Abstract: The new Spanish highway bridge, the Pujayo Viaduct, has a single-cell box girder. Owing to the large width of 26.1 m, the box girder had to be stiffened by transverse upper and lower ribs, by haunches in the connection web-flange and by inclined webs. Together with the variable girder depth, a relatively complicated geometry was created that was analysed by means of finite-shell-element calculation. Several unusual secondary structural effects are identified and explained. The longitudinal axial force resulting from global bending causes deviation forces in the curved bottom slab, which are responsible for transverse bending in the bottom slab and axial forces in the webs. Shear lag deformation of the box section causes moderate horizontal bending of the transverse ribs. Global deflection of the bridge girder causes out-of-plane bending of inclined webs. Global bending of box girders causes local bending moment output in finite shell elements. A further conclusion is that three-dimensional finite-shell-element models are an exact and appropriate complement to the common beam-element calculation models.

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