Why do I get high bolt forces in endplates?

Usually, we connect members with plates as thin as possible to save material. However, this material saving leads to higher bolt forces. This effect is caused by prying action in the interaction of endplate and flange of the column. The thinner the endplate is, the bigger the prying deformation you get. Additional tensile forces are applied to bolts. To show the difference please refer to the following pictures.

Endplate thickness 10mm

Bolts resultant 61.5x4=246kN Force applied 200kN

Endplate thickness 40mm

Bolts resultant 49.9x4=200kN Force applied 200kN