Evaluation of Airport Buildings Against Terrorist Attacks in the Context of Architecture and Planning Criteria: Five Case Study

During zoning planning, areas such as blind spots, hills due to topographical structure, reeds, and swamps around the land designated for the airport can be identified in advance and protection can be provided at the plan level. Infrastructure applications should be organized in a way that does not pose a potential threat to the area. Infrastructure systems should be organized in a way that does not allow access to the area and weapons storage. Airports should be planned so as not to create an urban density in the surrounding area and should be separated from areas of intensive use. In the selection of land for airports, land with a minimum level of uncontrolled areas and areas away from dense residential areas should be preferred.

Access of vehicles to the airport should be prevented by various solutions such as barriers, landscape elements, and high sidewalks. Especially uncontrolled vehicles should be kept away from the building. If the parking lot area is solved as a separate building, a protected distance between the risky area and the airport can be provided. In addition, the location of the streets and alleys around the building is also important for vehicle circulation. Multiple perpendicularly connected streets make it easier for vehicles to exceed maximum speed limits. Where necessary, speed barriers should prevent vehicles from accelerating. Ideal roads are those that are separated from the site by a pedestrian road, have no pedestrian access, and run parallel to the building site (Figure 2).

Figure 2.

Effect of street and alley layouts on vehicle speed (drawn by the authors based on FEMA 426)

All infrastructure lines around the airport must have at least one backup line. Infrastructure lines that are damaged in the event of an attack leave the structure and its surroundings vulnerable and cause disruption of emergency interventions. Components such as critical energy distribution locations for emergencies should be away from main entrances and parking areas.

Landscaping areas to be created in and around the building should not create potential hiding and surveillance areas for hazard centers (Figure 3). When landscaping, areas should be designed in a way that prevents information about the building and its surroundings from being obtained. Elevated areas are safer in terms of controlling the area. Insecure, uncontrollable areas such as water channels, dense landscape elements, hills, and ridges that can provide concealment should be avoided. The use of vegetation on its own may not have a direct impact on the safety of the structure, but landscape design organized with safety in mind contributes to its protection. Urban design elements such as curbstones, plant tanks, planters, trees, dividers, and electric and lighting poles should be used effectively for security as they restrict access to the building.

Figure 3.

Arrangement of the airport according to line of sight (drawn by the authors based on FEMA 426)

Protective barriers not only limit access to the building and its surroundings but also help to define, orient and block the building. Access to the building and surrounding areas should be controlled. Physical barriers, reinforced fences, etc. should be used to provide controlled access and concrete barriers should be used to stop large vehicles. For the security of the perimeter of the building, reinforced concrete curtain walls should be built to delimit the land; these walls should be a minimum of 3 meters in height and should be supported with barbed wire where necessary (Figure 4). Reinforced concrete walls protect the structure against possible blast effects by reducing the pressure effect on the structure. In addition, these areas should be regularly checked by patrol vehicles. Fences and security walls should be increased in more security-sensitive areas and these areas should be monitored by guard stations or cameras (Airport Planning Guide, 2015). In addition, barriers to be used to prevent vehicle passage should be 60 cm to 1 meter high as standard. The spacing between the barriers should be between 110 cm and 120 cm to prevent vehicle passage.

Figure 4.

Concrete walls and barriers around the airport (drawn by the authors based on FEMA 427)

Uncontrolled parking areas should not be allowed around the building. Designating parking areas in and around the plot and prohibiting parking on the periphery of the plot makes it easier to control vehicles. In particular, the greater the distance between the airport and parking areas, the greater the protection of the structure against vehicle-laden explosions. The ideal distance between the building and the parking lot should be a minimum of 10 meters and a maximum of 45 meters (Figure 5). In addition, measures should be taken to prevent the parking of vehicles closer than 50 meters to facilities and structures at risk of vehicle bomb attacks (FEMA, 2003).

Figure 5.

Safe area between the airport and parking areas (drawn by the authors based on FEMA 426)

When deciding on the building form, simple geometric forms without sharp corner lines should be preferred. While the effect of blast waves can be dampened in simple geometric forms, blast waves are more effective in forms with sharp lines. In addition, concave forms tend to reflect the shock waves generated by the explosive. Convex forms and circular forms should be preferred in building forms as they reduce the pressure of the shock wave (Figure 6). Parking floors, courtyards, protrusions, occupancy, and voids on the facade, buildings close to each other and with large surfaces are also severely damaged by the blast pressure. As a precaution, building forms that will absorb the blast pressure and cause the least damage should be preferred. Structures with a narrow surface area, convex, away from the street-road, and surrounded by trees are safer. Eaves, overhangs, recesses, niches, and protruding surfaces in buildings create pressure absorption points in the event of an explosion. Simpler and plainer forms and surfaces should be created in building design.

