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Extradosed Experience
The new bridge over the Narmada river at Bharuch in Gujarat, India, which has now been equipped with mageba disc bearings, spherical bearings and modular expansion joints, is just the latest impressive extradosed bridge for which we have supplied such key components.
Where the eight-lane Delhi-Mumbai Expressway crosses the Narmada river in the district of Bharuch in Gujarat, western India, a new eight-lane bridge has been constructed to ensure unhindered flow of traffic across the river at this particular location. The bridge is of the extradosed type, which combines the main elements of a prestressed box girder bridge and a cable-stayed bridge, but with the "stay cables" acting as external prestressing tendons – which explains the relatively small angle between the cables and the superstructure, and the correspondingly low height of the pylons, which reach just 13 m above the deck level. The bridge has a total length of 2.22 km, including the viaducts at each end. The parallel extradosed structures each have a length of 1020 m, with two modules of length 510 m each having spans of 75 m, 150 m, 150 m, 150 m and 75 m.
“Needle beam” design at mid-span hinge points
The bridge’s twin superstructures were built using the balanced cantilever method, with structural discontinuities at the mid-span locations where the cantilevers come together. To prevent relative vertical deflection of one side of the discontinuity relative to the other – for example, as traffic travels across – the ends of the cantilevers are connected together by means of large rectangular “needle beams”, which are threaded into slightly larger rectangular recesses in the end of each cantilever. Each needle beam (one at each side of each superstructure at each discontinuity) is supported by eight bearings – four at each side of the discontinuity, half above the beam and half below. The use of four bearings at each end of the needle beam (rather than just two) avoids the need for the bearings to be designed to resist uplift forces – which would not be possible given the limited space available.
mageba’s contribution
Bridges such as this, which combine specialised designs and construction methods and which include different structure types, require specialised knowledge and capabilities in relation to the key components – the bearings and expansion joints – that are so critical to the design and construction. For this bridge, mageba’s Indian subsidiary in Kolkata provided all of the bearings and expansion joints required for the bridge’s construction, including:
64 RESTON®DISC bearings with capacities of up to 10,900 kN, installed at the mid-span locations where the main structure’s balanced cantilevers come together – the preferred bearing type for this purpose since disc bearings can be relatively easily installed “upside down” as required by the eight-bearing solution proposed and developed by mageba
468 RESTON®SPHERICAL bearings designed for loads of up to 1030 kN, with tapered connection plates to accommodate the superstructure’s longitudinal slope – the chosen bearing type for the approach viaducts
648 m of TENSA®MODULAR expansion joints with up to six individual movement gaps each
124 m of TENSA®GRIP single-gap (strip seal) expansion joints
Extradosed experience
mageba’s ability to reliably provide optimal bearing and expansion joint solutions for bridges like this new Narmada river bridge is based on decades of experience on bridge construction and maintenance projects all over the world. Specifically, this includes our contribution to the construction of various extradosed bridges in India such as the 2nd Vivekananda Bridge near Kolkata, as well as extradosed bridges in other countries such as the New Kelani River Bridge in Sri Lanka, the Golden Ears Bridge in Canada, and the St. Croix Bridge in the United States.
Bridge designer: ASC Infratech Pvt Ltd.
Contractor: Ashoka Buildcon Limited
Owner: National Highway Authorities of India
