After the military vacated Stanley Barracks, the CNE made plans for the Barracks' demolition. However, until 1951, the buildings were used for emergency housing. The first phase of demolition in 1951 demolished all of the wooden buildings, leaving only the original stone buildings. In 1953, despite public opposition, three of the remaining four stone buildings were demolished for parking, leaving only the Officers' Quarters. In 1955, the Quarters found its first CNE use for Sports Hall of Fame exhibits before being turned into a year-round Maritime Museum in 1959. A new phase of building construction followed, replacing buildings destroyed by fire, demolished for the Gardiner Expressway, or needed expansions. The new buildings, mostly in the central block of the site, exhibited a new Modernist style of architecture. In 1946, the third Grandstand burned down. In its place was built the fourth Grandstand - a massive concrete construction and monumental cantilevered steel roof, which was a sharp contrast to the other buildings around it. The Modernist trend continued with the construction of other buildings and monuments typifying the modernist style including the Food Building (1954), the Shell Oil Tower (1955), Queen Elizabeth Building (1957) and the Princess Margaret Fountain (1958).
In the later 1950s, the new six-lane Gardiner Expressway was pushed through the grounds, which necessitated the demolition of the Dufferin Gate, the Women's Rest Building, and the Machinery Hall. The new parabolic arch Dufferin Gate was built in 1959. On January 3, 1961, the Manufacturer's Building and the Women's Building (the one built prior to the Queen Elizabeth Building) were destroyed by fire. The buildings were replaced by the Better Living Centre, which came with a distinctive Mondrian-inspired ornament on its roof. In 1961, the Hall of Fame building opened north of the Grandstand to house Canada's Sports Hall of Fame and the Hockey Hall of Fame. In 1963, the Coliseum was re-clad with a modernist south facade. To replace its exhibit in the Ontario Government Building, the Government of Ontario built Ontario Place on artificial islands to the south of Exhibition Place (accessible via two footbridges).
Coinciding with the opening of the ultra-modern Ontario Place, a new master plan for the Exhibition site was developed in 1971. The 1971 Master Plan was radical, calling for the demolition of many pre-World War II buildings, new Modernist buildings, and a massive central public space with a reflecting pool and fountains on the site of Exhibition Stadium, which was to be relocated. The plan proposed the demolition of the Fire Station, Art Gallery, General Exhibits Building, Railways Building, Government Building, Ontario Government Building, Automotive Building, Transportation Building, Band Shell, Grandstand, Shell Tower and the 1959 Dufferin Gate. A monorail was proposed to move people around the site and to and from the parking lots. It had first been proposed to connect Union Station and the Exhibition Grounds. Dufferin Street was to be connected to Lake Shore Boulevard, a new four-lane road along the north of the site and a new 1800-place parking lot taking the place of buildings to the west of Dufferin.
The plan resulted in some demolition, such as the Electrical and Engineering Building in 1972 and the General Exhibits Building and Art Gallery, which were in the path of the new road. In 1974, the International Building, to the west of the bandshell, burnt down. It was hosting an exhibit on Spain during the CNE when it caught fire and was destroyed. The building was demolished and not replaced and has since been used mostly as a parking lot. The 1971 plan was abandoned after Exhibition Stadium was redeveloped and enlarged to host the local Major League Baseball team in 1977. The site officially became Exhibition Place, partly in recognition that very little of the site was retained as parklands.
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