Abstract: A joint structure for removably attaching a ball member to an end of a bar member to form a truss structure is disclosed having an engagement member attached to the ball member, which engagement member has an exterior portion extending outwardly of the outer surface of the ball member, and an attachment device associated with the end of the bar member which removably engages the exterior portion of the engagement member. The joint structure according to the present invention may be utilized with bar members with or without tension rods extending through the bar member. The ball structure may be a spherical shell made of metal or fiber reinforced plastic which is located within a hollow concrete sphere. The spherical shell is not removed from the interior of the concrete sphere, but, instead, is used to increase the tensile force resistance of the ball member. The spherical shell may be imbedded in the ball member at the time of forming the concrete ball and can be used as a molding core.