Nurses at Brigham and Women's Hospital "voted overwhelmingly" on Tuesday to ratify a new contract that will increase wages and avert a threatened strike, union officials said in a statement. The Massachusetts Nurses Association, the union for 4,000 nurses, negotiated a wage increase of up to 30% over the next two and a half years for Brigham nurses, and a quadrupled hourly rate for some on-call nurses, the statement said. After 29 bargaining sessions over 11 months and intervention by a federal mediator, union nurses voted in July to authorize a one-day strike in hopes of jumpstarting negotiations.