Aging railroad bridges present complex challenges due to advancing deterioration and outdated design assumptions. This study develops a comprehensive analytical approach for assessing an aging steel truss railroad bridge through finite element (FE) modeling, sensitivity analysis, and model updating, supported by field testing. An initial FE model of the bridge was created based on original drawings and field observations. Field testing using a laser Doppler vibrometer captured the bridge’s dynamic response (vibrations and deflections) under regular train traffic. Key structural parameters (material properties, section properties, support conditions) were identified and varied in a sensitivity analysis to determine their influence on model outputs. A hybrid sensitivity analysis combining log-normal sampling and a genetic algorithm (GA) was employed to explore the parameter space and calibrate the model. The GA optimization tuned the FE model parameters to minimize discrepancies between simulated results and field measurements, focusing on vertical deflections and natural frequencies. The updated FE model showed significantly improved agreement with observed behavior; for example, vertical deflections under a representative train were matched within a few percent, and natural frequencies were accurately reproduced. This validated model provides a more reliable tool for predicting structural performance and fatigue life under various loading scenarios. The results demonstrate that integrating field data, sensitivity analysis, and model updating can greatly enhance the accuracy of structural assessments for aging railroad bridges, supporting more informed maintenance and management decisions.

This study presents a comprehensive methodology for determining temperature distributions inside a regolith-shielded dome-shaped lunar habitat structure. The three-dimensional heat diffusion equation in a spherical coordinate system was discretized using the explicit finite-difference method incorporating appropriate boundary conditions. The heat inputs on the structure included direct solar irradiation and lunar regolith albedo, while heat outputs comprised nonblackbody radiation with deep space and habitat albedo. The structural self-shadowing, as well as the shadow effect on the surrounding lunar regolith, were integrated into the temperature analysis to enhance its realism. The habitat structure was constructed using sintered lunar regolith simulant. Appropriate available thermophysical properties were assigned to the habitat wall structure and regolith protection cover, with the latter exhibiting temperature-dependent material properties. The temperature on the external surface of the habitat structure, critical for maintaining structural integrity and internal thermal stability, was evaluated for regolith thicknesses ranging from 0 cm (no cover) to 20 cm at selected points on the dome structure. The analysis revealed substantial diurnal temperature fluctuations on the outer surface of the regolith protection cover, ranging from the maximum value of approximately 395.5 K (122.4°C) during the day to the minimum value of 106 K ( − 167.1 ° C ) at night. Without the regolith cover, the dome apex surface exhibited the maximum temperature of 394.5 K (121.4°C) and the minimum temperature of 213.5 K ( − 59.7 ° C ), resulting in the extreme diurnal temperature fluctuation of 181 K (181°C). Even a thin 2 cm thick regolith cover substantially mitigated these extremes at the outer surface of the habitat structure, reducing the diurnal temperature fluctuations to as low as 56.5 K (56.5°C), with the maximum of 324.5 K (51.4°C) and the minimum of 268 K ( − 5.1 ° C ). With the 20 cm thick regolith cover, the maximum and minimum temperature values at the habitat outer surface were observed to be 294 K (20.9°C) and 290.5 K (17.3°C), respectively, leading to the diurnal fluctuation of only 3.5 K (3.5°C), highlighting the cover’s excellent thermal insulation. These findings are necessary for determining the optimal regolith cover thickness required to protect the habitat structure from extreme temperature limits, as well as for evaluating the structural responses, such as stresses and deflections, needed for the design of safe and resilient lunar habitat structures.