Concentric ribbed preform and bottle made from same

A plastic container comprising an upright hollow body having an upright longitudinal axis, said body having a tubular side wall merging at its lower end with a base structure, said base structure comprising:

• an upwardly concave central portion having an upwardly facing inner surface;
• an outer wall of annular shape surrounding said central portion and merging therewith, said outer wall also merging with said lower end of said side wall;
• a predetermined number of substantially continuous annular reinforcing ribs on said inner surface, said ribs being generally concentric about said axis and being of increased thickness, relative to said tubular side wall, the wall thickness of each rib being greater than the wall thickness of the preceding rib as the ribs progress toward the axis resulting in an increasing wall thickness of said concave portion in a direction radially inwardly toward said axis;
• a plurality of hollow ribs extending radially from said central portion to said outer wall and merging therewith, said radial ribs dividing said outer wall into a plurality of circumferentially spaced feet projecting downward below said radial ribs.

A plastic container comprising an upright hollow body having an upright longitudinal axis, said body having a tubular side wall merging at its lower end in a base structure, said base structure comprising:

• an outer wall extending downwardly and inwardly from said side wall;
• a bottom wall having an upwardly facing inner surface, said bottom wall having a generally horizontal outer portion and a central portion, said horizontal outer portion merging with the lower end of said outer wall;
• a predetermined number of substantially continuous annular reinforcing ribs on said inner surface, said ribs being generally concentric about said axis and being of increased thickness relative to said tubular side wall, the wall thickness of each rib being greater than the wall thickness of the preceding rib as the ribs progress toward the axis resulting in an increasing wall thickness of said bottom wall in a direction radially inwardly toward said axis;
• and
• a plurality of upwardly projecting hollow ribs extending radially from said central potion and merging with said outer wall, said ribs dividing said generally horizontal outer portion of said bottom wall into a plurality of circumferentially spaced hollow feet having flat bottom surfaces spaced with respect to said axis.

A plastic container comprising an upright hollow body having and upright longitudinal axis, said body having a tubular side wall merging at its lower end with a base structure having an upwardly facing inner surface, said base structure comprising:

• a plurality of meridian wall portions of a common hemisphere having a radius which is approximately equal to that of said tubular side wall, said meridian portions having a downward pole and extending upward from said pole;
• an outer wall portion between said meridian portions defining hollow legs terminating below said meridian portions in circumferentially spaced feet;
• and
• a predetermined number of substantially continuous annular reinforcing ribs on said inner surface, said ribs being generally concentric about said axis and being of increased thickness relative to said tubular side wall, the wall thickness of each rib being greater than the wall thickness of the preceding rib as the ribs progress toward the axis resulting in an increasing wall thickness of said base structure in a direction radially inwardly toward said axis.