u-shaped stairway
A stairway with ascending flights in three directions and two turns between floors, forming a rectangular half-helix.
A U-shaped or C-shaped stairway consists of multiple straight flights of stairs with two turns (usually close to 90 degrees) between each floor level. It basically forms a rectangular semi-helix, with climbers required to walk a short distance from the top of one flight to the bottom of the next. This form can be built around a central core, an open shaft, or a wide open space.
This configuration does not include stairways with stairs running in only 2 directions, separated by a long landing, even though they may form a U-shape. Such a form would be considered a very wide hairpin staircase. The defining feature of this form is that stairs run in 3 directions of a quadrilateral.
There must be stairs in the third direction. A long level landing connecting two oppositely directed flights remains a hairpin stairway, even if its overall outline resembles a U.
