Effect of pore water freezing on the natural frequency of concrete girder bridges

Abstract

Natural frequencies and modal shapes are critical parameters in bridge health monitoring, yet their sensitivity to environmental factors, particularly temperature and freezing, complicates evaluations. This study presents a framework for quantitatively assessing how pore-water freezing affects the effective modulus and natural frequencies of concrete girder bridges. Concrete is modeled as a multi-phase particle-reinforced composite, with the matrix obtained through homogenization of the solid phases, and pores filled with air, water, or ice as inclusions. Using composite mechanics and the Mori-Tanaka method, a predictive model with ice content is introduced, from which practical bounds for the effective modulus and natural frequencies under freezing conditions are derived. Validation through laboratory tests, scaled bridge model experiments, and field measurements shows excellent agreement between theory and experiment. The substantial increase in concrete’s elastic modulus caused by pore-water freezing markedly elevates the natural frequencies of concrete bridges, with the temperature at which this jump occurs depending on the lowest temperature previously experienced. This framework offers theoretical derivations and practical guidelines for improving safety assessment, design, and maintenance of concrete girder bridges in cold climates.