Initially, the design of the structure was called into question, and was immediately poo-pood. Had the design been faulty (including bolt grades), the review and redesign process would have taken months or years to occur. They were given the ok to continue the construction the next month after their investigation. The ultimate cause was determined to be faulty erection practices by the erector. When erecting large truss and girder structures, x-bracing, bridging and shoring is required to keep the structure upright. There was a wind event that night that caused the large trusses to twist due to inadequate bracing. That, in addition to lack of shoring on one of the main column lines ultimately caused the collapse.
I haven’t seen anything about bolt grades or shearing being a factor. If there were sheared bolts, they were a product of the collapse, not the cause. There was absolutely no load applied to the structure. Oh, and bolt quantities have nothing to do with deflection. Member sizes do. I think my hard hat is white, I can’t tell from the stickers.
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