A damage detection model for unbonded post-tensioning tendons based on relative strain variation in multi-strand anchors

Abstract

Post-tensioned segmental bridges are common throughout the US; however, in recent years, the incidence of tendon failure in bonded post-tensioned bridges has raised questions regarding their design, construction, and maintenance. These failures have led to the investigation of the applicability of using replaceable unbonded tendons in segmental construction and new methods for monitoring their condition. This paper presents a damage detection algorithm to identify strand breakage in unbonded tendons based on the relative variation of strains in the anchorage. In unbonded construction, the anchorage assembly usually undergoes a severe stress-state condition as the entire prestressing force only passes through the deviator and end anchorage locations. The strain distribution in the anchorage mechanism, therefore, goes through significant changes in response to the breakage of an individual wire or an entire strand in a multi-strand arrangement. In this way, breakage of a post-tensioning strand can be identified by observing a non-uniform variation of the strain field over the anchorage region in contrast to a uniform variation of strains due to environmental or traffic loading. A reduced scale laboratory experiment is performed followed by an extensive finite element simulation to conduct a parametric study with wire/strand breakages at different locations on multi-strand anchorages commonly used in industry. Based on the observed strain variations from simulation, a damage detection model is proposed that enables the adoption of an automated monitoring strategy to characterize the breakage programmatically.