EFFECTS OF AMBIENT TEMPERATURE ON LONG-TERM CAMBER OF PRECAST PRESTRESSED CONCRETE BEAMS

摘要

Measured long-term camber of 80 precast prestressed concrete beams (PPCBs) during storage revealed inconsistent trends. The variations from theory included significantly high camber at early ages and reduction or no significant increase in camber over time. The temperature gradient that develops down the beam depth due to solar radiation was suspected to be contributing to these discrepancies. If significant, the temperature gradient down the beam depth would cause construction difficulties when the PPCBs are erected and the slab elevations are set.rnConsidering that the thermal gradient is typically ignored in predicting the camber of PPCBs, a systematic investigation was undertaken. Twenty two different PPCBs were instrumented with string potentiometers and thermocouples to measure camber growth and surface temperature, respectively, and measurements were taken over 24 hours. The measured data indicated that camber can vary as much as 0.75 in. during the course of a day. Subsequently, this data were used to calibrate an analytical model to quantify the additional long-term camber induced by the temperature gradient. Eventually, a multiplier function was developed to take into account the increase in camber due to temperature gradient, ultimately improving accuracy of estimated camber at the time of erection.