Precast Concrete Stations for Metro Projects: A Challenge to Designers & Constructors

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Summary

Usually Metro Structures are provided in the busy areas, in order to reduce traffic congestion. A very common route for Metro Viaducts is to provide it over existing roads, with piers in the median. Hence, in most of the instances, the elevated station is located over the road, making it a challenge to construct, as the running road traffic can't be disturbed. Structural designs need to provide a scheme that is constructible over the running roads. The paper covers details of various such elevated stations in Delhi & Bangalore, designed by the author and constructed by others and other stations in Kolkata, being designed by the author. The precast elements include Post-Tensioned pier cap, Pretensioned Double- Tees, Post- Tensioned L-beams, Post-Tensioned Cantilever Arms, Pretensioned I-Girders, Pretensioned U-beams etc. Extensive use of Pretensioning and Post-Tensioning has been made. The concept is such that it entails a speedy construction, yet allowing the traffic to keep running during construction.

Figure 1: View of a Typical Metro Station	Figure 2: View of a Typical on Road Metro Station

General

As the world is moving towards speedy construction, it has become imperative to go for either of steel or precast concrete for construction. Incidentally, steel turns out more expensive in Indian conditions, and it also needs special considerations towards its fire proofness, well trained fabricators & aesthetics. Hence, Precast Concrete becomes an obvious choice with the owner. Use of techniques entailing speedy construction automatically reduces disturbance to the running traffic during construction. The other recent awakening in the field of construction is that of sustainability & environment concerns. It has been amplified in several forums that quantity of concrete used should be reduced to minimum, in order to conserve the natural resources and also reduce the emission of CO2, which is liberated during production of cement. This aspect has led to the use of prestressed concrete that entails lesser concrete volumes for the same spans and loadings. Use of prestressing also leads to reduced construction time. Hence, this paper discusses several projects of Overhead Metros Stations designed by the author for Delhi Metro, Bangalore Metro, Malaysian Metro, Gurgaon Metro and Kolkata Metro.