Structure of the new Zagreb airport passenger terminal

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Feb 18, 2014 - Structure of the new Zagreb airport passenger terminal. Abstract. The design of the new airport terminal by Branko Kincl, Velimir Neidhardt and ...
Structure of the new Zagreb airport passenger terminal Jure Radić Anđelko Vlašić

Prof. Jure Radić University of Zagreb Faculty of Civil Engineering Department of Structural Engineering dr. Anđelko Vlašić University of Zagreb Faculty of Civil Engineering Department of Structural Engineering

Scientific Symposium FUTURE TRENDS IN CIVIL ENGINEERING Zagreb, Croatia, 17-18 February 2014

Future Trends in Civil Engineering

Structure of the new Zagreb airport passenger terminal Abstract The design of the new airport terminal by Branko Kincl,Velimir Neidhardt and Jure Radić was awarded a first prize following an international competition organised by the City of Zagreb in 2008. The airport design comprises an multidimensional approach integrating construction, form, urbanism, ecology and functionality.An important part of the terminal’s architectural design is the fluid form of its roof and the tubular passenger piers sprouting out on each side. This recognisable form will define the new terminal’s identity and its surrounding area. In achieving this form, a new innovative solution was used for the roof structure, comprising a triangular steel grid space truss for the main building and truss arch vault for the piers.The concrete construction of the interior comprises three dilatations of mixed precast TT beam floor slabs, reinforced concrete beams and monolithic floor slabs. Horizontal forces are supported by 4 concrete cores and shear walls.With a gross building area of 65.800 m2 and a starting capacity for 5 million passengers per year, Zagreb airport is to become a major air traffic regional centre. Key words: airport, Zagreb city, form, architecture, steel space truss

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Konstrukcija novog zračnog putničkog terminala u Zagrebu Sažetak Projekt novog terminala zagrebačkog aerodroma autora, čiji su autori Branko Kincl, Velimir Neidhardt i Jure Radić, osvojio je prvu nagradu na međunarodnom natječaju Grada Zagreba 2008. godine. Ovaj projekt aerodroma rezultat je integralnog multidisciplinarnog pristupa, ujedinjujući elemente konstrukcije, forme, urbanizma, ekologije i funkcionalnosti. Važan dio arhitektonskog oblikovanja je fluidna forma njegovog krova s cjevastim putničkim izdancima sa svake strane glavne zgrade. Takav prepoznatljivi oblik definirat će identitet novog terminala i okolnog područja. Kako bi se postiglo ovakvo oblikovanje, primjenjuju se nova i inventivna rješenja prostorne rešetke krovišta glavne zgrade i rešetkastog svoda izdanaka. Betonska konstrukcija unutrašnjosti izvedena je u tri dilatacije i obuhvaća miješane sustave predgotovljenih TT stropnih sustava, armiranobetonskih greda i monolitnih stropnih ploča. Horizontalna djelovanja preuzimaju četiri betonske jezgre i posmični zidovi. Ukupne površine 65.800 m2 i početnog kapaciteta od 5 milijuna putnika godišnje, zagrebački aerodrom postati će vodeće regionalno središte zračnog prometa. Ključne riječi: zračna luka, grad Zagreb, oblikovanje, arhitektura, čelična prostorna rešetka

