Hollow Threaded Rebar for Cross Hole Sonic Logging Access Tubes Combined With Longitudinal Concrete Reinforcing in Drilled Shafts-Article

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The technical note proposes using TITAN T73/56 hollow threaded rebar as both longitudinal reinforcement and crosshole sonic logging (CSL) access tubes in drilled shafts. Conventional CSL uses separate smooth PVC or steel tubes, which add no structural capacity and can debond from concrete, potentially obstructing probes and requiring costly coring.<br /><br />The proposed hollow bar provides a 2.2-in. (56-mm) internal passage for CSL probes. Watertight couplers connect bar sections, while the bar’s deformations and stiffness are intended to improve bond with concrete and reduce debonding. Because the bars also act as reinforcement, they can reduce cage congestion and create larger openings for concrete flow.<br /><br />In an example 3-ft-diameter shaft, the conventional arrangement uses fourteen #9 reinforcing bars plus three access tubes (17 components). The alternative uses three hollow bars and eight #9 bars (11 components), with a comparable total steel area. The article argues that this may reduce material, assembly labor, and handling costs, though actual savings depend on project-specific pricing and design. The hollow bars may also be advantageous where reinforcement conflicts with anchor-bolt cages.<br /><br />The note reports preliminary testing indicating compliance with relevant ASTM A615 and A706 physical and chemical requirements, including ductility and bend-test performance. However, code acceptance is a significant limitation: at the time of publication, AASHTO had not adopted the cited allowance for high-strength reinforcement, and the note identifies restrictions related to seismic applications. Project engineers must therefore verify applicable design codes and obtain approval before substitution.<br /><br />Overall, the article presents hollow threaded rebar as a value-engineering option that combines CSL access and structural reinforcement, while acknowledging that code requirements and project conditions govern its use.

Keywords

hollow threaded rebar

crosshole sonic logging

drilled shafts

CSL access tubes

TITAN T73/56

longitudinal reinforcement

bond performance

concrete flow

cage congestion

ASTM A615 A706