Ronald G. Steinhart has announced his resignation as vice chairman of First RepublicBank Corp., effective Dec. 31. He said he would pursue other interests. Steinhart, 47, became vice chairman in June when First RepublicBank was formed from the merger of RepublicBank Corp. and InterFirst Corp. He had been Interfirst’s president and chief operating officer. First RepublicBank Corp., based in Dallas, is the largest banking organization headquartered in the Southwest.