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Design process and basis of design

Short answer

Design process: planning, load estimation, analysis, member and connection design, checks, and detailing. Basis: limit state design with partial factors γf on loads and γm on material (γm0=1.10 yielding, γm1=1.25 rupture) to ensure strength and serviceability limits per IS 800:2007.

Write the design process and basis of design of steel structures.

Design process

Structural design is an iterative process that goes from the client's need to a safe, serviceable and economical structure.

  1. Planning / functional requirements: use of the building, spans, heights, architectural layout, site conditions.
  2. Structural system selection: choose framing (portal frame, truss, braced or moment frame), material (steel grade) and joint types (bolted/welded).
  3. Estimation of loads: dead load (IS 875 Part 1), imposed load (Part 2), wind (Part 3), earthquake (IS 1893 / NBC 105), and other loads (snow, crane, temperature).
  4. Structural analysis: find axial force, shear force and bending moment in every member for the governing load combinations (IS 800:2007 Table 4).
  5. Member design: select sections, check strength (tension, compression, flexure, combined), slenderness and deflection.
  6. Connection design: design bolted/welded joints, splices, bases and gussets.
  7. Check and revise: if a check fails, change the section or system and repeat.
  8. Detailing and drawings: fabrication and erection drawings, bill of materials, specifications.

Basis of design (IS 800:2007)

  • Limit state design: the structure must not reach any limit state during its design life. Limit state of strength (yielding, buckling, rupture, fatigue, overturning) and limit state of serviceability (deflection, vibration, durability, fire).
  • Partial safety factors: on loads γf\gamma_f (e.g. 1.5 for DL+LL, 1.2 for DL+LL+WL) and on material γm0=1.10\gamma_{m0}=1.10 (yielding), γm1=1.25\gamma_{m1}=1.25 (rupture), γmb=1.25\gamma_{mb}=1.25 (bolts), γmw=1.25\gamma_{mw}=1.25 (shop weld), 1.50 (field weld).
  • Design strength == characteristic strength /γm/\gamma_m and must be ≥\ge the factored action effect γf×\gamma_f \times characteristic load.
  • Material: structural steel to IS 2062 (E250, E350 etc.), with E=2×105E=2\times10^5 N/mm², G=0.769×105G=0.769\times10^5 N/mm², μ=0.3\mu=0.3.
  • Load combinations: DL+LL, DL+LL+WL/EL, DL+WL/EL, with the load factors of Table 4.
  • Serviceability limits: deflection limits of Table 6 (e.g. span/300 for floor beams, span/150 for purlins with elastic cladding), slenderness limits of Table 3.
  • Other requirements: stability against overturning and sliding, ductility, robustness, fire resistance and durability.

✓ Answer checked by Claude Opus 5.5 (high effort)

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