International Commerce Centre – Hong Kong

International Commerce Centre – Hong Kong

As a city, Hong Kong contains the most skyscrapers in the world – there are over 1000 of them. So Hong Kongers are experienced in building tall – but the huge height of the International Commerce Centre still allowed for some creativity when the engineers planned its construction – notably ‘vertical phasing’ – see below.

Profile:

  • Height: 484m
  • Floors: 108, said to be 118 because floors containing the number ‘4’ were not included because of tetraphobia. This is a superstition in the Far East which makes 4 an unlucky number.
  • Built: 2010
  • Use: offices, hotel
  • Location: West Kowloon, Hong Kong – population 7.4 million

Background

Developed by MTR Corporation (Hong Kong’s metro operator) and Sun Hang Kai Properties (Hong Kong’s largest property developer).

A big focus during the design phase was that the tower was to be ‘transit integrated’ – it stands on top of Kowloon rail station, which is part of the underground network as well as having connections to mainland China. Hong Kong’s powerful transport authority, the MTRC, is investing in transport as part of sustainable, futuristic city development.

The International Commerce Centre (ICC) was the world’s 4th tallest building on completion. In fact, the original proposal was to be 574m tall, featuring a clear, pyramid top, but designs were scaled back after a change in regulation that meant it couldn’t be taller than surrounding mountains.

Contains the Ritz Carlton hotel, whose swimming pool sits on the 118th floor and guest rooms near the top of the tower. World’s highest hotel.

There is a Sky 100 observation deck on the 100th floor.

Design

By architects Kohn Pederson Fox Associates (KPF) with Wong & Ouyang. Arup structural engineers.

A square floor shape was chosen as it is desirable floor space for business tenants. However, being perfectly square is structurally inefficient and would require much more steel and concrete for stable construction. To overcome this problem, engineers came up with a gently sloping top third of the building and arcs that spread at the base to increase its size. This improves the structural integrity and stability of the building, making it respond to the wind in a very similar way to a building with a circular cross section. These measures are particularly important in an area which regularly experiences typhoons.

^ my sketch of the ICC tower – see the ‘dragon tail’ and curved top third

The facade surface is a curtain wall ‘shingle’ – overlapping panels that are said to mimic a dragon skin. (Being a curtain wall, they don’t take any of the building’s weight.) The ‘dragon tail’ connects the building to the rail station and is formed by gentle sloping of the base. Diagonal beams hold the cantilever up at 90˚ (see diagram).

< the ‘dragon tail’ link to Kowloon station, with its curtain wall shingle

Engineering

The tower is made of an inner ‘skeleton’ of concrete with a high Young’s modulus. More reinforced concrete forms eight ‘mega’ columns. Concrete required a high ‘slump retention’ (basically it stays workable for longer, not hardening too fast) to be poured into the deep foundation piles.

The ICC contains outrigger structures. I’ve learnt that these are essentially structures that keep the building from toppling from too much overturning moment. Lateral forces on the building are spread more evenly by connecting the central core of the building to its edge with a truss. This increases the sort of ‘base area’ the force is acting on, making toppling more difficult, a bit like how it’s harder to tip a cone over than a cylinder. Here, they are made of steel + prestressed concrete.

What’s prestressed concrete, and why is it used?

Normal concrete is a great material for construction, because it withstands high compressive forces – yet it’s unreliable tension, because it’s brittle and cracks quickly.

The solution?

1. Reinforced concrete – ie with steel cables inside. Steel is ductile and takes on the tensile forces the structure experiences, and it is less likely to fail. BUT sometime the concrete might still deflect and crack, even before the whole beam actually fails. > chemicals can then penetrate the cracks + weather the concrete until, eventually, it does fail.

2. Prestressed concrete – the steel cables are put into tension before the building’s construction. Therefore the concrete begins already in compression – any tensile strain moves the concrete to an unstretched, rather than elongated, position. So overall the structure deflects less. The steel cables can be tensioned either before or after the concrete cures. This is the material used in the ICC for the outrigger structures.

Foundation system: ‘shaft grouted friction barrettes’. Injecting concrete into the ground for this system enhances the friction capacity of the piles by controlling soil density as it is removed. Increased lateral pressure makes the system very stable in these geological conditions. Arup (the project’s structural engineers) conducted testing of this type of foundations first, as they are the first of their kind in Hong Kong, and they were found to be satisfactory for the intended load.

Highly energy efficient for such a tall building – the Energy Utilisation Index (EUI) in 2013 was 157.3 kWh/sqm, which is in the top 10% of similar commercial buildings. Energy-efficient measures include:

  • Life cycle testing with Hong Kong Polytechnic University
  • High voltage, water-cooled air conditioning system with a centrifugal separator (a turning component that uses the idea of ‘centrifugal force’ – the apparent pushing out of materials in a wheel – to separate fluids of different density, thereby removing particulates, which are pushed to the edge as they are the heaviest)
  • Natural lighting used in the atrium
  • Energy efficient LEDs
  • Triple glazed curtain wall façade. The panels have a silver coating which reflects infrared and ultraviolet rays (which generate heat) whilst transmitting visible light rays, keeping the building cooler.
  • A choice to make the temperature of communal areas 26˚, which is warmer than typical standards which tend to lie around 21˚. Energy consumption via air conditioning is thereby reduced.
  • Features the world’s first double-decker, destination-dispatch lifts. Commuters are assigned a lift as they move through the turnstiles which will transport them to the relevant floor as fast as possible. Some lifts are closed off during non-peak hours which reduces energy consumption.
  • Effective waste management systems, including recycling of paper, plastic bottles and aluminium.
  • All rainwater from the tower’s facades is collected.

Construction

Engineers used ‘vertical phasing’ to plan construction. This meant lower floors could begin to be occupied whilst upper floors were still under construction.

< Lower floors already occupied during construction of upper floors

[Image credits for this page: aspectasia.com.hk/projects, hongkongextras.com, ctbuh.org/papers]