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GATE 2026 CE (CE2) – Question 15

Steel Structures · Design of beams, beam-columns and column bases · 1 mark · Multiple choice

As per IS:800-2007, design of a cantilever steel beam section for its moment capacity requires fulfilment of an upper bound, expressed as:

$$M_d \le 1.5\, Z_e \frac{f_y}{\gamma_{m0}}$$

The reason for such upper bound is to

  1. control deflection
  2. restrain lateral-torsional buckling
  3. avoid plastic deformation under working load
  4. avoid yielding at ultimate load

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Show answer and explanation

Correct answer: (C) avoid plastic deformation under working load

Explanation

For a compact section the plastic moment can be much larger than the elastic moment $Z_e f_y/\gamma_{m0}$. IS 800 caps the design moment at $1.5 Z_e f_y/\gamma_{m0}$ for cantilevers (1.2 for simply supported beams) so that the section is not left with irreversible, plastic deformation under working loads.