Date of Award

May 2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

Committee Member

Brandon E. Ross

Committee Member

Brandon Ross

Committee Member

Thomas Cousins

Committee Member

Laura Redmon

Committee Member

Weichiang Pang

Abstract

This dissertation evaluates the behavior and capacity of single screw and adhesive anchors in thin concrete members that do not meet the minimum thickness requirements of current standards for anchorage. This dissertation focuses on the concept of full thickness embedment, wherein anchors are embedded through the entire thickness of the concrete member, and its implications. This is the first exclusive study on the concept of full thickness embedment anchors. In addition, this dissertation provides design models for single anchors in thin concrete members subjected to tension and shear loads.

Three experimental programs were conducted to investigate the tensile and shear capacity of screw and adhesive anchors with a total of 350 tests. Variables included are concrete compressive strength, concrete thickness, anchor type, anchor diameter, screw and adhesive manufacturer, and edge distance for shear tests. Experimental data were used to develop the aforementioned design models for anchors in tension and shear. Consistent with modern standards for anchor design, the proposed design models are based on the 5% lower fractile and 90% confidence.

It is shown that drilling through the concrete thickness causes the concrete to blowout at the back-face. The blowout is conical in shape with the depth of the blowout ranging from 0.65 to 0.96. This blowout affects the tensile capacity of screw anchors as the embedment depth is reduced by the depth of the blowout. However, back-face blowout effect was not noticeable in adhesive anchors as the adhesive fills the crack and fractures due to drilling. As a result, adhesive anchors have substantially higher tensile capacity compared to screw anchors. For example, typical adhesive anchor capacity in a 2-in. thick concrete member is almost four times larger than typical screw anchor capacity. In addition, adhesive anchors showed consistent performance independent of the adhesive supplier, unlike screw anchors wherein the failure mode and capacity were dependent on the product itself.

Back-face blowout also affects shear capacity of screw anchors. However, the effect is less significant than on tension capacity. The reduction in the capacity (relative to adhesive anchors) is attributed to the reduction of the anchor stiffness due to the blowout.

Modifications to the Concrete Capacity Design method are proposed to extend the method to full thickness embedment anchors in thin concrete members. To include the effect of back-face blowout on screw anchors in tension and shear, a reduced embedment depth and shear transfer length is proposed. In addition, a revised thickness modification factor is proposed for anchors subjected to shear loads.

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