Thin prestressed concrete panel and apparatus for making the same

Abstract

A thin, prestressed concrete panel, having a thickness of about one and one-half inch thickness or less, and apparatus for making the same is disclosed. Pairs of prestressed tendons extend between the side and end portions of the panel. The tendons of each pair are positioned on each side of the mid-plane of the panel and spaced from such mid-plane so as to increase panel strength and prevent warping of the panel. A molding apparatus for casting the panel comprises a bottom plate, a pair of opposite side portions, and a pair of opposite end portions. Slots are defined in the side and end portions through which tendons are inserted prior to pouring concrete in the mold. Tensioning means are provided for prestressing the tendons in the longitudinal and lateral directions of the panel.

1 - 32 . (canceled)  
   
   
       33 . Apparatus for casting thin reinforced concrete panels having a plurality of prestressed elongate tendons of a predetermined diameter extending therethrough, the apparatus comprising, 
 a mold having a bottom plate with a flat upper surface, a pair of spaced opposed side portions extending upwardly from said bottom plate and having upper edges, a pair of spaced opposed end portions extending upwardly from said bottom plate and having upper edges, said upper edges occupying a plane parallel to the upper surface of said bottom plate,    a first set of aligned slots defined in the end portions of the mold for receiving tendons extending therebetween,    a second set of aligned slots defined in the side portions of the mold for receiving tendons extending therebetween,    the first set of slots comprising a plurality of pairs of slots, each of said pairs of first set of slots comprising a first slot and a second slot, with the first slots each having a bottom surface spaced a first predetermined distance from the plate upper surface which is less than one half the distance between the bottom plate and said plane, the second slots each having a bottom surface spaced a second predetermined distance from the plate upper surface which is greater than one half the distance between the bottom plate and said plane, and the first and second slots in each pair are offset laterally from each other, and    the second set of slots comprising a plurality of pairs of slots, each of said pairs of said second set of slots comprising a third slot and a fourth slot, with the third slot having a bottom surface spaced a third predetermined distance from said plate upper surface which is less than one half the distance between the bottom plate and said plane, the fourth slot having a bottom surface spaced a fourth predetermined distance from said plate upper surface which is greater than one half the distance between the bottom plate and said plane, and the third and fourth slots of each pair are offset laterally from each other.    
   
   
       34 . The apparatus of  claim 33  further comprising first stressing mechanism mounted adjacent one of said side portions for prestressing a tendon extending between the side portions, and second stressing mechanism mounted adjacent one of said end portions for prestressing a tendon extending between the end portions.  
   
   
       35 . The apparatus of  claim 33  wherein said plate upper surface and said plane are spaced apart a distance no greater than about 1.5 inches.  
   
   
       36 . The apparatus of  claim 35  wherein the bottom surface of each of said slots is spaced from said plate upper surface a distance no less than 1½ times the diameter of said tendons.  
   
   
       37 . The apparatus of  claim 36  wherein the bottom surface of each of said slots is spaced from said plane a distance no less than 2½ times the diameter of a tendon.  
   
   
       38 . Apparatus for casting thin reinforced concrete panels having a plurality of prestressed elongate tendons of a predetermined diameter extending therethrough, the apparatus comprising, 
 a mold having a bottom plate with an upper surface, a pair of spaced opposed side portions extending upwardly from said bottom plate and having upper edges, a pair of spaced opposed end portions extending upwardly from said bottom plate and having upper edges, said upper edges occupying a plane parallel to the upper surface of said bottom plate,    a first set of aligned slots defined in the end portions of the mold for receiving tendons extending therebetween,    a second set of aligned slots defined in the side portions of the mold for receiving tendons extending therebetween,    the first set of slots comprising a plurality of pairs of slots, each of said pairs of first set of slots comprising a first slot and a second slot, with the first slots each having a bottom surface spaced a first predetermined distance from the plate upper surface which is less than one half the distance between the bottom plate and said plane, the second slots each having a bottom surface spaced a second predetermined distance from the plate upper surface which is greater than one half the distance between the bottom plate and said plane, and the first and second slots in each pair are offset laterally from each other, and    the second set of slots comprising a plurality of pairs of slots, each of said pairs of said second set of slots comprising a third slot and a fourth slot, with the third slot having a bottom surface spaced a third predetermined distance from said plate upper surface which is less than one half the distance between the bottom plate and said plane, the fourth slot having a bottom surface spaced a fourth predetermined distance from said plate upper surface which is greater than one half the distance between the bottom plate and said plane, and the third and fourth slots of each pair are offset laterally from each other.    
   
   
       39 . The apparatus of  claim 38  further comprising first stressing mechanism mounted adjacent one of said side portions for prestressing a tendon extending between the side portions, and second stressing mechanism mounted adjacent one of said end portions for prestressing a tendon extending between the end portions.  
   
   
       40 . The apparatus of  claim 38  wherein said plate upper surface and said plane are spaced apart a distance no greater than about 1.5 inches.  
   
   
       41 . The apparatus of  claim 40  wherein the bottom surface of each of said slots is spaced from said plate upper surface a distance no less than 1½ times the diameter of said tendons.  
   
   
       42 . The apparatus of  claim 41  wherein the bottom surface of each of said slots is spaced from said plane a distance no less than 2½ times the diameter of a tendon.