Igor Siotor, Thomas Hermeking, and Christian Schloegl of PFEIFER Structures recently produced a case study on the cable canopies at the Dubai Expo 2020 for the IASS 2020/2021 Conference. Below is the complete case study, from the initial design to engineering, fabrication, and installation.
It is a common belief that the imagination of artists precedes the advancement of the technologies of the human race. This specifically relates to the progress in technology invented by man. For example, the movies showed a man landing on the Moon over 50 years before it was technologically feasible. Futuristic authors described the fabrication lines serviced by robots, programmed by man, long before it was actually implemented in the industry. It is always an interesting (and never-ending) discussion as to what degree the visionary creations by artists inspired the work of the scientists, engineers, and builders who converted these creations into real machines, structures, and buildings, which improve our technological capabilities and enrich our environment. In our field of lightweight structures, there are many examples that support the theory above. Let us remind you of the names of Joseph Paxton, Vladimir Shukhov, Frei Otto, and many others who were inspired by the idea of how to create “more with less.” The development of building technology allowed these men to realize this idea.
This paper will present another example of man’s engineering achievement; a structure inspired by the visionary design of one of the modern times leading architects, Hopkins Architects. This example is the Thematic District Public Shading project for 2020 Expo in Dubai, UAE. 53 inverted cone structures connect the main 3 clusters of pavilions at the Expo site and, in terms of function, provide protection from the sun and illumination for the public areas leading to central Al Wasl Plaza. The concept was to create a man-made “forest of light,” where the natural sunlight would be diffused through perforated aluminum panels during a day and produce a similar radiance effect via a lighting system attached to the “trees” at night. The engineering challenge was that these trees had absolutely no branches, so the supporting structure had to be reduced to an absolute minimum and remain “almost invisible” at first glance. Lightweight construction technology and precise coordination of design 3D models made these design requirements possible. This paper will present the process of how the engineered structure, inspired by art, was successfully achieved in real form.
The main goal and long-standing tradition is that the World Expo and their predecessors will become the showcase displaying the industrial, scientific and cultural achievements of countries participating in the fair. As such, these events are also a canvas for the countries’ iconic architectural and engineering accomplishments. Many of the structures have become the turning point in the architectural styles, engineering approach and construction technology. This tradition dates back to very first World Fairs, which have seen some of the signature architectural creations realized by ambitious builders who pushed the development of the construction industry. Some of the examples include The Crystal Palace, designed by Joseph Paxton (a gardener by profession) for The Great Exhibition in London in 1851. This design arguably paved way for the development of steel and glass industry in construction globally. Another engineering structure built specifically for a World Fair generated so much excitement and controversy that the local noble people petitioned for it to be demolished before it was completed. This structure became the most recognizable symbol of the city and the most visited tourist attraction in the world, as of 2015: The Eiffel Tower in Paris. The Eiffel Tower was first designed by Maurice Koechlin and was built by Gustave Eiffel for 1889 World Fair.
Fig 1: Crystal Palace, London 1851
Fig 2: Eiffel Tower, Paris, 1889
Fig 3: USA Pavilion Biosphere, Montreal 1967
Another example that is closer to current times and to the technology of our common interest is geodesic dome designed by Buckminster Fuller for the USA pavilion at EXPO 1967 in Montreal, Canada. This structure remains to date one of the main attractions of Montreal, long after the closing of the event. It was a culmination of Fuller’s early work on geodesic domes in collaboration with the engineering firms Geodesics, Inc. and Synergetics, Inc., who obtained the design licenses and who have built the first domes developed by Fuller.
The close collaboration between the creative architect, inspired engineer, and a responsive builder is the subject of this paper and presentation.
2. Thematic District Public Shading Project
2.1. Project Schematic Design
The Thematic Districts form an integral part of the Expo site, comprising of 86 permanent buildings spread over three separate areas, which house 136 participating countries. Each of the three areas is given a unique and memorable character, portrayed through different geometry, landscaping and colors. Each district is designed to reflect the three main themes of the Expo 2020 Dubai: Mobility, Opportunity and Sustainability. The districts are to provide a mixture of exhibition spaces for participating countries, as well as hosting a variety of food, beverage and amenity offerings to cater for all ages, interests and tastes. The design is characterized by a series of tree-lined, self-shaded streets with a variety of different sized and themed courtyard spaces. A central corridor runs through each district, creating special shaded places with water features, event stages, activity areas and rest places, clustered underneath a series of dramatic and elegant tree shaped shade structures. The corridor will be a showcase of opportunity for participants, a hub for innovation as well as a canvas to display new ideas. The project, designed by Hopkins Architects and engineered by Webb Yates, both in London, UK, aimed to achieve LEED ‘Gold’ certification, and will be repurposed in legacy mode to create a campus of buildings, each interconnected via bridge links that overlook landscaped spaces. A total of 53 shading structures are located in the three districts of Expo 2020 area in random-like arrangements. Sometimes there was a stand-alone feature; sometimes the tree-like structures were grouped in a cluster of two or more, connected with infill panels at canopy level. The sunshade structures are equipped with spotlights and a LED system for illumination at night.