Figure 6.

Behavior of building forms in blasts (drawn by the authors based on FEMA 427)

In the design of terminal buildings, the low-rise horizontal settlement should be preferred instead of multi-story construction. In multi-story buildings, especially when the load-bearing structural system of the buildings is damaged, the possibility of the collapse of the building increases and causes great loss of life and property. Distributing the building units within the land as much as possible increases the safety of the structure against explosion risks.

The shock wave resulting from the explosion spreads globally and exerts high pressure on the surfaces of the objects closest to the explosion point. This pressure on the surface grows according to the intensity of the explosion and is reflected. This explosion pressure on the surface is continuously reflected; however, the pressure decreases after each reflection. Surfaces should be covered with pressure-absorbing elastic material (polyurethane foam, etc.) against explosions on the facade, and open chimneys should be arranged to absorb the explosion pressure. The materials used on the building facade should also be light, volatile, and resistant to fragmentation. The use of light materials such as wood and plastic instead of heavy materials such as stone, brick, and metal reduces the damage that may occur in explosions. Materials with a high probability of shrapnel should also be avoided. Durable materials with natural flexibility should be used.

The outer shell of the building is the most vulnerable part against explosion hazards. This is because the outer shell of the building is the first surface to be contacted by bombs, and since fragile materials such as glass are generally used, the risk of damage can be high. Therefore, the number of windows on the facade should be minimized and the ratio of openness to facade should be limited to a maximum of 15%. In addition, the transparency of the façade should be greatly reduced with the use of interior courtyards and atriums where light can be received. Thus, the glass surfaces on the facade, which have a high risk of damage in an explosion, will be reduced. The glass used in these buildings should be resistant to explosions and tempered and laminated glass should be used. Prestressed glasses do not shatter in the event of an explosion and cause less damage. In addition to the use of non-explosive glass, window films should also be used as a protective measure (The American Institute of Architects, 2001).

Building materials must have passed bomb resistance tests to take precautions against possible terrorist attacks and must have achieved successful results in “high security – no damage” protection classes. In airport buildings, “steel” is generally preferred as a building material due to its advantages. Therefore, the structures should be well insulated against fires that may occur in possible explosions. Since steel is a material that heats up quickly, load-bearing columns and floors should be insulated to withstand fire for at least 2 hours [18]. In addition, materials that have natural flexibility and can respond better to load reversals should be used in material selection. Building materials with a high probability of shrapnel formation should not be used. Ductile materials with plastic deformation should be used, especially on facades. Composite materials are the most preferred facade materials in this context.

Environmental conditions should also be taken into account for the orientation of buildings. The building façade should be oriented toward safe points. In uncontrolled areas, the building surface should be reduced and surface openings should be kept to a minimum (Figure 7). Narrow sides of buildings should be related to uncontrolled areas. Transparent surfaces should be avoided or minimized as much as possible in uncontrolled areas on building facades.

Figure 7.

Shaping facades according to risk areas at airports (drawn by the authors based on FEMA 427)

Explosion risks should be taken into consideration when placing structures on the land. Structures should be positioned in the center of the terrain as much as possible. Moving closer to one edge reduces the defense of that area against external threats. Areas of particular risk should not be close to the outer periphery of the terrain but should be located in a central and controllable location. In addition, a standoff distance should be maintained between the structure and a potential explosive threat. One of the most effective protection solutions is to increase the distance between the structure and the threat as much as possible. Although there is no ideal distance, measures should be taken depending on the importance of the structure and the intensity of use.

In the internal planning of the building, unsafe areas should be located as far away from the building as possible. Controlled and uncontrolled areas inside the building should be kept separate from each other. Horizontal and vertical zones should be created, and zones should not overlap each other. Buffer zones, reinforced walls, and floors should be left between them to separate.

Functionally unsafe areas such as the lobby, conveyor belt, and sales points should be kept away from the safe areas of the building. Waiting areas and emergency functions within the airport should be separated from busy circulation areas. Especially insecure areas such as parking areas should be away from the main walkways.

In the interior planning of buildings, the use of non-structural elements such as suspended ceilings, louvers, metal blinds, etc. that can cause heavy damage in possible explosions should be restricted. Placing heavy equipment such as air conditioners near the floors instead of the ceiling can reduce the damage in possible explosions. For interior facades, fabric curtains and plastic blinds should be used instead of metal blinds and shades. In addition, the joinery used on the facades should be explosion-proof and bullet-proof joinery. Interior lighting should be fixed to the ceiling, and work areas and offices should be located as far away from windows as possible [8].

