Bridges

The Ultra Girder: A Design Concept for a 300-foot Single Span Prestressed Ultra-High Performance Concrete Bridge Girder

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Abstract

The longest current pretensioned bridge girders are approximately 200 ft (61.0 m) long, with this limit being controlled by concrete mechanical properties, prestressing strand capabilities, and shipping/handling considerations. With compressive strength greater than 21.7 ksi (150 MPa) and sustained post-cracking direct tensile capacity exceeding 1.0 ksi (6.9 MPa), ultra-high performance concrete (UHPC) has emerged as new class of cementitious composites, unlocking opportunities for longer spans and structural optimization of bridge girders. This study builds on extensive research completed at the Federal Highway Administration’s Turner-Fairbank Highway Research Center to explore the viability of a 300 ft (91.4 m) single span pretensioned prestressed girder made with UHPC. The paper outlines the material modeling approaches, directly derived from experimental data, and utilizes the concept of strain compatibility to determine the flexural capacity and possible failure modes of the girder. The shear design approach is based on principal tensile stress trajectories to address the shear failure mode caused by a diagonal field of tensile forces in web of the girder. The shear capacity is then related to the tension strength of UHPC and the expected failure plane angles. By investigating these primary demands on the girder, this work demonstrates that the proposed cross section is a viable solution. The paper constitutes a discussion of UHPC bridge girder behavior and provides designers with insight on key aspects of the design procedure.

Keywords: UHPC, flexural behavior, shear capacity, bridge design, prestressed concrete

How to Cite:

El-Helou, R. G. & Graybeal, B. A., (2019) “The Ultra Girder: A Design Concept for a 300-foot Single Span Prestressed Ultra-High Performance Concrete Bridge Girder”, International Interactive Symposium on Ultra-High Performance Concrete 2(1). doi: https://doi.org/10.21838/uhpc.9707