Post-specific Technical / Engineering Subject Knowledge
Post-specific Technical / Engineering Subject Knowledge is the decisive section for DSSSB AE. The paper follows the discipline notified for the post; in the Civil stream, core areas are engineering mechanics, strength of materials, fluid mechanics, RCC, steel design, surveying, soil mechanics, and estimation. Electrical and Mechanical candidates should substitute their own core subjects, but the exam style is similar: short numericals, IS-code-based factual questions, and concept checks.
Core rules
- Strength of materials: bending stress σ = M y / I; for a rectangle, σ = 6M/(bd²). Shear stress τ = VQ/(Ib).
- Fluid mechanics: continuity A₁V₁ = A₂V₂; Bernoulli's equation applies along a streamline for steady, incompressible, frictionless flow.
- RCC: IS 456 uses limit state design; check partial safety factors, minimum grade, cover, and water–cement ratio.
- Steel: IS 800 limit state design; distinguish yield strength, ultimate strength, and design strength.
- Surveying: reduce levels by height of instrument or rise-and-fall method; bearings are measured clockwise from north.
Worked example
A simply supported rectangular beam of width 230 mm and effective depth 450 mm carries a bending moment of 50 kN·m. Find the extreme fibre bending stress. Convert M to N·mm: 50 × 10⁶ N·mm. Section modulus Z = bd²/6 = 230 × 450² / 6 = 7,762,500 mm³. Then σ = M/Z = 50,000,000 / 7,762,500 ≈ 6.44 N/mm². The reasoning shows why effective depth, not overall depth, is used.
Traps
- Mixing N·mm with kN·m.
- Using overall depth where effective depth is required.
- Applying working-stress formulas in a limit-state question.
- Forgetting partial safety factors for loads and materials.
- Treating characteristic strength as design strength.