"Tripod" Footbridge in Terni (Italy): On site Dynamic Characterization and Numerical Investigation of Lock-In

Benedetti Architects (formerly McDowell+Benedetti) and Manfroni Engineering Workshop were the winners of an international competition for a new 180m footbridge and improved railway station in Terni, Italy.

The structure, named “TRIPOD” due to its particular form, is made entirely of steel and the walking deck is finished with timber.

The bridge slenderness imposed to the designers much precaution to mitigate the oscillations due to both crowd and wind. Due to these precautions, during the design stage, wind tunnel tests were conducted to investigate the aero-elasticity of the structure. TMDs were also designed to account for vertical and lateral movement of the deck. They were placed under the floor at a location where the oscillations are at a maximum. Furthermore, on site dynamic characterization was undertaken to investigate the bridge's oscillations and to compare them with the design assumptions to properly calibrate the TMDs' performance.

Based on the amount of data recorded during construction of this bridge, this paper will investigate and present a model for the physical phenomenon of synchronization related to the oscillations induced on it by the passage of a group of people. Vortex shedding is also analyzed and reproduced by the same model.

Finally it will be shown that both phenomena are almost equivalent and that they can be reproduced in the same way. The base assumption for this paper comes from the theory of complex systems and the nonlinear dynamics which underlies these phenomena.

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