The use of shielded, or debonded, strands is an effective technique to reduce high tensile stresses in the end region of prestressed concrete members. However, damage in the ends of prestressed beams with shielded strands has been increasingly experienced during strand detensioning. Guidelines on the use of debonded strands, such as the AASHTO Specifications are mainly related to shear strength of pre-tensioned concrete elements with only minimal guidance for issues related to possible early damage during production. The bond behavior of shielded 0.6 in. (15.2 mm) diameter strand was evaluated by conducting experimental studies on unstressed (pull-out tests) and stressed (pretensioned beams) tests. The strands were debonded using single and double layer flexible-slit (tight fit) sheathing and their performance was compared to fully-bonded strand. Experimentally calibrated finite element models were then developed to numerically simulate bond behavior of shielded strand and assessed the induce stress state in the concrete element. A surface-contact interaction model was used to simulate load-transfer from the pre-tensioned strand to the concrete by calibrating the coefficient of friction defining the nonlinear tangential response. The effect of partial strand debonding on the anchorage zone of bridge girders was studied through numerical simulations within the context skew U-beam case study for which evidence of damage exists. The type of sheathing, flexible or rigid, and the effect of staggered distribution for debonded strands were the studied variables. Pull-out test results showed no evidence of residual bond on singular or doubly sheathed strand. However, small-scale beam tests showed that strand debonded with flexible split sheathing leads to high radial stresses along the debonded length in the concrete due to strand dilation from Poisson's effect. Such dilation also leads to the transmission of axial stresses due to a wedging mechanism. The use of rigid oversized sheathing was shown to decrease stresses in the transfer region and along the unbonded length. A staggered distribution of the debonded strands can reduce longitudinal shear stresses created by the uneven distribution of prestress forces in the beam-cross section. Thus, the use of rigid sheathing and a staggered arrangement distribution for debonded strands is recommended when the efficacy of debonding becomes essential.
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