Terrible, Terrible loss of 17 human lives and about 80 injured. IVRCL the contractor claim, they have done nothing wrong and that it is the act of God. !!!
From the many photos of the collapse available online, the failure appears to have initiated at the tapered, double-cantilevered box beams, adjacent to the single pier, steel box structure. Evidence of web plate buckling and tearing.
This cantilevered pier-beam arrangement supported three x 3-plate steel girders of approx 1.8m (6 feet) in depth, for each half of the overpass (6 plate girders on total). The cantilever length of the supporting beams is considerable, yet the tapered box girder depth looks rather shallow.
They appear to have used steel channels sections to achieve composite action to the CIP deck slab. But the collapse has resulted on very 'clean' failure planes across the welded channel.
