Title:
Behavior of Deep Beams with Large Headed Bars
Author(s):
Boyan I. Mihaylov, Evan C. Bentz, and Michael P. Collins
Publication:
Structural Journal
Volume:
110
Issue:
6
Appears on pages(s):
1013-1022
Keywords:
deep beams; headed reinforcement, hooks; shear
DOI:
10.14359/51686156
Date:
11/1/2013
Abstract:
While anchor heads are particularly useful in the case of large bars, which require significant development lengths, the ACI Code provides design guidance for bars No. 11 or smaller. This paper presents a test of a large deep beam reinforced with a single No. 18 headed bar. The behavior of the beam is evaluated in comparison to the behavior of a specimen with more conventional reinforcement of six No. 8 headed bars, and to the behavior of a specimen with lap-spliced anchor hooks. Despite the extreme detailing of the specimen with a single No. 18 bar, the beam had the same strength as the specimen with six No. 8 bars. The compressive stress in front of the anchor head reached approximately 1.5 times the compressive strength of the concrete, and the stress in the No. 18 bar reached approximately 414 MPa (60 ksi) before the beam failed in shear along a diagonal crack away from the anchorage zone. Shear strength calculations according to Appendix A of the ACI Code showed that the current strut-and-tie provisions can overestimate the shear strength of deep beams by as much as 23%.