The developers that plan to convert the former Chicago Athletic Association buildings into a 240-room hotel have landed a $61 million construction loan, clearing a key hurdle for the project across from Millennium Park. The joint venture between Chicago-based AJ Capital Partners LLC and San Francisco-based Geolo Capital have begun demolition inside the landmark buildings at 12 S. Michigan Ave. and 71 E. Madison St. and plan to finish construction in fall 2014, said Jasin Alfaro, AJ Capital’s chief operating officer. It is one of several hotel projects underway amid a building boom that will add 2,700 rooms to the downtown market.