Engineer Specs: Your Blueprint for Building Confidence & Quality

The Photograph above: By Valenciano – Self-photographed, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=29802079

Engineers Design Buildings for a Purpose

Engineers around the world will design a structure based on the brief given to them by a developer. The basis for any good design is to have a structure that is “fit for purpose” for which it is intended. Most international building codes, and this includes our South African National Building Regulations, are very specific in terms of engineers requirements. For instance, our National Building Regulations (NBR) state:

“Any building and any structural element or component” must be designed to “provide strength, stability, serviceability and durability”.

It is also vital that buildings are designed by engineers so that if the structural system is in any way overloaded they won’t collapse with disastrous consequences.

The Regulations also state that these engineers design requirements shall be “deemed to be satisfied” when buildings are designed in accordance with the relevant Part of SANS 10400, in this case, Structural Design.

Roof Design of Riga Mall

Even though the devastating collapse of the roof at Riga Mall in Latvia on Saturday November 23, 2013 was under investigation (see the addition to this story below) according to engineers there is some certainty that a roof garden being constructed on the roof of the mall played a significant role.

The engineers who designed the mall roof clearly did not intend for the roof structure to carry the extra weight that was being imposed on it. Tons of soil, concrete pavers and possibly water features, as well as many people walking on the roof, would put tremendous additional strain on a structure that was not designed by engineers to carry such loads.

So why are people surprised it collapsed?

This excerpt from Wikipedia has a speculation of the cause of the roof collapse:

“Initial Speculations”

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.^[51][52]

According to Ivars Sergets, the owner of 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.^[53] Later on, however, he admitted that trusses made of two pieces bolted together were used, while the original engineers design called for a single truss. This was a result of issues with transporting longer trusses to the building site.^[54]

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.^[55]

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 load on the bolts that were holding the bars was uneven and there were too few of them. The calculations of forces applied to bolts 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.^[56][57]

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. A solution would have been to either get stronger nuts, or place two of them on the end of the same bolt. According to Kaljas, 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.^[58] Latvian state police has called into question the competence of Kaljas stating that he was not able to produce his credentials. It is also speculated that he has connections to Vikom Industry, although he himself has denied it.^[59]

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.^[60]

Vikom 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.^[61]

The vice director of the Latvian Fire Safety and Civil Defence College, Vilis Students, who participated in the rescue work, said that the concrete components seemed unexpectedly fragile. Translated quote: “I am no specialist, but we could break the roof components with hammers and pliers. During exercises with concrete objects, we usually had to use a jackhammer.”^[62]

According to Maxima staff, the building had been dangerously unstable for about a year. The construction workers had told them that the foundation was cracked and needed reinforcement. At one point the storage room and store workers’ locker room were completely flooded. There had also been extra support columns under the ceiling of the storage room, but those had been removed later. The fire alarm sounded frequently. The staff believe that the reason for the alarm was that it was obsolete and could not distinguish smoke from dust. The store employees did not want to testify about this in front of a camera due to a fear of losing their jobs