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AIRPORT DESIGN Last modified on February 6, 2012

All in the design

HOK design director, Ernest Cirangle, explores how planners can help airports prepare for natural disasters.

On March 11, 2011, tsunami waves triggered by an 8.9-magnitude earthquake – the strongest in Japan for 140 years – slammed into Sendai Airport in north-eastern Japan.

In a terrifying scene viewed by millions online, waves up to ten metres high engulfed the airport, reaching the second level of the passenger terminal where some 1,300 people were stranded for two days before being rescued.

On April 22, 2011, the most powerful tornado to hit St Louis, Missouri, in nearly half a century touched down near the original 1956 terminal at Lambert-St Louis International Airport.

The building remained structurally intact, but 135 mph winds had blown the glass out of many of the main terminal's windows and swept a large section of roof off a concourse.

Designing for disasters

Whether it's earthquakes, tornadoes, tragic floods that devastated parts of China and Thailand, Hurricane Irene closing airports along the US eastern seaboard or the volcanic eruption in Iceland, the world is experiencing an alarming number of natural disasters
at the moment and airport officials are paying attention.

This may sound obvious, but one of the first things design teams must do today is identify what disasters an airport might need protecting against and decide how to minimise the risks for each.

There are many levels of preparedness and multiple strategies – some of which may conflict – for each disaster. But, the good news is that if we consider these threats early in the planning process and integrate our responses into the design, buildings with  disaster-resistant technologies will have exceptional long-term value. And these elements do not take significantly longer to construct and do not have to cost more.

Sendai earthquake and tsunami

HOK designed Sendai Airport with Japanese firm Nikken Sekkei. Though this airport was not planned to withstand a tsunami, it was able to perform well through two near-simultaneous natural disasters. The damage to the terminal was mostly caused by debris from the flooding.

How was this possible? With Japan sitting in one of the world's most active seismic areas, the level of earthquake preparation is extremely high. Building codes have stringent seismic design requirements and any additional costs for stabilisation are already built into project budgets.

'Integrated design' is a buzzword in our profession. In Japan, it's just part of the design process. In our experience working on three different-sized airports in Japan – Sendai Airport, Central Japan International Airport (Nagoya) and Kitakyushu Airport – the integration of architecture with structural and mechanical systems enabled us to create stable, welcoming and architecturally elegant buildings.

In the case of Sendai's terminal, the solution that emerged from the strict building codes, featured cluster columns that provide a stable footprint for the 44,130sqm structure.

The mechanical system fits into the void space between the four columns that make up each cluster. These 'umbrella' columns raise up to support the terminal roof and its series of undulating trusses and help distribute the structural load through the terminal, stabilising the building.

When the tsunami waves hit Sendai Airport, most passengers were above the submerged first level, since the design places most passengers on the second level of the terminal.

The design orients the terminal so the short side faces the ocean. As a result, less water was able to collect and exert force against the building.
The team oriented the terminal this way because the prevailing winds dictated that the runway be east-west. But, as with placing passenger activity on the  second level, it's a lesson for airports planning a terminal near a large  body of water.

Structure as the driving force

To ensure that all the components of a terminal have a clear, modular relationship with the structure, the structural systems need to be part of the early thinking about how to organise the building. The structure becomes the driving force.

In an earthquake, long-span structures such as airport terminals behave differently than other buildings.

"If you lock in both ends of a long-span structure, then you are locking in the stresses and it will be subject to buckling," says Nancy Hamilton, a structural engineer and the director of engineering services at HOK.

Though making the building extremely stiff at both ends, or 'strong-arming' it, is a common design approach for airports, this requires complex, expensive roof systems.

A better way to design a terminal in an active seismic region is to secure the roof system with lateral restraints at one end and to let the building flex and move at the other. If a local structural element fails in a disaster, others can take its place.

Hamilton, who has led the structural design of airport projects across the world, uses a skiing analogy to make the point about the effectiveness of such a method. "When you are skiing, you feel the impact of every bump if you lock your knees," she notes. "However, if you bend your knees and let them flex, you will be fine."

Designing for structural resiliency and redundancy has a significant impact on a terminal's plan and passenger flows. A plan, for example, may position most of a building's bracing elements at the front of the terminal so the structural system does not compete with passenger flows and baggage handling systems on the interior. "From the beginning of design, the team needs to think about where the building joints are, where to place the lateral restraint elements, how to keep the roof from being locked in with stresses and how the entire structural system will work," says Hamilton. "These are complex issues."

Designing against earthquakes in New Delhi

Delhi's Indira Gandhi International Airport is located in a high-risk, seismically active area in India meaning that earthquakes pose a threat to its new 502,000sqm, LEED-Gold certified Terminal 3 and ATC tower.

