The final piece is secure. On Tuesday, a steel beam was raised to the top of The Assembly, a structure located at Morewood and Centre avenues on the Bloomfield/Shadyside border at the former site of the Ford Motor Co. assembly plant. The original 250,000 square-foot building and the four-story addition will house University of Pittsburgh laboratories and offices, an event space, conference rooms, a 250-seat auditorium, and a restaurant and cafe with parking below. There will be 108,000 square feet available for lease. Construction is expected to be completed by January . A group of 305 construction workers applauded as they watched the beam being raised toward the sky in what’s called “topping out,” a ceremony that signals the uppermost steel member is going into place and that the structure has reached its height, according to the American Institute of Steel Construction.