Concrete and Steel Design (RCC and Steel Structures)
Concrete and Steel Design covers limit-state design of RCC members to IS 456:2000 and steel members to IS 800:2007, with IS 13920 detailing for ductility. The exam tests partial safety factors, balanced sections, shear and development length, bolt and weld capacity, compression members and connections.
Core rules
- RCC design strengths are 0.446f_ck and 0.87f_y; partial safety factors are 1.5 for load and 1.15 for steel.
- Singly reinforced rectangular beam: M_u=0.36f_ck b x_u(d−0.42x_u); x_u=0.87f_yA_st/(0.36f_ckb).
- Limits: x_u/d ≤0.48 for Fe415; minimum tension steel is 0.85bd/f_y.
- Steel design strength f_yd=f_y/γ_m0 with γ_m0=1.10; bolt shear capacity uses f_ub and net area.
- Block shear and bearing govern many steel connections.
Worked example
A singly reinforced beam has b=230 mm, d=450 mm, M25/Fe415 and M_u=120 kN m. Try A_st≈860 mm². Then x_u=0.87×415×860/(0.36×25×230)=149.7 mm. M_u=0.36×25×230×149.7×(450−0.42×149.7)=120.0 kN m. x_u/d=0.333<0.48, so the section is under-reinforced. Provide 3 bars of 20 mm (942 mm²).
Traps
- Using overall depth instead of effective depth.
- Omitting the 0.87 factor on f_y in x_u.
- Ignoring minimum steel and development length.
- Using gross area for net-section rupture in steel.
- Treating a balanced section as desirable in ductile design.