A low-interest-rate environment is wreaking havoc with corporate defined benefit plans, according to a new study from Wilshire Consulting, finding that 94 percent of pension plans are underfunded.

"The $282.3 billion funding shortfall at the beginning of the year expanded to a $342.5 billion deficit," Russ Walker, vice president, Wilshire Associates, said in a statement. "Defined benefit pension assets for S&P 500 Index companies increased by $113 billion, from $1.11 trillion to $1.22 trillion, while liabilities increased $174 billion, from $1.39 trillion to $1.56 trillion. The median corporate funded ratio is 76.9 percent, which represents a modest decline from 77.7 percent last year."

The defined benefit plans in Wilshire's study yielded a median 11.8 percent rate of return for 2012. This performance combines with the 3.6 percent median plan return for 2011, the 11.9 percent median plan return for 2010 and the 16 percent median plan return for 2009 to mark four consecutive years of gains for these plans after the global market dislocation events of 2007 and 2008.