Fig 4: Public shading as designed by Hopkins Architects
2.2. Project Implementation
While the design intent was clearly identified by the design team, the execution of project on site was a sole responsibility of a specialty contractor selected in a competitive, open tender process. The contractor who satisfied all pre-qualification requirements and who has demonstrated to be best prepared to perform the works was the PFEIFER Structures division from Memmingen, Germany. As part of the contractual scope of work, PFEIFER was fully responsible for the final engineering, fabrication and installation of structural steel, cable systems, aluminum cladding, connection clamps and lighting systems. The first step of this scope was to convert the schematic design and initial analysis produced by the designers into a complete engineering documentation suitable for the fabrication and for the installation on site.
Some of the engineering challenges that surfaced over the time of coordination are listed below:
- Verification and completion of a workable 3D model in accordance to final layout and actual site survey results,
- Determination of forms and geometry for the different sets and combination of shade structures. Introduction of webbing/infill between the canopies resulted in very different precamber of the individual canopies before connecting them with the webbing/infill,
- Determination of balanced geometry for the individual aluminum panels being supported at two points from the cables of cable net,
- Innovative solution and testing of a project-specific custom-made clamping system for cable net, considering connection for MEP,
- Innovative solution and testing of bearings for the support of the aluminum panels, allowing for swiveling of the panels on the wind,
- Enabling a pre-installation of compression ring and cables on the ground with a following lift step of both elements to the top,
- Implementing lighting control systems for 800 spots and LED lights on 53 structures for client’s light shows during the EXPO,
- The development of a complete Erection Engineering with a detailed sequence of erection
Once these challenges were addressed, the solutions were found, as illustrated below:
Fig 5: Individual tree, as designed
Fig 6: Cluster of trees with infill webbing
Since a number of specialists were engaged in the design process, the project success was highly dependent on the very clear communication and productive collaboration between all parties involved. The coordination of experts located in various countries was assumed and managed by PFEIFER. Initially, this was achieved by good old fashion face-to face meetings, workshops and discussions. Due to unfortunate circumstances, these personal engagements had to be substituted with the remote video conferences and interactive workshop sessions, which allow for screen sharing, video animations and file sharing that facilitated the progress of design, construction approach and scheduling to the works on site. The end results of this coordination can be illustrated below:
Fig 7: Tree base, schematic design
Fig 8: Tree base, design for construction
Fig 9: Infill webbing, schematic design
Fig 10: Infill webbing, as built
The unique architectural design and the specification of products that were custom made specifically for this project put a special attention to the production of mock-ups. These were developed to satisfy the requirements of visual inspections as well as very rigorous performance testing. It is worth noting that all components of the final structures were fabricated in shops holding current ISO Certificates and were tested in the in-house fully licensed labs and/or facilities, as shown below:
Fig 11: Cladding panels, schematic design
Fig 12: Cladding panels, mock-up for testing
Client approvals were obtained on an agreed schedule, with a pre-determined approval process, which included time contingencies in order to address and incorporate any revisions or additions. A range of measures was deployed to ensure that the planned approach was meticulous and reduced the inherent risks of construction to as low as possible. Before the construction, started PFEIFER has prepared completely engineered documentation for a detailed, step-by-step sequence of works on site.
Fig 13: Erection concept, schematic design
Fig 14: Erection assembly detail for construction
It may sound like a truism, but there is no successful project where there is no exemplary collaboration between all parties involved. No architectural landmark can be created without an experienced and qualified contractor. It was a case on this project where the team work and shared commitment materialized in an excellent structure that we were very proud of.
In detail, there were two specific tools that greatly helped in achieving the end success:
a) BIM was used during the entire project to communicate the design, reduce risk, manage costs, and optimize schedules. By using BIM models, the process of evaluating several options was made much easier and allowed the project team to fully evaluate different alternatives and select the optimum solution.
b) Creating mock-ups for confirmation of design assumptions. Where appropriate, mock-ups were created to enable the designers to visually assess the materials selected, details engineered, and they impact of the overall structure, when seen from a number of prominent vantage points. The mock-ups also included a scale test on site with marker balloons set at the height of the proposed structures.
Fig 15: Completed Thematic District Public Shading