RW Armstrong and Associates Inc., Indianapolis’ fourth-largest engineering firm, has completed a merger with CHA Consulting Inc. that makes the local company a wholly owned subsidiary of the Albany, N.Y.-based business.

The companies declined to divulge terms of the deal, which was announced Tuesday.

RW Armstrong will retain its name and continue to operate from its offices in historic Union Station at 300 S. Meridian St.

RW Armstrong had local billings of $31.8 million in 2011, according to IBJ statistics. It has roughly 500 local employees, including 185 engineers. The company was founded in 1961.

“Going forward, we needed a bigger platform on how we can get into some new markets,” RW Armstrong CEO Jim Wade said. “We have that component now.”

RW Armstrong is a global engineering and architecture firm with 16 offices in the United States, Middle East, North Africa and Azerbaijan. The firm serves local municipalities and the U.S. Department of Defense, in addition to the aviation, water and transportation industries.

CHA Consulting was founded in 1952 and has more than 730 employees in 30 offices nationwide.

Together, the merged firms boast annual revenue of $210 million and 1,200 employees in 46 locations.

Owners of R.W. Armstrong will become shareholders of CHA Consulting.