For limit state of collapse, the partial safety factors recommended by IS 456:2000 for estimating the design
strength of concrete and reinforcing steel are respectively-
-
A.
1.5 and 1.15
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B.
1.0 and 1.0
-
C.
1.15 and 1.5
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D.
1.5 and 1.0
Correct Answer:
A. 1.5 and 1.15
Explanation:
As per IS 456:2000, Clause 36.4.2, the design strength of materials is determined by applying partial safety factors to their characteristic strengths to account for uncertainties in material properties and manufacturing. For the limit state of collapse, the code recommends a partial safety factor of 1.5 for concrete and 1.15 for steel reinforcement.
The factor for concrete is higher because its strength is more variable, depending on site conditions like mixing, compaction, and curing, whereas steel is produced in controlled factory environments, ensuring more consistent quality. Applying these factors results in the following design strengths: - Design strength of concrete = 0.67 \* fck / 1.5 = 0.447 \* fck
- Design strength of steel = fy / 1.15 = 0.87 \* fy
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