Spacing effect on aerodynamic characteristics for a rail-cum-road bridge with twin asymmetrical parallel girders

Due to the asymmetrical cross section of long-span rail-cum-road twin-girder bridges, the aerodynamic interference effect and flow characteristics of the twin girders in the gap are complicated. To study the influence of spacing on their aerodynamic characteristics, section model wind tunnel tests were conducted on a long-span rail-cum-road twin-girder cable-stayed bridge. This study considered the two conditions of bare and completed girders and the two inflow directions of 0° and 180°, with a spacing ratio range of L/Br = 0.1–2.0, and tested the surface wind pressures of the twin girders. Their aerodynamic and flow characteristics were analyzed, and the influence of spacing on their aerodynamic interference was clarified. The results show that for asymmetrical twin girders, the spacing and direction of incoming flow are still the key factors affecting their wind pressure distribution and flow characteristics. Due to the asymmetry of twin-girder sections, the influence of spacing on the wind pressure distribution and flow pattern varies with different flow directions. Furthermore, the attachments to completed girders enhance the asymmetry, making the aerodynamic and flow characteristics more complex than those of bare girders. Finally, three flow patterns are summarized: the upstream girder lower surface wake acts on the downstream girder fairing lower surface, acts on its fairing upper surface, and acts at its fairing.