Applications of Ultra-High Performance Fiber-Reinforced Concrete on Flexural Structural and Architectural Members

Abstract

This thesis presents the test results of a study on flexural and shear behavior of Ultra-High-Performance Fiber-Reinforced concrete (UHP-FRC) beams, reinforced with Grade 60 steel (ASTM A615/A615M), Grade 100 steel (ASTM A1035/A1035M) and Basalt fiber reinforced polymer (BFRP) bars. Ultra-high-performance fiber-reinforced concrete (UHP-FRC) has high compressive strength (> 22 ksi (150 MPa)) and exceptional compressive ductility. The use of UHP-FRC provides new opportunities for future infrastructure. However, structural design criteria have not been developed to fully utilize UHP-FRC’s excellent mechanical properties. Maximum useable compressive strain, εcu, specified in the current design codes (ACI 318 Building Code and AASHTO LRFD Bridge Design Specifications) are limited to 0.003 for conventional plain concrete with little ductility and a maximum compressive strength of about 15 ksi (103 MPa). This maximum concrete compressive strain directly limits the amount of longitudinal reinforcement that could be used in flexural members, which in turn limits the flexural capacity of the members. Since the maximum useable strains of UHP-FRC are 5 to 10 times of that of plain concrete, it is apparent that the maximum compressive strain used for the current design needs to be reevaluated for UHP-FRC. In addition, unlike plain concrete, the tensile strength of UHP-FRC can also contribute to its bending capacity. The large amount of reinforcement also significantly affected the tensile behavior of UHP-FRC due to the tension-stiffening effect.

Ability of UHP-FRC to lend itself in to very complex shapes and thin elements make it well-suited to contemporary architectural needs. Columns articulated by non-Euclidean geometries offer a new type of architecture with formal and structural possibilities. Specifically, branching concrete columnar structures offer a unique opportunity to merge biomimetic structural geometry with new computationally controlled performance criteria. Typical plain concrete does not willingly lend itself to these types of geometries due to its brittle nature and sensitivity to stress concentration. The non-Euclidean geometries also make the conventional reinforcing methodology difficult to be practically implemented. In the work shown in this research, the introduction of ultra-high-performance fiber reinforced concrete (UHP-FRC) allows for a new way of advancing beyond some of the limitations of conventional construction methods which use reinforced concrete. The formwork used for these columns presents a unique solution for assembling 2D materials in complex 3D forms. In this research, the two-legged and three-legged branching and twisting scaled columns all rely upon developable geometry that has been cut via a CNC machine out of 1/16th inch polypropylene. The parts are seamed together by hand via a ‘zipper’ connection that is the result of running an algorithmic script on the edge geometry of each edge of adjoining parts.

The physical properties of UHP-FRC give significant advantages to design and develop structurally and thermally optimized precast cladding system. UHP-FRC is used for developing stronger, thinner and more durable concrete sandwich panels and to fabricate more detailed geometry that can create self-shading surface using UHP-FRC. Thickness of UHP-FRC required for minimum thermal heat transfer though the building envelope has also been investigated. This thesis discusses the progress of this novel UHP-FRC application and the experimental testing results of flexural structural members, columns designed with non-Euclidean geometries and also thin sandwich panels designed and developed with UHP-FRC.