Effects of exposure to elevated temperatures on the transfer length of pretensioned concrete elements

Abstract

Pretensioned concrete elements are widely used in bridges and precast buildings, which may be exposed to fire. The residual performance of a pretensioned element that has survived a fire event is dependent on the effects of elevated temperatures on steel, concrete, and the bond between these materials. This paper investigates changes in the transfer length of pretensioned beams due to exposure to elevated temperatures. Ten large-scale pretensioned concrete beams with different cross-sectional dimensions and strand layouts were fabricated. The transfer length of these elements was measured using demountable mechanical strain gages. The specimens were subjected to elevated temperature cycles with maximum temperatures of 500 and 700 degrees for two hours. After natural cool down, changes in the transfer length of specimens were determined. The results showed that heat exposure leads to an increase in the transfer length by up to 35% and 42% for maximum temperatures of 500 and 700 degrees Celsius, respectively. Strand arrangement, compressive strength of concrete, cross-sectional dimensions, and clear cover were found to affect the sensitivity of elements to heat exposure. A simplified equation was proposed for estimating the transfer length of pretensioned concrete beams that survive elevated temperatures, which may be used for structural assessment applications.