Title:
Multi-Span Members with Unbonded Tendons: Ultimate Strength Behavior
Author(s):
Marc Maguire, William N. Collins, Kedar R. Halbe, and Carin L. Roberts-Wollmann
Publication:
Structural Journal
Volume:
113
Issue:
2
Appears on pages(s):
195-204
Keywords:
span; strength; tendons
DOI:
10.14359/51688192
Date:
3/1/2016
Abstract:
Many researchers have proposed empirical methods to predict the strand stress increase at ultimate, relying heavily on simple span test data with little consideration for continuous members. The research team fabricated four two-span representative slab specimens. Tendon stresses were found to be conservatively predicted by three codified unbonded tendon stress prediction methods, but presented large scatter for the identically designed specimens. Following flexural failure, the measured-to-predicted strand stress increase ratio was found between 1.23 and 3.99 and observed tendon stress increases were between 42.4 and 61.1 ksi (292 and 421 MPa). The Naaman and Alkhairi method results in the most accurate prediction of tendon stress increases. Tendon stress increases were found to be significantly larger on the live end, indicating friction and external loading should be considered in prediction models. Inadequate top bar cutoff detailing provided an unexpected negative-moment failure mechanism, illustrating the importance of conservative detailing.