Pittsburgh Symphony Orchestra musicians went on strike Friday after unanimously rejecting calls for a 15 percent pay cut, but management contends those cuts and others are necessary because the orchestra is more than $20 million in debt.VIDEO: Watch David Kaplan's report"Pittsburgh Symphony Orchestra musicians are exceptional artists and deserve every dollar and every benefit we can afford to offer," said Melia Tourangeau, who took over as symphony president and CEO last year. "At the same time, we must squarely confront the very real financial crisis that we are facing."Tourangeau said management's demands are part of a "five-year growth model to sustainability." But the need for immediate cuts is necessary because of a recent financial assessment that showed the orchestra "would run out of cash and have to close the doors in May/June 2017," board chair Devin McGranahan said.    Symphony managers say the orchestra is running a $1.5 million annual deficit and faces more than $20 million in cumulative debt over the next five years.    They say the pension fund needs at least $10 million over the next five years to remain solvent. That's one reason they say they wants to freeze pensions for any musician with less than 30 years' experience, and move them into a 401(k) plan -- another move that prompted the strike.      The musicians have agreed to concessions in the past, most recently a nearly 10 percent pay cut in 2011 to help the orchestra deal with funding issues. The proposed immediate 15 percent pay cut would reduce each musician's base pay from $107,239 to $91,153, the union said, with annual raises of 2 percent and 3 percent in each of the next two years."The consequences of those cuts would be severe and immediate," the union said in a statement announcing the strike. It predicted musicians would leave, and the symphony would be unable to attract top-notch players.However, management contends several musicians earn more than double the base pay for certain position. Musicians also get up to 10 weeks' vacation and 12 weeks of sick time each year, plus overtime and seniority pay, management said.   The last three-year contract expired Sept. 5. Contract talks had continued with a federal mediator, but the union contends management wouldn't budge from its last offer, which was rejected Thursday. The musicians have offered unspecified "major" concessions on "salary, pension and size of the orchestra -- all the topics that are the focus of management's demands," the union said.    The union contends management also wants the right to unilaterally cut orchestra staff, currently 99 musicians and two librarians, by an unspecified number. Management said only that it wants to leave three vacant positions unfilled, but didn't otherwise address staffing numbers.    The union contends ticket sales are up and that donations to the orchestra's annual fund broke a record. Management doesn't dispute that but said the other changes still are necessary.