A seismically isolated airport terminal with ArcelorMittal structural steel: Sabiha Gökçen International Airport

Detailed information

Seismic design requirements: A seismic base isolation system to ensure effective damping

The Sabiha Gökçen International Airport offers a total area of more than 320 000 square metres and is comprised of an integrated domestic and international terminal building, a hotel, a new VIP terminal, and various other airport facilities.

Its location in a seismic hazard zone determined the design of the building's structure. The main requirements included special measures to ensure safety in case of an earthquake. According to the client’s requirements, two performance levels were defined for seismic analysis of the terminal building. These performance levels are as follows:

1. The building was designed for Operational Level. i.e. no structural and no non-structural damage for an earthquake hazard with a uniform 10% probability of exceedance in 50 years, which is equivalent to a hazard with a return period of 475 years. This earthquake hazard is commonly known as Design Basis Earthquake (DBE) or design earthquake in practice.

2. The building was designed for Structural Immediate Occupancy for an earthquake hazard with a uniform 2% probability of exceedance in 50 years, which is equivalent to a hazard with a return period of 2475 years. This earthquake hazard is known as Maximum Considered Earthquake (MCE).  

The design of a standard, fixed-based structure that can comply with the stringent seismic performance objectives listed above would be uneconomical and infeasible. Therefore, it was decided to implement a base isolation system.

A seismic base isolation system with energy dissipation capabilities enables shifting/elongation of the fundamental periods of structure and provides a significant increase in the effective damping. These two key features provide a significant reduction in the seismic design forces and inter-storey drifts of the superstructure; hence, reducing the risk of structural and non-structural earthquake damage. Triple friction pendulum devices were used to build the world’s largest seismically isolated building. There are 300 triple-friction pendulum isolators that are distributed over the entire plan. Note that the triple-friction pendulum bearings, with a theoretical period of 3 seconds and displacement limit of 345 mm, were selected on the basis of performance and cost. The effective damping provided by the isolators is 38% and 30% at DBE and MCE events, respectively.

The structural system: Steel as the main protagonist

The new SGIA Terminal building is a steel structure with a plan dimension of 160 m by 272 m. The total building height is approximately 32.5 m. The building consists of four storeys above and a basement floor below the isolation plane. Typical floor heights are 6 m at the ground floor and 5 m at the upper levels.

The gravity system of the superstructure is composed of concrete filled steel decks, composite steel beams, and composite steel columns. The superstructure resists lateral loads by a system of steel moment frames through rigid horizontal diaphragms. The clear span length supported by the columns is 16 m in both directions. All structural members, such as columns and beams, are built-up members. Plates were cut in appropriate shapes and were connected via welding in order to constitute the required structural sections. Floor rib beams are made of grade S235 steel plates and columns and main beams are made of grade S355 steel plates. Rib beam layout orientations are changed in every main cell (16m x 16 m), so that all the main beams are loaded with the same gravity loads. The framing for the stairs and elevators below the isolation plane is suspended from and braced by the isolated super structure above. The concrete compressive strength is 35 Mpa for composite columns.

The roof system consists of light steel space purlin systems running longitudinally and located at every 8 m and braced in the transverse direction. The purlin has a parabolic curve form with a depth of 12 m and 6 m placed evenly next to each other. They are pin-supported by the top of the columns at every 32 m and 48 m. Purlins consist of pipe members which are in grade S355. Unbalanced snow drift load was taken into consideration in the analysis due to the shape of the roof.

In total, 18 600 tonnes of structural steel was used for the construction of the SGIA's new terminal building. ArcelorMittal Distribution Solutions - Rozak was the main steel supplier for this project providing the majority of steel beams and plates.