Experimental Research on and Application of Twice-Prestressed Concrete Beam

High prestressing stress and concrete creep create many problems for the designing of small and medium span prestressed concrete bridges, such as the inverse camber being too large and curved beams bending laterally. A high camber is also not permitted for the reasons of safety and comfort. To solve these issues, the new concept of twice-prestressed concrete beam is discussed in this paper. Theoretical and experimental comparisons between this new beam and the conventional prestressed beam show that the application of twice prestressing technology can greatly improve the mechanical and deformation performance for small and medium span prestressed concrete bridges. The paper also presents computational formula derived by the authors to calculate creep strain and deformation of a twice-prestressed concrete beam over time and an experiment which was carried out to verify the correctness of these formulae derived by this paper.