**4.3 Aerodynamic analysis of cable-stayed bridges**

*Boundary Layer Flows - Theory, Applications and Numerical Methods*

Scanivalve pressure system.

modeling.

wind loads.

actions.

tion described in Section 2.3 was used.

structures, and the turbulent wake of wind turbines will be shown.

high-rise and low building, atmospheric pollutant dispersion, rain-wind action on

**4.1 Wind tunnel study of the local aerodynamic loads on a high-rise building**

A study of the wind loads on a high-rise building was realized in the Prof. Jacek Gorecki wind tunnel using a 1/400 scale model [13]. The building is 240 m high; it is named Infinity Tower and it is built in Camboriu, RS, Brazil. Local mean, maximum, minimum, and *rms* pressure coefficients were measured by means of a

Atmospheric boundary layer simulations similar to the full-depth simulation described in Section 2.2 were used. Some characteristics of the incident wind were modified according to the terrain features upwind model. Thus, two different mean velocity profiles were used according to the incident wind direction. Aerodynamic details were reproduced in the building model (**Figure 14**), and fluctuating local pressures in 511 tower points for 24 wind directions were measured. The effects of urban vicinity and topographic surrounding were considered by means of a detailed

Some considerations referred to the extreme values approximation were realized in this work. The graph in **Figure 14** illustrates a fluctuating pressure registered at a measurement point. Mean values associated with different duration times of wind gusts (1, 4, and 16 s full-scale) can be obtained by means of this technique, and statistical extreme value analysis can be applied to improve the calculation of local

**4.2 Wind tunnel study of the aerodynamic loads on a low structure**

There exist structures that due to its size, complexity, or importance justify turning to wind tunnel tests in order to optimize the structural design. A wind tunnel study of the Ezeiza Airport located in that village of Buenos Aires was realized in 2010 [14]. The study comprised the determination of both local and global wind

It was carried out at the Prof. Jacek Gorecki wind tunnel of the UNNE, using different 1/200 scale models (**Figure 15**) that were compatible with the scale factor of the wind simulated in the wind tunnel. The real neighbor conditions were taken into account as well as the turbulent features of the atmospheric wind in agreement with the type of terrain. In this case, an ABL flow similar to the part-depth simula-

In addition to the mean load coefficients, peak coefficients were obtained by extreme value analysis using the Cook and Mayne method [15]. It is shown how

*High-rise building scale model in the test section of the UNNE wind tunnel and detail of the fluctuating local* 

**136**

**Figure 14.**

*pressure.*

The prediction of the aerodynamic performance of concrete cable-stayed bridges can be realized by means of wind tunnel testing. The analyses of the structural stability under the aerodynamic actions must be included into the design verifications. The structural characteristics of cable-stayed bridges and the dynamic aspects of the aerodynamic actions implicate the application of special analyses of aerodynamic stability including flutter and vortex shedding. The determination of the critical velocity is very important in the design of cable-stayed bridges.

First, static forces are obtained through force balance measurements for simple models of the bridge deck and towers. Aerodynamic coefficients varying with wind incidence for the deck may be easily measured with pressure systems or force balance.

A sectional model is used for the dynamic modeling of the deck. The sectional model must be ideally rigid to avoid the influence of the own model vibration in the experimental results. Details of the bridge deck must be represented. **Figure 16**, left, shows a picture of a 1:60 dynamic sectional model mounted in the test section of the wind tunnel of Prof. Joaquim Blessmann of the UFRGS. The deck corresponds to the Octávio Frias de Oliveira cable-stayed bridge, and the obtained results permitted to observe the differences in the deck vertical and torsional responses [16].

The relevant parameters in aeroelastic modeling are length, specific mass (density), and acceleration. The design of a full-aeroelastic model must reproduce the aerodynamic and dynamic characteristics of the structure of interest. The flow and geometric similarities must be respected and the Reynolds number considered for aerodynamic similarity. The most relevant frequencies and mode shapes must be reproduced to obtain dynamic similarity. The design of full-aeroelastic model includes bridge deck, cables, masts, and end supports. The complexity of this type of model can be observed in **Figure 16**, right, showing the full-aeroelastic model, the Octávio Frias de Oliveira cable-stayed bridge tested at the wind tunnel Prof. Joaquim Blessmann of the UFRGS [17].

The incident wind used to test sectional models is normally a turbulent uniform flow similar to the flow obtained with empty tunnel out the wall boundary layer and described in Section 2.1. Meanwhile, the full-aeroelastic model of the Octávio Frias de Oliveira cable-stayed bridge was tested using a full-depth boundary layer simulated

**Figure 15.** *Ezeiza Airport 1/200 models (partial) in the test section of the UNNE wind tunnel.*

**Figure 16.**

*Sectional model and full-aeroelastic model of the Octávio Frias de Oliveira cable-stayed bridge in the wind tunnel Prof. Joaquim Blessmann.*

in the return section of the wind tunnel Prof. Joaquim Blessmann. The simulation devices and roughness elements are similar to those described in Section 2.2.
