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Road Over Bridges
Where the road has to go over instead of under — multi-span structures on pile foundations, combining precast concrete and composite steel decks across live running lines.
The work
Sometimes the road cannot go under.
A road under bridge needs depth — room to drop the carriageway below the formation and drain it. Where the ground water is high, the embankment is shallow, or the road carries heavy traffic that cannot take a dip, the crossing has to go over the top instead.
That means a bridge: piled foundations either side of the railway, piers, and girders long enough to clear every track with the statutory headroom for overhead electrification below.
Nothing may be dropped, and nothing may foul the overhead line. Every lift happens inside a block, at night, with the traction current off.
We built the two-lane road over bridge at Km 347/33–35 between Regadipalli and Vanganur stations for South Central Railway's Construction Organisation — three spans, on piles, crossing the railway at forty-five degrees.
The structure
Three spans, two girder types, one crossing.
Drawn to scale from the span arrangement in the letter of acceptance. The centre span is a composite girder — steel ‘I’ girders carrying an RCC deck slab — because it has to reach across every track in one clear span. The flanking spans are precast prestressed concrete.
Elevation drawn to scale from the span arrangement recorded in the letter of acceptance dated 16.08.2016.
Span lengths and girder types are as specified. Pier heights, pile depths and deck width are indicative only.
The hard part
The bridge crosses the railway at 45 degrees.
Read the contract dimensions carefully and a detail emerges: every span is quoted twice — once as a skew length and once as a square length. 28.284 m and 20.0 m. 42.496 m and 30.0 m.
Those are not two different measurements of the same thing by accident. 28.284 is 20 × √2. The road meets the railway at forty-five degrees, so each girder has to be roughly forty per cent longer than the distance it actually spans across the track.
A skew crossing is harder in every direction. Girders are longer and heavier for the same clearance. The deck is a parallelogram, not a rectangle. Load distributes unevenly towards the obtuse corners, bearings have to be set to the skew, and the pier caps sit at an angle to the deck they carry.
cos⁻¹ (1 ÷ 1.4142) = 45.0° Skew angle derived from the contract span dimensions
Scope of works
Six priced schedules.
The contract was let against six separate schedules, which between them describe the whole structure from pile to parapet.
General civil works
Earthwork, substructure and general items rated against the Unified Standard Schedule of Rates 2010.
Casing pipe & reinforcement
Providing, fabricating and installing casing pipe and reinforcement steel for the bored pile foundations.
Structural steel
Fabrication and erection of structural steelwork as non-schedule items.
Composite girder
The 42.496 m centre span — steel ‘I’ girders with an RCC deck slab acting compositely.
Non-schedule items
Bearings, expansion joints, crash barriers, railings, drainage and finishing items.
Cement
Cement supply for the pile foundations, substructure, PSC girders and deck slab.
Project record
Regadipalli–Vanganur Road Over Bridge
- Railway
- South Central RailwayChief Administrative Officer (Construction), Secunderabad · Guntakal Division
- Location
- Km 347/33–35, between Regadipalli and Vanganur stationsAndhra Pradesh
- Structure
- Two-lane road over bridge on pile foundations1 × 28.284 m PSC girder + 1 × 42.496 m composite girder (steel ‘I’ girder with RCC deck slab) + 1 × 28.284 m PSC girder
- Tender
- Notice No. 04/CAO/C/SC/2016 dated 05.02.2016Opened 14.03.2016 · negotiated offer 04.08.2016
- Acceptance
- 16.08.2016Letter No. W.CON.496/AG/ROB/RLL-VRN/S894/WC.3
- Agreement
- 54H/CAO/C/SC/2016 dated 24.11.2016
- Commenced
- 10.02.2017
- Completed
- 10.11.2018Extended to 31.12.2018 without penalty — completed ahead of the extended date
- Performance
- Certified satisfactoryWork completion certificate issued by Dy. Chief Engineer/Construction, Guntur
On site
During construction.
Click to enlarge. Three photographs of this package are on record; further site photography would strengthen this page.
Get in touch
Planning a crossing over the line?
Send the location, the number of tracks to be spanned and the skew, and we will come back with the span arrangement we would propose and our record on similar structures.