B2/2006Y Threat of Commercial Centre Roof Collapse in Savonlinna on 31 March, 2006
On Friday 31 March 2006 at 4.45 p.m., ruptures were detected within the ridge region in the upper flanges of the pre-stressed concrete beams supporting the roof. These defects were estimated to be severe enough to warrant the evacuation of the building, which was done. Upon the defects’ detection, only a driver transporting supplies to the store and four store employees were inside.
The driver detected grains of concrete on the floor. Since these were impeding him from pushing his roller cart, he began examining them. The driver informed a member of the store personnel about the grains. Together with the driver, the store employees examined the location of the grains, finding that a rupture had formed in the concrete support beam located above.
The commercial centre remained closed for a weekend, during which the beams that had sustained the most damage were shored up. Following this, a building inspector granted permission for the store to reopen on Monday.
The reasons for the rupture of the upper flange of the pre-stressed beam (HI beam) were failings in the design of the iron mounting and in the beam fitting inspection, inadequate iron mounting drawings and problems regarding the positioning of the irons during beam construction. A lack of detailed instructions, erroneous calculation estimates, low beam height and width with regard to load, and a lack of communication between the designers were the underlying factors for the inadequacies in design and fitting inspection. The positioning of reinforcing bars in the fabrication does not comply with the positioning tolerance of construction class 1 of the valid concrete standards.
To prevent similarly dangerous situations, the investigation commission recommends that unambiguous design instructions, including repair instructions, be drafted for HI beams, over ten-year-old HI beams be inspected, and that quality control, auditing and plan realisation monitoring in concrete factories be developed.