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1. Project history 1.1. Existing Zagreb airport Zagreb Airport was first built during World War II to serve as a military airport and it retained that function until 1959 when it was opened for civil traffic. In the sixties and seventies, it grew at the fastest rate ever with more than a 70% increase in traffic each year. Passenger traffic is dominated mostly by international flights, of which most passengers are local passengers (80%), followed by transfer passengers (20%). Since its beginning, Zagreb airport went through several reconstructions. In 1966, a new 5.000 m2 terminal extension was built, and in 1974 and 1984, additional extensions were added to increase the total airport area to about 15.000 m2, which remains unchanged to this day. In addition to the passenger terminal extensions, in 1984 a new cargo terminal with an area of 2.200 m² was also built, and the runway was reconstructed and prolonged to 3.250 m, along with the erection of some other supporting facilities. When Croatia became independent in 1990, Zagreb Airport consequently became national and capital city airport. The existing passenger terminal capacity of about 1.5 million passengers per year was already reached in 2005, while in 2007 the recorded peaked at 1.992 million passengers. Without doubt, the present situation does not permit further optimum development of traffic capacities. Therefore, the imperative is to take action in order to prevent stagnation in traffic capacities and to raise the level of the airport’s technical capability and services. Due to shortcomings of the existing location, it has been decided that the New Passenger Terminal must be built on a nearby location.The new location allows for a longer runaway and better layout of the building, so that the terminal building and other facilities can comply with all the new safety regulations with respect to minimal distances and infrastructure needs.

1.2. Evaluations of the new terminal After a decision was made in favour of a new terminal building, an international competition was announced. A total of 17 respectable authors responded to the call. An international panel of judges awarded first prize to the project by Branko Kincl, Velimir Neidhardt and Jure Radić (Figure 1). Second prize was awarded to the project by Shigeru Ban and Taro Okabe (Figure 2a), and the third prize when to Norman Foster for his project (Figure 2b). Of the other entries, two were awarded fourth and fifth prize, and four others were bought out.

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Figure 1. The 2008 Zagreb airport competition: first prize won by Branko Kincl, Velimir Neidhardt and Jure Radić

Figure 2. The 2008 Zagreb airport competition: a) second prize won by Shigeru Ban and Taro Okabe; b) third prize won by Norman Foster

In 2011, a concessionary agreement was signed with the French company Bouygues for the erection of the terminal according to the modified winning design, provided that the architectural concept of the authors was retained. Both the authors and the concessioner agreed to some changes in order to optimise the cost of the New Terminal, but at no expense to the visual identity defined in the competition design. Table 1 shows technical and economic information about both designs – the original winning design and the newly accepted cost-effective main design. Table shows information about the terminal that will be built in Phase 1. Phase 2 is to be built in the future when traffic increases, as an extension of the pier lengths on both sides to allow for more aircraft docking gateways. The agreed concession period is 30 years. At the end of the concession period, the overall extension built in the 2nd phase, which is not

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part of this main design project, shall serve 8 million passengers per year. In 2013, the main design was finished and the building permit issued. Major construction works will commence in spring 2014. Table 1. Design information and comparison (for Phase 1) Comparison Design information Passengers / year Layout area (Main building) Pier lengths Gross construction area Number of Levels Concrete construction Steel roof construction Estimated cost

Winning design

Cost effective main Design

5 million (phase 1); up to 8 million (phase 2) 155 x 165 m 129,6 x 136,8 m 353 m (left), 93 m (left) 50 m (right) 151 m (right) 73.320 m2 Basement, 0, 1-4 Monolithic Three-directional Plane Truss 280 – 300 mil €

65.883 m2 0, 1-3 Precast + Monolithic Triangular grid Space Truss 236 mil €

2. Architectural design, utilization and urbanism 2.1. Airport surroundings and interaction Zagreb Airport is to become the prime urban development factor, by directing its penetration force towards main Zagreb metropolitan environment, and more importantly, towards the city of Velika Gorica, which is located in its vicinity, and by facilitating merger of the two. Through its overall attraction and the inter-functioning of the new airport, all surrounding areas will acquire features conforming to the highest urban standards and will gain national importance, potentially becoming the key performing factors for the urban efficiency of metropolitan Zagreb. The landside surroundings of the terminal building is divided on two parts, the east in-bounding side and the west out-bounding side, both of which will have stands and vehicle parking facilities (Figure 3). The spatial organisation leads to the dominance of a pedestrian area in the middle of the landside complex, which designed shape similar to that of a central esplanade plateau. It is oriented along its axis towards the entrance facade of the terminal building. This pedestrian oasis with a variety of urban amenities connects in functional terms the front of the terminal with both eastern and western sides of the large parking area for vehicles, and finally reaches south towards the future development of Airport City through a future underground passage. Green landscaping provides an essence

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of nature blending in close to the centre of the new airport terminal building. This green concept is then further reiterated throughout the project, and especially in the new airport terminal, using greenery modular units as interior architectural elements, together with the outdoor extensions.The interior and especially the departure gallery, are interventions that will provide a natural effect on the microclimate. Transparent facades and discrete structural elements join the interior and exterior into one universal, multifunctional and diverse area.

