Arena Stage - The tallest free-standing timber-backed façade in the world

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Case Study: Arena Stage

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Learning Objectives 1. Describe how the architects and engineers designed the tallest

free-standing timber-backed façade in the world.

2. Explain how the use of wood allowed for time and labor savings for the Arena Stage project.

3. Observe how the Arena Stage design team satisfied code officials’ concerns to realize this groundbreaking project.

4. Examine how extensive modeling and prefabrication played an essential role in the construction of Arena Stage.

Case Study:

Arena Stage Washington, D.C.

Cheryl Ciecko, AIA, CSI , ALA, LEAD AP, GGP Senior Technical Director, WoodWorks

Arena Stage

Location: Washington, D.C.

Completed: 2010

Size: 200,000 s.f.

Budget: $100 million

Architect: Bing Thom Architects Engineer: Fast + Epp General contractor: Clark Construction Timber façade design-builder: StructureCraft Builders

Background

• Founded in 1950

• By late ’90s, facility was no longer meeting

needs spatially or technically

• Needed twice as much space

• Dated aesthetics

• Performances interrupted by outside noise

After its founding in 1950, Arena Stage built a reputation for cutting-edge performances in the Washington, DC area. A new artistic director who came in 1997 found herself with a complex that no longer met the theater company’s needs, spatially or technically: they needed twice as much space, the aesthetics were dated, and performances were interrupted by noise.

Design Vision

• Artistic director wanted to celebrate all that

was “deep, dark and dangerous” in the

American spirit

• Historic structure in a city that highly values

history

• Lobby large enough for 1,400 patrons from all

three theaters at the same time

In her direction to the architects, the artistic director said she wanted to celebrate all that was “deep, dark and dangerous” in the American spirit At the same time, it is a historic structure in a city that highly values history, so Bing Thom had to determine how to meet the director’s needs without compromising the character of the existing theaters.

Bing Thom and his team decided to cover and wrap the two existing theaters, and the new theater, with a heavy timber-supported roof and glazing system. The design enclosed the new and old spaces while creating a new, larger lobby and offices.

Developing a glass wall was important to create transparency and ensure the old theaters were visible. The insulated glass wall also provided much-needed acoustic separation from the nearby airport They added a new third theater, and covered it all with a 500-foot-long cantilevered roof, creating 200,000 square feet of enclosed space.

Overall Concept

200,000 s.f. of new space

created:

• Insulated glass wall

covers and wraps the

two existing theaters

• New third theater

• 500-foot-long

cantilever roof

enclosing everything

The premier feature of the new Arena Stage, the Insulated glass wall encloses the theaters and lobby, and is the tallest free-standing timber-backed façade in the world. It is 650 feet long and features large wood column cross-sections shaped according to the internal stresses, increasing transparency

The glass wall was created with 18 PSL columns around the perimeter of the façade. Each column measures 45 to 63 feet tall and supports the steel roof trusses, which cantilever beyond the envelope to create the overhang that runs around the structure. • The wood columns are spaced 36 feet apart and are elliptically shaped for structural efficiency, as well as to minimize their visual impact and to create a feeling of transparency into and throughout the space. • They’re designed to brace the tall glass façade against wind loads and to carry the roof loads (up to 400,000 pounds) from the steel roof trusses, some as long as 170 feet. • The PSL columns are unreinforced solid engineered wood using no internal steel support.

Glass Wall

18 parallel strand lumber

(PSL) columns around the

perimeter

• 45 to 63 feet tall, 36 feet

apart

• Elliptical shape

• No internal steel

support

The glass panels are supported by 324 muntins and 216 support arms, all made from custom-shaped PSL. Fifty-four spring-loaded stainless steel cables stretch between the roof and floor to carry the glazing. Conventionally, the designers would have a building structure holding up the roof, and then have a separate structure to hold the curtain wall. Here, wood did double duty: The columns hold up the windows and the roof. When comparing the cost of an integrated wood system against a conventional steel column and separate aluminum curtain wall system, the wood system came out as being less expensive.

Glass Wall

• Panels supported by

324 muntins and 216

support arms

• 54 spring-loaded

stainless steel cables

stretch between the

roof and floor to carry

the glazing

PSL consists of long veneer strands laid in parallel formation, bonded together with adhesive to form the finished structural section. PSL is commonly used for long-span beams, heavily loaded columns, and applications where high bending strength is needed.

PSL was chosen both for its structural capacity and its aesthetic—consistency, nice texture/pattern StructureCraft cut slabs from PSL, laminated them into larger billets, and bolted them together to create a rough rectangular cross-section. Bolting, rather than gluing, helped control checking The columns were then shaped into elliptical cross-sections with tapered ends. Finally, they were sanded and coated with two layers of clear coat. StructureCraft then de-slivered to the bottom 10 feet, and added a third layer of clear coat. The third coat was added to that section because they knew the beauty of the PSL would draw people to touch it. The beams were installed with the narrow direction in the same plane as the glazing to minimize them visually Muntins and support arms brace the columns against buckling Additional details: • Columns are tapered near the floor to

make them seem lighter and less obtrusive • Columns are sized identically for visual

consistency • Columns are installed at a four-degree tilt

to minimize glare from the glass

PSL Beams

• PSL slabs cut and shaped

into elliptical cross-sections

with tapered ends

• Installed with the narrow

direction in the same plane

as the glazing to minimize

them visually

• Muntins and support arms

brace the columns against

buckling

Connections were key to this design. With timber construction, the connections are usually the most expensive component, so when you develop a connection that can be repeated over and over again, you save money. Since they repeated the same connection 18 times, they could spend time making it quite beautiful. The custom-designed ductile-iron castings for the column bases bring enormous forces down to a single pin. The castings were mounted on all of the columns before they were shipped: It was a complex connection. With 400,000 pounds coming through the columns, they needed a positive bearing connection, which required accurate shaping between the bottom of the PSL column and the top of the casting.

