Behavior of High-Strength Concrete Members under Pure Flexure and Axial-Flexural Loading

Abstract

The AASHTO LRFD Bridge Design Specifications limits its applicability to a maximum concrete compressive strength of 10 ksi (69 MPa). These limitations reflect the lack of research data at the time, rather than the inability of the material to perform its intended function. The present study addresses the need for better understanding of the behavior of high-strength concrete under pure flexure and axial- flexural loading.

The research program, as part of NCHRP Project 12-64, was comprised of both experimental and analytical work. The experimental work included pure flexure tests, axial-flexural tests and ancillary material property tests for high-strength concrete specimens made with three target strengths of 10, 14, and 18 ksi. A total of eighteen specimens were cast and tested in the Constructed Facilities Lab at the North Carolina State University. Thirteen (13) specimens were tested in pure flexure, and five (5) were tested under axial-flexural loading. The variables considered were mainly concrete strength, reinforcement ratio and level of axial load for the axial-flexural tests. The specimens were instrumented so that the strain profile, mid-span deflections and crack widths could be recorded during the tests. Level of the axial load was recorded and maintained while testing the beam-columns. As part of the analytical work, various aspects of the behavior of high-strength concrete members were examined and compared with the measured test data as well as data from the literature. A finite element model was also developed using the general-purpose program, ANSYS.