Wood framing for an addition atop Karmel Square Somali Mall in South Minneapolis collapsed Tuesday morning, knocking out power in the area and closing roads.  Authorities arrived at the 2900 block of Pillsbury Avenue South shortly after 8:40 a.m. and evacuated Karmel Square and several ajoining structures.  "I (heard) a long crack, and I (went) outside. ... It fell apart," said Mohammed Bashir, 25, who said he lives in an apartment complex next to Karmel Square. "And the wall was just hanging there." There were no injuries, said Minneapolis police spokesman Scott Seroka.  More than 20 people were evacuated from the building, authorities said.  Wood framing for a third-level addition was still hanging from the edge of the building's rooftop shortly after 10:30 a.m. A building inspector was working to discover the cause of the collapse and ensure the rest of the building was structurally sound, authorities said.  The collapse casued a power outage in the area that technicians were working to fix, an Xcel Energy worker at the scene said.  Wind "may have contributed" to the collapse, Minneapolis police Cmdr. Todd Loining said. Construction was not ongoing when the framing collapsed, Loining said.  Karmel Square is a collection of small businesses and groceries, largely operated by the area's Somali community.