World Expo’s Grand Ring Rises Again as a 60-Metre Timber Tower
Steel dampers in the reused frame are a vertical version of the seismic system Kajima will build into its nine-storey timber flagship in Sendai.
A ceremonial ball splits open to celebrate the topping out of the KAJIMA TREE, the 60-metre tower Kajima has built from Grand Ring timber on the GREEN×EXPO 2027 site in Yokohama. (Photo Credit: Kajima Corporation)
A timber tower as tall as a 20-storey apartment block now stands over the site of next year’s horticultural expo in Yokohama, with crews taking seven weeks to raise its frame of columns and beams salvaged from the two-kilometre Grand Ring that circled Osaka’s World Expo, which Guinness World Records recognised as the world’s largest wooden architectural structure. That is according to Kajima, the Japanese construction company behind the KAJIMA TREE, which held a topping-out ceremony at the GREEN×EXPO 2027 site last Monday, five months after breaking ground there in June.
“With this technology, equipped to absorb the energy of wind and earthquakes, we are greatly improving the safety of timber buildings,” Haruhiko Kurino, who heads Kajima’s technical research institute, said in May of the damping system designed for the tower. Steel dampers join the timbers in what Kajima calls its kumiki, or interlocking-wood, system, with one set fitted between the columns and a second on the beams linking the clusters of columns at the tower’s four corners.
Those column dampers are a vertical version of the ranma, or transom, damping system Kajima will build into its new timber flagship, the nine-storey Tohoku branch building in Sendai, which the company says will meet the same seismic design standards as a skyscraper. Kajima’s Sendai building will use 1,810 cubic metres of fire-rated glulam, enough for more than 80 ordinary timber homes, with some of it from Kajima’s own forests.
“Not even a few millimetres of error is allowed, so we want to proceed carefully,” Takuya Nakayama, who heads the KAJIMA TREE site office at Kajima’s Yokohama branch, told reporters in September as the first reused columns went up. He said the slightest error in setting a unit would flow on to the dampers and to the joints with its neighbours, with Kajima pre-assembling the columns and beams on the ground for a faster, more precise build.
A crane lifts a frame of columns and beams out of the Grand Ring on Yumeshima, the reclaimed island in Osaka Bay, as organisers dismantle the world’s largest wooden structure piece by piece. (Photo Credit: World Expo)
Reused timber does the structural work, with the ring’s wood held in storage at Tatebayashi in Gunma Prefecture, north of Tokyo, as the dismantling went on, then put through the strength testing and repairs Kajima set out at the start of construction. Each piece was then cleaned, machined, sanded, and fitted with jointing hardware before going back into service as a column or beam of the tower.
Built as Kajima’s own exhibit, the tower is one of Japan’s largest buildings in reused timber, with its foundations also taking demolition material from the company’s former Yokohama branch building and paving blocks of carbon dioxide-absorbing concrete used at the Osaka Expo.
Kajima’s footage, filmed on the day of the topping-out ceremony, shows the 60-metre KAJIMA TREE standing at full height on the GREEN×EXPO 2027 site in Yokohama. (Video Credit: Kajima Corporation)
It comes as more than 80 councils and companies share the 4,200 cubic metres of ring timber going to new owners, as Wood Central reported, with Suzu, on the quake-hit Noto Peninsula, taking 1,200 cubic metres for 40 homes Pritzker laureate Shigeru Ban is designing. By contrast, association sources told the Yomiuri Shimbun that 15,900 of the ring’s 27,000 cubic metres was ruled out of reuse, after being set into foundations or embedded with rebar and bolts.
A render of the finished KAJIMA TREE rising over the gardens of GREEN×EXPO 2027, released when Kajima unveiled the tower in October last year. Render, not a photograph. (Image Credit: Kajima Corporation)
Exterior works come next, with Kajima expecting to finish the tower by the end of February, weeks before the expo opens next March, and to complete the Sendai flagship that shares its damping technology in the 2028 financial year.
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