Large Reinforcing Bars Spliced in UHPC

Presented By: Christina Freeman, FDOT Description: Construction time savings can be realized through replacement of cast-in-place substructure columns and/or piers with prefabricated bridge elements and systems (PBES). Typical cast-in-place substructure construction requires forming, placing steel, and pouring concrete at the construction site. Further work cannot progress until the concrete reaches a specified strength. Use of precast elements can decrease the extent of work required at the site and potentially reduce required concrete curing time. Ultra-high-performance concrete (UHPC) can be used as a joining material for PBES to enhance the connection details by minimizing reinforcement conflict and reducing the shoring or support requirements for PBES. UHPC has high early strength, requires less development or splice length than conventional concrete and has been used previously for accelerated construction projects. UHPC also has a discontinuous pore structure that reduces liquid ingress, significantly enhancing durability compared to conventional concrete. Although UHPC has been researched extensively, previous research for reinforcing bar splice and development lengths have focused on #9 and smaller diameter bars. Typically, larger diameter bars are used for substructures. Some research has been conducted for splice length of #11 bars, but the number of tests is limited. FDOT has completed research to determine the required splice and development lengths for large diameter bars with 1.75 to 3.75 in. clear cover. Bar sizes considered were #8, #9, #10 and #11 bars. The tested bar sizes are typical for substructure construction and include the maximum size permitted by the Florida Department of Transportation Structures Detailing Manual for footings, pier columns, piers and bent caps. Instrumentation used during testing included fiber optic strain gages adhered to the embedded reinforcing bar. The fiber optic strain gages recorded strain at 0.25 in. increments along the length of the reinforcing bar.