Prestress variations were measured in a prestressed concrete box girder bridge near Reno, Nevada, where the ambient relative humidity is highly variable. The data showed that the actual total creep and shrinkage losses are 30 percent higher than those calculated using a time-step analysis and 60 percent higher than those estimated by the AASHTO Specifications. The results also indicated that the prestress forces continue to change due to seasonal variation in temperature and humidity. The large prestress losses appear to be due to the high variation of the relative humidity in the area. It is suggested that the time-step method be used to estimate prestress losses in areas of highly variable relative humidity.
