Experimental characterization and strain distribution analysis of full-scale U-FREIs combining 3D-DIC with numerical modelling

The seismic mitigation and low-cost benefits of Unbonded Fiber-Reinforced Elastomeric Isolators (U-FREI) have been investigated in the literature through scaled experiments and numerical studies for various types of structures. However, applications to full-scale structures - whether in laboratory or in real practice - and real-time monitoring investigations of U-FREIs under service conditions remain limited. To address this gap, the present study experimentally investigated the compressive and shear behavior of full-scale U-FREI prototypes designed for a full-scale reinforced concrete structure to be tested under 3D shake table testing (STT). Two specific types of U-FREI specimens are considered in this study with different rubber compounds and reinforcement: Recycled Rubber - Polyester FREI (RP-FREI) and Virgin Rubber - Carbon FREI (VC-FREI). During the characterization tests, a 3D Digital Image Correlation (3D-DIC) analysis was conducted to evaluate peak strains and variations in principal strain distribution. Since DIC is limited to the external surface of the bearing, a properly calibrated Finite Element (FE) model was developed to assess the strain distribution in the internal section of the prototype and correlate with monitorable outer surface strains. Principal strains on the outer curved surface were observed to be localized along the trailing (crushing) diagonal, with peak values significantly lower than the deformation capacity, while rollover regions were confirmed to be relatively free from normal stresses. Such an integrated experimental-numerical study confirmed the high potential of U-FREIs for validation under 3D-STT and application to real structures. • Experimental characterization of full-scale U-FREIs for STT of a real building • Stable response with no damage was observed in U-FREIs up to shear strain of 200% • High vertical-to-horizontal stiffness ratios can prevent rocking motion • Lab monitoring of U-FREIs through 3D Digital Image Correlation for strain analysis • 3D-DIC and FEM show consistent trend with peak strains along compressive diagonal