As a result, HOK collaborated with Indian-based engineering firm Frischmann Prabhu to incorporate seismic design considerations into the terminal building structure.

The building design creates large column-free areas with wide spans and a tall roof. Columns are typically 15 metres high, but extend to 27 metres in some locations. This primary design feature provided one of the main structural challenges with respect to seismic design.

The team began by creating conceptual designs for two different structural systems for Terminal 3. One system used a combination of columns and bracings and the other was designed with moment-resisting frames that resist force by bending.

The structural system with bracings was effective in resisting the seismic shear loads, but was incompatible with the overall architectural intent for the building. As a result, the team selected the system with moment-resistant frames and wider columns.

Designing the columns as composite reinforced concrete with steel billets reduced their footprint. To ensure the ductility of the structure in a seismic event, the structural components were detailed as required by the Bureau of Indian Standards building codes.

Consider climate and place

Every airport in the world is vulnerable to some type of natural disaster, and every design strategy should be based on the local climate and place. Among the natural disasters we design for are:

Dust storms and sandstorms
In areas of the world threatened by dust and sand storms, a terminal must be designed to protect incoming air from the dust. We study the prevailing winds and strategically place air intakes and exhausts. Rooftop photovoltaic systems will collect dust unless the building is oriented so that the winds blow it off.

Many existing airports are in coastal regions on reclaimed areas. Here, they are exposed to hurricanes and ocean flooding around the perimeter. Designers can provide master drainage plans and underground storm retention basins that capture stormwater for re-use. These basins also act as overflow buffers that prevent an airfield from being flooded.

High winds
The intense storms we have experienced in recent years suggest that terminals could be exposed to higher winds than historic records (and the building codes based on these records) indicate. Because terminals have such large, open facades, they need to be redundant and ductile to withstand strains.

Unknown winds and atmospheric conditions create unknown forces. Our architects and engineers consider the potential for increased wind pressures, dramatic changes in atmospheric conditions and debris acting as projectile missiles that can breach the facade. Berms (an artificial ridge or embankment) around the terminal can provide a basic level of protection.

Snow and ice storms
Snow and ice storms generate higher structural loads than building codes allow for. The large roofs of terminals must be shaped to shed snow, ice and winds.

Sustainable and low-energy terminal design

A growing body of scientific evidence links long-term climate change to an increase in the frequency and intensity of extreme weather events. To reduce our impact on the planet's ecology, we need to design low-energy airports shaped by a response to the local natural environment.

At the new LEED-certified, 111,480sqm Colonel H Weir Cook Terminal at Indianapolis International Airport, the architecture is derived from simple approaches to reducing energy use.

Our team designed the sheltering roof form, skylight and high-performance curtain wall systems to work together to mitigate heat gain and assure that primary building lighting is not required on the departure level during daylight hours.

These strategies are joined with a unique mechanical system of radiant floors and stratified ventilation that only condition air to human comfort in the building's inhabited zone, below three metres.

The airport believes that these energy conservation features provide at least $2 million in annual savings.

Taking the terminal off the grid

The grid often fails in a natural disaster. We can add another layer of protection for airports by integrating the design of a terminal and its systems in order to take the systems and critical operational components off the grid.

HOK is pursuing strategies and technologies for reducing building and equipment loads and increasing the amount of renewable energy generated on site.

Indeed, as new technologies continue to develop, we hope to be able to design terminals that can operate substantially off the grid in normal and emergency modes.

"We want to reduce the building envelope and processing load, maximise passive design strategies, use high performance building systems and generate substantial energy from renewables, so that a terminal can be as self-sufficient as possible," says John Pulley, HOK's director of MEP engineering. "Net zero energy is the ultimate goal."

Because there are airport loads that cannot be handled passively, design teams need to provide a resilient back-up generation system. In a disaster situation, the terminal would be able to continue operating without being connected to utilities.

HOK uses building information modelling (BIM) software to test design ideas and model a terminal's performance during a natural disaster.

"Our BIM models test the terminal's renewable energy and redundant systems to ensure that the airport will function even if it goes off the grid," says Pulley. "We can't rely on assumptions when planning for potential disasters – it's too important."

Passive design strategies can also provide significant savings on airport operating costs.

"The capital costs of unused backup equipment are very high," adds Pulley. "It's much more cost effective to maximise passive design strategies than to  build another central plant that provides redundancy in the unlikely event that one gets destroyed."

A delicate balance: beauty and function

Airports are architectural icons representing a city and its people – visually striking pieces of environmentally responsible, high-performance machinery.

However, at the same time, travellers should feel comfortable and safe within the terminals we create.

The designer's challenge is to blend beauty and function to create inspiring airports that can withstand the increasingly brutal and always unpredictable whims of Mother Nature.

Airport World 2011 - Issue 6

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