Figure 3. New Zagreb Airport layout and surroundings

2.2. Architectural form The dominant architectural form of the terminal fulfils both its functionality and its desired landmark purpose. Main structural form is presented by a wavy roof, which levitates in a form of wind carried banner over the main building. This roof calmly transcends into an airside façade, which then fluidly continues as two pier structures for aircraft docking purposes. The whole terminal resembles an extended flagpole displaying the combination of the long linear inductive pole structure, softly wrapped in a dynamic envelope, which unwraps itself to levitate above the terminal hall generating the free dynamics of the flying roof – an iconic expression of the landscape. Such spatial harmony is apparent inside the terminal from a series of different function generated aesthetic attractions. The levitating roof envelope provides a maximum exposure of the hall interior and the widest possible panoramic orientation towards both Zagreb and its mountain, and the dynamic development on the approach side of the new airport terminal.

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2.3. Utilization flexibility The basic design principles deal with the overall rationality - with an unambiguous distribution of functions and with clear, spatial focal points - all designed to fulfil a perfect passenger orientated pattern.The design method focuses on the flexibility of the conceptual scheme. It provides adaptability to developing or changeable needs and in the end, to the optimal functional performance of the terminal.This consequently leads to possibilities of rational usage of spaces within any new and future air traffic scenarios.The architectural form of the terminal building rests on two discrete geometrical systems: a linear dynamic pier structure and a covered compact rational floor plan of the terminal hall.The large size of the hall is modular in space, totally flexible and ready to support any functional change, such as a switch from international to domestic capacity flows, from non-Schengen to Schengen regimes, and vice versa.The pier design provides flexibility, which is necessary for sustaining the expected increase of air traffic in the future.This is accomplished by the linear prolongation of piers or by the possible addition of air bridges to the south-west pier; all this in order to allow a double-sided pier function.

3. Construction 3.1. General The total layout dimensions of the main building are 136.8 m across to the pier and 129.6 m along the pier direction (Figure 4a). The total layout of the roof structure (roof shadow) is 151.2 m in width by 152.3 m in length.The highest roof point is at an elevation of 34 m. The piers are 82.8 m (left) and 39.6 m (right) long. The width of the piers is 14.4 m. The main building is a concrete structure that comprises the ground floor (GF) + 3 floors: ground floor 0.00 m, first floor +5.40 m, second floor +10.20 m and third floor 15.00 m.The roof structure is a steel space truss at an elevation of 20 m, and rises up to 34 m.The left and right piers are concrete structures comprising GF+2 floors: ground floor 0.00 m, first floor +5.40 m, and second floor +10.20 m (Figure 2b). The pier roof is an arch vault comprising a steel space truss construction (Figure 2c).

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Figure 4. Terminal layout and cross sections: a) layout plan; b) middle section of the main building; c) pier section

3.2. Concrete construction The terminal foundations comprise strip foundations b/h = (2.0, 2.4, 2.8, 3.0, 3.4, 4.0, 5.0) m / 1.2 m, isolated footings 4.0/4.0/1.20 m to 6.0/6.0/1.2 m and a local raft h=1.2 m under the thick core-walls. Foundations are horizontally connected with ground beams b/h = 40/40, 50/50 and 40/100 cm. Pier foundations comprise strip foundations b/h = 1.2 / 1.2 m with local rafts. Horizontal floor bearing structure of the main building mostly comprises precast elements (TT prestressed floor systems) except for areas next to the core walls and the front of the building (anchorage places for steel truss facade) which comprise monolithic flat slabs.The pier concrete floor bearing structure

