**8. Conclusion**

To gain insight into the flow topology, two-dimensional numerical simulations of the flow were carried out, employing unsteady Reynolds-averaged Navier-Stokes (URANS) equations. By comparing comprehensively, the numerical and experimental results, it was possible to understand that, at least for this particular deck section, VIV occurs whenever the flow pattern displays simultaneously the following two features (**Figure 7**): (a) above the deck, a large coherent vortex structure on the windward part or irregular flow anywhere; (b) below the box-girder base, separated flow without reattachment. This led to the conclusion that to eliminate, or at least attenuate, the oscillatory movements of the model at certain wind speeds

To reduce the dimensions of the recirculation bubble below the box-girder, whenever it was formed, in order to facilitate its reattachment and thus prevent vortex-shedding, the edges at the base of the box-girder were rounded. The border beam profile was also rounded. Wind tunnel tests of the deck with these slight geometric modifications showed that they were beneficial. The geometric modifications were then proposed to the engineering office undertaking the bridge design and a meticulous discussion followed to define the transposition of the modifications to the full-scale bridge. They are visible in **Figure 8**, and the dashed lines in the sketches therein refer

**Figure 7.** Streamlines from numerical simulation for fully equipped deck at *α* = +2 °, in configurations: (a) original, showing a large recirculation bubble over the deck, on the windward part, and separated flow without reattachment below the box-girder base; (b) modified, showing thinner bubbles and reattached flow below the girder (from [10]).

**Figure 8.** Photo and schemes of details of the Vila-Real Bridge deck, showing the modifications introduced by the

aerodynamic study (original photo courtesy of Prof. A.P.V. Urgueira, Universidade Nova de Lisboa).

it would suffice to prevent vortex-shedding from at least one side of deck.

to the original contour.

104 Bridge Engineering

The execution of projects of special structures is always complex and requires contributions from different branches of engineering. It is important that the structural design team is complemented, in due time, by aerodynamic specialists with the competence and access to the means to perform the required special studies. The Vila-Real Bridge case that has been discussed here is an example of how laboratorial means were made available, of the capacity of timely response, and of how modifications to improve the aerodynamic performance of a bridge deck can turn out to be very subtle from the geometric point of view (or even favour the aesthetics of the bridge) while being very effective with regards to aerodynamics.

It should be pointed out that major structures that very exposed to wind action are the ones that justify wind tunnel studies, and the costs of the aerodynamic studies are always a small parcel of the total investment for this kind of projects.
