Experimental–Numerical Determination of the Effective Bulk Thermal Conductivity of Suspension Bridge Main Cables

Abstract

Accurate thermal properties are crucial for modeling the response of infrastructure to fire scenarios. While other researchers have contributed significant effort toward characterizing the thermal behavior of parallel-wire structural cable stays, no method has been derived explicitly for suspension bridge main cables, which are typically two orders of magnitude larger in cross section. These cables cannot be treated as monolithic steel sections due to the nature of their composition, and their thermal behavior is greatly influenced by voids and point contacts between their constituent cylindrical wires. This study derives the first empirically driven estimation of the effective bulk thermal conductivity of suspension bridge main cables using the data collected from thermal experimentation on a full-scale mock-up of the main cable panel (approximately 10,000 wires, 52 cm diameter, 6 m long) and gradient-based optimization of a representative finite-element model. Results show that the effective thermal conductivity of suspension bridge main cables is more than an order of magnitude smaller in the radial direction than in the axial direction and that the effective radial conductivity is an order of magnitude smaller than previous theoretical estimates have predicted. The resulting bulk conductivity serves as a useful tool for engineers and researchers because it allows a large, thermally complex geometry to be modeled as a simple monolith with orthotropic thermal conductivity properties.