Extrapolating specification-level dynamic load factors for bridge performance analysis using deflection measurements during ambient traffic excitations

Field-measured dynamic load factors (DLFs) are underutilized for bridge health assessment. Bridge practitioners often face confusion when comparing field-measured DLFs to specification design values owing to significant DLF variations across different traffic load levels. However, mathematical relations or methods correlating bridge DLFs and load levels are lacking. To address this challenge, this study proposes practical methods for determining specification-level DLFs using field-deflection measurements during ambient traffic excitations. Deflections from a continuous rigid-frame bridge over six months were measured, and DLFs were computed using hourly maximal total deflections and their corresponding static deflections. Two approaches were developed and validated to extrapolate the specification-level DLF using field-measured DLFs of low load levels. Extrapolated DLFs from both methods illustrated a noticeable downward trend in DLFs relative to load levels. Both methods yielded consistent results, falling within the range of 0.03-0.09, equivalent to the design DLF value of 0.05 for the bridge under study. No significant temporal-dependent changes in extrapolated DLFs were evident, indicating that bridge performance and pavement roughness met design expectations and did not deteriorate significantly. This study provides an alternative data-driven approach that utilizes field-measured DLFs to assess the health condition of bridges.