Equivalent Unbonded Length for Modeling of Multistrand Tendons in Precast Segmental Construction

Abstract

Recently issued seismic design guidelines for precast segment construction require nonlinear modeling of segment-to-segment joints of important bridges. The response of segment joints is highly dependent on the length of debonding of the multistrand tendon. Neither the seismic design guidelines nor the literature provide sufficient guidance on how to determine the equivalent unbonded length of such tendons. This paper presents key results and conclusions of a large-scale experimental research program that investigated the debonding characteristics of multistrand tendons. Results indicate that tendon slip relative to the grout is small in comparison with slip between the duct and the surrounding concrete. An equation to evaluate the equivalent unbonded length of multistrand tendons was developed with direct application to modeling of the segment joint response.