The Hearst Tower contains twenty-one elevators in total. The stairways and elevators are placed in a service core along the western portion of the tower, the only side that does not face a street. The original plan had called for the core to be at the tower's center, but it was redesigned after the September 11 attacks in 2001, as a security precaution against possible attacks from the street. The offset core also enables the office floors to contain an open plan without interior columns. To accommodate the offset service core, and to compensate for the lack of interior columns, the tower's weight is supported by the exterior diagrid, which is braced with the service core.