Long-term effect analysis of prestressed concrete box-girder bridge widening

To make an analysis of long-term effect of prestressed concrete box-girder bridge widening, a revised method of shrinkage and creep is presented by incremental method on base of energy principle. Continuous change of stress aroused by concrete shrinkage and Young’s modulus of concrete over each time interval is considered, and creep effect due to constrained shrinkage strain is also taken into account. A calculating program was compiled according to this method, which was validated by test results. Then an example of prestressed concrete box-girder bridge widening was analyzed by use of this program. According to calculated results, longitudinal tensile stress at the flange of the new girder can reach 2.84 MPa due to shrinkage and creep effects of new box girder after 10 years, which may lead to crack of concrete. It is suggested that bridge widening should be performed 6 months after new girder is cast. Compared with new box girder not widened which is in service independently, the total prestressing loss of the widened new box girder decreases 31–35% 10 years after bridge widening. However, prestressing loss of the old box girder aroused by shrinkage and creep of the new box girder can be neglected.