Due to the dynamic effect created by the pressure during the explosion, the slabs and beams are translated upwards, which causes the slab to crumble and the structural elements (beams and columns) to articulate. For this reason, the thickness of the slab and the amount of reinforcement are important and thick slabs should be selected. Stub beams, hollow beams, and joistless slabs should be avoided as they are particularly vulnerable to earthquake and blast loads. In addition, prestressed slabs should not be preferred because they will show brittle behavior during an explosion [31].

Qualitative research method was used in the study. Qualitative research generally includes three types of data sets: data sets that focus on nature and the environment, data sets that emphasize the research process, and data sets that emphasize the way in which the event or phenomenon being researched is perceived [27]. In this study, the data set emphasizing nature and environment was used. Descriptive analysis method was used to analyze the data set. The data were classified according to the criteria determined according to the theoretical framework. Findings related to the classified data were summarized and summaries were interpreted. Cause-effect relationships between the findings were determined. At the same time, the differences between the findings are presented in a comparative table.

In determining the study sample, the first five airports with the highest capacity in our country were determined. The data are from the State Airports Authority (DHMI) for the year 2022. Istanbul Airport (2018), Antalya Airport (1998), Istanbul Sabiha Gökçen Airport (2001), Ankara Esenboğa Airport (1955) and Izmir Adnan Menderes Airport (1987) are the buildings analyzed. The buildings were analyzed through photographs, project drawings and maps obtained from Google maps application. The buildings were evaluated according to their current conditions.

Figure 8.

Work flow chart (drawn by the authors)

As a result of the examinations, possible problems of the buildings and their surroundings against terrorist attacks are identified and recommendations are developed. The buildings are evaluated within the scope of planning principles and architectural design criteria against terrorist attacks determined as a result of literature analysis. The building environment, vehicle and pedestrian circulation, infrastructure, landscape and urban design, access, and parking areas are evaluated within the scope of the planning of the buildings. Within the scope of the architectural design of the buildings, building form, floor area, facade, materials, orientation, location, and interior planning criteria are analyzed.

The city’s third airport after Sabiha Gökçen and Atatürk Airports, AGI was opened for use in 2018. The building, which has a capacity of 200 million passengers, has a T-plan form (Figure 9). A plan has been developed with the building area in the center and the aprons around it. Having sufficient access area between the building and open parking areas increases the security of the building against possible terrorist attacks. UV-filtered glasses and aluminum composite panels were used as facade materials in the building [19]. The materials used were preferred to be resistant to explosions. When the facade is evaluated in terms of opening ratio, the density of glass surfaces creates a disadvantage. In the interior planning of the building, the density of public use areas draws attention. While shopping streets increase the usage possibilities of the building, they make the interior spaces more risky areas against terrorist attacks. There is no clear distinction between controlled and uncontrolled areas. Intensive public uses negatively affects the holistic perception of the area. When the building land is evaluated, the airport is located in an area outside the urban settlement areas. This increases the safety of the building. However, the fact that the refueling units and technical service units are located on the outer perimeter of the building land puts the safety of these areas at risk. When the building area is evaluated in terms of environmental safety, wire mesh between concrete pillars is used on a concrete wall whose height varies from place to place. The perimeter wall poses a risk both visually and physically against possible attacks.

Figure 9.

İstanbul AGİ Airport (URL 1)

The building, which was first opened for use in 1955, was redesigned by the architect Ercan Çoban in 2006 and took its final form. The building has a construction area of 293,000 m² and is located 28 km from the city center. Access to the building is provided by taxi, private car, or public transportation. The building has a linear plan type that develops horizontally (Figure 10). In the two-story building, the upper floor serves the departing passengers, and the lower floor serves the arriving passengers. s. The west wing of the building is divided into domestic flights and the east wing is divided into international flights, and the middle part consists of transition halls [29]. The curvilinear form of the structure tends to reflect the shock waves generated by the explosives due to its concave structure. This creates a disadvantage for the building. In the interior planning of the building, a clear separation is provided between control points and service units, also stairs and elevators form a buffer between these spaces. Within the Esenboğa land, parking areas are designed in a separate area outside the airport. Glass and composite panels are used as materials on the facade of the building. It is not known whether the glass material is explosion-proof glass or not. But in general, it is positive that light materials are preferred on the facade. The density of the windows on the façade, that is, the opening ratio, is above the maximum 15% limit. This situation creates a handicap against possible explosion hazards. In addition, the eaves in the entrance areas can also pose a risk of explosions. On the other hand, positioning risky areas such as the oil office, flight control unit, and energy facility away from the airport building and in a central area of the land is a positive arrangement against terrorist attacks. The building site is located outside the city center, in an area where the density of construction is low. There is a concrete wall approximately 1 meter high on the outermost part of the building site. Above this wall, there is a wire fence approximately 2 meters high and barbed wire above it. The lack of high walls against the effects of explosions makes it easier to see the building site from the surrounding area and to access the area in case of a possible attack.

