Bridge Loadings Around The World
1966 Edition

IRC SP 4 specifies standard vehicular live loads including a uniform live load on bridge decks generally at 400 kg/m², with potential reduction to 250 kg/m² in certain cases. Transverse live loads on railings are set at 100 kg/m, with linear loads of 120 kg/m in urban areas and 80 kg/m elsewhere. Impact factors for steel bridges vary from 15% to 50% depending on span length. Vehicle load models cover Class A and B vehicles, aligning with heavier truck loadings such as H20-S16-44 or H25-S20 standards.

The standard mandates a minimum footbridge width of 1.5 meters to ensure safe pedestrian passage. For footbridge deck loading, it recommends uniform live loads of 500 kg/m² in urban settings and 350 kg/m² for rural main girders. Handrails must be designed to withstand horizontal and vertical loads of 250 kg per meter run. Additionally, the standard accounts for crowd loads and possible accidental vehicle mounting without permitting overstressing. For spans exceeding 30 meters, a specific formula is provided to calculate loading based on span length and footpath width. Surcharge effects on abutments due to approach fill live loads are typically considered equivalent to 2 feet of earth unless an RCC approach slab is present.

IRC SP 4 suggests impact factors depend on both material and span length. The general formula is p = 1.4 - 0.008 × L (L = span length in meters), with a minimum of 1.0. Steel bridges use this formula without differentiation by load type. Concrete bridges have a maximum impact factor of 1.3 (30%), applied to main girders and structural members, decreasing with longer spans. Timber bridges maintain a constant impact factor of 1.2 (20%) regardless of span or load. Additionally, HA loading includes a 25% impact on the heaviest axle, while HB loading does not apply any impact factor.

When a properly designed RCC approach slab extends at least 12 feet into the approach covering the full roadway width and resting on the abutment, no live load surcharge on the abutment is accounted for. Otherwise, surcharge loads are applied as uniform pressures on the backfill behind the abutment, commonly ranging from 0.4 to 0.5 t/m², representing the equivalent of 2 to 4 feet of earth fill surcharge. This surcharge increases lateral earth pressures and must be included in abutment stability and structural design. These provisions ensure safe design against live load effects on approach fills.

IRC SP 4 compares loading practices from multiple countries, focusing on load types like single truck, lane, and train loads, and their associated impact factors. For instance, concrete bridges internationally use impact factors up to 30%, with steel and prestressed concrete bridges showing similar span-dependent variations. Wind loads differ, with the USA applying 100 lb/ft on moving loads 6 ft above deck, Austria considering 2.5 m high rectangular traffic areas, and Canada specifying transverse and longitudinal forces for traffic. Load distribution methods vary, with the UK using three axles per lane spaced 1.5 m apart and limiting simultaneous lane loadings to two lanes. These comparisons aid in harmonizing Indian design with global standards.