Low Cycle Fatigue Behavior of Corroded Fuse-Type Dissipaters for Post-Tensioned Rocking Bridge Piers

Abstract eng:
This paper presents tensile and low cycle fatigue experimental results of dissipaters used in post-tensioned rocking bridge piers with varying degree of corrosion. The effects of varying degrees of chloride corrosion on the mechanical properties and low cycle fatigue life of dissipaters were studied via quasi-static axial and cyclic tests respectively. The use of bridge pier with permission to rocking motion in its lateral direction at the interface with its foundation is recognized as rocking pier. The rocking motion is controlled by axial post-tensioned load through use of dissipaters mounted to the rocking section to eliminate post-earthquake damage and limit residual drift after an earthquake event. The dissipaters, providing energy dissipation capacity, are uniaxial, tension-compression yielding mild steel bar elements, restrained against bucking and externally placed at the rocking section. The dissipaters were fabricated from 24mm diameter plan steel reinforcement and provided with reduced diameter to achieve 16mm equivalent diameter over a 245mm fused length. To meet this aim, three grooves were induced by milling along the fused length at 120º interval around the circumference of the plain steel reinforcement. To corrode dissipaters within a reasonable time period, an accelerated corrosion rate of 800 µA/cm2 was achieved by applying a constant electrical current to the dissipaters by a power supply. The two degrees of corrosion in terms of mass loss percentage were selected to corrode the dissipaters. The average mass loss percentage for low and high degree of corrosion were (≈ 7%) and (≈ 22%) respectively. The static tensile tests were conducted for 3 non-corroded and 6 corroded dissipaters. This investigation has resulted in clear quantification of the relationship between the degree of corrosion and the mechanical properties of the dissipaters. The cyclic (tensile-compression) tests were conducted for 6 non-corroded and 12 corroded dissipaters using two different deformation rates. The low cycle fatigue life of the dissipaters was obtained from correlated with the equivalent strain amplitude. The Fourpoint correlation (4-PC) method was used to estimate fatigue parameters that precisely predicted the low cycle fatigue life of the dissipaters. The deterioration models, developed for reduction in mechanical properties of the dissipaters based on the tensile tests, were employed to modify the fatigue properties presented in the 4-PC method. The proposed fatigue properties can be applied for low cycle fatigue prediction of both corroded and non-corroded dissipaters. The proposed fatigue life prediction method was validated through experimental results. The results can be used in seismic design, seismic evaluation and life cycle analysis of the post-tensioned rocking bridge piers subjected to earthquakes and corrosion.

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