Airport Runway Design
Super High Strength Fibre Reinforced Concrete for Airport Runway Design
Recent media articles about a third runway at Heathrow keep the discussion about the rationale for building airports alive and kicking. Here we will look at newer materials being used in airport runway design. The materials are super high strength fibre reinforced concrete.
First, let’s look at some of the considerations that have to be understood before a new runway pavement can be designed. The Federal Aviation Authority (FAA) airport runway design Spec. 150-5320-6E is an outstanding reference.
- Load. The gross weight of the airplane. The pavement should be designed for the maximum anticipated take-off weight of the airplane at the airport. Design should consider that 95% of the gross weight is carried by the main landing gear and 5% by the nose gear.
- Landing gear Type and Geometry. Gear and type dictate how airplane weight is distributed to a pavement and how the pavement will respond to the airplane loadings. See image below.
- Tyre Pressure. Tyre pressure varies depending on gear configuration, gross weight, and tyre size. Tyre pressure has significantly more influence on strains in the asphalt surface layer of the pavement than at the subgrade. Tyre pressures in excess of 221psi (1.5MPa) may be safely exceeded if the pavement surface course and base course meet the minimums design requirements for pavement loadings along with a high stability asphalt surface.
- Traffic Volume. Forecasts of annual departures by airplane type are needed for pavement design. Such information is available from Airport Master Plans, Terminal Area Forecasts, Airport Activity Statistics etc. Pavement engineers should consult such publications when developing forecasts of annual departures by airplane type. Only departures are considered because in most cases airplanes arrive at airports at a significantly lower weight than at take-off due to fuel consumption. During touch down impact, remaining lift on the wings further alleviates the dynamic vertical force that is actually transmitted to the pavement through the landing gear.
- Airplane Traffic Mixture. The design has to take into consideration the mix of airplanes and not be based upon one single airplane type. The FAA pavement design software FAARFIELD considers the traffic mix and provides a solution for a suitable pavement thickness.
- Design Life. A standard 20 year design life.
- Pass-to-Coverage Ratio. An airplane seldom travels the same pathway as it moves along a pavement. The lateral movement is known as airplane wander and is modelled by a statistically normal distribution. As an airplane moves along a runway, it may take several trips or passes along the pavement for a specific point on the pavement to receive full-load application. The ratio of the number of passes required to apply one full load application to a unit area of pavement is expressed by the pass-to-coverage (P/C) ratio.
The above list is far from exhaustive.
Super High Strength Fibre Reinforced Concrete mixes fibres of various kinds with concrete to produce a material that has increased fracture toughness and greater crack width control. The nature of the fibres used is important for achieving the desired properties such as reduced pavement slab thickness and increased joint spacing.
A recent example of an airport runway design constructed with super high strength fibre reinforced concrete is the new D runway at Tokyo International Airport. The runway was constructed from discrete slabs made with SUQCEM. SUQCEM reinforcement consists of two different lengths of ultra fine steel fibres. The advantage of using SUQCEM fibres was that the slabs were about half the weight of traditional slabs. Since the runway was constructed over open water the weight reduction reduced the need for extra piling.
Constructing a new airport runway design is a highly complex task. The standards and design codes are complex and very long. The FAA documentation is extremely detailed and if used by airport authorities or construction and architectural firms around the world as a reference for a new airport runway design then the documentation will require careful and very accurate translation. Constructive Translations can help clients with such complex translations.
An example of some of the FAA codes is shown below: