First PacTrust Bancorp Inc. in Irvine completed its merger with Manhattan Beach-based Beach Business Bank, a $39 million buy that has boosted the combined bank’s assets to about $1.3 billion.

That places First PacTrust’s subsidiary PacTrust Bank as the second-largest bank based in Orange County, behind Irvine-based Opus Bank, which has $2.4 billion in assets.

Robert Franko, who was chief executive of Beach Business, will be president of First PacTrust, a post previously held by First PacTrust Chief Executive Gregory Mitchell.

Four former Beach Business directors have joined the combined bank’s eight-person board.

The bank now operates through 18 offices across Southern California, from Santa Monica to the Mexican border.