Postprint version. Published in Proceedings of the First International Conference on High Strength Concrete: Kona, HI, July 13, 1997, pages 412-424. Copyright © 1997 American Society of Civil Engineers. The definitive version is available at http://cedb.asce.org.
NOTE: At the time of publication, the author Daniel Jansen was not yet affiliated with Cal Poly.
The mechanisms which lead to shear failure of longitudinally reinforced concrete beams are complex and often misunderstood. In this paper, a combination of a special closed loop test technique and machine vision are applied to tests on two reinforced concrete beams failing in shear: one made of normal strength concrete and the second of high strength concrete. To control the progression of the shear crack, a closed-loop test technique was devised and employed such that the crack propagation was stable even during the post peak. To locate the crack and to measure the crack displacements, machine vision, a nondestructive measuring technique, was employed which gives full-field displacements of a viewed area. The displacement measurements are obtained by first grabbing digital images of the observed area at different stages of loading during the test. By comparing discrete subsets of the reference and target images using normalized cross correlation matching, the displacement fields of the images are calculated. Shear crack initiation and progression are monitored for the two beams tested through complete failure, and differences in the shear failures between reinforced beams made of normal and high strength concretes are noted.
Civil and Environmental Engineering