Mertol, Rizkalla, Zia and Mirmiran 2006 CBC 1 FLEXURAL DESIGN USING HIGH-STRENGTH CONCRETE UP TO 20 KSI

This paper summarizes the research findings of the fundamental characteristics of high-strength concrete for the flexural design of bridge girders. The main objective of the research is to provide recommended provisions to the AASHTO-LRFD Bridge Design Specifications to extend the use of concrete strength up to 18 ksi. A total of 15 plain concrete specimens were tested under eccentric compression to evaluate the stress-strain distribution of high-strength concrete in the compression zone of flexural members. The variables considered in this investigation are the strength of concrete (11 ksi to 16 ksi) and the age of the concrete. Two independent loads, concentric and eccentric, were applied with a specific rate to the specimen so as to locate neutral-axis at one face of the specimen and the maximum strain at the opposite face. The specimens were 9 by 9 inches cross-section and 40 inches long. Stress-strain curves and stress block parameters for highstrength concrete were obtained, evaluated and compiled with the results available in the literature. The current equation for α1 specified by AASHTO LRFD Bridge Design Specifications needs to be modified to show a reduction for high-strength concrete. The current equation for β1 and current value for ultimate concrete strain specified by AASHTO LRFD Bridge Design Specifications is appropriate for high-strength concrete.