPS survey and terrestrial survey technique. Column SlabSteel bolt GPS antennaTripod   Column SlabSteel bolt GPS antennaTripod  Figure 6.0: Monitored point at roof top of the building column 2010 6th International Colloquium on Signal Processing & Its Applications (CSPA)98    Monitored points at Innovation Centre building are divided to two regions, beam regions and crack regions. Figure 7.0 shows the monitored point on beam region represented by points 3, 4 and 5. The reflectors (Leica plate) were used to mark the targeted points (Figure 6.0) to be monitored by terrestrial survey. Point 3Point 4Point 5 Reflector targetReflector targetReflector target   Point 3Point 4Point 5 Reflector targetReflector targetReflector target  Figure 7.0: Monitored at beam region, point 3, 4 and 5 Figure 8.0 shows the crack region represented by Schemes 2, 6 and 7. Every Scheme will be monitored by two techniques, terrestrial survey and crack width measurement. 2 V 2 H 6 V 6 S 6 H 6 A 6 B 7 V 7 S 7 H 7 B 7 A Scheme 6Scheme 7Scheme 2 2 A 2 B 2 S   2 V 2 H 6 V 6 S 6 H 6 A 6 B 7 V 7 S 7 H 7 B 7 A Scheme 6Scheme 7Scheme 2 2 A 2 B 2 S  Figure 8.0: Monitored at crack region, Scheme 2, 6 and 7 Terrestrial survey will be used to monitor the point marks by reflectors. Scheme 2 in Figure 8.0 shows the reflectors to mark points 2 A  and 2 B  (the other side of crack line and adjacent each other).  E. Monitoring Survey Techniques Three techniques are chosen for the monitoring exercises in this research. Figure 9.0 shows these three techniques, namely; GPS survey, terrestrial survey and crack width measurement. GPS and terrestrial survey are use to monitor South Tower building. Where else the Innovation Centre is monitored using terrestrial survey and crack measurement. GPS SurveyCrack WidthTerrestrial SurveyMonitoring TechniquesInnovation Centre South Tower   GPS SurveyCrack WidthTerrestrial SurveyMonitoring TechniquesInnovation Centre South Tower Figure 9.0: Monitoring Techniques  E1. GPS Surveys GPS instruments used (Trimble SE400) was calibrated at GPS calibration pillars, Section 7 adjacent to Bukit Raja-Damansara Highway. The calibration was carried out based on the procedures directed by Department of Survey and Mapping Malaysia (DSMM, 1999). GPS surveys were carried out at two epochs, to ensure the stability of the control stations. Monitoring of South Tower building was carried out using GPS survey by employing the rapid static technique. The survey was carried out at an interval of three (3) months. Using the rapid static technique as discussed in Section 2.2.1, the GPS receiver (main) is set at control station number one (no. 1) and another two receivers were setup at control stations no. 4 and no. 5 (Figure 6.0), this create a baseline between control station no. 1 and no 5. After 30 minutes of observation, GPS receiver at control station no. 4 will then be moved to control station no. 3. This observation process will take another 30 minutes before the GPS receiver will be moved to another control stations. The same goes to monitored points. The data collected using GPS survey will then be  process using Trimble Geodetic Office (TGO) software. The steps involved are as follows; i) Download data. Download is a process of transferring raw data from GPS receiver to the processing software. Data downloaded include antenna height, observation interval and the number of station observed. ii) Base line. Base line processing is to identify the baseline for the GPS observations. Figure 10.0 shows the  baseline processing using Trimble Geodetic Office (TGO) software. Figure 10.0: Base line processing iii) Network. Network processing is a process to determined coordinate based on known control station coordinate. iv) Coordinate transformation. Coordinate transformation is a process of transforming the coordinate from one system to another. Coordinate transformation include the  process of transforming GPS coordinate to Malaysian Revised Triangulation (MRT) coordinate. Figure 11.0 shows a control station no. 4 is transform from GPS coordinate to MRT using GPS coordinate conversion software. Figure 11.0: Coordinate transforming from GPS to MRT 2010 6th International Colloquium on Signal Processing & Its Applications (CSPA)99    v) Ultimate (final) coordinates. Ultimate coordinate is the finalised coordinate (control stations and monitored  points).  