For the next two years, he was employed as a soil and foundation engineer at Moran, Proctor, Freeman & Mueser (now Mueser Rutledge Consulting Engineers). Established by foundation engineering pioneer Daniel E. Moran, the firm was an excellent launching pad for Reuben’s professional career. From 1951 to 1954, however, he decided to return to the academic environment for studies in the doctoral program at Harvard. During that time, he was a teaching assistant to Professors Karl Terzaghi and Arthur Casagrande.
In 1954, Reuben began a long, intensely productive career at the Thomas Crimmins Contracting Company in New York City, a firm founded in 1848 that specialized in foundations and underground construction. He joined the firm as an engineer and estimator, was soon elected treasurer, and in 1956 became a director. He became chief engineer at Crimmins in 1957, vice president in 1963, president of Crimmins, Samuels & Associates in 1980, and president of Crimmins Constructors in 1987. He became chairman of the board in 1986.
At Crimmins, Reuben oversaw work on a wide range of projects, including foundation engineering and construction for several landmark buildings in New York City, including the MetLife Building on Park Avenue (originally known as the Pan Am Building), the largest commercial office building in the world when it was completed in 1963; the CBS Building on Manhattan’s west side, a massive 38-story tower completed in 1965; the Ford Foundation Building on the east side of Manhattan, completed in 1968, with offices arranged around a 12-story atrium; the 53-story office building at 55 Water Street, completed in 1972, which replaced the Pan Am Building as the world’s largest commercial office building; the 57-story office tower at One Penn Plaza near Madison Square Garden, also built in 1972 (where Reuben later worked as a senior consultant at Parsons Brinckerhoff); and the 68-story Trump Tower on Fifth Avenue in Manhattan, completed in 1983. Reuben also worked on the development of power plants and utilities, water-treatment facilities, airport terminals, hotels, shopping malls, educational buildings, and entertainment facilities designed for huge audiences.