| This investigation of the behaviour of uncorroded and corroded monostrand tendons with broken wires furthers the understanding of deteriorating unbonded post-tensioned concrete structures. Novel mechanical models are derived that describe the variation of strain in the broken and unbroken wires with distance from the wire break, and the remaining prestress force. Model verification used data from tests of three uncorroded tendons with two diametrically opposed broken wires and three with a single broken wire. Tests were conducted in a strongback beam that simulates the load and boundary constraint conditions typical of unbonded post-tensioned slabs. The effect of corrosion was assessed by testing six corroded tendons with broken wires.; Forces in the broken and unbroken wires are not equal over the affected length, centred at the break, but are equal beyond. A screwdriver penetration test performed beyond the affected length is unlikely to detect broken wires. For a tendon with a single broken wire, the unbroken wire strains within the affected length are not uniform and have maximum strains, up to 35% larger than the average tendon axial strain, occurring in the two unbroken wires adjacent the broken wire. For a tendon with two diametrically opposed broken wires, the unbroken wire strains within the affected length are uniform.; For short tendons with a length less than the affected length, the fraction of prestress force remaining after wire breaks approaches a lower limit. The lower limit for a tendon with two diametrically opposed broken wires is 0.72 while the lower limit for a single wire break, which is less than the ratio of net to gross cross-sectional area, is 0.79.; The coefficient of inter-wire friction, remaining prestress force, and affected length of tendons with broken wires is significantly affected by corrosion on the inner surfaces of the wires. The load-elongation response of corroded tendons approaches that of uncorroded tendons without broken wires. The shortened affected length reduces the efficacy of the screwdriver penetration test and other methods that attempt to assess the force in a tendon at a specific location. |
