Standard Plan for Highway Bridges — Prestressed Concrete Beams and RCC Slab Type Superstructure Volume-II
1997 Edition

The recommended materials for prestressed concrete beams according to MoRTH 256 Part 2 include a design mix concrete with a minimum 28-day characteristic strength of 40 MPa (tested on 150 mm cubes). Cement should comply with IS 269 (Ordinary Portland Cement) or IS 8112 (High Strength OPC) with cement content ranging from 400 to 540 kg/m³ and a maximum water-cement ratio of 0.40 for deck slabs and precast girders. Admixtures permissible under IS 6925 and IS 9103 should exclude those generating hydrogen, nitrogen, or chlorides. Reinforcement consists of HYSD bars of grade S 415 per IS 1786. Prestressing steel strands are single 12.7 mm diameter, 7-ply Class 2 strands conforming to IS 6006-1983, with a maximum allowable tension force of 128.6 kN per strand. External strands must be protected using polyethylene sheathing and grouted. Sheathing is typically of the "Drossbach" type with 75 mm internal diameter and at least 0.4 mm thick bright metal strip, adhering to IRC:18-1985 testing requirements.

The one-end prestressing strand system, per IS MoRTH 256 Part 2, employs cables consisting of 12 strands, each 12.7 mm in diameter and 7-ply Class 2 as per IS 6006-1983 for primary prestressing. Future prestressing provisions utilize single 12.7 mm diameter strands, tensioned up to 128.6 kN using mono strand jacks exclusively. Both live ends and dead ends use live-end type anchorages; buried dead-end anchorages are not permitted. At the dead end, strands are pre-blocked prior to tensioning to prevent slip, and if slippage occurs, the tensioning extension at the live end is adjusted accordingly. Sheathing employs the "Drossbach" type, 75 mm ID, minimum 0.4 mm bright metal strip tested as per IRC specifications. Minor adjustments to two-end system drawings are made, supplemented by new standard drawings specific to the one-end system.

For 30-meter span highway bridges under MoRTH 256 Part 2, the dimensions and reinforcement details vary based on footpath inclusion. With footpaths, each footpath typically measures between 1.5 to 2.0 meters in width, designed to carry a load of 5 kN/m². Public utility ducts of 150 mm diameter are embedded within the footpaths. Wearing coat comprises a 6 mm mastic asphalt layer plus 50 mm of asphaltic concrete. RCC railings follow SD/305 drawings. Deck slab thickness ranges from 200 to 250 mm. Reinforcement consists of HYSD bars grade S415 per IS 1786, with concrete strength at 40 MPa. Prestressing strands are 12.7 mm diameter, 7-ply as per IS 6006-1983. Without footpaths, carriageway width corresponds to lane requirements, commonly 7.5 m for two lanes, with a similar wearing coat and deck slab thickness. RCC railing conforms to SD/304. Reinforcement and concrete specifications remain consistent, but no footpath loads or utility ducts are accounted for.

To maintain structural integrity during prestressing per MoRTH 256 Part 2, tensioning should be carried out using multistrand jacks equipped with pressure gauges as specified by the prestressing system manufacturer. Anchorage devices at dead ends must be identical to those at live ends, with buried dead-end anchorages prohibited. Strands at the dead end must be pre-blocked prior to tensioning from the live end to prevent slip. If slip is detected during stressing at the dead end, the slip distance should be added to the extension length at the live end. The cables are 12.7 mm diameter, 7-ply Class 2 strands as per IS 6006-1983, sheathed with Drossbach-type sheathing (75 mm ID, minimum 0.4 mm bright metal strip). This procedure ensures full force transfer without loss due to slippage and preserves the bridge's structural safety.

MoRTH 256 Part 2 provides for future prestressing by incorporating single 12.7 mm diameter, 7-ply Class 2 strands as per IS 6006-1983, with a maximum tensioning force of 128.6 kN per strand, tensioned using approved mono strand jacks. All externally placed strands are to be protected with polyethylene sheathing and grouted to prevent corrosion. Maintenance requirements include a bituminous wearing coat consisting of a 6 mm thick mastic asphalt layer (12 mm in high rainfall zones) applied over a prime coat, topped by 50 mm of asphaltic concrete in two layers of 25 mm each. An alternative for high traffic areas is a combination of 40 mm bituminous concrete plus 25 mm of bitumen mastic. Anti-corrosion treatments must be applied to reinforcement and exposed concrete in severe exposure conditions as approved. Provision for 150 mm diameter utility ducts is included within footpaths, with a maximum load of 1.0 kN/m. These measures ensure the bridge superstructure can accommodate future prestressing needs and maintain long-term durability.