SA-based concrete seismic stress monitoring: The influence of stirrup confinement and concentric compression

Piezoelectric-based smart aggregates (SA) stress monitoring relies on the establishment of the relationship between macro- and meso-stress of concrete. However, the high-level transversal confinement induced by stirrup confinement and concentric compression can significantly affect the randomness of concrete meso-stress and failure patterns. This study investigates the influence of such high-level confinement on SA-based seismic stress monitoring in concrete. In this light, four identical transversely confined concrete columns and four counterpart plain concrete specimens were prepared, each with a height of 400 mm and a circular cross-section with a diameter of 185 mm. Each specimen has six SAs embedded and a total of 24 SAs were used for confined and unconfined specimens, respectively. Two distinct concentrically compressive loads were successively adopted, including repeated and monotonic loading. The core concrete stress was determined using a finite element model coupled with load and strain monitoring. Additionally, the coefficient of variations of SA output was computed to demonstrate the randomness of meso-scale stress in confined and unconfined concrete. Furthermore, we calculated the SA stress rates for confined and unconfined concrete specimens during the monotonic loading test to detect concrete unloading. The test results show that the influence of the stirrup-confined concrete under concentric compression on SA-based concrete stress monitoring reduces the randomness of meso-stress. Moreover, the stress variation ratio proves effective in identifying concrete crushing in both confined and unconfined concrete.