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Jewel Changi Airport, Singapore-Complex Structural System and Joints

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Dr. N. Subramanian
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PostPosted: Fri Sep 09, 2022 8:10 pm    Post subject: Jewel Changi Airport, Singapore-Complex Structural System and Joints Reply with quote

Jewel Changi Airport, Singapore-Complex Structural System and Joints
Fulfilling its mission as a connector between the existing terminals, Jewel combines two environments—an intense marketplace and a paradise garden—to create a new community-centric typology as the heart, and soul, of Changi Airport. Jewel re-imagines the center of an airport as a major public realm attraction. Jewel offers a range of facilities for landside airport operations, indoor gardens, leisure attractions, retail offerings and hotel facilities, all under one roof. A distinctive dome-shaped façade made of glass and steel adds to Changi Airport's appeal as one of the world's leading air hubs.

Jewel Changi Airport, a nature-themed entertainment and retail complex on the landside at Changi Airport, Singapore, is their newest development, opening this year. The unusual building, conceived by the firm Safdie Architects, extends the airport’s principal function as a transit hub to enfold an interactive civic plaza and marketplace, combining landside airport operations with expansive indoor gardens and waterfall, leisure facilities, retail, restaurants, a hotel, and other spaces for community activities. The combined intensive marketplace and paradise garden create a new civic center – “the heart and soul” of Changi Airport, as the airport leaders call it – and a new paradigm for community-centered airport design.

Toroidal form of Grid Shell

A toroidal form was chosen by the design team for the 1.4 million-square-foot glass-enclosed building. Buro Happold and Safdie Architects conceived a “grid shell” concept for Jewel’s roof and façade system that sits at the edge of level five of the ring-shaped steel and concrete base building. This perimeter support defined a span of more than 650 feet (200 meters) at its widest point. With only intermittent supports in the garden, this resulted in a nearly column-free interior. The geometry of the roof also accommodated an indoor rain-fed waterfall at its center, activated by pumped water during dry weather.

Plan and cross-section of the airport

Idea of The Steel and Glass Shell
The initial “grid shell” concept was a single layer structural system that would maximize light and transparency within the space. This steel and glass shell is made of prismatic steel elements intersecting at solid steel nodes.

The offset toroidal roof shape of the Jewel is the product of an elaborate architectural program that incorporated a forest valley, entrances to adjoining terminals at the gateway gardens, an indoor waterfall, and an oculus. The roof asymmetry and offset of the oculus were created to allow for the passage of the airport train through the project. The steel grid shell meets the base building at its 5th level where a steel ring beam circles the building, arching up at each of the gateway gardens. This ring beam allows for a uniform transition of the thrust and vertical forces from the springing of the grid shell into the base building.

Discovery slides at canopy. Courtesy of Jewel Changi Airport
Traditional steel grid shells generally strive for thinness by resisting compression and tension forces only in the plane of the shell (with only modest bending capacity). This can be seen, for example, in the British Museum’s Great Court Roof.

The Jewel at Changi Airport goes beyond the traditional shell by accommodating not only the membrane forces in the shell but also the out-of-plane forces that bend the shell. To resist this combination of forces, the design team examined the forces in the shell and introduced deeper elements at locations subjected to bending, making the shell expressive of the forces flowing through the different zones.

For example, the inner zone of the toroid moving from the internal support columns toward the oculus functions as a tension cone, with the waterfall and oculus suspended and pulling down on the structure. These membrane surface tensions act in two directions: hoop and meridional. With no risk of buckling and minimal bending, these steel elements are the shallowest in the project with only 200 mm depths.

An oculus, at the heart of its glass roof, showers water through a primary multistory garden, five stories through to the forest-valley garden at ground level.

In contrast, the outer section of the shell – between the perimeter support and moving toward the internal supports – has primarily compression hoop and meridional membrane forces with a force distribution similar to a dome. This area was designed for buckling and is made up of members 300mm deep.

The most significant complexity is found in the zone around the intermediate supports. Here, the tension and compression fields that are pulling and pushing towards the center converge and are resisted by a compression ring zone. This is analogous to the spokes of a bicycle pulling inward and being resisted by the compression ring of the wheel rim. Also, the intermediate column supports of the shell in this ring create bending out of plane. Bending demands are highest here with very deep elements of up to 750mm  in the final constructed system.

