'Fire protection' for structural steel (IS 800 Cl. 16) is needed because:
Choose the correct answer
Steel corrodes rapidly in fire
Steel strength drops to 60% at 500°C — fire protection maintains structural integrity until evacuation; required FRR by IS 800 Cl. 16
Steel expands too much without protection
Fire protection only improves aesthetics
Correct Answer
B. Steel strength drops to 60% at 500°C — fire protection maintains structural integrity until evacuation; required FRR by IS 800 Cl. 16
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Steel at elevated temperatures: yield strength fy drops to 60% at 500°C and 23% at 700°C (IS 800 Table 21). Structural failure when steel temperature reaches critical temperature (typically 550°C for members at design load ratio). Protection methods: (1) Intumescent coating (expands and chars at heat → insulating layer); (2) Board/spray fire protection (gypsum boards, vermiculite spray); (3) Concrete encasement; (4) Water-filling hollow sections. Fire resistance rating (FRR) depends on protection thickness and material.
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