Mechanical behavior of deteriorated unbonded prestressed concrete hollow slabs

This study investigates the residual mechanical behavior of deteriorated unbonded prestressed concrete hollow slabs extracted from a 20-year-old highway bridge. Three full-scale slabs were tested under four-point bending to evaluate cracking resistance, load-bearing capacity, failure modes, anchorage performance, and material degradation. The exterior slab exhibited a cracking load of only 190 kN, just 12% above the design service load, indicating significantly reduced crack resistance. Failure loads ranged from 529 to 581 kN, with corresponding deflections between 287.7 and 413.6 mm. Two slabs failed prematurely due to tendon rupture at the anchorage, with ductility coefficients reduced by up to 30% compared to the ductile failure observed in Slab 1. Anchorage efficiency coefficients ranged from 0.84 to 0.88, below the code requirement of 0.95, and tendon elongation at maximum load was only 1.0–1.4%, far below the 2% minimum standard. In contrast, concrete, reinforcement, and tendons remained largely intact, with concrete compressive strength reaching 61.8 MPa, exceeding the design requirement. The residual flexural capacity decreased by 3.2–5.2% relative to theoretical values, primarily due to anchorage deterioration rather than material aging. These findings quantify the dominant role of anchorage degradation in reducing structural performance and provide critical data for assessing and rehabilitating aging unbonded PC hollow-slab bridges.