Development of Design Recommendations for Noncontact Hooked Bar Lap Splices for Large Reinforcing Bars

About the report

On wide bridges, precast concrete pier caps are often constructed in multiple segments and connected on site because of transportation or construction limitations. When these segments are connected through closure joints, contractors use lap splices of straight reinforcing bars. However, the splice lengths of large (e.g., No. 11) straight bars must be very long to develop the yield strength of the bars. The cost of long splices may offset the benefit of using precast concrete. To reduce splice lengths, bridge designers use hooked bars in noncontact lap splices, presuming that hooked bars allow for shorter splice lengths. The use of noncontact splices avoids conflicts during fit-up in the field. However, neither substantial design guidance nor studies of the behavior of hooked bar lap splices in large concrete elements exists to justify this design philosophy.

To develop design guidance for noncontact hooked bar lap splices, 73 large-scale beam-splice specimens were tested to simulate the closure connection between precast pieces. The bond and anchorage parameters of the noncontact hooked bar lap splices varied, including parameters such as the splice spacing, concrete compressive strength, cover depth, casting position, number of spliced reinforcement layers, hook shape, splice length, number of bundled bars, number of lap splices, amount of transverse reinforcement, and dosage of steel fibers. In addition, nonlinear finite element analyses were conducted to investigate the force transfer mechanism in noncontact hooked lap bar splices and predict splice strength over a wider range of splice configurations than tested in the laboratory.

Results indicated that noncontact hooked bar lap splices without transverse reinforcement (e.g., ties) can fail because the eccentricity between lapped bars causes “hook side bulging,” a tension failure concentrated at the hooked ends closest to the sides of a beam. In contrast, splices with transverse reinforcement experienced failure modes such as side-face blowout and concrete crushing. Noncontact hooked bar lap splices had weaker splice strengths than contact splices. Nevertheless, hooked bars are an effective means of reducing required splice lengths. On average, the use of steel fibers and increases in lap length, concrete compressive strength, cover, amount of transverse reinforcement, or the number of lap splices allowed for greater stress to be developed in spliced bars. All else being equal, an increase in either bar size or the number of spliced reinforcement layers decreased the stress that could be developed in the spliced bars. A design equation was developed for the minimum required lap length of hooked bars, which uniformly characterizes the influence of the variables over the ranges explored in this study. To enable immediate implementation of the design equation in practice, design examples and proposed code language were also prepared for incorporation into relevant standards.

On completion of this research, the researchers acknowledged the potential of applying the results beyond the project’s original scope. Supplemental information on these additional applications can be found at https://library.vdot.virginia.gov/vtrc/supplements. 

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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