Preventing the wind-induced vibration of arches during construction

Arches are the most prominent architectural feature of tied-arch bridges and offer a dramatic visual impact. Arches rarely exhibit aerodynamic instabilities once tied to the bridge deck; however, during construction they typically have low fundamental frequencies, low inherent structural damping and low mass. This combination makes them especially vulnerable to wind-induced vibrations. The three-dimensionality of the arch shape is best examined through aeroelastic model wind tunnel testing as opposed to sectional model based approaches. In many cases vortex-induced oscillations have been observed for certain discrete stages of arch construction. In some cases, the loads induced by these vortex-induced oscillations can be tolerated by the structure; however, in other cases the responses can be sufficiently large that they must be prevented. Therefore, to prevent vortex-induced oscillations of the arches during construction, different damping strategies have been employed. Two practical methods that have been recently deployed include: (i) an in- line cable damper attached by a cable to the arch and anchored to a firm foundation, and (ii) tuned mass dampers (TMD). In this paper a background on the sources of wind-induced vibrations is presented along with methods to predict the response followed by several mitigation strategies.