Question

Beam sections of reinforced concrete designed in accordance with ultimate strength or limit state design approach, as compared to sections designed by working stress method for the same conditions of load and span, and the same width, usually have

• A. a larger depth and smaller amount of reinforcement
• B. the same depth and same reinforcement
• C. smaller depth and more reinforcement
• D. same depth as that of a deep beam

Answer 1

The correct option is C smaller depth and more reinforcement

(c)
LSM and ULM follow non linear stress-strain curve of steel and concrete i.e. utilize the strength in plastic zone. So sections designed have lesser depth in comparison to member designed by WSM. For the same load, bending moment is more in case of LSM compared to WSM due to provisions for partial safety factors. As depth decreases in LSM, lever arm decreases and hence larger area of reinforcement is required as compared to WSM.