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Prototypes: Bridging the Gap Between Representation and Production

A small pavilion along a frozen river trail offers wintertime skaters a place to rest and architects and designers an object lesson in developing new ways to bring designs from concept to reality.

By Kevin Erickson, Assoc. AIA,
Principal of KNEstudio

AIA-Slideshow

ROPE Pavilion

The ROPE Pavilion at night. Image courtesy of Brian Gould Photography.

ROPE Pavilion

The pavilion sits along the Assiniboine River Trail in Winnipeg. Image courtesy of KNEstudio.

ROPE Pavilion

The Assiniboine River Trail is the Guinness World Record-holder for the longest naturally frozen skating trail. It stretches for 10 kilometers from the city center, and its frigid temperatures mean that the humblest structures that can provide a break from the wind and the cold are vital. Image courtesy of KNEstudio.

ROPE Pavilion

An early sketch of the ROPE Pavilion.  Image courtesy of KNEstudio.

ROPE Pavilion

A model of the pavilion. Its designers used more than 25 scale models of the structure to help refine their design concept. Image courtesy of KNEstudio.

ROPE Pavilion

Layers of vertical structural ribs were glued together on a specially constructed table.  The design team developed a combination of notches and holes to secure the rope to the structural members. The rope alternates on every other rib by either being seated in a notch or strung through a hole. Image courtesy of KNEstudio.

ROPE Pavilion

The exterior of the pavilion is made of unmanila polystyrene rope.  Image courtesy of KNEstudio.

ROPE Pavilion

Unlike most wrapped surface materials, rope is ’particlized’, allowing the designers to create enclosure with porosity, emitting daylight. Image courtesy of KNEstudio.

ROPE Pavilion

The ROPE Pavilion’s dome-like form is optimized for heat retention, bifurcating only for an entry threshold and oculus to the sky above. The structure’s dense shell blocks winter winds while still being perforated for light and views. The wood interior creates a sense of warmth through color and texture, and its multilayered rope exterior collects snow, further embedding it within the site.  Image courtesy of KNEstudio.

ROPE Pavilion

The ROPE Pavilion during the day. Image courtesy of Brian Gould Photography.

Instead of relying solely on standard architectural and fabrication drawings to communicate intent and for construction, ROPE pavilion – a 100-square-foot design-build competition project, employed over 25 full-scale prototypes and models to help bridge the gap between representation and production. Prototypes, often used to verify assumptions rather than innovate, were pushed in an iterative fashion to develop knowledge about material, connections, and fabrication, which was used to establish design criteria. This methodology brought forward various latent potentials and proved invaluable during all phases of the project.

Through the combination of simple materials, ROPE pavilion creates a highly articulated form and space while nestling itself into the Assiniboine River Trail’s landscape. Its relationship of skin – unmanila rope and structure – birch frame, merge to form a pavilion whose dense shell blocks winter winds while still being perforated for light and views. The wood interior creates a sense of warmth through color and texture, and its multilayered rope exterior collects snow, further embedding it within the site. The pavilion’s dome-like form is optimized for heat retention, bifurcating only for an entry threshold and oculus to the sky above.

In Winnipeg, the Assiniboine River Trail is the Guinness World Record-holder for the longest naturally frozen skating trail. Stretching west 10 kilometers from the city center, it receives over 4 million visitors annually. With temperatures exceeding -40 degrees Celsius, shelters are placed along the trail for visitors to escape the cold.

In 2009, Warming Huts: An Art + Architecture Exposition on Ice launched an annual international design competition to create five very different pieces of art and architecture each year, giving visitors a chance to engage the site in unique ways. Concurrent to the competition, a prominent firm is asked to design and build a warming hut – Antoine Predock, FAIA, in 2010, Patkau Architects in 2011, and this year Frank Gehry, FAIA. ROPE pavilion was one of three proposals selected out of 140 submissions in the 2011-12 open competition.

Sited in such an interesting and extreme condition, creating porosity between the pavilion’s interior and surrounding landscape was important. In placing an object within this field, we put a lot of emphasis on creating a sympathetic artifact, mainly through form and material. The form originated from an idea to create a simple wrapped frame which could be shaped effortlessly, and the use of rope carried over from a previous competition project which we didn’t win but continued developing.

Unlike most wrapped surface materials, rope is ‘particlized’, allowing us to create enclosure with porosity.

Predicting how this material would behave was difficult. Digital models provided information on how much material was needed, but failed to accurately illustrate the overall geometry, even with multiple Grasshopper scripts.

The first attempt to use only arched vertical ribs supported horizontally by rope helped us discover the challenge of creating a curvilinear form with a ‘point-to-point’ material. By developing unique curves on each rib it, generated enough variation to blend the rope’s linear movement in both plan and elevation. Using a series of digital models, scaled prototypes, and structural calculations, we created a balance between the rope’s physical behavior and desired appearance.

