* New CEO Ulrich Spiesshofer pruning ABB's portfolio
* To sell Thomas & Betts' steel structures business
* All-cash deal expected to close in third-quarter. (Adds details, background)
ZURICH, June 27 (Reuters) - Swiss engineering group ABB said on Friday it had agreed to sell Thomas & Betts' steel structures business to Trinity Industries Inc for $600 million in cash, part of a plan to sell off assets outside its core expertise.
ABB, which is pruning its portfolio under new Chief Executive Ulrich Spiesshofer, said it expected the sale to close in the third quarter of this year, subject to regulatory approval.
The sale is the latest in a string of divestments by the Zurich-based company as industrial groups focus on their core strengths to ride out a tentative economic recovery.
"This divestment is in line with our strategy for continuous portfolio optimization and reflects the limited synergies that the steel structures business has with our core business," Spiesshofer said in a statement.
Shares in ABB were trading up 0.5 percent at 20.41 francs by 1231 GMT compared to a 0.3 percent firmer European Industrial Goods and Services index.
Reuters reported in February that ABB was looking to hive off parts of Thomas & Betts Corp, the U.S. electrical components maker it acquired two years ago for $3.9 billion, and from Power-One Inc, the U.S. solar energy company it bought for about $1 billion last year.
In March, ABB agreed to sell Thomas & Betts' heating, ventilation and air conditioning business to U.S. conglomerate Nortek for $260 million in cash.
It also sold the assets of Baldor's generator-set business to Generac Holdings last October for an undisclosed price.
Thomas & Betts' Meyer Steel Structures business manufactures steel mono pole structures for utility companies in North America. The Memphis, Tennessee-based firm employs more than 1,100 people and has four U.S.-based manufacturing sites. (Reporting by Caroline Copley; Editing by Sophie Hares)