Figure 10.

Ankara Esenboğa Airport (Şahin ve Aslanöz, 2022)

Opened in 1998, the building was expanded with new additions in 2005. Thus, the passenger capacity increased from 5 million to 8 million. The building has two floors, a horizontal layout, and an inverted T-shape in plan (Figure 11). Arriving and departing passengers access the building from the same level (URL 2). The concave form of the building has a tendency to reflect blast waves, which creates a disadvantage for the building. In the interior planning of the building, a clear distinction was made between controlled and uncontrolled areas. Stairs and elevators form a buffer zone between the spaces. Glass and aluminum composite panels were used as materials on the facades of the building. It is not known whether the glass material is explosion-proof glass or not. But in general, it is positive that light materials are preferred on the facade. The openness ratio of the facade meets the necessary conditions (maximum 15%). The lack of a certain distance between the entrance of the building and the open parking areas poses a risk of explosions. The building site is located in an area with intense urban use. Therefore, it is located in a risky area against terrorist attacks. Areas such as refueling areas, flight control, and energy facilities are located far away from the airport building and in a central area of the land. On the other hand, there are approximately 50 cm of concrete walls outside the building site. On top of these walls, perimeter security is provided with wire fences between concrete pillars with a height of approximately 2 meters. The existing perimeter wall poses a risk against possible terrorist attacks. Both the perceptibility of the building land from the environment is high and the access to the area is facilitated through the wire fences.

Figure 11.

Antalya Airport (URL 2)

The building, which was first opened for use in 1987, was renovated in 2006. Located 14 km from the city center, the airport has a construction area of 310,000 m2. It can serve 20 million passengers. In the project obtained through the competition, the project of architect Yakup Hazan was selected and implemented (URL 3). In the interior planning of the building, all visual barriers between the land side and the air side were removed and complete transparency was achieved between the two parts (Figure 12). Galleries and hanging gardens are placed between the land and air sides. This design approach creates spaces that pose a risk against terrorist attacks. The building has a linear form. The concave surfaces in the building form tend to reflect the shock waves that explosions may generate. In the entrance area of the two-story building, bridges provide access to the multi-story car park areas. The design diversity of the building has the potential to create risks against terrorist attacks. Glass and aluminum composite panels was used as materials on the exterior of the building. It is not known whether the glass material is explosion resistant or not. As in other buildings, the use of lightweight materials on the facade of this building is a positive feature. When the façade is evaluated in terms of opening ratio, it is seen that glass surfaces are dominant in the building. When the land of the building is examined; it is seen that the area where urbanization has developed towards this area has a partial density. Units such as refueling areas, flight control, and energy facilities are located far away from the airport building but close to the outer perimeters of the building site. Landscaping around this area creates potential areas for surveillance and concealment. The sloping nature of the land also increases the danger for risky areas. When the perimeter walls of the building site are examined, it is seen that border security is provided with wire fences between concrete pillars. The existing perimeter wall provides insufficient protection both visually and physically against possible terrorist attacks. Perennial trees on the building site also increase the risk potential against possible terrorist attacks.

Figure 12.

İzmir Adnan Menderes Airport (URL 3)

The airport, which has a construction area of 320,000 square meters, was first opened for use in 2001 and was renovated in 2009. The structure, which has a passenger capacity of 25 million, was designed by Doğan Tekeli and Sami Sisa and was carried out under the consultancy of ARUP (URL 4). The building has a plan form close to a square (Figure 13). The absence of concave surfaces increases the strength of the structure against shock waves created by explosions. Glass, fiber concrete panels, and wood-like aluminum sunshades are used as materials on the exterior of the building. Information on the resistance of the glass and other materials against explosions could not be obtained. In terms of the facade openness ratio, the intensive use of glass poses a risk in terms of possible terrorist attacks. In the interior planning of the building, it is understood that clear distinctions between controlled and uncontrolled areas are not as legible as in other buildings. The compact form of the building causes the spaces to be intertwined. When the building land is evaluated, the open car park area in front of the building does not have sufficient distance. The building site is located among the areas where urban use is intense. Therefore, the surrounding of the building is in a risky position against possible terrorist attacks. Especially the airport building is located on the periphery of the land and in an area with dense urban settlement. When the perimeter walls of the building site are examined, there are concrete walls with a height of approximately 2 meters. Above these walls are wire mesh walls of the same height and barbed wires above them. The perimeter wall prevents access to the building site both visually and physically.

Figure 13.

Sabiha Gökçen Airport (URL 4)