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Behavior of deep beams with short longitudinal bar anchorages

TitleBehavior of deep beams with short longitudinal bar anchorages
Publication TypeJournal Article
Year of Publication2008
AuthorsRoy NC, Breña SF
JournalACI Structural Journal
Volume105
Issue4
Start Page460
Pagination460-470
Date Published07/2008
ISSN0889-3241
Accession Number01109922
KeywordsAnchorages, Beams, Bond strength (Materials), Force, Laboratory tests, Longitudinal reinforcement, Strut and tie method
Abstract

Anchorage length for deep beams calculated using provisions of ACI 318-05 does not account for the effects of lateral pressure on bond strength. This paper seeks to identify changes in the force transfer mechanism in deep beams as a result of short longitudinal bar anchorages and to incorporate the effect of lateral pressure on bond strength of bars anchored in nodal regions of deep beams. Laboratory tests of 12 deep beams were conducted 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. Differences in general and local behavior in the anchorage region are highlighted between groups of beams. A physical model to estimate the anchorage length of straight bars subjected to lateral pressure over part of the anchorage length is presented. The test results show that shorter anchorage lengths than required by ACI 318-05 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 force 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.