Nebraska LTAP


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Wood, R. L., Liao, Y., Mohammadi, M. E., Wipf, J. "Design Procedures of Retrofitted Bridge Rail" (2016) Nebraska Department of Roads Research Report Report 26-1121-4024-001 SPR-P1 (15) M028


The use of shallow embedment anchors in concrete is essential for retrofit applications; however, the combination of steel anchors, chemical adhesive, and concrete acting as a single tensile mechanism creates uncertainties in anchor strength and failure modes. Differences in concrete compressive strengths and in specifications of adhesives between manufacturers increases uncertainty further. In addition to these issues, prior research conducted by others examines the behavior of such anchors with respect to cracked versus uncracked concrete, partial bonding of the embedded length, and strength reductions due to anchor proximity to edges. While it is understood, anchors require a proper installation detail, the goal of this research is to understand the failure mechanisms and capacity when such conditions cannot be met. One example of a limiting case is a retrofitted bridge where shallow anchors are the only option. For this application, experiments were conducted to determine the failure modes and capacities for a 4.75 inch embedment depth anchors of No. 4 reinforcement bars in accordance with a retrofit special provision. Additional experimental investigations were conducted to determine what, if any, differences existed between these provisions and specifications that included partially bonded anchors, anchors installed within an edge condition, and the differences between reinforcement surface coatings (epoxy vs plain or black). Excluding the edge tests which exhibited poor performance, most anchors exhibited a combined failure mode of concrete cone with steel rupture and reached capacities of 11.5 to 12.5 kips. No discernable difference in strength capacity was observed when the anchor embedment depth was reduced from 4.75 inches to 3.5 inches.