Construction of the huge six-lane Lu Pu Bridge began in October 2000 and has cost 2.25 billion yuan (272 million US dollars). The main section of the 3,900 meter-long bridge is 750 meters long and 28.7 meters wide. The 550 meter-long main arch is made up of 27 box connectors, assembled by jointing, and 28 pairs of hangers linking the bridge deck. Over 35,000 tons of steel has been used in its construction.
The final stage of installation — the connection of the two bridge sections — has proven to be the most difficult part of the project. In order to ensure that the final two segments from both sides of the river met exactly, precision surveying equipment of Leica Geosystems was also used in this phase of construction by monitoring the movements of the arch elements with an automated laser Total Station Leica TCA2003 providing an accuracy of fractions of a millimetre.
Final construction work involves the laying of the bridge deck and roadway. The last deck section of the Lu Pu Bridge was successfully installed in February 2003, and it is anticipated that the whole project will be completed by June 2003.
According to Vice-mayor Han Zheng, the bridge will help to relieve traffic crossing the river, and also contribute to Shanghai’s bid for the World Expo 2010. The Lu Pu Suspension Bridge represents one of the three new river crossings to be opened for public in 2003 in the fast developing metropolitan area of Shanghai, the two other crossings being constructed in form of tunnels.
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A challenge for surveyors: Five highly accurate measurements per second
According to Mr. Bian, Director of the Surveying Division in the Shanghai Building & Construction Group, the swing, torsion and deformation of the iron-structured connectors caused by such environment factors as temperature, wind and sunlight, made the installation of the three connectors right in the middle of the bridge quite a challenge. The task required extremely precise surveying before the next box connector was lifted and jointed to the previous one, section-by-section. Consequently, the last three connectors had to be custom-made according to the precise data offered by the on-the-spot surveying, a task undertaken by Jiang Nan Ship Building Factory.
During the assembly surveying, Leica Geosystems’ total stations (TCA 2003) were used to obtain the real-time coordinates of the targets fastened on the connectors. These were used to adjust the connectors by comparing them to the designed data.
Another problem that was encountered was the extent of the swing range between the two connecting parts of the bridge. According to the data derived from the wind tunnel test in advance, the largest swing range of the connectors right in the middle of the bridge was estimated to be a maximum of 0.8 meters. Under such circumstances, the traditional surveying method, of setting up surveying on the structure and aiming the target manually, would not work because the two segments of the bridge were continually moving.
Consequently, a remote method of surveying and calculating the dimensions of the linking section had to be developed. Fortunately, Leica Geosystems’ Total Stations were not only able to perform measurements at a rate of 5 Hz under tracking mode, but also calculate easy and quick customizations. This was achieved using GeoBASIC, software oriented to engineering technicians, and developed by the Software Development Center (Shanghai).
GeoBASIC provided dynamic 3D measurements at 5 times/sec, calculating both the swing center of the tracking target according to the movement model provided, and the maximum range of the movement. The Software Development Center was able to complete the development of this application for the project successfully within two weeks, finally solving the problem of dynamic targets surveying.
PictureCaption:
The world’s longest steel arch bridge — the 3,900 metre-long Lu Pu bridge — now crosses the Huang Pu River in Shanghai. With automated laser total surveying stations Leica TCA2003, the positioning of the elements was possible to millimetre accuracy by providing real-time data five times per second.
