Steel Design
Steel design in BTSC JE Civil follows IS 800:2007 limit-state philosophy: bolted and welded connections, tension members, compression members, beams and column bases. Numerical questions on bolt strength, net area and slenderness are common.
Core rules
- Partial safety factors: γm0 = 1.10 for yielding, γm1 = 1.25 for ultimate resistance, γmb = 1.25 for bolts, γmw = 1.50 for site welds and 1.25 for shop welds.
- Tension: design gross yielding strength Tdg = Ag fy/γm0; net section rupture Tdn = 0.9 An fu/γm1; the smaller governs.
- Bolt shear: Vdsb = (fub/√3)(nn Anb + ns Asb)/γmb. Bearing: Vdpb = 2.5 kb d t fu/γmb.
- Compression member slenderness KL/r should not exceed 180; tension members 400.
- Weld throat = 0.7 × size; effective length of fillet weld is the actual length minus end returns.
Worked example
A 100 mm × 10 mm plate of fy = 250 N/mm² and fu = 410 N/mm² has one line of two M20 bolts. Gross area = 1000 mm²; Tdg = 1000 × 250/1.10 = 227.3 kN. For M20 bolts the hole is 22 mm, so An = (100 − 22) × 10 = 780 mm²; Tdn = 0.9 × 780 × 410/1.25 = 230.3 kN. Design tensile strength = smaller = 227.3 kN, governed by yielding.
Traps
Using bolt diameter instead of hole diameter; applying γm1 to gross yielding; ignoring block shear in short connections; taking weld size as throat thickness.