Weight bearing apparatus for hanging on upright structures

An apparatus for supporting weight on an upright structure having opposite, generally vertical side edges, the apparatus comprising

• a frame having a weight bearing surface,
• first and second gripping arms carried on the frame, each having an outer end portion that extends beyond the frame, each outer end portion including a gripping edge,
• first linkage means joining the gripping arms for moving the outer end portions away from and toward each other to thereby open and close the distance between the gripping edges, and
• second linkage means that joins the first linkage means to the frame and serves to open and close the gripping arms in response to forces applied to the frame relative to the structure,
• the second linkage means being operative for attaching the frame to the structure when the gripping arms are opened a sufficient distance to receive the structure and in contact with at least one side edge of the received structure, by serving, in response to a subsequent force that moves the frame into contact with the structure, to close the gripping arms a sufficient distance to bring both gripping edges into contact with the side edges of the structure,
• the second linkage means also being operative for supporting weight on the frame when attached to the structure, by serving, in response to the downward force of the weight applied to the weight bearing surface of the frame, to urge the gripping arms continuously toward each other to thereby continuously secure an engagement of both the gripping edges on the structure as weight is applied, and
• the second linkage means being further operative for detaching the frame from the structure when weight ceases to be applied to the weight bearing surface of the frame, by serving, in response to a force that moves the frame in a direction away from the ground, to open the gripping arms a sufficient distance to bring both gripping edges out of contact with structure.