Modelling dynamic behaviour of a cantilever grandstand

This paper investigates the dynamic behaviour of a cantilever grandstand using two-dimensional (2D) frame, three-dimensional (3D) open-ended and 3D enclosed finite-element models. The effects of bracing systems, stiffness of seating decks and eccentricity of connections are examined. This comparative study also considers the relative advantages of the typical 2D and 3D models used in the study of dynamic behaviour and the response of grandstands to human loads. It is concluded that a 2D frame model is accurate enough for examining the dynamic behaviour of the grandstand in the vertical and front-to-back (also termed transverse) directions, and appropriate bracing systems can effectively increase structural stiffness of grandstands in the side-to-side (or longitudinal) and front-to-back directions. (The terms side-to-side and front-to-back have been used from the spectator's point of view.) While designing a grandstand for dynamic loads, it is customary to include the first few modes in a mode superposition based analysis. However, from the present study it has been observed that some vibration modes of interest could be at a much higher order than normally anticipated.