大跨桥梁伸缩变形对梁端有砟道床细观力学行为的影响分析OA

To address the critical issues of mechanical degradation in the ballast bed at girder ends and the resulting deterioration of track regularity caused by the thermal expansion and contraction of long-span bridges,a bridge-ballast-sleeper coupling model is established based on the coupled discrete ele-ment method(DEM)and multi-body dynamics.This study reveals the meso-mechanical behaviors of ballast particles at girder ends,specifically their motion characteristics,compactness evolution,and force chain transmission mechanisms,under the effects of main girder deformation and sleeper group displacement.The results indicate that during the expansion and contraction of the main girder,the bal-last particles at the girder end and the bottom of the ballast bed exhibit the highest movement veloci-ties,while those between the sleepers show the lowest velocities with a significant upward arching ten-dency.The lateral displacement of ballast particles remains consistently at approximately 2 mm.The longitudinal displacement of the particles beneath the sleeper is significantly greater than that at the sleeper ends,increasing with depth and reaching a peak of 7.36 mm.The compactness of the ballast bed beneath the sleepers at the girder end decreases as the main girder elongates and increases as it con-tracts,whereas the compactness in the sleeper box regions.The contact force between ballast particles increases during the elongation of the main girder,and initially decreases before increasing during con-traction.The internal force chains within the ballast bed are transmitted from the bottom to the surface at an angle of approximately 45°,with an average peak contact force of 18.90 N.Under the displace-ment of the sleeper group,the ballast on the sides of the sleepers undergoes longitudinal flow,while the ballast beneath the sleepers experiences rotational dislocation.The compactness in the sleeper bot-tom and crib regions fluctuates,and the overall compactness of the ballast bed can decrease by 1.89％.Contact forces are transmitted downward from the sleeper bottom and sides to the base of the ballast bed at an angle of roughly 45°.The contact forces on the sleepers are primarily concentrated on the sides and bottom,resulting in a longitudinal resistance of approximately 10 kN per sleeper,which is lower than the longitudinal resistance measured in single-sleeper tests.These findings clarify the mechanisms by which bridge expansion deformation influences the meso-mechanical behavior of the ballast bed at girder ends,providing theoretical support for understanding the evolution of track regu-larity at girder ends and ensuring the safety of railway operations.