July 30, 2002

Takenaka Corporation (Head Office: Osaka, President: Toichi Takenaka) and Odakyu Construction Co., Ltd. (Head Office: Shinjuku-ku, President: Michikatsu Ishihara) adopted "Base Isolation Retrofit Work Done on Intermediate Floors While the Building Is Being Used" which does not interfere with the operations of tenants in the work to strengthen the earthquake resistance of Shinjuku Station West Entrance Main Building, owned by Odakyu Electric Railway Co., Ltd. (Head Office: Shinjuku-ku, President: Makoto Kitanaka). The building is home to Odakyu Electric Railway Shinjuku Station Terminal and Odakyu Department Store, and the main work, the installation of rubber bearings, was completed without event, with the project to be completed at the end of July.
This construction work was carried out without interfering with the operations of the Odakyu Department Store, located immediately above Japan's busiest station, Shinjuku. It entailed cutting sections of all columns on the third floor above ground, and installing base isolation devices in the intervening gaps. By minimizing the noise and vibration caused by construction work, all work was completed without stopping the operation of tenants.

In recent years, inner city department stores constructed under old earthquake resistance design standards are rushing to start work to improve earthquake resistance, in a bid to ensure the safety of customers in the event of an earthquake and to preserve their products. Among these projects, Shinjuku Odakyu Department Store has achieved an environment in which customers can shop with peace of mind, by using base isolation with an outstanding grade of earthquake resistance, which ensures building safety and ensures that products will not fall from showcases or displays will not fall over, possibly injuring customers in the event of a major earthquake striking a facility visited by such a large number of people.

Project overview

The building involved in this work was Shinjuku Station West Entrance Main Building owned by Odakyu Electric Railway Co., Ltd., with Odakyu Shinjuku Station occupying the first floor and the first floor below ground, and the second floor and up being a composite commercial facility with Odakyu Department Store as a tenant.
Recent years have seen an increase in earthquake resistance retrofit work (including base isolation and structural control work) being carried out on office buildings and other types of buildings, but this project involved carrying out complex improvements safely and over a short time frame, minimizing the noise and vibrations caused by the construction work while maintaining the building function of a department store and the station facility of the Shinjuku Terminal. Being one of Japan's busiest stations, well-thought out construction planning and thorough on-site management were carried out.

Overview of construction work

To minimize the impact during and after construction work on the complex building function of station facility and department store, work was carried out adopting the "Base Isolation Retrofit Work Done on Intermediate Floors While the Building Is Being Used" in which the third floor, previously used as the store backyard, was base isolated. In the work of cutting out sections from the 32 columns on the third floor and then installing rubber bearings, columns were grouped into threes, and with work on each group carried out over approximately two weeks, the construction schedule was kept within approximately five months, and installation of bearings completed.
In cutting the columns, to prevent water used in the construction work from leaking through to stores in floors immediately below, instead of cutting the columns using a wire saw, the process which is generally used, a method combining core boring and chipping was adopted as a means of minimizing the quantity of water used. With the upper floor stores and a napping room for railway crew in the floor immediately below, construction work was carried out under the restriction of only being able to carry out noisy work for four hours a day, late at night and early in the morning.
In addition, by installing eight oil dampers as damping devices on the base isolation floor, seismic energy is absorbed efficiently, suppressing deformation and avoiding collision with adjoining buildings.

Core removal	Column section cutout	Installation of rubber bearings

Construction procedure

1. Attach strengthening steel plates to the section below the column to be cut
2. Attach temporary supports to three locations around the column
3. Attach equipment to measure the load and deformation sustained by temporary supports
4. Push up the temporary supports using hydraulic jacks, transferring the building weight from the column to the temporary supports
5. Cut out the concrete section of column using core boring and chipping
6. Melt the core steel reinforcement of the column
7. Attach steel plates for mounting rubber bearings to the top and bottom of the cut column
8. Mount rubber bearings between the top and bottom steel plates
9. Hydraulic jack is released, transferring the building load to the rubber bearing, and the temporary supports are removed

Overview of the earthquake resistance retrofit work

Project name	Eearthquake Resistance Retrofit Work of Shinjuku Station West Entrance Main Building
Client	Odakyu Electric Railway Co., Ltd.
Design supervision	Tokyo Associated Architects
Design	A joint venture of Takenaka Corporation and Odakyu Construction, Odakyu Design Consultants
Construction	A joint venture of Takenaka Corporation and Odakyu Construction Co., Ltd.
Work period	September 2001 to July 2002 (11 months)

Building Overview

Building name	Shinjuku Station West Entrance Main Building (A' Building)
Location	1-1-3 Nishi-shinjuku, Shinjuku-ku, Tokyo
Completed	1966
Number of floors	2 Fl. below and 8 Fl. above ground, and 2 Fl. penthouse, Height of building: 31 m
Structure	Steel-framed reinforced concrete
Building area	2,467 m2
Total floor space	20,291 m2