Effects of Size and Gauge length on the Stress-Strain Response of UHPC in Tension

Abstract

The use of UHPC continues to grow rapidly and a great deal of present-day research focuses on understanding and fine tuning of this material composition. This work is aimed at understanding the effects of size on the tensile behavior of UHPC in relation to the fiber percentage. The paper also discusses the variation in the stress-strain responses based on the chosen gauge length for the tension characterization. Several UHPC dog bone shaped specimens have been tested in the laboratory under the displacement controlled mode. The size effect is assessed by comparing the results of the specimens with cross sections of 2 in. x 2 in., 2 in. x 4 in., and 4 in. x 4 in. The response of the specimens was measured with LVDT and a 3D optical tracking system. The LEDs for the optical tracking measurements were placed at 1 in. interval over a length of 14 in. in the critical zone of the specimen where failure was anticipated. The results show that the effect of size on the stress-strain curves is not consistent between different fiber ratios and there is noticeable variation in the formation of micro cracking along the member length. The chosen gauge length for the measurement of the stress-strain curves can have significant effect on the peak and ultimate strain values. Larger gauge lengths can include micro-cracks over a longer length, averaging the micro-crack behavior more accurately. However, they can have significantly lower peak strain and post-peak behavior when compared with a smaller gauge length.