Expansible bottom structure for fiberglass reinforced plastic tanks

An upstanding fiberglass reinforced plastic tank adapted to receive and store a fluid exposed to atmospheric pressure, said tank having a bottom resting on a support and having an annular side wall structure, the head of a fluid stored within said tank exerting hydrostatic pressure on said side wall structure which urges said side wall structure to expand outwardly in a radial direction, wherein the improvement comprises:

• movable means forming a slidable foot at a lowermost portion of said side wall structure for permitting radial expansion of a lower portion of said side wall structure due to hydrostatic pressure of a stored fluid, said slidable foot including a portion having a surface resting on and unattached to said support and substantially coplanar with the lower surface of the tank bottom, said foot being separated from said tank bottom;
• and
• joining means interconnecting said tank bottom and side wall structure, said joining means including annular batten means formed of fiberglass reinforced plastic material and having an upper portion bonded to said side wall structure, having a lower portion bonded to said tank bottom, and having an intermediate transitional portion adapted to flex during such radial expansion of said side wall structure;
• whereby, during such radial expansion, said slidable foot may slide outwardly along said support without significant deformation of its original shape.