B1/2004Y Collapse of the Roof of a Maintenance Building built by Voluntary Workers at a Slalom Centre in the Municipality of Pohja on 1 February 2004
Early in the morning of Sunday 1 February 2004, approximately 250 m2 of a maintenance building of 720 m2 collapsed at a slalom centre in the Municipality of Pohja. The building housed a cafeteria, ski hire business, machinery shelter and an open space for victory ceremonies, karaoke events etc. and functioning as a lounge. At the time of the accident, the slalom centre was closed, although staff engaged in preparations for the day’s competition had already arrived. However, no one was injured and there was only slight material damage.
Inside the building, a staff member noticed a board hanging from the ceiling, which had bowed, and some exposed insulation, while it was evident from outside that the roof’s ridge was slightly bowed in the middle. The fire brigade was called out, bringing two vehicles with elevating platforms with the intention of clearing the snow from the building. Unfortunately, they were too late to prevent four of its nine steel trusses from buckling and the consequent collapse of the roof.
The technical cause of the accident was a flexural moment, significantly higher than the capacity of the rafters and which was exerted on the rafters near the ridge. This could have been avoided by designing the truss diagonals to extend all the way up to the ridge, whereas in the actual truss, the diagonals extended along the rafters, but stopped 1.5 metres short of the ridge. The trusses were therefore poorly dimensioned, and the flexural moment and other force values for the rafters incorrectly calculated.
The slalom centre is owned by a local sports club, and the maintenance building was designed and built by voluntary workers in 1993 and 1994. In the opinion of the Board of Inquiry, the structural deficiencies were caused by the construction organisation’s lack of experience.
The prerequisites for safe construction are thoroughly specified as part of the construction standards currently in force. However, in order to avoid similar accidents, the Board of Inquiry suggests that building officials and those within municipalities granting subsidies should actively ensure the employment of safe building methods in buildings built by voluntary workers for public use. In this respect, the municipalities have an excellent opportunity to improve safety, since they are aware of such projects and are often financing them.
For existing buildings of this type, the Board of Inquiry recommends that municipalities, local building officials and building owners establish whether buildings exist within their areas whose structural safety should be examined. If their structural safety cannot be established based on the designs and other material, additional studies and reinforcement of the structures may be necessary.