AN EXPERIMENTAL STUDY ON THE TIME-DEPENDENT BEHAVIOUR OF CONCRETE BEAMS PRESTRESSED BY AFRP TENDONS

摘要

This paper presents experimental results on the time-dependent deflection of normal and high strength concrete beams prestressed by non-metallic Aramid Fibre Reinforced Polymer (AFRP) tendons under sustained service load. Three simply-supported 3 m span beams were cast with 40 and 80 MPa concrete and were initially loaded at the age of 35 days with a sustained uniformly distributed load of about 65% of the load required to cause cracking at midspan. After a period of 60 days the load was doubled so that the beams cracked and the load was then maintained for a further period of 120 days. In addition, one 6 m span beam was also cast with 80 MPa concrete and AFRP tendons and was loaded at 28 days with a uniformly distributed load which created a moment at midspan equal to 1.2 times the cracking moment. The beams with AFRP tendons behaved in a similar manner to those with steel strands for both the normal and the high strength concrete cases. In the case of beams with uncracked sections, significant increase of deflection only occurred in the first 30 days after loading and in the case of beams with cracked sections, the deflection continued to increase throughout the period of sustained loading. The ratio of long-term to instantaneous deflections of beams with uncracked sections was about 1.13 for beams with high strength concrete (HSC) and 1.64 for beams with normal strength concrete (NSC). During the second loading stage, ie in the case of beams with cracked sections, the ratio was about 1.55 for the 3 m span beams. For the 6 m span beam, the ratio was 2.48. With an increase of concrete strength, the deflection decreased for both the uncracked and cracked beams under the same loading level. However, the ratio of long-term to short-term deflection was similar regardless of the concrete strength.