On 21 November 2013, the roof of a shopping centre in the
Zolitūdeneighbourhood of
Riga,
Latvia, collapsed at 17:41 local time. The disaster killed 54 people, including three rescue workers; another 41 were injured.
[1][2]
...
So far it is not known what caused the disaster, but the police are investigating three theories: first, that there was an error in
structural design, and authorities overseeing planning had been negligent; second, that the cause is related to initial building procedures; third, that it was caused by the construction of the green roof.
[31][38]
...
The preliminary findings from the controlled collapse, which took place from 14 April to 17 April showed prolonged deformation of the metal support structures, which started well before the target weight of the roof was reached and ended with the constructions eventually breaking, suggesting that the roof was built improperly and the actual collapse was not caused by a sudden change, but by overloading structures for prolonged period of time and possibly
metal fatigue.
[43][44]
...
According to Re & Re's preliminary report, the cause was likely a design error. The report is a result of three independent civil engineers' examination of the project documentation. The rooftop garden was included in the original design, but the building was still "designed with insufficient load carrying capacity, three times less than required". The report states that the main reasons for the collapse are, faulty estimation of the maximum load to be carried by the roof, and the design of the connections in the structural steel supporting the roof.
[48][49]
According to Ivars Sergets, the owner of the HND Grupa which was responsible for the construction of the building, the collapse may have been caused by overload, created by materials being loaded onto weaker points of the roof. He rejected the possibility that the disaster had been caused by the design of the garden, since the store had been operating for two winters and the stress created by the weight of snow had been up to twice as great as the stress caused by the garden at the time of the collapse. He pointed out that too many of the building materials were stored on the roof.
[16][
not in citation given] Later on, however, he admitted that trusses made of two pieces bolted together were used, while the original design called for a single truss. This was a result of issues with transporting longer trusses to the building site.
[50]
Lilita Ozola, an engineer teaching at the Latvian University of Agriculture, suggested that for changing the trusses the entire design plan should have been revised and reapproved by authorities. With the two-piece trusses installed, the joint between them would bear most of the roof's weight. She pointed out that there is a video recording of the shopping centre's roof collapsing in which it is obvious that it failed at the exact position of the joints. She also criticised construction work taking place on the roof when there were people in the building.
[51]
Toomas Kaljas, who claims to be a
structural engineer working for a Finnish company, has published research based on photographs from the site, suggesting the connections between the horizontal bars that held the roof were inadequately designed. The garden on the roof played a minimal role. The load on the
bolts that were holding the bars was uneven and there were too few of them. The calculations of bolt forces were wrong. A better design would have resulted in components bending and cracking over time, instead of the whole building suddenly collapsing like
dominoes without warning.
[52][53] Kaljas tested some
nuts which were built to meet
DIN 934 standard and which, according to him, are available in any hardware store. He found that these are not strong enough.[
clarification needed] A solution would have been to either get stronger nuts, or place two of them on the end of the same bolt. According to Toomas, the building designer should have issued a standard for the required nuts or, if not, then the builders should have asked for it. He thinks all public buildings that use these bolts should get additional nuts.
[54] Latvian state police has called in question competence of Kaljas stating that he was not able to produce his credentials. It is also speculated that he is connected with Vikom Industry, although he himself has denied it.
[55]
According to a press representative of Kubs, the architect bureau that designed the building, the possibly faulty metal joint components were supplied by Vikom Industry. The management at Vikom Industry had said that they were unable to provide single-piece components and offered components that would be assembled out of two halves, but which would be just as strong as the ones ordered. Therefore, according to Kubs, Vikom Industry is solely responsible for the component and bolt force and strength calculations. Vladislavs Podgurskis, a representative of Vikom Industry, said in response that all metal components were made and assembled strictly according to the building design and that it must be a design error.
[56]
Industry said the bolts for joining the trusses had been supplied by the Eurobolts company. On 25 November Vikom Industry requested a manufacturer's certificate from Eurobolts for a certain batch of bolts. The owner and CEO of Eurobolts, Olga Romanova, said that the company has no information on what the bolts they sell are used for, however, the bolts in the batch Vikom Industry was interested in were not strong enough for joining trusses for the roof and that Vikom Industry had in fact never bought bolts that would be strong enough for that purpose. She added that judging from photographs of the trusses on the scene of the incident even smaller bolts were used. An anonymous fireman told TV3 News that the bolts he had seen on scene had not been broken, rather pulled out from fastenings, indicating the bolts were not designed for bearing the weight of the roof.
[57][URL='https://en.wikipedia.org/wiki/Zolit%C5%ABde_shopping_centre_roof_collapse#Investigation_and_causeVikom']https://en.wikipedia.org/wiki/Zolitūde_shopping_centre_roof_collapse#Investigation_and_causeVikom[/URL]
may need debunking
