Flexural response of UHPC beams post-tensioned with internal unbonded tendons: Experimental study

Abstract

This paper presents the results of an experimental study that deals with the characterization of the complete flexural response of post-tensioned (PT) ultra-high-performance concrete (UHPC) beams with internal unbonded tendons. A total of 6 PT UHPC beams were monotonically loaded to failure. The variables investigated include volumetric fiber content, non-prestressed reinforcement ratio, and loading configuration. Flexural response is characterized in terms of crack pattern formation, propagation, and localization as well as failure mode identification. The influence of the investigated variables on change in: strand strain, UHPC compressive and tensile strains, strand stress, moment capacity, curvature ductility and member level ductility is presented including explanations of observed phenomena. The measured flexural response and capacity are compared with the predicted response using two mechanics-based methods and a numerical method. Prestress losses are quantified and used to obtain the predicted response. UHPC material characterization is conducted to obtain the necessary inputs for the prediction models. The measured to predicted ratio of flexural capacity and the corresponding COV for the considered prediction methods vary from 0.95 to 1.02, and from 6% to 11% suggesting good predictive capabilities. The use of nonprestressed flexural reinforcement in PT UHPC flexural members is recommended from the perspective of crack distribution, delay in the precipitation of flexural failure through crack localization and subsequent hinging, and member level ductility.