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

Marunouchi Architects was also contracted to work for clients other than Mitsubishi from an early stage. The Bank of Taiwan 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). The head designer was Sakurai Kotaro (hereafter affectionately referred to as "Kotaro-san"). The bank and tenants coexist on the upper and lower levels of this building, and it is interesting to see the ingenuity shown in the way it was designed to separate the building for security while accommodating future expansion of the bank. What particularly caught my attention was the shape of the foundation. The foundation protrudes significantly beyond 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 was compiled before Kotaro joined the company, but it did not have a protruding foundation. However, Mitsubishi Building No. 22 (Mitsubishi Temporary Headquarters), which Kotaro worked on after the Bank of Taiwan and was completed in 1918 (Taisho 7), also had a cantilever foundation, with a huge number of pine piles driven into the ground beneath it. It is likely that the aim was to make the surface area of the foundation as large as possible to deal with the soft ground, and to support it with friction piles. So what about Maru Building, Kotaro's representative work, which was completed in 1923 (Taisho 12)? According to a paper by Director Ogawa of Structural Engineering Department, Maru Building has independent footings beneath each of its columns, which are not connected by beams but only by the floor slab on the B1 floor. However, the pine piles beneath the footings reached a length of about 20m into the hard Tokyo gravel layer. It is interesting to see how the foundation shape has changed so rapidly in just 10 years.