Characterization of bridge substructures explored by leveraging structural identification of a scaled bridge model

Characterization and evaluation of bridge substructures, especially when as-built information is missing, are needed to assess the vulnerability of bridges to natural hazards, other possible causes of bridge failure, and as prerequisites for bridge substructure and foundation reuse. Structural identification has been investigated as a tool for characterizing and evaluating bridge substructures. Structural identification offers advantages over conventional methods especially by integrating information from structural testing and local NDE approaches. During field investigations the authors observed significant challenges to assessing substructure characteristics such as embedded depth, even for simple piers on spread footing foundations. It is found that impact excitation on bridge superstructure or even directly on substructure aiming for conventional flexural modes in the lower frequency band is not sufficient for a reliable identification of the substructure and its surrounding soil. To understand better the challenges limiting reliable structural identification of bridge substructures, a phenomenological scaled bridge model with strip footing, mimicking an actual bridge on shallow foundations, was designed, fabricated and utilized for controlled laboratory testing. The scaled bridge model could be modified to comprehend the sensitivity of bridge substructure modal properties to: i) stiffness of bridge bearings (causing coupling between superstructure and substructure) and ii) foundation substrate compliance. A finite element representation of the physical model, with a Multiphysics Simulation Finite Element Software, was calibrated and was then exploited to perform further sensitivity studies which confirmed the potential of high frequency axial and flexural modes of the substructures to: iii) identify shallow foundation embedded depth, and iv) characterize the soil substructure interaction. Throughout the paper, different challenges affecting structural identification for characterization and evaluation of bridge substructures and possible countermeasures are discussed. Findings of the study indicate that a high frequency bandwidth covering the axial vibrational modes of the substructure is necessary if structural identification is used for estimating shallow foundation embedded depth. Such a bandwidth is not possible in conjunction with ambient monitoring, pointing to the necessity of a controlled multi-inputmultioutput (MIMO) dynamic testing.

Automated summary

Characterization and evaluation of bridge substructures using structural identification methods face challenges in assessing substructure characteristics, especially in determining embedded depth, highlighting the need for further research and development in this area.