Crowd-Induced vibrations in sports stadia analysis of Thomond Park Stadium under concert events

The potential of dynamic structural response to cause serviceability or even ultimate failure in building structures has long been known. The availability of stronger structural materials and more precise analysis tools has allowed ever more slender structures to be realised. However, as spans increase and structural mass decreases dynamic response emerges more often as a concern for structural engineers. Design for the redevelopment of Thomond Park stadium, Limerick was completed between 2005 and 2007 and the new stadium was opened in August 2008. Conscious of recently reported incidents and aware that the venue might be used in the future for concerts, the designers carried out a dynamic assessment of the grandstand structures to rhythmic crowd movements using a ‘Performance-based Assessment’ method. A localised scenario of potential concern in one area of one grandstand was identified and appropriate crowd management arrangements were identified. Updated guidance from the Institution of Structural Engineers, termed the ‘Route 2 Method’, was published after the stadium opened in 2008. A statically designed cantilever beam was first analysed as part of this research work using the Performance-based Assessment and the Route 2 methods. While both methods illustrated that the structure did not perform satisfactorily under crowd induced loading typical of concert events, the results of Route 2 method was lower than that of the Performance-based Assessment. Importantly however, the Route 2 method provides a more consistent and rigorous approach to the design of the structure and accounts for the crowd-structure interaction. An analysis of a single bay of the West Grandstand of Thomond Park was then carried out using both methods. While the results of the Performance-based Assessment were broadly aligned with that of the original design, the results of the updated Route 2 method indicate that the structure performs adequately under all concert types and that the crowd management measures originally recommended may no longer be required. The results are particularly sensitive to the Young’s Modulus of the concrete and further work is recommended to verify the natural frequencies and mode shapes of the structure through dynamic testing of the stadium itself.