Hyperboloidal shell for roof vaults and the like

Claim 1

A CONCRETE STRUCTURE ADAPTED TO BE USED IN ROOF CONSTRUCTION AND THE LIKE, COMPRISING AN APPROXIMATELY HORIZONTAL CONCRETE SHELL OF SUBSTANTIALLY CONSTANT THICKNESS SUBSTANTIALLY IN THE SHAPE OF A SECTION OF A ONE-SHEET HYPERBOLOID OF GENERALLY RECTANGULAR OUTLINE WITH A LENGTH RANGING SUBSTANTIALLY BETWEEN FIVE AND TEN TIMES ITS WIDTH, SAID SHELL BEING UPWARDLY CAMBERED IN LONGITUDINAL DIRECTION OF THE RECTANGLE WITH A RADIUS OF CURVATURE SO CHOSEN THAT THE ELEVATION OF THE SHELL VERTEX ABOVE THE LOWEST POINTS OF THE SHELL AT THE MINOR SIDES OF THE RECTANGLE RANGES BETWEEN SUBSTANTIALLY 1.5% AND 0.5% OF THE LENGTH OF SAID SHELL, TWO SETS OF TENSIONED ELONGATED PRESTRESSING ELEMENTS EXTENDING WITHIN SAID SHELL SUBSTANTIALLY ALONG STRAIGHT-LINE GENERATRICES OF SAID HYPERBOLOID FROM RESPECTIVE HALVES OF ONE MINOR SIDE OF THE RECTANGLE TO OPPOSITE HALVES OF THE OTHER MINOR SIDE, EACH OF SAID SETS INCLUDING A PRINCIPAL PRESTRESSING ELEMENT PASSING SUBSTANTIALLY THROUGH THE CENTER OF SAID SHELL AND EMERGING SUBSTANTIALLY WITHIN THE MIDDLE THIRD OF A RESPECTIVE HALF OF EACH OF SAID MINOR SIDES, AND PIERS SUPPORTING SAID SHELL ALONG SAID MINOR SIDES, THE CENTER OF THE UNDERSIDE OF SAID SHELL BEING LOCATED SUBSTANTIALLY AT A LEVEL WHICH PASSES THROUGH THE OUTERMOST CROSS-SECTIONS OF SAID SHELL AT SAID MINOR SIDES ALONG THE LOWER HALF OF THE ALTITUDE OF SAID CROSS-SECTIONS, SAID ALTITUDE RANGING BETWEEN SUBSTANTIALLY ONE FIFTH AND ONE THIRD OF THE WIDTH OF SAID MINOR SIDES.