Experimental and analytical studies of size effects on compressive ductility response of Ultra-High-Performance Fiber-Reinforced concrete

Abstract

Ultra-high-performance fiber-reinforced concrete (UHPFRC) has gained a great deal of increasing interest in structural engineering applications, particularly where high ductility, strength, and high impact resistance are of prime concern. This study focuses primarily on the size effects ductility characteristics of UHPFRC with varying fiber concentrations subjected to uniaxial compressive load. It shows how to process the data from compression cylinder tests to extract the size-dependent strain at peak stress to provide a generic size-dependent stress–strain analytical model. For a slenderness factor of 2, the predicted peak stress from the analytical model deviated 0.34%, 0.26%, and 10.5% from the experimental peak stress results for a fiber concentration of 1%, 2%, and 3%, respectively, indicating good estimate of the analytical model with the experimental results. Furthermore, a numerical flexural segmental moment-rotation approach is applied to incorporate an analytical model to quantify apparently disparate UHPFRC member strength and ductility. Tests have shown that it is not the enhancement in the material concrete compressive strength but the phenomenal brittle ductility nature, observed as a result of increasing the slenderness of the specimen; in contrast, a substantial increase in ductility was achieved after crushing of concrete due to the addition of fibers. A size-dependent analytical approach has estimated good fit with the experimental and other published results. Finally, numerical simulation using a segmental approach at the ultimate limit state of rotation dealing with flexural ductility is significantly influenced by the increase in slenderness factor of the specimens and fiber concentrations.This is evident as the rotation capacity decreased by 62% and 75% for a slenderness factor of 3 and 4, respectively, compared to the slenderness factor 2, when the fiber concentration was 1%. Furthermore, for 2% fiber concentration, the decrease was 54%, and 80%, and for 3% fiber concentration, the decrease was found to be 49%, and 79% for the slenderness factor of 3 and 4, respectively in comparison to the slenderness factor 2, suggesting both slenderness factor and fiber concentration have a significant impact on the flexural ductility.