A Pittsburgh mother of three was killed in a freak accident when a giant steel cylinder fell on her while she was walking on a sidewalk. It happened around 10:30 a.m. Friday near the Petersen Events Center. Aleia Lopez had “significant, grave injuries to her head,” according to police. She was pronounced deceased at the scene a short time later. Witnesses said Lopez, who works at a nearby hospital, was walking with her colleagues when a large steel cylindrical drum broke free from a nearby construction site. Police say the drum rolled down a hill within the construction site, went through adja…