Union Pacific Railroad intends to restart freight operations near the heavily damaged Centennial Mills building, which officials have warned could trigger the collapse of the building. But on Monday, city officials briefed reporters on Union Pacific’s plans to restart running trains on a narrow rail corridor that passes the now-hazardous eight-story structure. The city has limited authority to stop the trains, according to Portland City Administrator Raymond C. Lee III. “What we would tell Union Pacific is…be a partner with us. Along with BNSF, Union Pacific is one of two railroads that use the corridor near the building for freight rail.