Complex sentence: Many believe, incorrectly, that the rings are made from the steel of a beam from the first Quebec Bridge, which collapsed during construction in 1907 killing 75 construction workers, due to poor planning and design by the overseeing engineers.
Split into simpler sentences: Many believe, incorrectly, that the rings are made from the steel of a beam from the first Quebec Bridge, which collapsed during construction in 1907. Seventy-five construction workers died in the collapse which was attibuted to poor planning and design by the overseeing engineers.