Behavior of deep beams with short longitudinal bar anchorages

This paper presents laboratory test results of 12 deep beams in which the longitudinal reinforcement was anchored into the support using short straight bar anchorages. Specimens were constructed using three different shear span-depth ratios (a/d). Differences in general and local behavior in the anchorage region are high-lighted between groups of beams. The test results show that shorter anchorage lengths than required by ACI 318-05, Chapter 12, are effective in developing the yield stress of bars at the end of the extended nodal zone. This result is consistent with shorter anchorage length required by bars embedded in concrete regions subjected to lateral confining pressure. In cases where the reinforcement did not reach yield, the forre transfer mechanism in the deep beams apparently changed from a predominantly tied-arch mode to a truss mode allowing the specimens to achieve approximately the same load during the tests and fail by strut crushing. A physical model to estimate the anchorage length of straight bars subjected to lateral pressure over part of the anchorage length is presented. Copyright © 2008, American Concrete Institute. All rights reserved.