Extensible crane boom structure

An extensible crane boom assembly having telescopically interfitting boom sections that include a base section, an intermediate section slidably fitted within the base section, and a top section slidably fitted within the intermediate section;

• each boom section having four elongated angle chords with normally disposed flanges that are positioned to define the longitudinal corner edges of a box-like configuration, and four elongated plates extending between adjacent angle chords and welded thereto to form the sides, top and bottom of the boom section;
• each of said elongated plates which form the side webs of the boom section being of uniform thickness and having a top edge, a bottom edge, a pair of side surfaces that are located in spaced apart parallel planes at the junctures of the side surfaces with said top and bottom edges, and a plurality of shaped portions being formed within the plates at locations intermediate the top and bottom edges to space those portions of the plate laterally from said parallel planes, said shaped portions being located at spaced intervals longitudinally of the plate, each shaped portion having a regular geometrical pattern that forms a laterally projecting protuberance on one side of the plate and a corresponding depression on the opposite side of the plate, said shaped portion geometrical pattern being a frustum of a pyramid with a generally diamond-shaped base thereby stiffening the plate between adjacent shaped portions and between these shaped portions and adjacent top and bottom edges of the plate to resist buckling, said plate between adjacent shaped portions having side surfaces within the parallel planes from the top edge to the bottom edge of the plate and providing longitudinal spacing between parallel diagonal lines that coincide with adjacent edges of adjacent shaped portions, each of said shaped portions having an interior panel that is offset from and parallel with the spaced apart parallel planes, some of said shaped portions in the intermediate boom section and in the tip boom section having central openings within the interior panel to reduce the weight of the plates forming the sides of the boom sections, and said shaped portions in the base section having solid interior panels to protect interior components of the boom assembly during storage.