Title:
Strength and Detailing of Beams with High-Strength Headed and Hooked Stirrups
Author(s):
R. D. Lequesne, A. Al-Sabawy, D. Darwin, A. Lepage, M. O’Reilly, E. Guillén, and D. Spradling
Publication:
Structural Journal
Volume:
122
Issue:
4
Appears on pages(s):
139-153
Keywords:
headed stirrup; high-strength steel; hooked stirrup; minimum shear reinforcement; shear strength; stirrup detailing
DOI:
10.14359/51745469
Date:
7/1/2025
Abstract:
Thirty-nine large-scale reinforced concrete beams were tested
under monotonic three-point bending to investigate the use of stirrups with mechanical anchors (heads) or hooks and Grade 80 (550) reinforcing steel. Grade 60 and 80 (420 and 550) No. 3, No. 4, and No. 6 (0.375, 0.5, and 0.75 in. [10, 13, and 19 mm]) bars were
used as stirrups, which were spaced at one-quarter to one-half of
the member effective depth. Other variables included beam depth
(12 to 48 in. [310 to 1220 mm]), beam width (24 and 42 in. [620
and 1070 mm]), longitudinal reinforcement strain corresponding
to the nominal beam shear strength (nominally 0.0011, 0.0017, or
0.018), and concrete compressive strength (4000 and 10,000 psi
[28 and 69 MPa]). Headed stirrups that: a) engage (are in contact
with) the longitudinal bars; or b) have a side cover of at least six
headed bar diameters and at least one longitudinal bar within the
side cover, produce equivalent shear strengths as hooked stirrups,
and both details allow stirrups to yield. The results affirm that
beams designed for the same Vn with either Grade 60 or 80 (420 or
550) stirrups exhibit equivalent shear strengths. A nominal shear
strength based on a concrete contribution equal to 2 √ fc bwd may be
unconservative when ρtfytm < 85 psi (0.59 MPa) in members with
a/d = 3, h ≥ 36 in. (910 mm), ρ < 1.5%, and no skin reinforcement.