Abstract: A casement window assembly includes a rectangular sash frame enclosing an insulated glass panel unit and supported for swinging movement by a surrounding main window support frame. At least one set of interfitting and interlocking members are positioned in opposing relation on adjacent vertical members of the sash frame and support frame and have hook portions positioned to pass each other when the sash frame is pivoted between a closed position and an open position. The hook portions are effective to engage and hook each other in response to a substantial positive or negative windload or such windload applied after an impact breaks the glass to limit deflection and prevent permanent deformation of the sash frame. The hook portions also produce a snubbing action for compressing a flexible seal between the sash frame and support frame.

Abstract: A casement window assembly includes a rectangular sash frame enclosing an insulated glass panel unit and supported for swinging movement by a surrounding main window support frame. At least one set of interfitting and interlocking members are positioned in opposing relation on adjacent vertical members of the sash frame and support frame in opposing relation and have hook portions positioned to pass each other when the sash frame is pivoted between a closed position and an open position. The hook portions are effective to engage and hook each other in response to a substantial positive or negative windload or such windload applied after an impact breaks the glass to limit deflection and prevent permanent deformation of the sash frame. The hook portions also produce a snubbing action for compressing a flexible seal between the sash frame and support frame.