Conventional and High-Strength Headed Bars—Part 1: Anchorage Tests

Abstract

Results of an experimental program on the anchorage strength of headed reinforcing bars are presented. Two hundred and two exterior beam-column joint specimens with concrete compressive strengths ranging from 3960 to 16,030 psi (27.3 to 110.6 MPa) were tested under monotonic loading. Key parameters included concrete compressive strength, embedment length, bar size, head size, spacing between headed bars, and confining reinforcement within the joint region. Bar stresses at failure ranged from 26,100 to 153,200 psi (180 to 1057 MPa). Specimens exhibited concrete breakout, side-face blowout, or a combination of the two failure modes, with concrete breakout being the dominant failure mode. A comparison of bar stress at anchorage failure with the stress calculated based on ACI 318-14 shows that ACI 318-14 provides a very conservative estimate of anchorage strength for No. 5 (No. 16) bars and low concrete compressive strengths. The estimate becomes progressively less conservative with increasing bar size and concrete compressive strength.

Headed Bars in Beam-Column Joints Subjected to Reversed Cyclic Loading

“…Thus, the load in the bars at the peak moment, on average, exceeded the value of T h obtained using Eq. ( 1) or (2), and the peak joint shear in the tests V p , as represented by Eq. ( 3), was greater, on average, than a value corresponding to the anchorage strength of the bars.…”

“…To address the limitations in ACI 318-14 for the anchorage of headed bars in concrete, a test program was undertaken to characterize the anchorage strength of headed bars that included 202 exterior beam-column joint specimens under monotonic loading. [2][3][4] The key parameters in those tests were concrete compressive strength (3960 to 16,000 psi [27 to 110 MPa]); embedment length (4 to 19.25 in. [102 to 489 mm]); bar size (No.…”

“…The test data were used to support the development of descriptive equations for the anchorage strength of headed bars without and with confining reinforcement, shown in Eq. ( 1) and (2), respectively. The equations incorporate the effects of embedment length, concrete compressive strength, bar diameter, bar spacing, and confining reinforcement.…”

“…or mm); A tt is total cross-sectional area of effective confining reinforcement within the joint and parallel to the headed bars being developed (in. 2 or mm 2 ) equal to the product of the cross-sectional area of a single leg of confining reinforcement (A tr,l ) and the total number (N) of single legs of confining reinforcement parallel to the headed bars within 7.5d b of the centerline of No. In Eq.…”

“…The goal of the work reported in this article is to evaluate the applicability of those equations (based on members subjected to monotonic loading) to members subjected to reversed cyclic loading. The test programs and development of the descriptive equations are presented by Shao et al 3 and Ghimire et al 2,4,7 RESEARCH SIGNIFICANCE Generalized equations to characterize the anchorage strength of headed bars are scarce in the literature, limiting the development of versatile design provisions for headed bars that account for a wide range of parameters, including concrete compressive strength, reinforcement yield strength, and member geometry and detailing. Based on recent research on headed bars, this paper establishes the applicability of descriptive equations developed for headed bars anchored in beam-column joints under monotonic loading to headed bars anchored in beam-column joints subjected to reversed cyclic loading.…”