Thursday 24th September 8.00pm
Continuing this week is the documentary series that explores how disasters have influenced the evolution of modern structural engineering. This instalment examines how a series of tragic events at sports stadiums forced architects to incorporate a number of safety features into their designs for the arenas of the future.
Sport stadiums are amongst the most iconic, eyecatching structures of the modern world. Symbols of local and national pride, they play host to huge crowds on a weekly basis. No other structure holds so many people in such close proximity and in such an emotionally charged atmosphere – so when the structures fail, the effects can be catastrophic. Over the past century, more than 1,600 people have died at stadiums across the world. To prevent disasters happening in the stadiums of the future, engineers have had to learn what went wrong in the past.
For the designers of today’s stadiums, like the Nou Mestalla being built in Valencia, Spain, there are three main dangers to be addressed: fire, structural collapse and crowd control. On 11 May 1985, 56 people were killed when a fire ripped through a wooden stand at Valley Parade football stadium, home to Bradford City. Paul Firth, a fan who saw the tragedy unfold, recalls how quickly the fire spread: “From that first flame to the entire stand being on fire, top to bottom, took four minutes.”
Since the Bradford City disaster, all materials used in stadium construction must be flame retardant. The Nou Mestalla is built from fireproof reinforced concrete and clad in steel treated with hi-tech intumescent paint. The roof is made of a lightweight plastic called polytetrafluoroethylene (PTFE) that vaporises when burnt, starving the fire below of oxygen. Alongside the fire-safety features, the Nou Mestalla boasts an evacuation system that allows a capacity-crowd of 75,000 people to disperse in under eight minutes. Architect J Parrish has been involved with stadium design for over 30 years. “If ever any disaster happens, then we need to learn from it,” he says.
In 1900, Ibrox Park in Glasgow was the biggest purpose-built stadium in the world, with a capacity of 80,000. Two years after its completion, it played host to an international football match between Scotland and England. During the game, part of one of the terraces suddenly gave way, resulting in 26 deaths and more than 500 injuries. While engineers had accounted for the dead weight of the fans, they had not factored in the extra pressure caused by movement – known as live weight.
The stands of the Nou Mestalla can cope with 800kg of pressure per square metre. To prevent the cantilevered stands from vibrating, the structure is strengthened at key points identified by complex computer analysis. “We model how [the stadium] will react to people jumping up and down, and that gives us a more efficient design,” explains structural engineer David Castro. “It allows us to place stiffness where it is required.”
As a result of the Heysel Stadium disaster in 1985, in which hooliganism among Liverpool and Juventus fans led to a crush that killed 39 people, fencing became an important factor in crowd control in football stadiums across the world. Perimeter fencing prevented fans from invading the pitch, while high wire fences kept supporters from opposing teams apart. However, this crude solution to a complex problem led directly to the worst stadium disaster in western European history.
During the FA Cup semi-final clash between Liverpool and Nottingham Forest at Hillsborough Stadium on 15 April 1989, incoming Liverpool fans were herded into two central pens at one end of the stadium. To ease a bottleneck outside, police opened a gate usually reserved as an exit. The resultant surge of people flooding into the stadium caused a crush that killed 96 people. Immediately after the Hillsborough disaster, all perimeter fences in England were removed, and the big clubs began to replace terraces with all-seater stands. In modern stadiums, crowds are managed by hi-tech control rooms, from which supporters are monitored at all times. The flow of incoming fans is electronically controlled to avoid overcrowding, while any troublemakers can be identified and removed.
