Lack of lateral support between roof trusses could have contributed to the fatal collapse last week of a Dutch stadium roof during an expansion programme, experts told NCE this week.
Dutch football club FC Twente’s Grolsch Veste stadium in Enschede was undergoing a second phase of expansion in preparation for the start of the new season in August. The cause of the accident is still unknown, but experts point to an apparent lack of lateral bracing between the roof trusses as a possible factor.
“There [appears] to be some lateral bracing missing at the rear nodes,” said Delft University of Technology lecturer in structural design and safety Karel Terwel.
“Horizontal bars that were in place on the constructed part of the stadium are not there in the collapsed roof,” he added.
The collapsed south east stand roof is an exo-skeleton cantilever roof which was being built around an existing stand. Engineers were close to completing the work at the south-eastern end of the ground, which began in February.
The stadium roof comprised eight trusses that cantilevered above the new stand. This was an addition to an extension to the adjoining stand along the side of the pitch − completed in 2008 − which used the same design.
“When the restraint is lost, the compression member coming up to the node literally flicks over”
Mark Whitby, Davies Maguire & Whitby
The 2008 extension along with the corner section connecting the two stands remain in place.
“What might have happened is that the rear node [where the truss parts meet] close to the [south-eastern] corner either was badly fixed, knocked or removed,” said past ICE President Mark Whitby, now a director of consultant Davies Maguire & Whitby.
Whitby said that once this happened it could have triggered a loss or restrain in all of the nodes on that section.
“When the restraint is lost, the compression member coming up to the node literally flicks over, which is evident from the bend at the bottom of this member where it is fixed to the concrete,” said Whitby.
“Prone to instability”
Confidential Reporting on Structural Safety (Cross) director Alistair Soane added that cantilevers must be treated with “extreme care” as there is no redundancy. Each part is essential to the structure functioning − meaning it is difficult to achieve robustness.
Engineers contacted by NCE agreed that until the steelwork had been fully erected it would have been prone to instability.
They said a construction methodology that takes this into account was “essential”. Phasing the work is critical as instability would be exacerbated if bracing was not installed at the right time.
2 killed, 14 injured
Dutch officials are investigating the accident. It occurred at about 12pm on Thursday 7 July, killing two and injuring a further 14 construction workers.
The extension is part of a £44.1M project to expand the stadium from 13,500 capacity − as it was in 2006 − to 32,000.The design team for the expansion programme includes Enshede-based IAA Architecten and engineering and planning consultants The Stadium Consultants, Matrix Installatien-Advisuers and Aveco de Bondt.
Contractor VolkerWessels led the Bouwcombinatie Grolsch Veste construction consortium − also comprising Te Pas Construction, Construction Trebbe East & North and Dura Vermeer Bouw Hengelo. All parties involved refused to comment.