Process for producing high-capacity concrete beams or girders

Abstract

A prescribed prestressing process is employed to construct precast concrete beams and girders. The process is utilized where an early concrete strength is too low for transfer of the full pre-tensioning force on a daily schedule to avert an otherwise serious and costly production delay. The process described provides the producer a reliable way of making beams and girders that are prestressed to take advantage of the higher concrete strength characteristics. The consequent economic advantage of higher structural capacity beams and girders is thereby realized. Additionally, beam or girder camber is controlled by the process, fostering production of a superior quality product.

1 . An improved process using high strength concrete and employing a substantially greater prestressing force to fabricate a concrete beam or girder having a significantly higher structural capacity, the improvement comprising the steps of a) applying only a portion of a predetermined prestressing force by pre-tensioning while the beam or girder is on a prestressing bed and b) applying the remainder of the predetermined prestressing force to the beam or girder by post-tensioning at a later selectable time, thereby avoiding unwanted camber growth and whereby a high structural capacity beam or girder is produced that reduces the number of beams or girders of lesser structural capacity required in a given structure, thus offering substantial cost savings. 
     
     
         2 . The process of  claim 1  wherein step a) applies a pre-tensioning force that is at least a magnitude that enables the beam or girder to be removed from the prestressing bed and withstands stresses experienced in handling during removal, thereby allowing early removal of a partially prestressed beam or girder from a form on the prestressing bed and thus permitting subsequent fabrication of a next beam or girder without substantial delay. 
     
     
         3 . The process of  claim 1  wherein step a) applies a partial pre-tensioning force to the beam or girder, the partial pre-tensioning force being adequate, at a minimum, to withstand handling and hauling stresses, thereby enabling practical fabrication and stockpiling of beams or girders for emergency or other future uses over the course of a prolonged period of time. 
     
     
         4 . The process of  claim 2 , further comprising the steps of c) removing the beam or girder from the form on the prestressing bed after step a) and d) storing the beam or girder on supports near respective ends of the beam or girder, whereby gravity acting on the beam or girder counteracts the prestressing force and thus resists camber growth due to flexural stresses so that inelastic concrete creep and camber growth are reduced. 
     
     
         5 . The process of  claim 1  wherein step a) applies a pre-tensioning force having a selectable magnitude to control a horizontal trajectory of the beam or girder, the pre-tensioning force being a magnitude less than a pre-tensioning force that would cause the beam or girder to bow significantly, thereby avoiding unwanted camber in a cost-effective manner. 
     
     
         6 . The process of  claim 1  wherein step a) applies a pre-tensioning force having a selectable magnitude, the pre-tensioning force being a magnitude adequate to produce an internal bending moment in the beam or girder that balances an external self-weight bending moment of the beam or girder, whereby the balance of internal and external bending moments negates beam or girder camber growth, thereby enabling practical storage of beams or girders for deployment at an indefinite future time. 
     
     
         7 .- 12 . (canceled)