Questions
8 questions per paper
Difficulty
Medium-Hard
Importance
Core — never skip
Overview
RCC and Steel Design form the backbone of Structural Engineering in PSU exams, focusing on the limit state philosophy for reinforced concrete and the plastic/elastic design principles for steel structures. Mastery of IS 456:2000 and IS 800:2007 codes is essential, as the majority of questions test your ability to apply empirical formulas to practical design scenarios.
Limit State Design (LSD) of RCC
LSD focuses on the safety and serviceability of structures under factored loads. Candidates must prioritize the stress-strain distribution diagrams and the calculation of the depth of the neutral axis.
- Xu,max = 0.48d for Fe415 and 0.46d for Fe500
- Factored load = 1.5 * (Dead Load + Live Load)
- Partial safety factor for concrete (gamma_m) = 1.5
- Partial safety factor for steel (gamma_s) = 1.15
- Modulus of elasticity of concrete (Ec) = 5000 * sqrt(fck)
Flexure, Shear, and Torsion
These topics deal with internal stresses induced by bending moments, shear forces, and twisting moments. Questions frequently ask for minimum shear reinforcement or the design of singly/doubly reinforced beams.
- Mu,lim = 0.36 * fck * b * Xu,max * (d - 0.42 * Xu,max)
- Minimum shear reinforcement (Asv/bsv) >= 0.4 / (0.87 * fy)
- Equivalent shear = Vu + (1.6 * Tu / b)
- Equivalent moment = Mu + Tu * (1 + D/b) / 1.7
- Spacing of stirrups (sv) <= 0.75d or 300mm
Columns and Footings
Design of compression members involves checking slenderness ratios and minimum eccentricities. Focus on short column load-carrying capacity formulas and area of steel reinforcement.
- Pu = 0.4 * fck * Ac + 0.67 * fy * Asc
- Minimum longitudinal reinforcement = 0.8% of Gross Area
- Minimum eccentricity (emin) = (L/500) + (D/30) >= 20mm
- Maximum longitudinal reinforcement = 6% of Gross Area
- Pitch of lateral ties <= least lateral dimension, 16*phi, or 300mm
Steel Design: Welded & Bolted Connections
Steel design relies heavily on calculating the strength of joints. Know the difference between shear capacity, bearing capacity, and the throat thickness of fillet welds.
- Bolt Strength = min(Shear capacity, Bearing capacity)
- Shear capacity (Vdsb) = (fub / (sqrt(3) * gamma_mb)) * Anb
- Bearing capacity (Vdpb) = 2.5 * kb * d * t * fu
- Effective throat thickness (te) = k * s (k = 0.7 for 90 deg)
- Design strength of weld = (lw * te * fu) / (sqrt(3) * gamma_mw)
Formula Sheet
Mu,lim = 0.36 * fck * b * Xu,max * (d - 0.42 * Xu,max)
Pu = 0.4 * fck * Ac + 0.67 * fy * Asc
Vdsb = (fub / (sqrt(3) * 1.25)) * Anb
Vdpb = 2.5 * kb * d * t * fu
Effective throat thickness = 0.7 * size of weld
Ec = 5000 * sqrt(fck)
Xu,max = (700 / (1100 + 0.87 * fy)) * d
Exam Tip
Memorize the limit state values for Xu,max/d and the constant partial safety factors, as these are the starting points for almost every numerical problem.
Common Mistakes
- Confusing partial safety factors for concrete and steel leading to incorrect factored load calculations.
- Neglecting the k-factor (fusion factor) when calculating the effective throat thickness in fillet welds.
- Incorrectly assuming the neutral axis depth equals the maximum depth (Xu,max) for all beam design problems.
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