The 'fire resistance' of an RC member depends primarily on:
Choose the correct answer
Only the grade of concrete (fck value)
Cover (delays heat to steel), section size (thermal mass), and concrete/aggregate type — IS 456 Annex A fire ratings
Only the shape of the section (circular vs rectangular)
Only the yield strength of steel bars
Correct Answer
B. Cover (delays heat to steel), section size (thermal mass), and concrete/aggregate type — IS 456 Annex A fire ratings
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Fire resistance (IS 456 Annex A; IS 3809): (1) Cover to reinforcement — deeper cover delays heat reaching steel; (2) Concrete type (NWC, LWC — lightweight better insulator); (3) Section size — larger section = longer time before temperature rise; (4) Aggregate type (calcareous better, siliceous spall). Fire rating: 0.5hr, 1hr, 1.5hr, 2hr, 3hr, 4hr. Cover requirement: 20mm (0.5hr), 40mm (2hr), 50mm (4hr). Exposed columns: larger minimum dimension required.
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