The work consists of construction of cast-in-situ and pre-cast, pre-stressed concrete box girders for up and down tracks up to a maximum span of 30 M including parapets, kerbs, gang path made from pre-cast slabs complete at an elevation of 5 to 10 M from ground level. The work was done in the densely populated area of Chennai at Luz-corner, crossing a very busy main road where vehicular traffic remains open for 24 hours. Most of the PSC box girder beams were casted over temporary trusses spanning between the trestle columns. Centering has been specially designed for bottom, sides and top slab considering the weight of beam and various sequences of operation of casting of beams.
A high strength concrete of M-50 grade along with super plasticizer and admixtures were used for beams and cantilevers. Before casting the beams, 9 number cables to particular profile were installed at pre-designed location. After casting of beams, designed number of strand wires, duly painted with waterproof epoxy paint, were inserted in the cables and on pre-determined sequences they were stressed to designed load by special heavy duty hydraulic Jacks.
Pre-cast box beams were casted on already completed area, on specially prepared beds at design elevation, practically using the same sequence of operations as that of cast-in-situ girder beams. The entire work was completed in two and half year’s period against heavy odds of busy traffic area, involving around 70 Nos. of PSC box girder beams with other related items.