Why do I get high bolt forces in end plates
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 column. The thinner the endplate is, the bigger prying deformation you get. Additional tensile forces are applied to bolts. To show the difference please refer to following pictures.
End plate thickness 10mm
Bolts resultant 61.5x4=246kN Force applied 200kN
End plate thickness 40mm
Bolts resultant 49.9x4=200kN Force applied 200kN