B1/2000Y Breaking of laminated beam in roof of indoor swimming pool centre at Iisalmi, on 29 March, 2000
On Wednesday 29 March 2000 early in the morning an incident arose when the roof of the Indoor Swimming Pool Centre at Iisalmi threatened to collapse. In fact one of the laminated beams supporting the roof structures above a swimming pool broke entailing a gradual slow settlement of the roof.
The first customers that morning had gone over to the multi-function pool when the swimming supervisor discovered a crack in the roof beam. In the swimming pool directly below the laminated beam referred to, there was not yet anybody swimming. As the beam kept sinking steadily with jerking movements, the swimming supervisor told the customers to return to the washing premises. Then the maintenance officer of the Swimming Pool Centre called the fire brigade which arrived to support rapidly the roof structures with the trunks of trees chopped down in the yard.
The Indoor Swimming Pool Centre had been expanded and renovated during 1995 and 1996 with the combined flat and arched roof construction having been changed to a mono-pitch roof construction. After the change the laminated beam in question had to carry the stress of an area twice as big as the earlier one, as the arched roof construction transmits the vertical stress of the rounded area to the support structures of the beam ends. But in connection with the change of the roof construction the corresponding increase in the stress had failed to be appropriately considered and as a result, in the bolted joint area of the beam end, a tension fracture perpendicular to the grain of the beam was generated by the shearing stress. The beam first cracked in its elevation in many places to finally break as due to the bending stress. The snow load of the roof featured about 2/3 of the standard specific load, implying that it was not exceptionally heavy.
In addition to the roof damage in the Iisalmi Indoor Swimming Pool Centre, the Accident Investigation Board of Finland studied three other roof damage cases having occurred in early spring 2000. In one case the specific snow load as specified in the relevant standards, had been exceeded. However the exceeding was only slight and any correctly dimensioned structures ought to have endured it without being damaged.
To end this investigation report, the Accident Investigation Board of Finland herewith gives its recommendations for an enhanced safety of buildings and constructions. The Board actually recommends that the building inspection authority require structure calculations and dimensioning criteria to be produced on a more regular basis. Moreover the Board recommends that the resources at the disposal of the building inspection authority be increased, a database be set up featuring structure designers and their respective qualifications and fields of specialisation, and that joints corresponding to the case under discussion be realised so as to transfer the entire shearing stress to the steel part by a connection from the lower edge of the beam. Finally it would be very reasonable that the woodworking industries engage more efficient study and research activities concerning wooden structures and initiate a corresponding publication activity focusing on guidelines and instructions intended for the design and planning sector.