Last week marked the formal dedication of the Tycon Courthouse office compex at Tysons Corner. Virginia Gov. Charles Robb, Fairfax County Board of Supervisors' Chairman John Herrity and other officials were on hand for the ceremonies. The complex, built on the site of the county's first courthouse, offers 400,000 square feet of office space, about 70 percent of which is leased. The highlight of the building is a 120-foot-high arch made of 270 tons of precast concrete and supported by a tubular steel frame. Other buildings by Tycon Developers at Tysons, Tycon I, II and III, when added to the Courthouse, total almost a million square feet . . . The architectural and engineering firm of Dewberry and Davis is expanding its Prince William office, moving to a new office in the second phase of the Lake Ridge Executive Park . . . Granville Corp., a management consulting firm, has leased 13,727 square feet of office space at 1425 K St. NW. Jon Kaylor of Smithy Braedon assisted in the transaction... American Bell Inc., a newly formed subsidiary of AT&T, has leased 53,000 square feet at 1100 Wayne Ave. in Silver Spring from which it will market communications equipment to federal agencies and small-business customers. Benjamin C. Trotter III and Kathleen M. Murphy of Spaulding & Slye negotiated the five-year lease.