is nearly due exclusively to the flexibility of the column web,

The M-~ curves related to four tests on bolted joints with end plates are shown in figure 9. Both tests AI and A4 (using IPE sections as column) are represented by two nearly identical curves ; they provide a same value of the initial stiffness K., of the strain hardening stiffness K and of the yield bending moment M • 1 The strain hardening stiffness K loo~s like ·approximately constant t6f the four tests, i.e. whichever thepslenderness h /a of the column web in the range 16-36. The initial stiffness K. and the a yield moment M are shown to increase rapidly when the slendefness h /a decreases. The y~xperimental values of M are plotted in figure 10 ag~inst the web slenderness. ye