Behavior of Concrete Bridges Reinforced with High-Performance Steel Reinforcing Bars

Abstract

High-performance (HP) steel reinforcing bars are characterized by their high tensile strength and enhanced corrosion resistance in comparison to conventional ASTM A 615 Grade 60 steel. Use of HP steel in concrete bridges could lead to potential savings by reducing the amount of steel required based on its higher strength characteristics and expanding the service life of bridges due to its enhanced corrosion resistance. A commercially available steel know Micro-Composite Multi-Structural Formable (MMFX) steel which is conforming to ASTM A 1035, was selected for this study because of its high tensile strength and enhanced corrosion resistance. Comprehensive experimental and analytical programs were carried out to evaluate the mechanical properties of the HP steel bars, its bond characteristics, and the behavior of concrete bridge decks reinforced with HP steel.

Research findings showed that HP steel used in this study exhibited much higher tensile strength than that of conventional Grade 60. In addition, the HP steel bars had much lower corrosion rate than Grade 60 bars. Bending HP steel bars reduce its ultimate strength and strain by 6 and 70 percent, respectively. However, when HP steel bent bars are bonded to concrete they develop their full stress-strain capacity.

Bond test results indicated that a stress level up to 90 ksi can be developed in #8 HP steel bars without the use of transverse reinforcement. The use of transverse reinforcement increases the bond strength of HP steel reinforcing bars, consequently reaching stress levels in the bars up to 150 ksi. When possible, it is recommended to use a minimum amount of transverse reinforcement to confine spliced bars to ensure ductile behavior and provide warning prior to failure.

Direct replacement of Grade 60 with HP steel bars in bridge decks is a conservative approach. However, reducing the amount of HP steel by 33 percent does not impair the ultimate-load carrying capacity or alter the serviceability behavior of bridge decks. Under service load, the behavior of bridge decks is two-way flexural behavior. Increasing the applied load leads to development of internal membrane action, known as arching action. The presence of these forces significantly increases the ultimate load-carrying capacity of concrete bridge decks until failure typically occurs by punching shear due to the nature of the applied concentrated loads simulating truck wheel loads.

Based on the study presented herein, design yield stress of 90 ksi is recommended for design of concrete bridge decks reinforced with HP steel reinforcing bars. However, the requirements of the AASHTO LRFD Bridge Design Specifications for maximum spacing of reinforcement shall be satisfied. Use of HP steel bars will expand the service life of concrete bridges due to its enhanced corrosion resistance.