The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008 
and (van Gosliga et al., 2006), at large dams, e.g. (Grimm- 
Pitzinger and Rudig, 2005) and (Zogg and Schulz, 2007), and at 
lock gates, e.g. (Schäfer et al., 2004) and (Hesse and Stramm, 
2004). Furthermore, deformation monitoring for structural 
deformation measurements of a concrete and timber beam is 
described in (Gordon et al., 2004). 
Figure 1. Felsenau viaduct, completed in 1975. 
Main objectives of the deformation monitoring by TLS on the 
Felsenau viaduct were on the one hand to get to know the 
advantages and limits of the new measurement technology for 
load test in the field of bridge monitoring, and on the other hand, 
a comparison with precise levelling should point out the 
possibilities of TLS with focus on the measurement accuracy 
and detection of deformations. 
In section 2 of this paper, the load tests are described as well as 
the geodetic instruments which were used for the load tests. 
Section 3 deals with processing of the TLS data and section 4 
compares the results of TLS and precise levelling. Finally, 
section 5 discusses the results, and conclusions are given in 
section 6. 
2. LOAD TESTS 
For the load tests, the Felsenau viaduct was closed for traffic in 
order to minimize vibrations of the bridge girder. The traffic 
was diverted. Several parties were involved for the proper 
accomplishment of the tests, i.e. the Office of Civil Engineering 
of the Canton of Berne, the Federal Traffic Office, a local 
engineering company, and the ETH Zurich. The Institute of 
Structural Engineering at ETH Zurich had the technical lead. 
The IGP was responsible for the geodetic measurements. 
1 
settlement 
Figure 2. Expected deformation behaviours of the cantilever 
slabs and bridge girder under loading. 
2.1 Initial situation 
The load tests were performed during two nights when the 
weight was positioned on different sections of the viaduct. Two 
tanks, each weighting approximately 54 tons, were used as a 
load. The load tests were performed at several sections of the 
viaduct. The descriptions and analyses below refer to the first 
night when the weight was positioned in the middle section of 
the viaduct. The span length and the height were 156 m and 
60 m respectively. 
The load was positioned on the northern outer side of the 
prestressed cantilever slabs (Figure 5). Hence, deformations 
were expected as a deflection of the cantilever slab and a tilting 
and settlement of the bridge girder (Figure 2). The deflection of 
the cantilever slabs were of main interest for the civil engineers. 
The procedure of the load test was scheduled in four main steps: 
initial measurement, loading PI with one tank, loading P2 with 
two tanks, final measurements P3 without any load. Recovery 
periods of about 30 minutes represented an important aspect. 
They allowed the viaduct to relax and to minimize the 
vibrations and oscillations caused by the traffic, respectively by 
the tanks. This was a very important aspect for the precise 
levelling due to the fact that sensitive levelling compensator 
would not work under oscillating movements of the 
underground. The measurements of the deformations were 
performed with a tacheometer, a precise level and a terrestrial 
laser scanner. 
2.2 Terrestrial laser scanning (TLS) 
For the measurements by TLS, the terrestrial laser scanner 
Imager 5006 by Zoller+Froehlich (http://www.zf-laser.com) 
was chosen (Figure 3). The choice was based on the scanning 
speed of about 500’000 points per second, the measurement 
accuracy and the availability of the instrument. According to 
specifications by the manufacturer, the range noise is about 
2.0 mm in a distance of 25 m and a target reflectivity of 20% 
(dark-grey target). The scans were performed on the bridge 
girder of the Felsenau viaduct. The carriageway surface was 
dark-grey due to the asphalt. Furthermore, the time for a scan 
was an essential factor due to a tight schedule of the load tests. 
The measurements had to be planned fur a minimum closing 
time of the viaduct for traffic. 
Figure 3. Terrestrial laser scanner Imager 5006 by 
Zoller+Froehlich (http://www.zf-laser.com). 
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