Conventional and High-Strength Headed Bars—Part 2: Data Analysis

Abstract

Equations to characterize the anchorage strength of headed bars were developed, incorporating key factors affecting anchorage strength: concrete compressive strength; embedment length; bar diameter; spacing between the bars; and confining reinforcement parallel to the headed bars. Results from tests of 138 exterior beam-column joints, 64 without and 74 with confining reinforcement within the joint region, were used to develop the equations. Concrete compressive strengths ranged from 4050 to 16,030 psi (27.9 to 110.6 MPa) and bar stresses at failure ranged from 33,100 to 153,160 psi (228 to 1056 MPa). The bearing area of the headed bars ranged from 3.8 to 9.5 times the area of the bar. Some headed bars contained obstructions adjacent to the head that exceeded the dimensions permitted for HA heads in ACI 318-14 and ASTM A970-13a but are now permitted by ASTM A970-18. The test results show that headed bar anchorage strength is proportional to the concrete compressive strength raised to the power 0.24. The contribution of confining reinforcement is proportional to the area of confining reinforcement parallel to the headed bar within eight to 10 bar diameters of the headed bar. Headed bars with obstructions larger than those permitted in ACI 318-14 that meet the provisions in ASTM A970-18 exhibit anchorage strengths that are similar to those that meet the provisions in ACI 318-14.

A parametric finite element study of concrete cone failure in headed bars under tensile loading

“…Additionally, increasing the nominal strength of concrete can effectively reduce the compressive deformation of the local concrete under the head and postpone the cracking of the failed concrete, thereby increasing the critical load and critical deformation of the anchor concrete (Zhuang et al 2021). Similar behaviors were observed in studies by Eligehausen et al (2006) and Ghimire et al (2019).…”

“…The specific failure mode depends on parameters such as concrete compressive strength, embedment depths, steel strength, edge distance, spacing between headed bars, and other variables, as discussed in detail by Karmokar et al (2021). In recent decades, the successful use of a headed bar as a replacement for the traditional method has been demonstrated in experimental research studies by DeVries (1996), Thompson et al (2005), Ghimire et al (2019), Ferreira et al (2021), and Santana et al (2022). These studies investigated concrete cone failure under various installation conditions and provided valuable results to validate and improve existing normative calculation models.…”

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

“…The applicability of the descriptive equations for the anchorage strength of headed bars in beam-column joints under monotonic load 3,4 to headed bars in beam-column joints subjected to reversed cyclic loading was evaluated. Test results from 23 studies that included 84 exterior and seven roof-level interior beam-column joints subjected to reversed cyclic loading were analyzed.…”

“…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 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.…”