New York's Trump Tower, a 58-story, 644-foot-high multiuse building is an all-concrete structure with an unusual structural design. Rather than using a tubular frame whose many closely spaced columns would have obstructed window views, designers chose a complex combination of core walls, shear walls and columns instead. Only 8 of the 52 columns in the upper residential floors (the top 38) extend all the way to the ground. At the 19th floor level, load from the 44 other columns is picked up by transfer girders which are about 24 feet high and 18 to 24 inches thick. Below the 19th floor shear and core walls and the remaining 8 columns carry the load through the lower stories where office and retail use requires column-free space.
Limited access to a tight urban site posed problems in selecting the best concrete placement method. Because a crane was needed on the site to raise forms and reinforcing steel and because several different strengths of concrete had to be placed, a crane and bucket were chosen; the contractor estimated that power buggies would have called for three times more men. Rather than raising the height of the crane by adding extension sections to the mast, the mast itself climbed up the interior of the building on a steel climbing column.
To improve the workability and thus ease the placement of concrete in the 6000-psi circular layers and the highly reinforced columns, a superplasticizer was used. Unlike the more familiar superplasticizers, however, the type used here was added at the ready mix plant, not at the jobsite. Referred to as a rheoplasticizer, this admixture has been described as a synthesized sulfonated complex polymer. It provided an 8- to 10-inch slump with no segregation and little or no bleeding. The concrete reportedly retained this high slump and remained workable for over an hour at 68 degrees F. Longer periods of slump are available up to 3 hours with other types of superplasticizers from the same manufacturer.