Vincent Tse, Managing Director of Buildings MEP in China, talks about the technical challenges of designing vertical transportation systems for super-and-mega-tall towers, and his solutions for achieving the most efficient designs.
Article Originally Published by WSP
Vertical transportation (VT) system design in super-and-mega-tall buildings is extremely challenging. As VT designers, we have to meet with the basic international standards at the same time as dealing with the many conflicting design priorities, parameters and the wide-ranging requirements of architects, building developers and operators. It involves the art of design coordination, integrating the needs of all stakeholders into one harmonious solution.
There is no end to the creativity of architects when it comes to designing extremely tall, iconic buildings. Building developers and designers want their projects to stand out, with attractive eye-catching building shapes to differentiate them from their neighbours. These can take any form, from conventional squares and rectangles to circles, ellipses, triangles, rhomboids, fans and any other variety of shape that the designers can imagine.
The shape of the building impacts on the vertical transportation design. For example, for a round office building with a circular central core, the elevators may have to be designed in a ‘fan’ shape to increase handling capacity, floor efficiency and also to match the building form.
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.
We coordinate closely with the architects and structural engineers to ensure our elevator systems enhance the overall building floor efficiency.
Since the construction cost of super-tall towers is 30-50% higher than for low-rise buildings, floor efficiency is a key design priority. Developers must maximise available lettable floor space to ensure an optimum rate of return on the overall capital cost investment.
Life and fire safety adds further complexity to VT systems in mixed-use tall buildings.
We work closely with all authorities to ensure safe evacuation procedures in any emergency, such as fire or power failure. In most cities around the world, fire authorities do not allow fireman’s elevators to be designed or used for occupant evacuation. However, many building authorities do accept the utilisation of shuttle or express elevators as emergency evacuation elevators for building occupants.
One of the biggest challenges we face is the difference between outdoor and indoor temperature.
It’s a very different matter designing the system for a tall building in the Middle East to a building in Toronto, where at night the temperature could be -30oF outside and 50oF inside the building. This temperature difference creates a severe sucking pressure in the lift shaft, which can prevent the doors from closing properly. This in turn can lead to a severe whistling sound, which at the extreme can be damaging to the hearing. Even in less severe cases, guests of an expensive 6 star hotel at the top of the building are not going to tolerate noisy lifts. VT designers must be very experienced to understand how to design for different environments.
Super-and-mega-tall buildings are only possible because of advances in lift technology.
Imagine, in a 500m tall building, the weight of the elevator cables, where every elevator is supported by 6 to 8 steel cables, each going up and down 500 m to make them 1 kilometre in length. That’s going to amount to several thousands of kilograms, so today the technology is moving towards the use of fibre cables in the forthcoming mega tall buildings of over 700 – 800m.
High speed motors are another innovation, along with highly reliable breaking devices that prevent the elevator car from falling. Sophisticated sway and vibration systems are also needed to ensure the elevator system is unaffected by the natural movement of very tall buildings.
Article courtesy of WSP