Steel for: long spans (>30m), rapid construction, curved alignment, replacement bridges. Concrete for: short-medium spans, lower maintenance, longer life, availability of materials.

IRC 24:2010 primarily adopts the Limit State Method (LSM) for design. LSM considers multiple limit states, including the ultimate limit state (for safety against collapse) and the serviceability limit state (for performance under normal use). This contrasts with the Working Stress Method (WSM), which uses a factor of safety to keep stresses below the elastic limit under service loads. LSM generally leads to more economical and realistic designs by considering the actual behavior of materials and structures.

IRC 24:2010 mandates the consideration of various loads including dead loads (self-weight of the structure, wearing coat), live loads (traffic loads as per IRC:6), wind loads, seismic loads, braking forces, and centrifugal forces. These loads are combined using appropriate load factors and combinations as specified in Table 3 to ensure the bridge can withstand all critical scenarios.

The design of plate girders involves ensuring adequate bending strength, shear strength, and stability of the web and flanges. Key considerations include determining the appropriate thickness and depth of the web and flanges, calculating the required stiffeners (longitudinal and transverse) to prevent buckling, and checking for local buckling of flanges and web panels. Clause 10 provides detailed guidance on these aspects.

Stiffeners, both longitudinal and transverse, are crucial for the stability of the web in plate girders. Transverse stiffeners prevent the web from buckling under shear forces and bending moments, while longitudinal stiffeners enhance the flexural rigidity and buckling resistance of the web. Table 5 provides guidelines on their spacing and minimum dimensions, which are critical for preventing web instability.

IRC 24:2010 includes provisions for composite steel-concrete bridges, where steel girders work compositely with a concrete deck slab. The design focuses on ensuring adequate shear transfer between the steel and concrete elements through shear connectors (like shear studs) and checking the combined flexural capacity and serviceability of the composite section. Clause 16 outlines the fundamental principles for this type of construction.

Steel bridges typically use riveted, bolted, or welded connections. IRC 24:2010 provides guidance on the design of these connections based on tensile, shear, and bearing strengths of the fasteners or welds. Design considerations include ensuring sufficient number of fasteners or weld size, proper edge distances, and checks for block shear failure and net section fracture for bolted connections.

Fatigue is a critical consideration, particularly for bridges subjected to repeated cycles of heavy traffic loading. IRC 24:2010 emphasizes checking critical details, connections, and welds for potential fatigue failure. The design should account for stress ranges and the number of cycles expected during the bridge's design life to prevent premature failure.

IRC 24:2010 specifies minimum vertical and horizontal clearances for underbridges to ensure safe passage of road and rail traffic below. A typical minimum vertical clearance is 5.4 meters, and a minimum horizontal clearance is 7.5 meters. However, these values can vary based on the type of traffic and specific site conditions, and are often governed by other IRC codes as well.

Lateral torsional buckling (LTB) is a critical stability issue for compression flanges of flexural members like plate girders. IRC 24:2010 provides methods to check for LTB, which often involves calculating the effective length of the compression flange and applying appropriate reduction factors to the bending strength based on the slenderness of the member. The maximum unsupported length of a compression flange is also stipulated.

IRC 24:2010, based on the Limit State Method, uses partial safety factors for materials rather than directly permissible stresses for ultimate strength. However, for serviceability checks, stresses are compared against yield stress and ultimate tensile strength with appropriate reduction factors. Table 2 provides permissible stresses for various conditions, primarily for understanding behavior under service loads and for certain detailing aspects.

Yes, IRC 24:2010 includes requirements for bearing plates and connection plates to ensure adequate strength and prevent local failure. Minimum thicknesses are specified, and design checks for bearing pressure, shear, and bending are necessary. These components are critical for transferring loads to supports or connecting different structural elements.

The Indian Roads Congress (IRC) is the premier body responsible for formulating and updating standards and codes of practice for roads and bridges in India. IRC 24:2010 is one such code, providing comprehensive guidelines for the design, construction, and material specifications for steel road bridges, ensuring uniformity, safety, and efficiency across national and state highway projects managed by MoRTH and NHAI.