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comprises monolithic slabs of 30-40 cm thickness. Monolithic and precast parts of the slabs can be seen in Table 2, whereas the colour scheme is shown in Figure 5. Table 2. Types of concrete construction for the main terminal building (colour scheme as shown in Figure 5)

Figure 5. Representation of the concrete structure for the main terminal building (upper) and pier (lower)

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The main building’s concrete floor supporting grid structure (defined by columns and beams) is 7.2 x 14.4 m, and 7.2 m x 7.2 m and located next to the core walls. Parts of the structure extend through two floors (overall height of 10.2 m) with the support grid 14.4 m x 14.4 m. The pier’s concrete floor supporting grid structure is 7.2 m x 7.2 m. Horizontal stability of the main building is ensured by utilising a hybrid system consisting of four concrete cores (red areas in Figure 5) and shear walls (40 cm thick). Horizontal stability of the piers is ensured by combined system of walls and frames running in both directions.The column layout grid is 7.2/7.2 m, 7.2/14.4 m and 14.4/14.4 m. Its cross-section is rectangular 60/60 cm and circular Ø70 cm. Concrete pedestals for the branching steel supports of the roof steel structure are 1.5 m in diameter.

3.3. Steel truss roof construction The roof structure of the main building is a steel space truss structure. The roof is a wavy shape running in both directions, and merges with the facade that faces the runway, and which has a tubular shape with variable elevation (Figure 6). The piers roofs on both sides of the main building are also a tubular section with variable height. Between the space trusses of the main building’s front facade and the piers there is a dilatation separating the space trusses (and the concrete floors).

Figure 6. Terminal roof exhibiting a wavy form

The basic disposition view of the main building comprises triangular grid shapes with each triangle having a base of 3.6 m and a height of 3.6 m. These triangles define the axes of the chord truss members. The grid of the bottom chord is displaced 1.8 m longitudinally and 1.2 m transversely with respect to the top chord (Figure 8).The top and bottom chord are joined together with diagonal members. The basic layout plan

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of the pier space truss is ≈3.6 x 2.4 m. Grid shapes are also triangular. The top chord axes are offset with respect to bottom chord axes, in a manner similar to the main building area. The roof structure layout of piers is harmonized with the layout of the main building roof structure. The axial height of the space structure is 3.0 m in the main building area and 1.4 m in the pier area. The steel space truss (Figure 7.) is made of tubular circular members with connecting elements and spherical nodes with threaded holes. A conical element, with a sleevefastened bolt, is welded at the end of each round pipe member. Members are assembled by connecting them with bolts onto spherical nodes. The tensile force is transferred via nodes, bolts, cones and pipes, while the compressive force is transferred via nodes, sleeves, cones and pipes.Truss pipe members vary from Ø76.1x2.9 mm to Ø219.1x20 mm depending on the position in the truss, and the compression or tension forces. Circular hollow sections are made of S355J0H and S235JRH. Rolled sections, sheeting elements and nodal cones are made of S355J0 and S235J0. The main building roof structure is supported by 18 columns, with a span layout of 43.2 x 28.8 m. Columns are shaped as branched inverted cones and each of them comprises six members, with the exception of the edge columns (outside of the facade) which comprise five members. Column members are made of round pipe sections Ø406x16 mm. The columns are supported by reinforced-concrete pedestals, and by the bottom reinforced-concrete structure at levels +10.20 m and +15.00 m. Near the building-pier connection, instead of columns the roof is supported by truss walls which continue into the pier structure (Figure 10). The roof structure comprising piers is supported on both sides by the bottom reinforced-concrete structure at levels +10.20 m (inner chord) and +5.40 m (outer chord).The structure’s roofing is made of trapezoidal steel sheeting with thermal insulation, and possesses a minimum bearing capacity of qk=2 kN/m2 (for imposed loads) and a span of L ≤ 4 m. The assembly method for the space truss will be decided after completing the design and selecting the contracting company, meaning that the assembly can be adjusted in accordance with the contractor’s capability and available equipment.

