Need for quick launch of bridges for vehicles

The successful completion of bridges depends upon construction methodology, resource planning, appropriate choice of materials and technology.“There is a huge requirement of bridges just for crossing purposes, which may not require IRC loadings,” says NN Sinha, Chairman, National Highways Authority of India (NHAI), and Managing Director, National Highways & Infrastructure Development Corporation (NHIDCL). “This calls for quick launch of bridges for light vehicles, which may be segmental, precast or steel girder, which can be launched within the shortest possible time. Further, the structure needs to be made lean and thin to save quantities and working time. Use of fibre reinforcement has reportedly resulted in leaner and longer span structures.”Earlier, limited computation facilities and decisions based on least capital cost led to conventional small-span bridges. Today, the contractor or concessionaire is free to design based on lifecycle cost, including the time required for project implementation. “Now, long-span bridges are a common feature,” observes Sinha, adding that the use of high-strength concrete is routine. The facility for bigger diameter pile foundations has replaced conventional well foundation and precast segmental construction has taken over the conventional cast-in-situ method.“Ways to reduce execution time include parallel activities such as pre-casting superstructure elements, increasing the length of precast segments, using superior grade, high-performance concrete for early de-moulding, steam curing, etc,” says SV Desai, Executive Vice-President & Head - Heavy Civil Infrastructure IC, L&T Construction. “Design considerations such as low permeability to chlorides and sulphates, smooth external surface blemishes and reduction in joints in piers are some challenges.” The third Narmada Bridge in Bharuch was constructed in a record time of 33 months, safely handling heavy segments. L&T is currently executing four more iconic bridges: Hyderabad’s Durgam Cheruvu, Amaravati Bridge, MTHL Packages 1 and 3, and the Mumbai Coastal Road Project. “When we bid for the Bogibeel Bridge project, the plan was to commence construction from both ends of Dibrugarh district as well as Silapathar simultaneously,” shares RVR Kishore, Project Director, Hindustan Construction Company. “However, after bagging the work order, we reviewed all the assumptions made at the tendering stage. Considering ground conditions, we decided to start construction from one end, not both ends. This resulted in savings in terms of construction time, mobilisation of resources and availability of resources.”For Tata Projects, a standout project is Bridge HTMJ 2+3, an open web girder launched in Hathras (Lot 103, Aldesa project). “This bridge, launched over an existing Indian Railways track, is one of a kind, where both tracks of DFCC are on a single bridge,” says Vivek Gautam, COO - Strategic Business Group – Core Infra, Tata Projects. Another landmark project for a Tata Projects-led JV is a 7.8-km bridge section across Mumbai Bay, including Shivaji Nagar Interchange at Navi Mumbai, as part of MTHL. “The project will use reverse circulation drill (RCD) method for foundation and erection of a large block (180 m) orthotropic steel deck structure at navigational span,” he adds. This is a method of piling in hard rock strata wherein the machine drills through the rock and the cut material gets mixed with water, which the machine brings back to the surface by using pressurised air. An orthotropic steel desk structure, with a structural steel plate and extended arm located at the obligatory span, enables navigation.Dineshchandra R Agrawal Infracon has executed several bridge projects in various states, including Gujarat, Delhi, Maharashtra, West Bengal and Rajasthan. Hardik Agrawal, Director, refers to the flyover at Indian Institute of Management, Ahmedabad as a landmark project. “It is not just a bridge project; we have also built a public recreation area with a library and tea lounge under the bridge,” he elaborates. “There is another open space or design with intricate glasswork and a green patch that provides for public events. This project aims to make the urban ecosystem better.”  Meanwhile, Nitesh Kumar Asati, Joint General Manager, IRCON, says, “We usually follow RDSO standard drawings for railway spans. We have constructed a RoB in Rajasthan, where we designed the railway span with composite girders having 100-m radius curvature based on the alignment of the bridge, to make the structure more aesthetic, as per the client’s (GoR) requirement. Since no drawing was available in the RDSO drawing list, we have submitted our design to the Railways and RDSO and accorded approval from them.”SHRIYAL SETHUMADHAVAN