TIME-DEPENDENT FLEXURAL CRACK WIDTH PREDICTION OF CONCRETE BEAMS PRESTRESSED WITH CFRP TENDONS

摘要

Fibre reinforced polymers (FRP) are non-corrosive, lighter and stronger than their steel counterparts, however, they usually possess a lower modulus of elasticity than steel. Substantial research has been conducted on concrete beams prestressed with steel strands, but considerably less research has been conducted on concrete beams prestressed with FRP tendons. The limited research on concrete beams prestressed with FRP tendons has mainly been confined to ultimate limit state behaviour with a significant void therefore existing in their serviceability limit state behaviour. This paper presents experimental and analytical results of the time-dependent cracking behaviour of concrete beams prestressed with carbon FRP (CFRP) tendons or steel strands, under sustained service loads. Six full-scale beams were tested and the variables considered in the experimental program were the level of prestress, level of sustained service load, and concrete strength. The results of three existing models to predict crack widths of concrete beams reinforced with steel bars, following a brief review of each of the models, are compared with the measured instantaneous and time-dependent crack widths. Shortcomings in these existing crack width models are identified and important parameters to be included in a new time-dependent crack width model are suggested.