Ductile detailing of beams and columns

Ductile detailing makes the structure deform plastically in a controlled way during an earthquake without sudden collapse. IS 13920 governs the detailing of beams, columns and joints.

Beam

• $b \ge 200$ mm, $b/D \ge 0.3$, $D \le L/4$.
• Two bars continuous at top and bottom; $\rho$ between $0.24\sqrt{f_{ck}}/f_y$ and 2.5%.
• Bottom steel at a joint face $\ge 50\%$ of top steel.
• Splices in the middle half only, with hoops at 150 mm or closer.
• Closed stirrups with $135^\circ$ hooks. Within $2d$ of the support, spacing $\le \min(d/4,\ 8\phi,\ 100\text{ mm})$; elsewhere $\le d/2$.

Column

• Minimum size 200 mm, $b/D \ge 0.4$.
• Special confining hoops over $l_o = \max(D,\ h/6,\ 450\text{ mm})$ at each end, at 75-100 mm spacing and $\le b_{min}/4$.
• $135^\circ$ hooks with $6\phi$ tail; splices only in the middle half.
• Strong-column weak-beam: the columns at a joint should be stronger than the beams so that hinges form in the beams.

   BEAM                              COLUMN
  |-2d-|--- d/2 ---|-2d-|        ---------
  |||||| | | | | | ||||||        | ##### |  s=75-100
                                 | ##### |  over lo
                                 |  # #  |  s per IS456
                                 | ##### |  s=75-100
                                 ---------

Members are also designed for the shear produced by plastic hinge capacity, not only by analysis, so that shear failure (brittle) cannot precede flexural yielding (ductile).