Abstract: Disclosed herein is a method for manufacturing preflex beams. The method includes the step of connecting the upper and lower plate girders 10a and 10b of a first set to each other. Thereafter, the upper and lower plate girders 10a′ and 10b′ of a second set are connected to each other. The first set and the second set are arranged in parallel. The upper plate girders 10a and 10a′ are connected to each other, and the lower plate girders 10b and 10b′ are connected to each other. A plurality of lower supporting stands 6 are placed under the lower crossbeams 7. A plurality of hydraulic jacks 4 are placed between the upper and lower plate girders 10a and 10b, and 10a′ and 10b′. The upper flanges of the upper plate girders 10a and 10a′ and the lower flanges of the lower plate girders 10b and 10b′ are covered with concrete.

Abstract: A method for connecting prestressed beams having lower flanges cast with compressively prestressed concrete to construct a prestressed continuous beam having a moment equal to zero at both ends thereof and negative moments at at least one connection point of the prestressed beams. The method includes the step of placing the prestressed beams in end to end relation. Adjacent ends of the prestressed beams define at least one connection point. The method further includes connecting the prestressed beams together at the connection point, deflecting the prestressed beams at at least one connection point within the limitation of elasticity of the prestressed beams to a deflected position, casting and curing concrete on the prestressed beams at the connection point, and at least partially returning the prestressed beams at the connection point from the deflected position whereby compressive stress is introduced to the concrete cast and cured on the prestressed beams at the connection point.