Define ductility, joint detailing sketch

Ductility

Ductility is the property of a structure or member to undergo large plastic (inelastic) deformation before failure without a significant reduction in load capacity. It is expressed by the displacement ductility ratio $\mu = \Delta_u/\Delta_y$ or the curvature ductility $\phi_u/\phi_y$.

Beam-column joint with ductile details

          Column above (hoops s=75-100)
                  | | | |
           +------#########------+
 top bars  =====>#  joint  #<====  top bars
 anchored  |     #  hoops   #     |  continuous
 Ld from   |     #  s<=100  #     |
 inner face|=====>#         #<====|
 + 90 bend +------#########------+
 (10 phi)         | | | |
          Column below (hoops s=75-100)

  Beam: hoops 50 mm from face, s <= d/4, 8phi, 100

Ductile details shown:

• Column confining hoops (closed, $135^\circ$ hooks, $6\phi$ tail) run continuously through the joint at $\le 100$ mm (up to 150 mm if beams frame in on all four faces).
• Beam longitudinal bars at an exterior joint extend to the far face of the column, are anchored for $L_d$ measured from the inside face, and end in a $90^\circ$ bend with a standing leg of $\ge 10\phi$ turned into the joint (top bars bent down, bottom bars bent up).
• Column bars are continuous through the joint; no lap splice is made within the joint (column laps go in the central half of the column height).
• Beam stirrups start 50 mm from the joint face, with spacing $\le \min(d/4,\ 8\phi,\ 100\text{ mm})$ over $2d$; no beam lap splice within $2d$ of the joint face.
• Strong-column weak-beam proportioning, so that hinges form in the beams and the joint and columns remain essentially elastic.