Jinlong Huang

To address structural deficiencies—including web cracking, transverse cracking at the girder bottom, and inadequate load-bearing capacity—in existing prestressed concrete continuous box-girder bridges with large cantilevers and thin webs, this study employed field inspections, static and dynamic load tests, and numerical simulations. Longitudinal frame models, transverse solid models, and refined interface models were developed to systematically investigate the effects of prestress loss, vehicle live loads, and temperature on crack formation. Furthermore, the effectiveness of a combined strengthening strategy involving web cross-section enlargement and internal prestressing was evaluated, with particular emphasis on the transfer efficiency of the added prestress across the interface. The results indicate that long-term prestress loss reduces the compressive stress reserve in the box-girder section and is a primary contributor to transverse cracking at the girder bottom, whereas inclined web cracking is primarily caused by the combined effects of shear stress and vertical tensile stress. Eccentric vehicle loading has a pronounced effect on the vertical tensile stress in the web; at the mid-span section, the maximum vertical tensile stress on the inner web face reached 4.24 MPa, of which 2.23 MPa was attributable to eccentric loading. After implementation of the combined strengthening strategy, the bottom-edge stress at the mid-span section decreased from 4.40 MPa to 1.74 MPa, representing a 60.45% reduction, while the mid-span deflection decreased from 30.6 mm to 20.13 mm, corresponding to a 24.54% reduction. In addition, the shear safety factor at the support increased from 0.78 to 1.10, demonstrating substantial improvements in crack resistance and overall structural stiffness. Finally, the interface stress-transfer efficiency reduction in the added internal prestress was 12.87%, indicating that the effect of interface transfer efficiency on the actual strengthening performance should be fully considered when applying the combined cross-section enlargement and internal prestressing method.

Workability of asphalt is crucial for pavement construction and quality assurance. The macroscopic and mesoscopic mixing workability of different base and polymer-modified asphalt mixtures was evaluated using a modified testing device and simulated by the three-dimensional discrete element method via the three-dimensional Particle Flow Code, respectively. The experimental results demonstrate that polymer-modified asphalt mixtures exhibited inferior mixing workability compared with base asphalt mixtures, consistent with their higher binder viscosity. The mixing workability decreased with the elevated nominal maximum aggregate size, and the open-graded mixtures showed inferior mixing ability compared with those of continuous and gap-graded mixtures. The sensitivity analysis demonstrates that temperature appeared to be the most significant influencing factor of the mixing workability, followed by gradation and asphalt binder type. The denser contact force chains of mixtures under lower temperatures observed by the numerical simulation provided evidence of the decreased mixing workability. The gradation appeared to only provide a path for load transfer without influencing the contact force properties. These findings provide a theoretical basis for understanding the mixing behaviors of asphalt mixtures.