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RRJ was retained by the structural design engineer to assist in the evaluation of the collapse of a portion of the roof at the retailer’s Spearfish location. At the time of the collapse, there had been a deep snow followed by rain. This was the second collapse under snow loads at that store and was adjacent to the first collapse area. RRJ arrived at the store site hours after the collapse to provide independent documentation and investigation of the roof structure to determine the cause. RRJ assisted with the preservation of evidence, testing, and developing a repair program to assure no more roofing failures would occur in this building.
The investigation of the roof snow loading found that at the time of collapse, the roof snow loads were similar to the design snow load, showing that the roof should not have collapsed if properly designed and constructed. Field documentation found many fractured welds in the roofing joist trusses. Close examination and measurements of the fractured welds showed thorough fusion areas of some welds much less than should have been for the apparent size and length of the welds, an obvious likely cause of the collapse.
RRJ assisted in the development of and participated in a testing program of the roofing joist trusses and connection welds taken from the collapse area of the building. RRJ made measurements of the failed and tested welds that, along with calculations, demonstrated that the as-built strength of many of the truss welds was less than required by building code. A few welds less than the force demand on the welds at the time of the collapse revealed the understrength (defective) welds as the direct cause of the roof collapse. These measurements and calculations also provided minimum as-built strength values of potential understrength welds not visible when inspecting intact welds that allowed a reduction in the scope of roofing structure repairs. A nine-month program was undertaken to reinforce the roof truss weld connections throughout the building.