Bank of Taiwan Tokyo Branch (1916-late Showa) [Changes in basic shape as seen by Kotaro Sakurai]

Marunouchi Architects was an early adopter of projects for clients other than Mitsubishi. The Bank of Taiwan's Tokyo branch stood at the intersection of Daimyo-koji and Eitai-dori. It was a relatively early steel-framed, reinforced concrete structure, completed in 1916 (Taisho 5). Its chief designer was Kotaro Sakurai (hereafter affectionately referred to as "Kotaro-san"). The building houses the bank and tenants on the upper and lower levels, and its ingenious design, including the ability to separate the bank for security while accommodating future expansion, is fascinating. What particularly caught my attention was the shape of the foundation. It juts outward from the outer wall. I wondered why. So I looked at design development drawings for Mitsubishi Building No. 21, which was completed in 1914 (Taisho 3) and had been compiled before Kotaro joined the company, but it did not have a cantilevered foundation. However, Kotaro's next project after the Bank of Taiwan, Mitsubishi Building No. 22 (Mitsubishi Temporary Headquarters), completed in 1918 (Taisho 7), also featured a cantilever foundation with a massive number of pine piles driven into the ground beneath it. Presumably, the intention was to maximize the foundation area and support it with friction piles to accommodate the soft ground. So what about Kotaro's masterpiece, the Maru Building, completed in 1923 (Taisho 12)? According to a paper by Structural Engineering Department Manager Ogawa, Maru Building's columns have independent footings beneath them, which are not connected by beams but only by the floor slab on the B1 floor. However, the pine piles beneath the footings reach a length of approximately 20 meters into the hard Tokyo gravel layer. It's fascinating to see how rapidly the foundation shape changed in just 10 years.