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Structural Behavior of Ultra High Performance Concrete Columns
AdvisorA. Moustafa, Mohamed
Civil and Environmental Engineering
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Ultra-high performance concrete (UHPC) is a relatively new class of concrete and cementitious materials with much higher strength and durability than conventional concretes. The use of UHPC is currently expanding worldwide from bridge deck joints and connections to full components and larger applications. With the superior mechanical properties of UHPC, future UHPC columns in buildings and bridges, among other structural components, will have compact cross-sections and smaller footprint. The overarching goal of this research study is to provide better understanding of UHPC columns behavior that can enable future design of more durable, slender, and efficient alternative for conventional concrete columns to use for accelerated construction and reduced footprint. To accomplish this goal, a total of 13 large- and full-scale UHPC columns were tested under different loading conditions to comprehensively investigate the effect of different variables on the structural behavior and strength of UHPC columns. This experimental investigation aimed at providing a first of its kind knowledge needed to optimize the design of UHPC columns under the different types of loading. It also aimed at contributing to the design codes and guidelines by conducting evaluation of the existing provisions in estimating the columns axial strength (i.e. short and long columns) and by providing exclusive UHPC-sensible design recommendations for UHPC columns. This doctoral study addressed several specific research objectives and conducted major tasks which had the following components: (1) conducting a comprehensive comparison between the combined axial and lateral cyclic behavior of an experimentally tested UHPC column and a similar analytically-simulated normal strength concrete column; (2) investigating the effect of varying the reinforcement grade and using high strength steel (Grade 100 bars) on the cyclic behavior of three large-scale UHPC columns for the purpose of fully utilizing the UHPC high compressive strength and increasing the columns bending-moment capacity; (3) investigating the effect of increasing the UHPC column slenderness ratio on the stability and strength of five full-scale experimentally tested UHPC columns under axial load with varied slenderness ratios, and using test results to assess the current ACI 318 procedure for slenderness effects using the moment magnification method; and (4) analyzing the experimental behavior of full-scale UHPC columns with negligible slenderness effects and varying reinforcement details, i.e. different longitudinal, transverse, and fiber reinforcement ratios, under concentric axial loading. This mostly-experimental study provided exclusive first-time demonstration and reliable datasets of UHPC columns to validate current analytical procedures and inform future designs. The study is then concluded by design guidance and several recommendations for the design of short and slender UHPC columns, which can be readily incorporated into future design codes.