E2. Terrestrial Surveys Calibration process was done at calibration site, Section 6, Shah Alam. This process is to make sure the total station is in good condition (DSMM, 1986). A total station was used to survey the reference networks using first class order specification to determine the coordinates of the reference networks. Two sets of datasets acquire is to prove the condition control stations. The result obtained based on traversing is to be compared with the result obtain by GPS surveys. Monitoring excercises for the South Tower building are carried out at four (4) epochs. Figure 12.0 shows an example of the observations from control stations 3 and 4 to the monitored points at South Tower. South Tower North Tower  CS 3 RS 4RS 3 CS 4 Monitored point RS ; Reference station CS ; Control stationObservation line   South Tower North Tower  CS 3 RS 4RS 3 CS 4 Monitored point RS ; Reference station CS ; Control stationObservation lineMonitored point RS ; Reference station CS ; Control stationObservation line  Figure 12.0: Observation from control station to monitored  points at Twin Tower. Monitoring of Innovation Centre by terrestrial approach is by intersection technique. The observations are within three (3) months interval for twelve (12) months. Two control stations (CS 1 and Stn 1A) as shown in Figure 13.0 are been established adjacent to the monitored building. The control stations are established using first classes order traverse and GPS survey.    3   2   5   o    3   5   ’   0   4   ”         7        0  .        2        8        3 2 8 7  o  19 ’  2 1” 16 .2 2 3                         0                       5                o                        4                       5                       ’                       2                       5                        ”        6       5 .        7       2       3 Innovation Centre   CS 1Stn. 1ARS 1 Point 3      3   2   5   o    3   5   ’   0   4   ”         7        0  .        2        8        3 2 8 7  o  19 ’  2 1” 16 .2 2 3                         0                       5                o                        4                       5                       ’                       2                       5                        ”        6       5 .        7       2       3 Innovation Centre   CS 1Stn. 1ARS 1 Point 3  Figure 13.0: Observation from control station to monitored  points at Innovation Centre. Monitoring process by terrestrial survey using the intersection method observed bearing and distance from two control stations to the monitored points located at the beam and crack regions of the Innovation Centre building. The data gathered are process to determine the coordinates of the monitored points.  F. Crack Width Measurements. Crack width measurement is carried out simultaneously during the intersection survey. This measurement using crack gauge is to monitor the development of the crack. The schedule for monitoring is synchronized with the intersection survey. Crack width measurement using digital movement gauge measures crack regions of constructed triangle where one or two boundaries of the triangle cross the crack line. Before measurements are made, the instrument (Digital Movement Gauge) has to be calibrated. Figure 14.0 shows the measuring process for one of the triangle sides using digital movement gauge. The boundaries of the triangle (horizontal and diagonal) were measured to represent the development of the crack width whereas the vertical  boundary serves as checking. Five (5) sets of data for every  boundaries of triangles were measured and the mean value of the crack width were computed (USACE, 2002).   Triangle   Triangle Figure 14.0: Measurement for vertical side of triangle. IV.   R  ESULT  For the result,   the difference between computed coordinates for the control stations between two epochs (observation on 8 th  March and 5 th  June 2004) vary from 2 mm to 43 mm. From Table 1.0 control station no. 1 and no. 3 experiencing discrepancies of 1 mm and 24 mm in the northerly direction respectively. Control stations no. 2 and 5 experiencing movement of 32 mm and 5 mm respectively in the southerly direction .   T ABLE 1.0 C ONTROL STATIONS COORDINATES BY GPS  SURVEY   The difference between computed coordinates for the control stations between observation on 8 th  March and 5 th  June 2004 vary from 2 mm to 43 mm. From Table 1.0 control station no. 1 and no. 3 experiencing discrepancies of 1 mm and 24 mm in the northerly direction respectively. 2010 6th International Colloquium on Signal Processing & Its Applications (CSPA)100
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