Expo Osaka 2025: How Sou Fujimoto Built the World’s Largest Wooden Structure

When Expo 2025 opens in Osaka, one structure will dominate not just the skyline — but the global architectural conversation itself.

That structure is the Grand Ring:
a breathtaking 60-meter (197 ft) tall, 690-meter (2,263 ft) circumference circular timber megastructure designed by world-renowned architect Sou Fujimoto.

This is not a pavilion.
This is not a sculpture.
This is a manifesto in wood — the largest free-standing wooden structure ever built.

And it’s doing something even more ambitious than breaking records:

It’s proving that timber can shape the future of monumental architecture.

🌍 A Global Symbol for a Post-Carbon Future

The theme of Expo 2025 is “Designing Future Society for Our Lives.”
The Grand Ring doesn’t just support this message.

👉 It is the message.

Its perfect circular form represents:

• the cycle of nature
• the regeneration of resources
• the continuity of human culture

Instead of concrete dominance and steel excess, Fujimoto chose a material that grows, breathes and stores carbon:

Wood.

🏯 A Vision Rooted in Ancient Craft — Built with Digital Precision

At first glance, the Grand Ring feels timeless.
Its elevated timber columns echo the post-and-beam systems of Japanese temples and farmhouses (minka), where structures are held together through interlocking wooden joints, not brute-force fasteners.

But here’s the twist:

This ancient logic was rebuilt using fully digital design and fabrication.

Instead of hand-cut mortises, Fujimoto’s team used:

• 3D timber modeling
• parametric node design
• CNC-fabricated joinery components

Every single connection was:

• digitally modeled
• structurally optimized
• fabricated with millimeter-level precision

The entire coordination process ran through timber-specific CAD/CAM workflows, enabling seamless alignment between architect, engineer and fabricator.

🪵 The Timber Arsenal: Glulam, CLT & 4,500 m³ of Wood

The Grand Ring is built primarily from:

• Glulam beams → primary structural ribs
• CLT panels → decking and diaphragm stabilization

Total timber volume:

Over 4,500 cubic meters of wood
Equivalent to ~1,800 mature trees

All timber was sustainably sourced Japanese:

• Sugi (Japanese cedar)
• Hinoki (Japanese cypress)
  certified through national forest stewardship programs.

This wasn’t just construction.

👉 It was a national forestry statement.

🧠 Engineering the Impossible: How a 690-Meter Wooden Ring Stays Standing

By all normal logic, a 690-meter timber loop should collapse.

Gravity.
Wind.
Seismic forces.
Buckling.

So why doesn’t it?

Because the Grand Ring uses a three-layered structural strategy:

✅ 1. Double-Curved Glulam Lattice

The ring is not a flat circle.

Its section is subtly vaulted and double-curved, forming:

• a horizontal arch
• and a vertical shell

This dramatically increases:

• stiffness
• load redistribution
• buckling resistance

It’s a shell structure — executed entirely in wood.

✅ 2. Hidden Steel Tension System

Discreetly embedded inside the wood:

• high-tensile steel tension cables

These act like:

• tendons in a muscle
• restraining outward thrust
• absorbing seismic energy

👉 No steel is visible.
The purity of the timber expression remains untouched.

✅ 3. Modular Segmented Assembly

The structure was fabricated as:

• 24 massive timber segments
• each approx. 28.75 m (94 ft) long

Assembled nearby off-site.
Then lifted into position over:

Just 72 hours.

This was a logistical ballet in wood and cranes — proving that mass timber scales not just in size, but in speed.

📡 A Living Digital Twin

Sensors are embedded directly into the structure, tracking:

• moisture levels
• structural stress
• deformation
• thermal movement

All of this feeds into a real-time digital twin, allowing engineers to:

• monitor long-term behavior
• optimize maintenance
• validate mass-timber performance at megastructure scale

This is timber engineering in the age of live data.

🔁 The World’s First Truly Circular Expo Megastructure

Here’s the most revolutionary part:

The Grand Ring was never meant to die with the Expo.

After Expo 2025 closes, the structure will be:

• carefully disassembled
• transported to Nara Prefecture
• rebuilt as a permanent eco-cultural retreat and forest education center

Its components were designed for deconstruction from day one:

• columns become new pavilions
• CLT panels form floors and walls
• foundation materials are locally recycled

This is a closed-loop lifecycle, not demolition theater.

Expo → Forest → Education → Second Life.

🏆 Why the Grand Ring Changes Everything

The Grand Ring has already been long-listed for:

• Dezeen Awards 2025
• Japan Institute of Architects Award

But awards are not the real story.

The real proof is this:

✅ Timber can now reach monumental scale
✅ Tradition and technology are no longer opposites
✅ Sustainability is not a trend — it’s an engineering discipline
✅ Buildings can be designed for their second life before the first ends

🌀 Final Thought: The Future Is Circular

As visitors walk beneath the Grand Ring at Expo Osaka 2025, they won’t just see architecture.

They will experience:

• a forest that became a building
• a building that will become a forest again
• a structure that proves one truth:

The future of architecture isn’t vertical steel.
It’s circular wood.

Built with algorithms.
Connected by joints.
Designed to live more than once.

And that future?

It’s already standing in Osaka.