A simple and cost effective way to connect to hollow structural section members is to use a branch plate connections. In plate-to-HSS connections, as thin walled HSS members are generally very flexible, this arrangement causes significant deformations in the hollow section for relatively low loads, often reaching practical deformation limits well before ultimate failure or peak strength-dictating. Therefore, by conducting numerical analyses of plate-to-HSS under axial or bending, the behavior of plate-to-steel connections was verified. Further, numerical analyses were performed to review design standards that prohibit or restrict the use of high-strength steel in tubular structures. The numerical analysis confirmed that the high-strength steel plate-to-HSS connections under compression or bending moment showed comparable performance to that of mild steel, and that the current restrictions on high-strength steel may be relaxed. The numerical analysis method was verified by the experimental data of the plate-to-HSS connections.