Pullout Strength of Embed Plates with Welded Anchor Bars in Concrete
Jungil Seo, Ata Ur Rehman, Amit H. Varma, and Sungmin Kim
Appears on pages(s):
concrete breakout; deformed reinforcing bars; deformed wire anchors; embedded plates; pullout strength
Embedded plates are used to support external attachments such as heavy piping, brackets, sprinkler systems, or other equipment in concrete structures. The plates are typically welded with deformed reinforcing bars or deformed wires, which are embedded in reinforced concrete walls. The ACI Codes (ACI 318-19 and ACI 349-13) provide design equations to calculate the pullout strength of anchors in concrete under tension loading. However, these empirical equations are based on experiments conducted on headed studs, hooked bars, headed bolts, and adhesive anchors. With the lack of experimental data and resulting Code provisions on straight
deformed reinforcing bars or deformed wires used as anchors, it is believed that anchoring bars with the embedment length as per the Code-prescribed development length will provide sufficient strength to transfer tensile forces to the concrete, ignoring other failure modes such as concrete breakout and pullout. The applicability of the concrete-governed adhesive bond model of ACI 318-19 for bonded anchors is evaluated to estimate the strength and failure modes of these connections. The current ACI adhesive bond model does not capture the correct failure mode and the influence of anchor spacing and bond strength on the capacity. The issue is addressed by incorporating the correction factor (ψg,N). This paper presents eight large-scale group-anchor test results to evaluate their concrete breakout strength and the applicability of
the ACI 318-19 adhesive anchor/bond model to estimate connection capacities and failure modes. The mean average back-calculated effective k value is 33.3 for deformed reinforcing bar anchors (DRAs) and 36.5 for deformed wire anchors (DWAs). Single-anchor tests were also performed to evaluate the bond behavior per the ACI 318-19 uniform bond model. The experimental study confirms that the axial tension capacity of embedded plates anchored to concrete using deformed reinforcing bars or deformed wires can
be limited by concrete breakout strength. The ACI bond model with the correction factor appropriately estimates the failure mode and strength of such connections.