In July 2008, a benchmark study on the aerodynamics of a stationary rectangular cylinder with chord-to-depth ratio equal to 5 (BARC) was launched. This paper gives an outline of the state of the art on the aerodynamics of 5:1 rectangular cylinders prior to the starting of BARC, and summarizes the results obtained by the contributors during the first four years of activity. The results of about 70 realizations of the BARC flow configuration obtained under a nominally common set-up in both wind tunnel experiments and numerical simulations are compared among themselves and with the data available in the literature prior to BARC, in terms of bulk parameters, flow and aerodynamic load statistics, pressure and force spanwise correlations. It is shown that the near wake flow, the base pressure and, hence, the drag coefficient obtained in the different flow realizations are in very good agreement. Conversely, the flow features along the cylinder lateral surfaces and, hence, the lift, are strongly sensitive to set-up and modelling, leading to a significant dispersion of both wind tunnel measurements and numerical predictions. Finally, a possible asymmetry of the time averaged flow has been recognized both in wind tunnel tests and in numerical simulations

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New trends in the architectural design of footbridges feature an unprecedented slenderness, especially when these are located in the urban environment. For this reason, static analyses and a design towards the ultimate limit state have proven inadequate in many circumstances, and the main objective in the structural design is becoming that of assessing the serviceability limit state through dynamic analyses. On the other hand, the key issue of dynamic analyses is the availability of reliable models for the structure and for loads, and in the particular case of pedestrian action the lack of commonly accepted models for walking, running and jumping has become the weak link in the whole structural design process. In a first stage of the present work, vibration measurements were taken on a recently built cable-stayed footbridge, whose second vibration mode was excited by runners. As a second step, a dynamic loading model for the vertical component of the running-induced force was developed, which was used for the finite element analyses of the footbridge. Finally, tuned mass dampers (TMDs) represent a quite mature technology for reducing the resonant response of flexible structures, but their effectiveness is heavily dependent on the tuning ratio. In the case of footbridges, pedestrians can act as a significant part of the vibrating mass; thus, varying the vibration frequency, which makes it difficult to properly tune the damper frequency. Semi-active TMDs can be looked at as passive devices able to adjust their dynamic parameters according to a given control logic. A physical description of a control algorithm is given in the paper, and its performance is discussed.

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