UHPC girder multi-modal deformation measurements: Photogrammetry, physical sensing, and FEA

Abstract

Ultra-high performance concrete (UHPC) has become increasingly popular in flexural design of structural members that require high performance. Although numerous experimental studies on passively reinforced UHPC flexural members exist, studies on monolithic members with larger cross sections are limited, and no information exists on full-field deformation measurements of such specimens. An experimental program consisting of 8 large-scale UHPC doubly-reinforced specimens with continuous longitudinal rebars was conducted under 4-point monotonic loading. The experimental objectives were to investigate rebar slip from one side of the specimens (longitudinal rebar with hooks only on one side), track crack propagation, and capture the full-field displacement and strain measurements during the loading. The noncontact measurements from the multi-camera computer vision system using 3D digital image correlation (3D-DIC) and AprilTag-based photogrammetry were compared with the physical (contact) displacement measurement system. Strain fields were obtained using dual-camera 3D-DIC and finite element (FE) analysis. Results showed a close agreement of the point-wise displacements obtained from the physical and computer vision monitoring systems. The asymmetric structural design caused slip that delayed rebar fracture and reduced the peak load below that predicted by sectional analysis. The measured global force-deflection curve was predicted by the FE model when using a calibrated bond-slip model between rebar and UHPC. Comparison between the full-field measurements using 3D-DIC and FE numerical models showed that the evolution of principal strains and cracking were consistent. 3D-DIC proved to be a promising measurement method for monitoring strain/displacement and calibrating/confirming FE model that conventional methods without full-field measurements cannot provide.