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. Guillen, 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 testedunder 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 wereused as stirrups, which were spaced at one-quarter to one-half ofthe member effective depth. Other variables included beam depth(12 to 48 in. [310 to 1220 mm]), beam width (24 and 42 in. [620and 1070 mm]), longitudinal reinforcement strain correspondingto the nominal beam shear strength (nominally 0.0011, 0.0017, or0.018), and concrete compressive strength (4000 and 10,000 psi[28 and 69 MPa]). Headed stirrups that: a) engage (are in contactwith) the longitudinal bars; or b) have a side cover of at least sixheaded bar diameters and at least one longitudinal bar within theside cover, produce equivalent shear strengths as hooked stirrups,and both details allow stirrups to yield. The results affirm thatbeams designed for the same Vn with either Grade 60 or 80 (420 or550) stirrups exhibit equivalent shear strengths. A nominal shearstrength based on a concrete contribution equal to 2 √ fc bwd may beunconservative when ρtfytm < 85 psi (0.59 MPa) in members witha/d = 3, h ≥ 36 in. (910 mm), ρ < 1.5%, and no skin reinforcement.
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