After testing this system with engineers from Arup, we realized additional horizontal bracing was required. Moving forward with the curvilinear form – because of its visual relationship to the landscape and ability to deflect wind – adjustments were made to the wooden ribs so they could withstand loads from snow, wind, and weight of the rope (nearly 1,300 pounds).

Originally we intended to use manila hemp rope. After consulting with a supplier, we learned this material could expand and contract up to 10 percent depending on temperature, humidity, and precipitation. ROPE pavilion called for nearly 6,000 linear feet of rope, meaning the surface could shrink by 600 feet, potentially crushing the wooden frame.

Deciding on which diameter of rope to use involved several factors – visual pattern, coverage, and most importantly, cost per linear foot. Due to their varied curvature, each vertical rib has a different length, so we developed another Grasshopper script to consistently distribute the layers of rope across the overall geometry based on the shortest member. This resulted in 128 layers of ¾ inch unmanila rope (made of polystyrene), which proved best in terms of rope size to coverage cost.

A first attempt to connect the rope and frame was through steel looped pins. Rather than adding another component, we began testing the rib’s ability to hold the rope through a series of notches on their perimeter edges. Strictly using notches failed because the rope slipped from its seating when the frame’s curvature became extreme. Eventually we developed a combination of notches and holes to secure the rope. The rope alternates on every other rib by either being seated in a notch or strung through a hole. This oscillating pattern created a nice subtle texture across the pavilion’s surface.

After solving the rope’s connection, we began working out how to fabricate and assemble the wooden structure. With temperatures exceeding -40 degrees Celsius, assembly time became a major factor. The frame is made of 12 vertical ribs that span between 12 base members and a continuous compression ring on top. It’s further supported by three intermittent layers of horizontal bracing that create stiffness through custom steel plates. The entire system bolts together and was assembled and dissembled in our shop prior to transportation to Winnipeg.

The wood structure is a composite of multiple layers of exterior grade plywood, which provides stability for load transfer. Each layer had to be separated into several pieces due to the 4’x8’ stock material size that were later bonded together. In order to bond the vertical ribs together, a special table was constructed to accommodate multiple clamps and ensure equal pressure. After each member was bonded they were sanded, sealed, and the custom steel plates were inserted.

Thirty-five custom steel plates were the only component we could not fabricate in-house. Each rib had 3 unique 11-gauge plates inserted to form a moment connection between the vertical ‘column’ and horizontal bracing. This detail proved, by far, to be the most difficult. The plates were plasma cut, bent on one side, inserted into the ribs, scored, bent, welded, and then bolted to both the vertical rib and horizontal members.

The process of creating ROPE pavilion occurred at a very accelerated pace. After being notified of winning the competition, we had two weeks to complete a feasibility study, another four for engineering and technical drawings, leaving roughly seven weeks for fabrication, transportation, and construction. Prototyping each component and connection at full scale made this possible.

As with many projects of this type, budgets are limited. Therefore we tested relationships such as: form vs. structure, material vs. form, structure vs. material, and fabrication vs. material to arrive at optimal conditions for both production and cost. In the end, physical artifacts, digital scripting, and time spent on efficient machining played the most significant roles in expediting the process. It would have been impossible to develop this project using only architectural drawings or a parametric model.

Working through various media, we realized the value of testing pieces physically early in the process. The rope’s behavior would have been impossible to calculate without gravity or physically pulling on it. (The pavilion was climbed, on several occasions while on the trail). Developing a quality script, which allowed us to populate the rope notches and holes on each rib, was invaluable. This detail changed at least 10 times, and if we had to manually locate 128 holes on all 12 ribs, we would never have finished. Finally, testing how the wooden structure was going to be manufactured at the beginning saved time in post-processing. Each screw and bolt hole was located using the CNC router. Careful tool/ bit selection saved time on sanding, while accurate tolerances ensured each piece fit perfectly both in the shop and on site, where temperatures varied by over 100 degrees.

The gap between design ideas and end products is an interesting and fertile territory. When any new idea is translated into a product for the first time, success or failure is often difficult to recognize while being absorbed within the process. In the case of ROPE pavilion, we relied heavily on making full-scale working prototypes to test and advance our original premises. This method of working, made possible by commonplace digital technologies, which enabled us to understand our failures and capitalize on our successes. The ease and fluidity in which we were able to produce so many prototypes eradicated many linear processes, enabling us to produce a highly articulated pavilion whose final figure was greatly enhanced through the process of production.

This article was originally published in the summer 2012 edition (18 MB download) of the National Associates Committee Journal Forward.

Reference:

Visit the National Associates Committee (NAC) webpage.

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