2013-2017 | Arrah to Chhapra, Bihar, India
This four-lane highway bridge over the Ganga (Ganges) River near Patna in Bihar, India, was procured through a Design-Build contract. McElhanney successfully value engineered an extradosed segmental bridge concept with 16 back-to-back 120m-long spans that reduced construction duration and material consumption for the 1,920m navigation spans portion of the 4km bridge. Approach spans outside the navigation spans utilizes precast segmental erected in span-by-span. The bridge opened in June 2017.
The extradosed superstructure consists of a 20.5m wide single cell precast concrete box girder with a plane of stay cables and pylons down the median, erected through balanced cantilevering. The exterior dimensions of the box girder were maintained from the segmental approach spans so forms could be reused; however, the interior core forms were modified to suit the demands of the longer stay supported spans. Stay cables consist of 5 parallel stays each with 61 strands anchored within the box girder and passing through saddles in the 1m wide pylons.
The substructure consists of integral twin thin-walled bladed piers supported on sunken well foundations (caissons). During the value engineering process, the well foundations were already being installed based on the original bridge design, so the locations and capacity had to be respected and incorporated into the revised concept. The team provided for mid-span expansion joints in every third span, along with internal steel shear beams to transfer bending moments and vertical shear forces across the expansion joint gap.
The site conditions have proved challenging due to extreme scour depths, high seismicity, high water currents, and exceptionally large water level variations. Additionally, the construction means and methods needed to address the river level fluctuations and extreme rains associated with monsoon season.
The project earned a 2018 ACEC-BC Award of Merit.
McElhanney provided the following services:
- Concept development and detailed design of the extradosed system
- Construction engineering including preparation of construction manual and geometry control manual
- Preparation of precast segment shop drawings
- Review of shop drawings prepared by suppliers and fabricators
- Development of construction program and schedule
- Vetting of supplier proposals
- On-site support and Quality Assurance
- Load testing protocol development