Figure 7. Triangular roof construction incorporating the steel space truss

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Figure 8. Main building space truss plan-view (left) and pier space truss section (right) (blue: top chord, magenta: bottom chord, orange: diagonals)

Steel bridge structures that spread from the main building and piers toward the runway incorporate steel truss systems, which rest on the the main building and pier structures, on the reinforced-concrete ’towers’, and on columns. (Figure 9.) Where the main building and piers connect, chords of bridges are supported by a reinforced-concrete structure at the levels +10.20 m (top ‘tunnel’ of the bridge) and +5.40 m (bottom ‘tunnel’ of the bridge). The supports on the main building and piers are movable in the direction along the bridge, and fixed in the transverse direction. Where reinforced-concrete ‘towers’ connect, bridge chords are supported by hinges, horizontally immovable in both directions. Each bridge is also supported by two columns, with supporting spans of 14.5 m and 16 m, in a direction running from the reinforced-concrete ‘tower’ towards the runway.At the bottom, columns are fixed into reinforced concrete footings. Flanges, verticals and top cross-beams of the bridges are steel sections. The bottom crossbeams are rolled IPE sections and above the columns H sections are welded. Bridge footways are made of corrugated steel sheeting strengthened longitudinally with rolled L sections.The total axial length of each bridge, between supports at the main building and the facade at the end of the bridge, amounts to 49.5 m.

Figure 9. Bridge for entering the pier and running towards the docked planes

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Figure 10. Steel truss arch connection between the building and pier

4. Wind tunnel testing In order to determine the wind loads for the structural design, pressure measurements were performed in a wind tunnel with a 1:300 scale model (Figure 11) of the main building with piers. The wind loads for the structural design were calculated based on a basic wind speed at the site of vb,0 = 25 m/s. In accordance with the rules given in Eurocode EN 1991-1-4, the corresponding design gust pressure for a maximum roof height (H=34 m) was calculated to be qp=1.25 kN/m2. The wind loads derived from wind tunnel testing were based on this design gust pressure. The most important vibration modes have the lowest eigenfrequencies higher than 1.6 Hz and comprise horizontal deflections. Therefore, there was no need to consider significant dynamic load augmentations caused by gust-induced vibrations. The measured effective static net wind load patterns for different wind directions ranged from 0.25 kN/m2 to 0.75 kN/m2.The patterns were given in the top views and elevations of the roof and facades. The measurements were performed in wind direction increments of 10°. In order to reduce the amount of load for cases that required consideration in the structural design, the wind load patterns were given for wind direction sectors in increments of 30°. The measured wind loads are exterior wind loads with the exception of the overhanging roof parts, where net wind loads are measured (difference between topside and underside wind loads was considered). The wind loads act always normal to the considered surface. Internal pressures were not measured - the recommended value _ was taken from Eurocode as wi = +0.20 kN/m2 and wi = 0.30 kN/m2. 121

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Figure 11. Wind tunnel testing on a 1:300 scale model

In addition to wind loads resulting from wind pressure acting perpendicular to the surfaces, wind induced friction loads were also considered. Due to the wavy structure of the terminal roof, horizontally acting wind forces caused by the pressure differences between the windward and leeward inclined roof surfaces were taken into account. These pressure differences were measured in the wind tunnel and recalculated into corresponding friction forces and produced the same horizontal wind force while assuming a smooth roof surface (no considerable ribs). The friction coefficients vary from cfr = 0.05 for the main building (wavy inner part) to cfr = 0.02 for the pier roof. The friction forces act in the wind direction and are used along the whole roof surface for all wind directions.

References [1] Main design of the New Passenger Terminal Airport Zagreb: Book 1-1 (Architectural design), Book 2-1 (Steel construction design), Book 2-2 (Reinforced concrete construction design), 2013 [2] Zagreb International Airport New Passenger Terminal: Wind load study (wind tunnel tests), Interim report: Structural wind loads, Project engineer A. Bitzer, 2014

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