Evaluation of Load Transfer and Strut Strength of Deep Beams with Short Longitudinal Bar Anchorages

Abstract

This paper examines the behavior of struts and nodes in deep beams fabricated using short longitudinal bar anchorages. Laboratory tests were conducted of 12 deep beams in which the longitudinal reinforcement was anchored into the support using short straight bar anchorages. The shortest anchorage lengths provided were below 50% of those required by ACI 318-08 Chapter 12 provisions. Four different specimen groups were constructed using three different shear span-depth ratios (a/d) and two longitudinal bar sizes. Most of the beams failed by strut crushing after yielding of the main longitudinal reinforcement at midspan. Only those specimens with the shortest anchorage length in each group developed concrete splitting failures along the anchorage region. The effect of a/d and anchorage length on strut strength and load transfer mechanism observed in the tests is presented and discussed. Test results indicate that a significant portion of the applied shear force may be transferred through truss action even in beams with low a/d. Short anchorage length affected the load transfer characteristics of the deep beams. These findings can be used in better understanding the merits of different strut-and-tie models for design of deep beams.