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Design flaws suspected in Riga roof collapse

An investigation has begun into whether design flaws were to blame for a supermarket roof collapse which killed 54 people in Riga last week

No official explanation has so far emerged for the tragic accident which left shoppers and rescue workers buried under rubble inside the Maxima supermarket in the Latvian capital last Thursday evening (21 November).

Initially it was thought the award-winning building – designed by locally based KUBS and built by Re&Re – collapsed because of the excessively heavy materials used for a garden being constructed on the roof.

But commentators have questioned this explanation, arguing the structure had previously carried roofing pebbles and heavy snow.

Furthermore at a press conference on Friday all companies involved in the building’s construction and alterations said they had checked project documentation and there had been no violation of building codes – reported The Baltic Course.

Markuss Molls of CE Consulting – which supervised the construction – said: ‘All internal processes were checked, no violations were established.

‘On Tuesday, while inspecting the roof, we also checked the thickness of substrata on that part of the roof that later caved in, and it did not exceed 15 centimeters, which is the thickness stipulated in the construction project.’

The contractor Re&Re has also asked the Latvian Architects’ Association to lead an independent examination of the building’s design.

Toomas Kaljas, chief engineer of Finnish Rak Tek Solutions, has meanwhile argued connections between horizontal bars holding the roof were inadequately designed.

Writing in the same newspaper, he said: ‘Based on photographic evidence presented in media, it is obvious that the primary cause for such collapse is the steel truss bolted tension connection.

‘Steel truss, is made out of two pieces, which are assembled on site using bolted connections. The bottom chord tension connection is at least two times under-designed.’

Latvia’s president said the collapse was ‘our own made disaster’ and promised a criminal investigation to be led by independent experts from abroad.

With 54 dead and more than 36 injured the collapse has been the focus of national mourning and labelled the Baltic country’s worst disaster in more than 50 years.

The shopping centre won the Latvian Building of the Year award in 2011. The roof garden project had been due to complete on 29 November.

Further comment

Gordon Gibb of Gibb Architects

‘Often building failures occur as a result of a number of unfortunate factors coming together at one point in time.  The Ronan Point disaster in Newham 1968 was such an occurrence, where the inadequacies of the structural system and cladding connections in that case were discovered by their failure and the progressive disproportionate collapse that occurred due to a small gas explosion in a kitchen. 

‘In the case of the Riga supermarket, from the published reports to date, it appears that the inadequacy of the design of the steelwork connections in the roof girder trusses may appear to be the inherent defect, but the contributing factor may have been the storage of building materials on the roof in a localised area, with the resultant creation of loads beyond the structural capabilities of the connections where the materials were stored, which potentially led to a single area of failure followed by progressive collapse over a period of time. 

‘I note that the roof garden works have been discounted as the cause by some, because the roof had already endured and supported a greater snow load.  However, the uniformly distributed snow load would not necessarily cause the trusses to fail under a greater load than that which may have been exerted by materials in one area of the roof. 

‘There may be other contributing factors which have not yet come to light, including, potentially the quality of the construction and even the effects of the fire that occurred near the end of the construction period.  What is certain is that during the period of analysis there will be competing theories as the issues of liability are considered, and the weight of the various contributing factors will be debated.  In that process there will be questions to be asked of the architects and the engineers, the government authorities and the contractors whilst the cause and the fault are determined. 

‘In addition, it will be necessary for the construction health and safety regime to be considered and some really obvious questions have to be asked, such as ‘Why were materials being stored on a roof above an occupied shop, and were the risks considered’ and ‘What was the protocol for investigation of the cause of a fire alarm sounding, before deciding it was a false alarm’.  All of these issues need to be debated in the light of the building failure, which, although important, is not as important as the fact that apparently preventable deaths occurred.

‘Some may also say that such a disaster could not happen in the UK.  However it is important to remember that our complex building regulations and standards and our health and safety measures have been developed by careful analysis of home-grown disasters such as this.’

 

 

 

 

 

 

 

 

 

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