Deflection Control of Prestressed Box Girder Bridges

The models for prediction of creep in codes and design guides are mainly based on tests in which the load is sustained for a number of years, rarely exceeding 10; however, most models predict that creep reaches its extreme after approximately 30 years. An exception is the frequently accepted Model B3; it predicts indefinite increase of creep with the logarithm of the number of days of sustained loading. Analysis of deflection using Model B3 of a large number of bridges agrees with measured deflection in terms of magnitude and continued increasing tendency. Modern design requires satisfactory serviceability sustainable for a long life span. The absolute value of camber or deflection must not be excessive. This paper shows that by adopting Model B3, combined with appropriate prestressing, it is possible to satisfy this requirement for 125 years.