Network

An absolute network design was used. This is when the reference points are out-side of the body being surveyed. The sta-bility of the reference points is very im-portant. Static GPS was used to retrace the previous survey and determine the stability of previous placed azimuth marks in 2005. Once stability of azimuth marks was confirmed, redundant meas-urements would be taken on the monitor-ing stations.

Field Techniques

Static observations at 10 minutes + 2.5 minutes per KM.

Instrument Heights changed between observations.

Heights measured in feet and meters.

Tribrachs rotated between observations.

ATR (automatic target recognition)

2 face total station measurement

Link traverse with compass closure.

Field resection reduced using onboard L.S.A.

Field notes taken along with digital data stored.

Introduction How to monitor a bridge horizon-tally to determine if deformation has occurred using GPS and con-ventional methods of survey? To answer the question, research was done, a field work project de-signed then executed, finally processing and analysis on the data. The benefits gained were: proper field techniques and data analysis in deformation survey.

Observation Results

less than 1mm std.dev. (X,Y) on observations @ 68.3% conf..

less than 2.4mm error ellipses on observations @ 95% conf..

Colin Mang

Centre of Geographic Science

2011

Deformation Survey

Background

Deformation is a type of engineer-ing survey usually used for public safety and construction insur-ance. Bodies deform from exter-nal forces, producing loads caus-ing it to change shape. Since de-formations are very small & can be at the margin of measuring er-rors, careful analysis & statistical testing of the results is required. [Chrzanowski A.,Chen Y.Q., 1986]

Location

Bridgetown Bridge was chosen. A previous survey in 2005 was done on the structure with existing azi-muth marks and monitoring sta-tions remaining. This survey will be used for comparison.

Errors

There are 3 errors in geomatics measure-ments. Random, Systematic and Blun-ders. Systematic errors can be greatly re-duced or cancelled using field tech-niques. Blunders that fail an outlier test will be removed. Random errors that fol-low normal distribution will be reduced through L.S.A.

Analysis

Least Squares analysis is used to remove any blunders and adjust the network. This pro-vides the best position for measurements taken along with std.dev. and error el-lipse’s at 95 % confi-dence. Once blunders are removed and the network adjusted a simple differencing of coordinates is used to determine if deforma-tion has occurred.

Analysis of Results

Easting Difference 2005 to 2010

Analysis of Results

Northing Difference 2005 to 2010

Conclusion

Results indicate bridge movement in the S-W direction. Possible causes: Deformation or Survey Er-ror. Expected displacement was unknown therefore acceptable amount of movement is also un-known. The deformation survey is considered successful.

Ellipse Scale exag-geration 3500.

Drawing scale 1:1

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