Hollow article with zigzag projections

Claim 1

A hollow article subjected to an external radial load and having the shape defined by a tubular wall with an inner surface, said wall and an outer surface braced with generally transverse and circumferential ribs projecting outwardly from the outer surface and having corrugations imparting rigidity to the ribs, preventing the ribs from buckling under bending induced radial and shear loads and substantially averting caving in of the ribs, the critical mode of the article failure being the buckling of the ribs, and the wall providing semirigid response to loading therealong, wherein in the cross-section of the tube said corrugations form chordal lines not crossing the longitudinal axis of the tube, said lines being selected from the group consisting of lines forming radial-tooth-like corrugations and parallel lines directed vertically to said axis when the article is buried underground, and wherein the corrugations with said parallel lines are located on the tube in an area defined by that which is between two vertical lines tangent to the tube at the horizontal axis, and the remaining regions of the tube located on the opposite sides vertical of said lines being devoid of corrugations, having radial projected corrugations or having tooth-like corrugations.