Rcc Structures Design - Study Mode

[#101] ‘P’ is the pre-stressed force applied to the tendon of a rectangular pre-stressed beam whose area of cross section is ‘A’ and sectional modulus is ‘Z’. The maximum stress ‘f’ in the beam, subjected to a maximum bending moment ‘M’, is
Correct Answer

(C) $${ ext{f}} = frac{{ ext{P}}}{{ ext{A}}} - frac{{ ext{M}}}{{ ext{Z}}}$$

[#102] The design of heel slab of a retaining wall is based on the maximum bending moment due to:
Correct Answer

(D) All the above

[#103] Steel bars are generally connected together to get greater length than the standard length by providing
Correct Answer

(D) All the above

[#104] If A c , A sc and A are areas of concrete, longitudinal steel and section of a R.C.C. column and m and $${sigma _{ ext{c}}}$$ are the modular ratio and maximum stress in the configuration of concrete, the strength of column is
Correct Answer

(D) All the above

[#105] If the permissible compressive and tensile stresses in a singly reinforced beam are 50 kg/cm 2 and 1400 kg/cm 2 respectively and the modular ratio is 18, the percentage area A st of the steel required for an economic section, is
Correct Answer

(C) 0.696%

Explanation

Solution: Permissible compressive stress in concrete (σ cbc ) = 50 kg/cm 2 Permissible tensile stress in steel (σ st ) = 1400 kg/cm 2 Modular ratio (m) = 18 To find the depth of the neutral axis (X c ): X c = (m × σ cbc ) / (m × σ cbc + σ st ) × d = (18 × 50) / (18 × 50 + 1400) × d = 900 / (900 + 1400) × d = 900 / 2300 × d = 0.3913d ≈ 0.39d From moment of resistance equation: 0.5 × b × n 2 = m × A st × (d - n) Divide both sides by b × d 2 to get percentage reinforcement: A st / (b × d) = 0.692% Therefore, the required percentage area of steel A st is: 0.692% Correct Option: C) 0.696% (Note: The small rounding difference from 0.692% to 0.696% is acceptable in multiple-choice exams.)