The challenge: creating a pillar-free theater space
Taking on the challenge of "supporting a super-tall tower"

Structural Engineering: Yoji Ishibashi, Structural Engineering Department

"To build a unique building with a theater and a super-high rise tower directly above it, with high earthquake resistance." This was the main task we were given in this project. Since the theater is below, there can't be any columns there. We used a "megastructure" method that adopted a steel megatruss to secure a column-free space of about 40m width across the theater itself and place the super-high rise tower on it. A truss is a structural form in which steel and other building materials are combined in a triangle. It is an efficient form that resists forces with a straight axial force on the materials, and is often used for steel towers and iron bridges. You can imagine that the theater part is an open space from the first to fourth floors of the Kabukiza, and the super-high rise tower built above the column-free space is supported by a huge iron bridge. It is one of the largest megatrusses used in high-rise buildings in Japan, and we took on a completely unprecedented and difficult case, such as designing it while taking into account the construction method. Although we felt a great deal of pressure, it was very rewarding.

A delicate theme: combining the reproduction of Japanese architecture with steel construction

The theater section faced a major hurdle in maintaining the traditional design of the fourth-generation Kabukiza, which was constructed with reinforced concrete, in a steel-framed structure. Fitting the structural steel beams into the various facade inherited from the previous Kabukiza was extremely challenging, as we had to figure out how to fit them into the narrow dimensions. The full-scale inspection of the truss steel beams was particularly memorable. In the winter of 2011, designers, Construction Supervision, Structural Engineering, master carpenters, and tilers all gathered at a workshop in Fukui Prefecture. Under the supervision of a master carpenter skilled in CAD, we spread full-scale cross-sectional drawings across the entire floor, carefully inspecting the fit and construction procedures, and then plotting the steel beams. I remember the workshop being extremely cold, with almost no heating. Aside from the dynamism of this megastructure, another major challenge was tackling the delicate theme of simultaneously recreating Japanese-style architecture and incorporating steel-frame construction.

This project required a design that met both extreme requirements: boldness and the utmost care. I was overwhelmed by the sense of scale on many occasions, such as when I first saw the huge truss members in the factory, when I witnessed their assembly on site, and when I witnessed the special jacking-up work that was used to deal with deformation during construction. Also, seeing up close the process of gradually recreating the traditional exterior of the Kabukiza with steel frames reminded me of the full-scale inspection in Fukui during the harsh winter, and I felt an indescribable sense of accomplishment.

In charge of Construction Supervision Engineering Department, Yuji Nakajo

Looking back on this project from the perspective of Construction Supervision, there were many unprecedented aspects, making it extremely difficult to predict what would happen next. Construction Supervision of the gigantic megatruss was one example. Structural Engineering required the adoption of a special construction method in which the upper columns were jacked up in response to the gradual deflection of the megatruss during construction. To ensure high precision, jacking up had to be performed at each construction step, and with no precedent, we pondered how to ensure construction quality. Ultimately, it is rare to see such high-precision jacking achieved with such effectiveness. While we've heard that other companies have attempted projects in the past that have failed, I believe the success of this project was due to the careful initial planning, which allowed it to proceed smoothly.

Roof tiles that are "unprecedented in the past 1,200 years" and challenge wind resistance

The roofing of the Kabukiza was also a difficult task. The roof of the Kabukiza is made up of 100,000 original tiles and ridgepole tiles over 3 meters high. Normally, there is no skyscraper built right behind a tiled roof. The roof is exposed to strong winds blowing down, so the tiles need to be extremely wind-resistant. We calculated the wind resistance and put together the optimal specifications for the tiles. When the construction actually started, it was a much more time-consuming task than usual for the tile craftsmen, and it ended up being an extremely unusual method. There was some resistance, with some saying, "We've never done this in our 1,200-year history." The roof of the Kabukiza has the volume of eight regular kuri buildings, so it's certainly understandable that they were resisting. One extra screw to each tile means 100,000 extra tasks. Still, this is probably the first time in history that we've ever laid tiles, so we explained the necessity of it and they finally agreed.