Explanatory Handbook to IRC:112-2011: Code of Practice for Concrete Roads Bridges
2015 Edition

Key considerations for punching shear in concrete bridge decks per IRC SP 105 include evaluating shear stresses at the loaded area face to prevent crushing of concrete struts and assessing shear capacity along the control perimeter to determine the necessity for shear reinforcement. If the capacity is inadequate, measures such as increasing slab thickness, expanding the loaded area perimeter, or using higher grade concrete are recommended. Loads located within two times the effective depth from supports experience reduced shear effects due to arching action, and this reduction is accounted for in design. Shear reinforcement design must consider loads between half and twice the effective depth separately using reduction factors, combining reinforcement requirements from all loads. Ensuring a ductile failure mode by maintaining under-reinforced sections in line with strain limits is vital for safety.

The handbook guides bending moment calculations for continuous beams by providing formulae for ultimate limit state moments due to dead and live loads. For example, mid-span dead load moments and support reactions are calculated as proportions of load intensity times span length squared. It notes restrictions on applying certain formulas near intermediate supports and points of contraflexure due to heightened bending and cracking risks. For prestressed concrete beams, the state of cracking determines the formula used; uncracked sections permit simplified expressions, while cracked sections require more detailed calculations and provision of shear reinforcement.

Reinforcement steel must comply with IS 1786 standards for high strength deformed bars, including options for galvanized and stainless steel to enhance corrosion resistance, with mechanical properties verified per Indian codes. Concrete grades are selected based on exposure conditions and abrasion severity, with durability requirements guided by environmental classification. Quality control encompasses mix design validation, proper curing regimes, and strength testing in accordance with IS 456 and related standards. These measures ensure that materials possess adequate strength, ductility, and durability for bridge construction.

Designing curved prestressing tendons in thin concrete sections requires accounting for induced inward, in-plane, and out-of-plane pressures that create local punching shear risks. Internal tensile stresses due to tendon curvature must be evaluated, and shear reinforcement such as links or stirrups should be provided near curved tendons to resist these forces. Sudden changes in cross-section or tendon profile should be avoided or checked with detailed stress analysis. Prestressing forces are treated as external loads for reinforcement stress checks. Anchorage zones must be reinforced following supplier guidelines, and horizontal or inclined closed links or bent-up bars spaced proportionally to slab depth are employed to enhance shear resistance. This detailed approach ensures structural integrity and crack control.

The handbook recommends first-order linear-elastic analysis without moment redistribution for global stability assessments. For ultimate and serviceability limit state load effects in integral or continuous bridges, first-order linear-elastic analysis with moment redistribution capped at 10% is advised. Verification of imposed deformations, such as buckling, requires second-order linear-elastic analysis with limits on second-order effects. Section design under ultimate limit states involving material non-linearity utilizes first-order non-linear analysis with bi-linear stress-strain models, while slender element designs employ second-order non-linear analysis. Plastic analysis incorporating hinge mechanisms and ductility considerations is applied for accidental and seismic load cases. Local non-linear strain zones like corbels and anchorages are analyzed using the strut-and-tie method. Detailed non-linear analyses are reserved for rare situations involving inelastic seismic deformation.