Digha Patna Extradosed Bridge

The project involves the construction of a 6.3KM six/four-lane road from R' Block-Digha (Phase-1) in Patna, Bihar. It includes structures such as flyovers, underpasses, drains, and service roads, executed in an Engineering, Procurement & Construction (EPC) procurement. The authority's primary goal was to enhance the locality's aesthetic appeal, which led to the transformation of the short span junction over Bailey Road into an extradosed bridge.

Our team conducted an independent design review of a the extradosed bridge. This flyover traverses a busy junction at Bailey Road with a span configuration of 25m - 50m - 25m and a central single plane of stay cables. The superstructure comprises a 3-span continuous post-tensioned two-cell box girder with a constant depth of 2.5m. The total deck width is 18.5m, divided into two 3.75m lanes in each direction with a 2.5m wide median in between. Every integral pier is supported by ten - 1.2m diameter cast-in-place bored piles.

Using a form traveler was not feasible due to clearance requirements. Operation of the roadway underneath ruled out casting on falsework. Therefore, a unique method was chosen, which involved supporting each cantilever segment over shifting ground-supported shoring. This reduced the structural demands during construction and simplified the verification process during erection. The risk of the form traveler falling, a critical condition, was not a concern in this scenario, resulting in further savings for the developer. Another unique feature was the distinctive lower pylon configuration. To mitigate thermal forces, the pier was divided into four columns. This division created portal action in the transverse direction and increased the footprint of the piers. As a result, it was possible to simultaneously simplify the reinforcement in the pier table and diaphragm region.