United States Department of Transportation
i
Seismic-Resistant Connections between Precast Concrete Columns and Drilled Shafts
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2012-06-01
[PDF-6.28 MB]
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Edition:Final technical report.
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Abstract:In most areas of the country traffic is becoming more congested, and delays, more common. Highway construction, and especially construction that requires lane closures, exacerbates the delays, and imposes costs that can be measured in dollars, wasted fuel, carbon emissions, safety and personal stress levels. Methods of constructing bridges that require less time on site are therefore being developed in order to address these costs, and are referred to collectively as Accelerated Bridge Construction (ABC).
One approach to ABC involves prefabricating concrete elements of the bridge off-site, and connecting them on-site. This procedure saves the time needed to erect formwork, assemble reinforcement cages and wait while the concrete gains strength. The elements are most conveniently cast and transported if they are line elements, such a straight beams and columns. In non-seismic regions, this presents no special problems. However, in seismic regions, precasting line elements means that the connections must be made at the intersections between them, which is where the moments are highest and the inelastic cyclic deformations the largest. Designing connections that are sufficiently robust to withstand severe seismic loading and are at the same time simple to complete is a challenge.
This report described a method of connecting a precast concrete column to a drilled shaft foundation in a way that is suitable for use in a high seismic region. The method was adapted from the existing way of constructing a cast-in-place drilled shaft-to-column connection, and involves embedding the precast column into the top of the cast-in-place drilled shaft. The quantity and detailing of the reinforcement in the transition region, where the embedment occurs, is critical to achieving good seismic performance. Two scale specimens were tested in the laboratory, and the test results provided a lower bound on the amount of spiral reinforcement needed in the transition region. Analytical models were developed to describe the behavior of the connection.
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