ABSTRACT

The objective of the study was to compare and assess suitability of three methods of geodetic measurements used to determine changes of the geometric condition of building and engineering structures. The following three measurement methods were tested: (i) tachymetry, (ii) photogrammetric, and (iii) laser scanning. The above-mentioned methods were tested at the main span of the suspension bridge of 165 m on the Oder River (Fig. 1). Information on the change in the shape of bridge structure under the influence of service load are very significant concerning maintenance (exploitation). The examined bridge comprises 5 spans – four outmost flood spans and the main river span of suspended structure. The structure serves as a technological bridge. Through the bridge passes a belt conveyor connecting lime quarry with a cement factory. The scope of examinations included performing measurements of the changes in the bridge and bearing cable deflection values during the belt conveyor operation and stoppage, using the abovementioned methods. The most accurate among the used methods was the tachymetry method, thus the results obtained with this method were considered as the reference data. The tachymetry measurements were conducted using precise tachymetry manufactured by Leica TC2002. In the photogrammetric method, digital photography was used, i.e. a Canon 650D camera with high resolution, photographic turntable and the newest software. In the case of the laser scanning, a FARO Focus 3D X130 scanner was used. View of the bridge from the upper water side. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig304_1.jpg"/>

As a result of measurements of changes in the displacements of the suspension bridge under in-service conditions, the following conclusions can be drawn:

The maximum displacements of the bridge obtained using the tachymetry method were observed in the middle of the span and were 72 mm. The highest displacements of the bridge created as a result of the influence of the service load need to be considered relatively small. They were significantly lower than the limit value for the bridge-type in every case. Based on the photogrammetric method, the results obtained for the values of the bridge displacements were underestimated in comparison to the tachymetry method (in the case of this bridge 16–27%).

In the case of the photogrammetric method the camera’s focus needs to be chosen in such a way that the value of a pixel was about 2 mm. Higher scale of the photograms will allow to obtain additional information on the surroundings of the measured point, e.g. permanent deformations, cracks, etc.

The laser scanning method proved to be the least accurate in the case of the bridge. It was a result of too high distance from the bridge and too little resolution of the scanner (points density). In the future, a scanner of higher resolution would need to be used, which would enable more precise identification of details such as: edges or elements of the circular section.