When doors open at the new location for the Museum of History and Industry (MOHAI) at South Lake Union this December, visitors will be greeted by an audacious, 56-foot-tall kinetic sculpture: the permanent marquee installation by Northwest artist John Grade.

Wawona sculpture by John Grade

Finished wood for the Wawona sculpture at John Grade’s studio. Photo: John Grade

Over 130 cubic-feet of computer-cut and hand-carved, old-growth timber planks, reclaimed from the recently dismantled Wawona Schooner, will be entwined with 5,500 pounds of water-jet-cut steel ribs and concealed hangar rods. The assembled parts will create a form that evokes the shape of a ship’s hull, suspended vertically from the building’s roof. The base of the artwork will hover just 12 inches off the floor, creating an enclosed volume of space and allowing the installation to be experienced from the inside-out, as if venturing within the trunk of a hollowed-out, old growth tree. No red velvet rope; the dialogue is open.

I have collaborated on a number of artwork projects over the years – including John Grade’s Wawona sculpture – and they’ve been some of my most challenging and rewarding experiences as a structural engineer. But the reality is that as an engineer, my career has been primarily defined by conventional building-type projects. The engineer’s role in artwork projects is not immediately apparent, especially if you focus on the stereotypes:

• Engineers are grounded—artists shoot for the stars.
• Artists live outside of the box—engineers make boxes.
• Engineers wear their pragmatism like a badge of honor—artists strive to transcend convention.

Yet in spite of these apparent paradoxes (or maybe because of them?), somehow things come together; the dialogue is opened and the vision begins to grow. Perhaps an artist is doing a project on a larger scale, working to find the right team, walking the line of control—how to let go of their work to some degree, entrusting others with the execution. When done right and with the collective parties working collaboratively, finding interplay between skills and talents, personalities and world-views provides opportunities for the art itself to exceed expectations.

As always, listening is key. In fact, for myself and others at Arup Seattle, listening might have been the most enjoyable part of the Wawona sculpture project. From the outset we had to understand John’s vision. What was he after? What parts of the project did he consider sacrosanct? What pieces were negotiable? How could we ensure the integrity of the structural system while letting it complement rather than get in the way of things? This round of discussions at the concept stage led to a period during which we could settle in and define the engineering performance objectives of the sculpture:

• It has to hang exactly vertical from the ceiling as an 11,000-pound pendulum.
• It has to survive the effects of a large earthquake.
• Durability is important, with the scultpure’s design life exceeding 50 years.
• There must be safety in the midst of movement. Visitors will be welcome to interact with the sculpture – to push or pull – and this cannot create a hazard.

In addition, the wood used was reclaimed from below the Wawona Schooner’s waterline. This portion of the boat survived for over 100 years because it was in contact with the water. A process that included kiln drying the wood before the onset of fabrication was necessary to ensure it wouldn’t warp or split too much in its future use. Finally, the sculpture had to be constructible, and in this instance, prefabricated in nine separate sections enabling it to be transported to the site and bolted in place, top down, from the building roof trusses.

Wawona sculpture renderings

1) Rendering of structural analysis model. Structural analysis results depicting global horizontal displacement resulting from human loading near the base of the sculpture. Rendering: Arup 2) 3D fabrication model looking up the interior of the sculpture. Rendering: Jeff Hudak, Studio Fifty50 3) Structural detail at ribs and wood. Drawing: Arup

With objectives and requirements firmly in place, we were off to roll up our sleeves and get down to the craft. Pencils and straight edges, calculators, spreadsheets, computer analyses, 3D visual models: We used every tool at our disposal. Permit drawings, calculations and final construction documents of the sculpture’s structure were also required. Every component of the wood, steel and connections was subjected to a detailed structural analysis, so its state of stress under all conditions of its use could be quantified and validated.

Even from our first meetings with John, we knew that the actual fabrication of the sculpture would be no simple task. The wood surface geometry is curved in two directions. No two pieces of wood or steel would be exactly the same. Tolerances and fit-up between all of the components would be tight—1/16th of an inch maximum. Even though the sculpture will present itself as something organic and hand-crafted, its underlying form would be made digitally—the cutting of the steel and wood components happen via manufacturing equipment communicating directly with a fully defined 3D computer model of the sculpture.

So for the past five months, at the University of Washington College of Built Environment’s Computer- Aided-Design and Manufacturing Department, each of the approximately 190 4-inch-thick wood planks for the sculpture have been individually fabricated using their 3-axis CNC mill. The resulting product comprises individual wood elements that are trapezoid shaped in cross-section and have all of their finer coping and block-out cuts at interfaces with the steel components incorporated. This allows the flat faces of each plank to fit piece-wise planar to the sculpture’s double-curved surface. From this point, John has been able to get physical with the wood in his studio, hand-carving and drilling to create a fantastically textured and patterned surface topography. For the most tightly curved pieces, the digital fabrication process allows curved guidelines to be milled in the wood at intermittent intervals to ensure the localized depth of hand-carving stays true to the sculpture’s overall geometric shape.

Wood at John Grade’s studio. Photo: Hans-Erik Blomgren, Arup

Wood at John Grade’s studio. Photo: Hans-Erik Blomgren, Arup

Each of the nine tiers of sculpted wood planks will be captured by 3/4 by 2 1/2 inch steel ledgers at the top and bottom which have been CNC water-jet cut from plate material to match the sculpture’s curved cross-section at the given elevation of each tier. An array of slightly angled ½ inch diameter, high-strength steel rods concealed within the vertical seams of the wood planks will then fasten at their ends to the steel ledgers to complete the structural system. Each of the nine tiers will be preassembled and transferred to the museum this fall to be bolted together top down from the building’s roof structure by a specialty rigging crew.

Throughout these many months of design and fabrication, the anticipation of seeing the final installed sculpture has been mounting. Everyone involved is engaged, fully invested in the outcome—and that’s the way it has to be if you are ever going to achieve something that rises above the fray. The mutual collaboration between artist and engineer is allowing Wawona, initially born as an image in John’s mind, to become fully realized.