The choice of structural solutions for buildings over 300m high also affects the concept design of the elevator system. As the building height increases, structural engineers opt for a range of solutions, the most common being mega columns, regular columns, or a tube-in-tube design with a composite or steel central core. Some projects have an outrigger structural design, providing sky lobbies, which are accessed by shuttle elevators, and from which building users are transferred to higher zones via another group of direct local elevators.
VT system design is also greatly influenced by the way the shape of tall buildings tends to change from lower to higher levels, as well as by the window to wall (WTW) distances on different floors. For example, many towers get narrower towards the top, with decreasing floorplates favouring a variety of different functions. There may be offices on the lower floors, which commonly have a WTW distance of 12-16m to optimise natural daylight and achieve the most effective floor to floor height. Above there may be serviced apartments whose WTW distance is generally 10-13m for effective layout planning; while a hotel at the top of the building will have an even shorter WTW distance for guestrooms, at around 8-11m. As the towers get narrower the higher they go, their central cores become smaller, making the elevator stacking arrangement even more complicated and sophisticated.
90% of all mega-tall towers (500m and above) under construction or on the drawing board will be of mixed use type. Together with the varying building shapes, the mixed-use nature of mega-tall towers adds further complexity to the VT solutions. If a building contains offices, a hotel, serviced apartments and an observation deck, different groups of elevators will be required to serve each different function. These will need their own independent elevator lobbies with their own services elevator group for better security control and individual management. This will affect the elevator arrangement and grouping in the central structural core.