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Koto Ward Office Building Seismic Reinforcing Work, Which Permits Simultaneous Base Isolation Retrofitting and Liquefaction Countermeasures While the Building Is Still Being Used


March 9, 2012Takenaka Corporation

Takenaka Corporation (President: Toichi Takenaka) is carrying out Koto Ward Office Building Seismic Reinforcement and Associated Works including base isolation retrofitting in Koto ward, Tokyo with the end of March, 2013 as the projected completion date.
The project has adopted “Intermediate Floor Base Isolation Retrofitting Work While the Building Is Still Being Used”®: a method which permits normal work to continue in the building during the construction period. Installing the base isolation devices above the columns of the first story, which is primarily used as an automobile parking area, will sharply reduce shaking of the building during earthquakes. When intermediate floor base isolation retrofitting work is done, normally the floor where the base isolation devices are installed becomes the work area, which cannot be used. Dividing the work area into six parts and executing the work in each part in succession allows execution while maintaining the functions not only of office space in the second and higher floors, but also of the parking area.
In addition, to protect the building from the soft ground, the ground is improved by carries out liquefaction prevention countermeasure work; building a lattice shaped wall in the ground directly under the building at the same time as the base isolation work is done.

This building retrofitting work is being executed by the design-build contract method. From the planning stage, the personnel in charge of design and of construction cooperate to achieve improvement work which is as rational as possible.
In the future, Takenaka will aggressively propose base isolation retrofitting work and at the same time, demonstrate its technological ability to perform retrofitting work of buildings on soft ground by simultaneously executing liquefaction countermeasures work.

Background to the Execution of this Work

A 2009 earthquake-resistance diagnosis of the Koto Ward Office Building (completed in 1973) revealed that its earthquake resistance was inadequate. The Ward Office Building plays a core role during disasters, for example as the location of the disaster countermeasures headquarters of Koto ward during an earthquake disaster. Seismic retrofitting work designed and executed by Takenaka Corporation is being done in order to maintain the administrative functions of the office building and to preserve the lives of its users.

Outline of the Koto Ward Office Building

Project name Koto Ward Office Building Seismic Reinforcement and Associated Works
Location 4-11-28 Toyo, Koto-ku, Tokyo
Structure/Number of floors Steel-framed reinforced concrete/1 fl. below and 9 fl. above ground
Design/Construction of seismic reinforcing work Takenaka Corporation
Use Koto Ward office building
Total floor space approx. 8,037 m²
Planned work period October 20, 2011 to the end of March 2013