Compression Bond Lengths: Study of Test Data and Design Equations

Compression development and lap-splice length provisions in ACI 318-19 §25.4.9 and §25.5.5 are reexamined after an example was used to show that existing provisions can produce unexpected results in some design conditions, such as compression lap splices longer than tension lap splices. A historical review of ACI Building Codes shows that existing compression bond length provisions are largely based on provisions adopted before test data were available. The provisions in ACI 318-19 are compared with a database of 89 test results and shown to poorly fit the data. Several compression and tension bond equations are also examined and found to fit the data better. It is shown that compression development and lap-splice lengths can be based on several expressions available in the literature for tension development length with minor modification, including the ACI 318-19 equation for tension development length. Using this approach would simplify design by eliminating the use of different expressions to calculate tension and compression development lengths, prevent calculated lengths from being longer in compression than in tension, and provide a better fit to available data.