Connections

• Custom-designed ductile-

iron castings for column

bases

• Delicate-looking but

structurally efficient

• Castings mounted on

columns before shipping

Here’s an additional interior view of the glass wall

The director wanted the third theater to be smaller than the other two and designed in a way that allowed the actors to take more risks. The resulting, unique space is womb-shaped, with a spiraling entrance form, lending itself to the name “The Cradle” The Cradle also played an important role because it serves as a structural anchor to support the roof.

The Cradle

• Third theater

• Smaller, womb-

shaped

• Structural anchor of

roof

This rendering provides a better idea of the theater’s unique shape. But while it’s unique aesthetically, unfortunately, the shape created strange sound reflections

To solve the acoustic challenge, Bing Thom developed a wall system that would appear visually substantive, but could absorb and disperse sound. The result was a wood slat system, made from poplar, designed in a basketweave. The material and shape provided character as well as the necessary acoustic dispersion. Despite its intricate appearance, the slat system was simple enough to be installed by the drywall contractor.

The Cradle

Poplar slat

system in

basketweave

pattern

Here’s a wider view of the poplar slat system

Performance Assurance

• Column cross-section governed by deflection under

wind-loading

• Scale model underwent wind-tunnel test

• Full-height mock-up five panels wide, lab-tested to

hurricane conditions

Column cross-section was governed by deflection under wind loading. While some supported smaller tributary areas, all columns were sized identically for visual consistency. To verify the design, the team built a scale model and conducted a wind tunnel test in London, Ontario. StructureCraft also built a full-height mock-up five panels wide, and the general contractor tested the assembly in a Pennsylvania lab under hurricane conditions. Although cost of the mock-up and testing was considerable, the process helped the team fine-tune connection details and erection procedures. The investment more than paid for itself in terms of avoiding problems during installation.

3-D Modeling

• Customized production process linked to a

parametric 3-D solids computer model; tied together

shop prefabrication, quality control, and on-site

erection

The pre-fabricated elements were made off-site while the base structure was being constructed, which simplified and shortened installation time. And StructureCraft used its own crews for installation.

Overcoming Fire Concerns

• In-depth fire report

• Smoke study

• Computer modeling

• Char analysis

Local code authorities were skeptical about allowing wood; they had concerns about fire safety. So the design team presented an in-depth fire report, along with a smoke study done by a code consultant working for the team. Through computer modeling, they showed that effects of a fire on the structure would be minimal, and there would be plenty of time for safe building evacuation. They also did a char analysis, and showed District of Columbia code officials how char actually protects the interior of the wood. While charring would leave a column of reduced size, calculations showed that because the column was sized mainly for deflection, it already had additional strength capacity. It was a long but productive process educating D.C. code officials. As a result, the process will be much easier for the next project.

Wood at this scale isn’t common in Washington, D.C., which is dominated by historic masonry and stone, or modern concrete and glass. As mentioned, code officials required convincing from a fire perspective. But wood was the right material for several reasons. First was budget. The warm aesthetic achieved via the PSL columns came without the need for expensive finishes, and is a natural complement to the views outside the wall. It also served triple duty—holding up the roof, holding up the glass, and serving as a finish material. Arena Stage demonstrated what’s possible with wood, how timber can be used for structures in ways that may not have been considered before. The beauty is that wood works well with other materials—for Arena Stage, they integrated wood with the steel roof trusses and cables, with the aluminum connection plates, with the ductile iron castings and the glass curtain wall, and with other connections.

Benefits of Wood to Arena Stage

Budget

• Beautiful without

pricey finishes

• Triple duty—holds

up the roof, holds

up the glass, final

finish material

Wood lowers a building’s carbon footprint in two ways. • It continues to store carbon absorbed during the tree’s growing cycle, keeping it out of the atmosphere for the lifetime of the building—longer if the wood is reclaimed and used elsewhere. • When used in place of fossil fuel-intensive materials such as steel and concrete, it also results in ‘avoided’ greenhouse gas emissions. As a result, the total potential carbon benefit for Arena stage is 675 metric tons of CO2. This is in addition to wood’s other sustainable benefits: renewability, responsible sourcing, and biophilia, to name a few.

Benefits of Wood to Arena Stage

Carbon Reduction

• Stores carbon

• Replaces fossil-fuel-

intensive materials

Wood was definitely the right material to use for this project. Arena Stage is an indicator of not only what’s possible, but what we plan for the future—which is to keep innovating with wood.

Contact Information

Cheryl Cieko AIA, CSI , ALA, LEAD AP, GGP

Midwest Regional Director, WoodWorks

708. 354.3480 | [email protected]