Analysis, Design, and Full-Scale Testing of Prestressed Ultra-High Performance Concrete Girders

Abstract

The use of ultra-high performance concrete (UHPC) in Texas bridges has the potential to produce substantial improvements to bridge construction. The advanced material properties and superior durability of UHPC can result in significant design and construction benefits. An analytical feasibility study conducted as part of a larger research study showed that UHPC bridge girders provide increased design efficiency over conventional concrete (CC) girders, including reduced cross-sections, longer spans, and larger girder spacings. The characteristic material properties attained using nonproprietary UHPC mixtures were used to design prototype bridge girders and full-scale Tx34 and Tx54 girder specimens with CC decks for laboratory testing. Three UHPC girder specimens were tested under the prototype design load demands and to failure in some cases, to evaluate the girder response with respect to flexure, web shear, and interface shear. The fiber distribution and tensile strength impacted both the flexure and web shear behavior. The flexure and web shear performance were enhanced relative to typical CC girders in the literature due to the presence of the steel fibers in the UHPC girders. During flexure testing, no cracking was observed up to the design factored moment demands. The moment applied to each girder was 30–50 percent higher than the corresponding factored design moment. The use of harped strands and minimum transverse reinforcement also enhanced the web shear performance. The Tx34 girder with straight strands had a lower UHPC tensile strength based on direct tension testing of the companion samples, and the applied shear during girder testing was slightly below the factored design shear at the unreinforced end. For all other girder ends, the experimental shear capacity was at least twice the design factored shear demand. Mild steel reinforcement in the form of bundled U-bars at the interface of the UHPC girder and cast-in-place CC deck effectively transferred shear up to the factored design loads with negligible slip, although some limited slip was observed at loads exceeding design factored shear demands. The selected analytical prediction models and the recommended design approach provided results consistent with the measured behavior.