In the end, this grid shell geometry with various shell depths creates a form that expresses the structural force patterns within the grid shell roof.

Using SAP2000 software, the engineering team experimented with varying the depths in the shell, rerunning analyses, and adding material where needed. These analyses included elastic as well as inelastic behavior. Buckling was addressed in an analysis that employed the provisions of the Eurocodes with Singapore amendments and was reviewed by the Singapore Building Authority as well as the Singapore EOR RSP-S.

Discretizing the Design
After resolving the overall form, the shape was discretized using triangular panels made of steel and glass. A series of horizontal hoop elements along the surface is overlaid by continuous bias or vertical elements, or both, to discretize the form as triangles. Larger triangles required larger steel elements, impacting the aesthetics. The project leaders traveled to visit grid shells in Europe and the United States to understand scale and to review similar triangulated forms in person and best understand how proportions and scale would affect the aesthetics and user experience. Another variable was the impact on procurement and manufacturing; the project leaders hoped for numerous competitive bids to reduce installed cost, resulting in the engineers recommending an upper-bound dimension on the triangle sizes.

As the continuous bias lines arch from the perimeter to the center, the triangles become progressively smaller, creating congestion and practical construction issues at the element intersections. The design team pruned the bias lines – removing elements as they got closer to the center, giving rise to different transitional geometries.

Sketch of distribution of the forces

Precision Steel Node
The project team defined and developed a precision steel node that was machine fabricated to connect sections of the diagrid roof system. Using mathematical analysis, the engineers developed standardized families of components to facilitate efficient fabrication and detailing, depending on the tolerances that might be possible to achieve in fabrication and detailing. In the end, based on the specialty contractor capability post-bid, unique nodes were found to be competitive and about 5,000 nodes and 14,000 steel elements, all unique, were produced to construct the toroidal shell assembly.

Details at the Node point and the Special Node
The German company MERO employed a 3-D computer-numeric-controlled (CNC) milling machine to create nodes with stubs at the exact angles required to meet these connecting steel elements. On-site, one of five of the node-to-steel-piece connections are welded, and about 80% were pre-drilled with bolt holes. In China, the glass was fabricated, laminated, and assembled into panels, all cut from standard rectangular sheets based on a packing study by the engineers to optimize efficiency and reduce waste.

The glazing has been hardened at vehicle drop-off points for improved security and blast resilience. Glass fritting, which adds texture and opacity to the glass surfaces, helps reduce and finetune daylight transmission to allow optimal ultraviolet (UV) penetration for the garden areas while also helping to control solar heat gain for occupant comfort.

Construction Sequence
In any shell structure the construction Sequence is very important for the safety of the structure. Based on the design team’s analysis, Buro Happold suggested a construction sequence for the grid shell that began with the installation of the perimeter ring beam and support columns on the base building. This was to be followed by the building of the compression ring zone of the shell over the columns and then the sequential installation of pie-shaped wedges spanning between perimeter ring beam and compression ring. Last, the central oculus would be completed. The contractors Woh-Hup along with Yong-Nam and MERO, however, had a better idea. Based on their extensive experience and evaluation of the task ahead, they decided to begin with the oculus and then to assemble pie-shaped sections from oculus to perimeter ring beam using a moveable crash deck, which helped accommodate sequencing required for the construction of the base building.

The project received a Platinum rating from Singapore’s 'GreenMark' program for environmentally sustainable buildings. Its integrated system of glazing, static and dynamic shading, and an innovative and efficient displacement ventilation system achieved the required high level of comfort for a diversity of activities, as well as the ability to sustain the vast array of plant life.
Correa, C. and Craig Schwitter, C. "Engineering an Icon-Complex Structural Systems for the Jewel Changi Airport", STRUCTURE Magazine, Oct. 2019
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PostPosted: Mon Sep 12, 2022 11:06 am    Post subject: Jewel Changi Airport, Singapore-Complex Structural System and Joints Reply with quote

Dear Sir,

Very interesting. Looks like some force balancing concept in shell, ring elements.


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