Huge Bearings For The New Beauty Of Delhi
Mr. Jitendra Rathore, C.O.O – Technical Marketing, Sanfield (India) Limited
The new bridge in the north of Delhi features a total length of 675 m, a width of 35 m and a main span of 251 m. With four traffic lanes in each direction, it will relieve the traffic load of the Wazirabad Bridge situated further to the north. The Signature Bridge was planned in 2004 and is scheduled for opening to traffic by the end of year 2018. Already now it is considered a particularly beautiful bridge.
Inclined Pylon, Asymmetric Cable Arrangement
The architectural highlight of the cable-stayed bridge is its inclined pylon with a height of 156 m (above ground), the top of which is a 30 metres high steel-glass construction. This will be the highest scenic outpost of Delhi, which – when illuminated at night – will be visible over a long distance. The two inclined pillars merge at half height of the pylon. Above that point, the backstay cables and the inclined cables lead into the pylon. The latter are fanned out as usual; the backstay cables on the other side, however, are guided into so called pendulum bearings. Since proper function of cable-stayed bridges can only be ensured with a prevailing equilibrium of forces, the inclined pylon acts as a counterweight. This reduces the tensile forces in the pendulum bearings to a manageable magnitude, albeit the incline causes very high longitudinal forces on the pylon footing bearings.
With dimensions of 3.0 x 3.0 mm and a height of 480 mm, the two MSM® spherical bearings underneath the pylon footings are the largest CE-marked bearings that have ever been installed in a bridge or a building. Each of them weighs 26t; they accommodate structural loads of up to 231,000 kN and balance rotations of the pylon.
A further challenge besides the mere size was erecting the pylons on these bearings. When the pylon gains height segment by segment, it gets continuously heavier and the two bearings push outwards. The restraint forces thus created would have been very difficult to accommodate.
Therefore MAURER developed a solution that allowed for transverse movement during the construction phase: one of the bearings was not completely fixed from the beginning but featured a temporary sliding plane transversally to the structure. This moveable bearing was locked in place after pretension of the last inclined cables. Even with this measure the horizontal forces still amount to 45,000 kN.
Besides the two large bearings, the pendulum bearings posed a further challenge. They are positioned in pairs underneath the eight backstay cables, with each pendulum transmitting the tensile force of one cable, approx. 8,000 kN. In total, at this point 63,800 kN are transferred into the foundations.
The pendulum bearings each consist of two steel mounting plates. These are positioned laterally at the two rod ends at the top of the steel superstructure and at the bottom at the anchoring plate. Mounting plates and rod ends were connected with large bolts. Inside the rod ends there are large axial pivoting bearings. These bearings allow for rotations and enable longitudinal displacement of the bridge.
The interface superstructure-bearing posed another challenge. The steel superstructure was manufactured in China, the pendulum including its special bearings in Munich. An intensive coordination process ensured that the bearings fit precisely into the superstructure.
Shear Keys and Spherical Bearings
MAURER supplied further bearings for the Signature Bridge. At the ends of the main bridge and the feeder bridge, one shear key each was installed. 34 spherical bearings have been placed on the bridge pillars.
Building owner is Delhi Tourism and Transportation Development Corporation (DTTDC); building contractor is a joint venture of Gammon (India), Construtora Cidade (Brazil) and Tensacciai (Italy).
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