New Horizons in Structural Design April, 2008
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20FACT NIKKEN SEKKEI    構造デザインの最前線Advances in computer technology are making it possible to design unique, previously unimaginable building forms, such as the Olym-pic Stadium in Beijing and various buildings seen in Dubai. In today’s environment, all kinds of structures are finding favor and it is important to respond to these circumstances by clarifying our philosophies as structural designers.Inner Truss Tube Bears Seismic ForceMode Gakuen Spiral Towers stands in front of Nagoya Station. The building is twisted in helical forms to demonstrate the concept of an upwards spiraling of student energy. The three clusters of class-rooms, called wings, are arranged around core facilities such as stairways and elevator shafts. The wings spiral upward, gradually decreasing in size, while the axes of the spirals deviate from the centerline.Some people may raise the concern that "a twisted building might twist further in the event of an earthquake." However, despite its unique and light appearance, the central core of the building is a highly rigid cylindrical structure. Like the central pillar in a house, this structure securely protects the building against twisting and earthquakes. This cylindrical structure is called an inner truss tube and comprises concrete-filled steel tubular col-umns and braces deployed around the core.Simple, Rational Structural Design Today, it is possible to design columns, beams, and the like by inputting a free-form frame structure for computer analysis. How-ever, it is the task of a structural designer to propose rational framework structures that are consistent with overall plans and to design simple structural plans without being compromised by the form of a building. This building achieves high aseismic capacity through a strong inner truss tube and two vibration damping sys-tems that efficiently attenuate seismic energy. Vibration-damping columns that efficiently absorb seismic energy by means of viscos-ity dampers are installed at 26 points on the periphery. Taking into account the fact that the top portions of the building deform sig-nificantly, 1% of the overall building weight is accounted for by a mass damper located on the rooftop. During an earthquake, roll-ing bearings and laminated rubber allow the weight to self-adjust and sway against the movement of the building according to its natural period. The lead dampers are designed to efficiently absorb seismic energy. The foundation and the inner truss tube, which are the most important elements of the building, have large bearing force margins. Even if an unexpectedly large earthquake should occur, the building will consistently resist its impact.New Trends in Structural DesignAdoption of a rational structure system has allowed for unique columns on the periphery. Spiral Towers appears to change shape slightly when viewed from different angles, giving an elegant yet dynamic impression. The strong inner truss tube is visible through gaps between the three wings, highlighting the bold design and structure and demonstrating the overall consistency. We believe that Spiral Towers represents an architectural approach that her-alds a new structural design trend.Toru Kobori, Keisuke Yoshie, Katsuhiko Yamawaki鉛ダンパーLead damper転がり支承Rolling bearing緩衝装置Shock absorber積層ゴムアイソレータLaminatedrubber isolater付加質量AddedmassRooftop damper: absorption of seismic energy with added moving mass swaying against the movement of the building屋上制震(マスダンパー):付加質量が建物と逆方向に動くことで地震エネルギーを吸収制振カラム:伸縮することで地震エネルギーを熱に変換して吸収Vibration-damping columns ef ciently absorb seismic energy.モード学園スパイラルタワーズMode Gakuen Spiral Towers自由な形態と構造デザインInnovative Forms and Structural DesignNote: The reason why the single building is named "Towers" is due to the fact that it houses three different schools; fashion, computer, and healthcare. The building is designed to demonstrate the idea that "the energies of students studying at the three schools are spiraling upward."

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