The Influence of Dynamics in Footbridge Design

The excessive sway motion of the Millennium Bridge in London has focused a great deal of attention on serviceability issues associated with Pedestrian-Induced Vibration (PIV).

A recent CEB-FIP publication Bulletin 32 Guidelines to the Design of Footbridges (November, 2005) devotes an entire chapter to dynamics but includes little or no discussion of any other aspect of footbridge dynamics (wind, seismic, member loss). While PIV represents a critical aspect of design and dominate current footbridge research, a number of recent major footbridges in the US have been very much influenced by other dynamic design considerations.

This paper explores aspects of non-pedestrian induced dynamics on footbridge design, and the interplay between i) competing design requirements with a focus on footbridge dynamics, ii) superstructure typology, iii) constructability and iv) construction cost and project viability.

For this paper, three recent US bridge projects, the Missouri River Pedestrian Bridge, the Mary Avenue Pedestrian Bridge, and the Happy Hollow Pedestrian Bridge are of particular interest and will be explored in some depth. All three footbridges share a common heritage; each bridge as initially conceptualized and designed has been bid in a competitive process, each project has been significantly over-budget (more than double the project budget), and had been cancelled. In each case, the bridges have been redesigned with a clear focus in the redesign effort on cost savings based upon enhanced dynamic performance.