In this paper, out-of-plane bending stiffness of column-end connection between square hollow section column and thick panel with different width was investigated by loading test and finite element analysis. From the results, column-end connection of corner-type under 45-degree directional force has the smallest stiffness, and of which section dose not remain plane, and proportion of bending resistance caused by partial deformation of column in column-end bending resistance is very small. Therefore, method to estimate out-of-plane bending stiffness of column-end was proposed based on deformation of diaphragm of hollow section of panel and directly above panel.
