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Monitoring high-rise building deformation using Global Positioning System
Case Study The KOMTAR building in Penang has been chosen for the purpose of the deformation monitoring study. Figure 1 shows the view of the building, which is the tallest building in Penang. It is located in the little colonial and touristic George Town at 245 meter high (65 floors). The observation network consists of 2 base stations, and 6 monitoring stations. Two observation campaigns are made for this study: The first campaign was carried out in November 2000 and the other in February 2001. All stations were surveyed by using 3 units of Leica 300 dual-frequency receivers. Static GPS surveying mode with relative positioning was used for all stations. Two GPS base stations, TLDM (P314) and Kg. Penaga (P288), were used for each GPS survey. In this study, geodetic control survey has been carried out to identify the stability of the monitoring stations KT1, KT2, KT3, KT4, KT5 and KT6 from the GPS observation. In order to achieve the maximum possible accuracy in deformation surveys, we try to keep all possible systematic errors constant by using only the same type of receiver in all survey campaign, use the same software, try to use similar geometry of satellites in the repeated measurements of individual baselines, and finally try to conduct all survey campaign in similar environmental conditions. Result and Analysis The GPS network adjustment of data from both epochs is accomplished using the Ski TM software with constrains network adjustment. The coordinates and standard deviations are shown in Table 1 and 2 for the 1 st epoch and 2 nd epoch, respectively. The comparison of standard deviations from these two GPS campaigns is plotted in Figure 2. As indicated in Figure 2, the standard deviations for the 1 st epoch are varied from 0 mm to 5 mm in horizontal components and from 0 to -3mm in vertical component, while in the 2 nd epoch, the corresponding values are varied from 0 mm to 9 mm in horizontal component and 0 mm to 6 mm in vertical component. Practically, the overall analyses have shown that the qualities of the observation data for these GPS campaigns are good. The result for the residuals, standardised residuals, and internal/ external reliability is summarized in Table 3 - 6, respectively. Figure 3 and 4 depicts the accepted residual values and standardized residuals for epoch 1 and 2, respectively. It can be seen that the residual values in Table 3 and 5 are smaller than the standard deviation of the observations (see Table 1 and 2). Figure 5 and 6 shows the internal and external reliability for both epochs. The internal reliability for the first epoch is varies from 0.05 to 0.26 in horizontal and 0.04 to 0.07 in vertical component. While the second epoch varies from 0.06 to 0.24 in horizontal component and 0.06 to 0.012 in vertical component. The external reliability also small whereby it values is varies from 0.0001 to 0.0107 in horizontal and 0.0001 to 0.0072 in vertical component. The overall results have shown that the network has a good reliability. The comparison of different adjusted coordinates has also been carried out for this experiment, and it is summarized in Table 7. Figure 7 illustrates this results. Here, it can be seen that the smallest and the biggest values is occured at station KT1 and KT5, respectively. The station KT5 has the values of –8.8 mm and 57.7 mm for the horizontal component and –10.6 mm for the vertical component. The station KT1 has the value of 1.3 mm and 16.7 mm for the horizontal components and –2.5 mm for the vertical component. Table 1: Coordinate and standard deviation for 1st epoch
Table. 2 : Coordinate and standard deviation for 2nd epoch
 Fig.2: Standard deviation for both epochs A statistical test known as the congruency test is required to determine whether significant movements is occurred between the monitoring campaigns, i.e. to evaluate the stability of the control points. The application of congruency tests is quite simple. Initially, the congruency of common datum points at each epoch is evaluated by the global congruency test. If the test indicates that there is a significant movements, then the localization process is performed, follows by a similar test on the remaining datum points through the partial congruency test. In this study, the GPSAD200 software has been used to analyse the stability of all control points located at the KOMTAR building. Table 8 shows the baseline vector with two fixed points for epoch 1 and epoch 2. The deformation analysis is carried out for all observations. Results for the variance ratio and congruency test is summarised in Table 9. It can be seen form this table that the variance ratio test at significance level of 0.05 is passed for all observations, whereby the value is smaller than the critical value, i.e. (1.204 < 2.405). This shows that the variance factor is same for both GPS campaigns. The global congruency test at significance level 0.05 for the results is also implemented. The output of this global test indicates that all control points are in stable conditions – see Table 10. |