Effects of heat-transfer time lag and bearing friction on the temperature-induced displacement of a steel truss bridge

Long-span steel truss bridges are strongly affected by environmental temperature, which governs thermal expansion, bearing movement, and long-term service performance. Under ideal free-sliding conditions, bearing displacement should vary approximately linearly with structural temperature. Field monitoring, however, often shows nonlinear temperature-displacement hysteresis, and the separate roles of heat-transfer time lag and bearing friction remain unclear. This study combines field monitoring, refined heat-transfer simulation, and nonlinear bearing-friction modeling to examine the temperature-induced displacement of a continuous steel truss bridge. A normalized path-separation index, A r * , was used to quantify the relative separation between heating and cooling paths. Seasonal monitoring data confirmed that the measured temperature-displacement hysteresis occurs under different thermal conditions. Refined solid-element models of representative members showed that local peak-time offsets depend strongly on member position, plate exposure, and deck-induced shading, with offsets up to 240 min relative to the section-averaged temperature. The local plate temperatures produced markedly different in normalized path separation depending on their thermal timing relative to displacement. After bearing friction was introduced, the simulated displacement amplitudes were markedly reduced, and the displacement amplitude ratio approached the measured value of approximately 1.2. These results indicate that heat-transfer time lag and temperature selection can modulate the apparent path separation, whereas bearing friction markedly suppresses displacement amplitude and may also contribute to relative path dependence through stick-slip behavior.