Giant jackhammers reduced 220 feet of the 6th Street Bridge roadway to rubble by Saturday morning and were working on bringing down three massive support columns, said Mary Nemick of the city Public Works Department. Detouring drivers on other freeways didn't find too much of a problem, with delays ranging from about 15 minutes to 25 minutes, said Laurie Wonder of the California Department of Transportation. People are heeding the detour rules and heeding our warnings to stay away from the area, she said. Considered state-of-the-art when it was built in 1932, the bridge has been suffering from a chemical reaction that for decades has weakened its concrete.