Experimental study of the transfer length of pre-tensioned CFRP strands using distributed fiber optic sensors

Abstract

Carbon fiber reinforced polymer strands offer a corrosion-resistant alternative to steel prestressing, but their short transfer lengths increase susceptibility to splitting cracking and challenge conventional pointwise measurements. Once splitting occurs during prestress release, these methods cannot determine a valid transfer length. This study develops an experimental framework for pre-tensioned beams based on distributed fiber optic sensor data and a semi-automated evaluation method. The method determines transfer length from unsmoothed strain profiles without manual plateau selection and remains applicable to cracked specimens by identifying the last valid pre-cracking profile. It was calibrated using small-scale tests, compared with manually determined values, and benchmarked against conventional evaluation methods. Within the investigated configurations, higher concrete strength and lower prestress led to shorter transfer lengths. The ACI model agreed with measurements within 10 %, whereas other provisions overestimated transfer length by factors of 1.5–3.2, potentially underestimating the risk of end-region cracking.