B1/2010Y Collapse of a Sports Hall Roof in Järvenpää on 23 February 2010, and Other Structural Failures in Early 2010
On 23 February 2010 an accident occurred in Järvenpää, due to the sudden, almost wholesale collapse of a steelwork roof on a floorball hall. At the time of the accident, 15 persons were present in the hall, two of whom sustained minor injuries. The accident was caused by errors in the design of the hall, which was constructed in 2001. Loads were underestimated and load-bearing capacities overestimated. Further problems were caused by the use of a truss analogy in the design, which was poorly applicable to the structure. Furthermore, the design of the joint between the pillar and truss was not dimensioned.
The scope of the investigation was extended to include 10 other accidents and incidents which occurred in early 2010. One of these pertained to a hall with a steel construction, situated in Lieto, which collapsed due to design errors. No one sustained injuries, since the building, used as a riding manege, collapsed overnight. Because many halls similar to those in Järvenpää and Lieto have been constructed in various locations, a high number of properties need be inspected and possibly repaired.
Glulam beams over 30 years old were involved in two roof failures. The roof of a bowling hall in Kuopio partially collapsed when a single beam failed. Due to unsuccessful gluing, the finger joint in the beam’s bottom layer had failed. In Raasepori, a glulam beam cracked, causing a danger of collapse. A great deal of snow had been drifted on the roof, a factor which, according to the guidelines in force at the time of construction, was not considered relevant to this design. A contributory factor to the failure was the mounting method of the beam head, which did not allow for timber shrinkage perpendicular to the grain direction.
A severe collapse occurred in a production facility in Teuva, where plate-connected trusses failed across an area of 800 square metres. This was due to insufficient support of the truss structures. While the support had been designed appropriately, it had not been implemented properly. This had not been detected during approximately ten years of use.
The profile steel-sheet roofing on two buildings was damaged. In both cases, it was found out that significant amount of snow had drifted at certain points. One of the buildings was an icehall in Espoo, constructed on forest terrain at the foot of a hill. The floorball hall in Helsinki was a tall building constructed on open terrain. It would seem that sites like these are more exposed to the risk of drifting snow, a factor which the design guidelines state should be taken into account.
In both cases, although there was no effective danger of collapse, this could not have been known at the moment of occurrence. It was safe to exit the buildings and assess the potential danger. In these cases, there was inadequate spacing between load-bearing structures and the non-load bearing interior structures. The discovered failures were due to normal bending of the load-bearing structures.
A canopy used to shelter firewood collapsed onto an employee, causing fatal injuries. This structure was not subject to a building permit. The working conditions posed inherent risks, since firewood was being taken out in a horizontal direction under an unsupported canopy. Due to the snow load, the canopy weighed approximately one metric ton. As this case demonstrates, structures not subject to a building permit can also involve fundamental risks.
The investigation commission decided to reiterate two safety recommendations issued previously and to issue three new ones. Moreover, the investigation gave rise to eight further remarks and proposals. The recommendations propose that a systematic and regular inspection procedure be established for old buildings, which could be termed an inspection, for example. The second recommendation reiterated calls for the development of a database for building-related accidents and incidents. A current problem lies in the fact that no information has been collected, for example, on the more than one hundred collapses and incidents which probably occurred during early 2010. Such information could be exploited in safety enhancement work.
An investigation of the collapsed steelwork halls revealed that, once defects in the buildings had been identified, no appropriate communication channel was available. Nor was it possible to obtain properly assembled information on whether similar defects had been detected or repaired in other halls. The investigation committee recommends that a procedure be developed to this end.
With respect to large new buildings, the investigation commission recommends that a third-party review of the structural design be required, in the case of buildings designed to accommodate large numbers of people.
Furthermore, the investigation commission recommends that the design requirements set for loads caused by drifted snow be re-considered. In particular, it should be investigated whether more careful account might be taken of the following during the design phase: the possibility of proportionally greater snow drifts on roofs significantly higher than the surrounding terrain or located at the foot of a hill.
If needed, additional information about the investigation will be given by Chief Accident Investigator Kai Valonen (e-mail first name.last name(at)om.fi or tel. +358 9 1606 7902, +358 40 500 9992).