Value Engineering of Reinforcement Used in Large Diameter Drilled Shafts-Paper

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The paper presents value engineering for large-diameter drilled shafts by replacing congested bundles of conventional Grade 60 reinforcing bars with fewer, larger, higher-strength threaded bars—typically Grade 75, 80, or 100. Threaded couplers replace lap splices, while end terminators can replace hooked bars.<br /><br />Conventional reinforcement can obstruct concrete flow, complicate cage fabrication and placement, and increase labor and crane requirements. These problems are especially significant in deep shafts, seismic designs requiring dense transverse reinforcement, and cages installed in multiple sections. The authors note that adequate spacing is essential because tremie-placed concrete is not vibrated for consolidation.<br /><br />Several U.S. bridge projects illustrate the approach. At the I-35W Bridge, Grade 80 threadbars reduced the number of vertical bars and eliminated splices. At the St. Croix Bridge, Grade 75 threadbars replaced two longitudinal cages with one, reducing reinforcing-steel weight by 16%. Other projects also reported fewer bars, lower steel weight, simplified installation, and reduced congestion. In a comparison for a 9-foot-diameter shaft, 21 Grade 100 bars replaced 60 Grade 60 bars, cutting the number of bars by 65% and their weight by about 38%.<br /><br />The authors conclude that high-strength threadbars can improve constructability and concrete flow while reducing tying, fabrication, installation, and crane demands. Mechanical couplers also facilitate splicing cage sections in the borehole. The paper emphasizes that such substitutions must meet applicable design requirements and receive agency approval.

Keywords

value engineering

large-diameter drilled shafts

high-strength threadbars

Grade 75

Grade 80

Grade 100

mechanical couplers

reinforcing congestion

bridge projects

constructability