Tendon Stress in Unbonded Posttensioned Masonry Walls at Nominal In-Plane Strength

Abstract

Accurate estimation of stress in unbonded tendons at the nominal strength limit state is essential for calculating the in-plane flexural strength of posttensioned masonry walls. These walls gain their lateral strength and desirable seismic properties through the utilization of vertical unbonded posttensioning. Unlike walls with bonded tendons where the tendon stress can be found through strain compatibility with the surrounding masonry, the stress in unbonded tendons results from wall deformation between the two tendon anchorages. International masonry codes, including ASCE 5-05 (Masonry Standards Joint Committee), provide varying equations for calculating tendon stress at the nominal strength limit state but in no case have these equations been verified for in-plane loading. A finite-element model validated against large-scale in-plane structural testing of posttensioned concrete masonry walls is used to demonstrate the accuracy of existing code equations. A revised equation is then shown to provide a more accurate prediction of tendon stress for walls loaded in-plane and is recommended for inclusion in future masonry code revisions.