Stadiums become living structures
Like bridges and skyscrapers, stadiums have natural frequencies at which they vibrate when impacted by external forces. During events such as the FIFA World Cup, those forces come from the tens of thousands of people jumping, stamping, chanting, and performing the wave. When the frequency of the crowd movement synchronises with the stadium’s natural frequency, which is typically between 2 and 4 hertz, vibrations amplify. For spectators, especially those in sections experiencing the largest movement, this can be uncomfortable and even scary, or conversely, invigorating.
“It feels like being on a ship in a rough sea,” Roland says. “You are wobbling and, depending on the intensity of the vibrations, you might think the structure is about to collapse. But modern stadiums are designed with these conditions in mind.”
Stadiums are very complex structures comprising multiple interconnected tiers. Each section, therefore, may respond differently to crowd-induced movement depending on factors such as geometry and occupancy. “You might feel your seat is shaking while the whole grandstand is barely moving,” Roland says. “But once everyone in the tier starts jumping, the structural behaviour changes. And that is so fascinating: the stadium and the crowd become one dynamic whole.”
A packed stadium like a swaying bridge
“In terms of structural dynamics, stadiums behave very much like large traffic bridges,” he says. In the past, for example, when troops marched across a bridge, it would start swaying. A well-known example is the Millennium Bridge in London, which began to sway in 2000 when thousands of people crossed it at the same time. Today, engineers apply many of the same monitoring techniques used in bridge engineering to assess the structural health of stadiums.
Roland’s research focuses on camera-based systems for measuring structural vibrations in bridges. These non-contact systems could also be used across entire sections of a stadium to capture vibrations during live events. “Traditional sensors measure motion only at isolated points. With computer vision, you can observe the behaviour of a whole grandstand simultaneously, so you can better understand how stadiums respond to extreme crowd loading.” Using high-resolution cameras, engineers analyse minute movements frame by frame and convert pixel displacement into measurements such as millimetres of movement and acceleration.
The data helps them monitor whether vibrations remain within acceptable limits as well as assess how spectators experience them. According to Roland, a missing element in spectators' comfort assessment is measuring the duration of vibration. “People respond not only to how strong a vibration is but also to how long it lasts.” For example, a brief burst of movement after a goal may feel exhilarating, but vibrations that continue for several minutes, or longer, can be agitating.
So, where is the best seat during the World Cup?
Roland laughs at the question. “It is more fun if you can feel the stadium come alive. The upper overhanging sections, for example, can experience slightly more vibrations than the lower sections, and they also offer good visibility. You can feel the movement and the energy of the crowd, and this makes people feel physically connected to the crowd and the event itself.”
