Structures experts said this week that the UK was likely to seek to review its procedures and codes for temporary structures following a month of catastrophic stage collapses worldwide triggered by extreme weather.
Dramatic stage collapses during festivals in Canada, the USA and Belgium have left 11 people dead and dozens more injured.
Last week saw five people killed by collapsing stages at the Indiana State Fair in the USA and six killed at the Pukkelpop music festival in Belgium. Fatalities were narrowly avoided during a similar stage collapse at the Ottawa Bluesfest in mid-July.
The UK’s Temporary Works Forum (TWF) said that with an ever-increasing number of events such as summer festivals − as well as the Olympics next year − the UK should be looking to learn lessons from recent events and could consider raising standards.
“It’s very important for the UK industry to find out the background and understand what happened to learn the lessons,” said technical secretary John Carpenter. The TWF was set up by the Standing Committee on Structural Safety (SCOSS), along with the ICE and the Institution of Structural Engineers earlier this year to promote safe use of temporary works.
“Three in a row isn’t entirely a coincidence.Things don’t quite work like that”
Arup director and wind engineer Andrew Allsop
Arup director and wind engineer Andrew Allsop agreed the UK industry would be very interested in the outcomes of detailed investigations. “Three in a row isn’t entirely a coincidence,” he said, adding that it would be too easy to blame extreme weather events. “Things don’t quite work like that,” he said.
In Indiana, organisers and officials initially repeatedly blamed the collapse on a “freakish accident” and a “significant” gust of wind that shortly preceded an expected severe storm. The storm had been expected to hit at around 9.15pm and at 8.39pm officials started preparing to make an evacuation announcement. However, the gust that triggered the collapse occurred at 8.55pm, before any announcement.
‘Difficult to predict’
It is less clear whether there were such unusual wind gusts in the two storms that triggered the Belgian and Ottawa incidents.
Allsop said such unusual weather events can be difficult to fully predict, meaning that proper use of factors of safety is vital.
“With convective gusts it can be very difficult to predict how gusty these can be − so there is a certain element of unpredictability, which is why it is very important to stick to safety factors,” he said.
Temporary works specialist RMD Kwikform chief engineer Ian Fryer said that factors of safety are sometimes reduced on temporary works on construction sites, but added that it is more straightforward because in high winds, sites shut down.
“On fairly non-critical parts of temporary works with a short duration the wind load [design] might be reduced. But once the wind gets to a certain speed you’ll not have any people on site − sites don’t operate once you get to a speed of about 18m/s,” he said.
With large groups of people a much greater level of attention was required, he said. Carpenter added that temporary structures have a number of features that make them vulnerable.”Temporary structures do have some unique features − they are made up of bits of kit that have been used before, so fatigue and damaged parts can be a problem,” he said.
‘Larger and more extravagant’ designs
He also said that with the trend towards larger and more extravagant events the design of stages was becoming more elaborate. “These structures are getting more and more sophisticated with all sort of parts bolted on to them,” he said. “It all needs very careful and competent design.” Fryer said the speed with which event structures are erected is also a concern.
“Structures won’t be designed against every extreme weather event so throughout the event there needs to be competent individuals”
TWF technical secretary John Carpenter
“The events industry is an extremely fast-moving industry − in my experience much faster than temporary works industry, which is already fast moving,” he said. “There’s a frenetic energy to get structures up.
“It comes down to risk assessment,” he said. Carpenter added that even if properly designed and erected, events need to be properly managed. “Structures won’t be designed against every extreme weather event so throughout the event there needs to be competent individuals who can understand the weather predictions and prepare an evacuation [if needed],” said Carpenter.
Indiana’s State Fair Committee has brought in Thornton Tomasetti to investigate what went wrong. The consultant previously investigated the 2007 collapse of the I35-W bridge in Minnesota, which revealed fatigue in bearing plates and a flawed maintenance regime.
The Ottawa stage collapse is understood to be under investigation by Ontario’s Ministry of Labour. As NCE went to press Belgian officials had not released details of any investigation into the Pukkelpop disaster.