The 2005 World Sustainable Building Conference, 10-009 Tokyo, 27-29 September 2005 (SB05Tokyo)

DEVELOPMENT OF ELEMENT TECHNOLOGIES SUPPORTING SKELETON/SUPPORT INFILL HOUSE (DEMONSTRATIVE EXPERIMENT FOR NEXT GENERATION STRUCTURAL HOUSING)

Takashi MARUMO1 Yutaka HIGUCHI 2 Tadashi GOTOU3 Hirotaka KONISHI4 Yoshihiro KATSURAGAWA5 Kiyotake SUZUKI6

1 Building Design Department, Branch, Takenaka Corporation, 1-18-22 Nishiki, Naka-ku, Nagoya 460-8633, , [email protected] 2 Building Design Department, Nagoya Branch, Takenaka Corporation, 1-18-22 Nishiki, Naka-ku, Nagoya 460-8633, Japan, [email protected] 3 Building Design Department, Nagoya Branch, Takenaka Corporation, 1-18-22 Nishiki, Naka-ku, Nagoya 460-8633, Japan, [email protected] 4 Building Design Department, Nagoya Branch, Takenaka Corporation, 1-18-22 Nishiki, Naka-ku, Nagoya 460-8633, Japan, [email protected] 5 Building Design Department, Nagoya Branch, Takenaka Corporation, 1-18-22 Nishiki, Naka-ku, Nagoya 460-8633, Japan, [email protected] 6 Engineering & Technology Department, Tokyo Main Office, Takenaka Corporation, 2-5-14, Minamisuna, Koto-ku, Tokyo 136-0076, Japan, [email protected]

Keywords: skeleton/support, infill, long-term, base-isolator, flat-slab, high-durability, infill-rules, flexibility

Summary The presented Flexsus House is the experimental Skeleton/Support Infill (SI) apartment house expandable in space and durable for over 100 years with the “Skeleton”, highly durable flat slab structure embedded with long-term base isolators. Six companies that participated in the experiment took partial charges of 11 housing units for developing the element technologies supporting SI houses, with the different development subjects assigned to them. Common “Support” forms the main parts of the adaptable building independent of the life spans different among the parts. The exterior wall, the intermediate part between the “Support” and the ”Infill”, is in the high- precision and easily renewable cladding system. The “Infill”, the housing units produced by different designers and contractors, was subjected to the development of the element technologies serving various SI houses. Through the design and construction processes, the “Infill Rules” were prepared and verified. With this project, the element technologies to realize the concept of flexible, adaptable and available SI houses were reviewed throughout all the processes and presented as the technologies available for actual use. The presented Flexsus House is expected to gradually grow as a group of housing units reflecting the individual residents’ characters over a long period of time.

1. Introduction As a part of the housing technology development effort of the Ministry of International Trade and Industry (MITI, currently Ministry of Economy, Trade and Industry (METI)), numerous developments were undertaken by the House Japan Association, many of which were focused on the Skeleton/Support Infill (SI) housing. This paper presents the results of the Flexsus House 22 Next Generation Structural Housing which was the experimental SI apartment house completed as one of the developments in Seto City, , Japan, in 2000.

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Nowadays in Japan, apartment houses undergo a demolition/reconstruction cycle of about 30 to 40 years. The current situation is undesirable in terms of effective usage of environmental resources and effective socio-economic investments, which has come to require change of this existent system. Accordingly, the Project was devised with the objectives of enhancing the social “stockability” of apartment houses and developing a system that would allow asset values to be maintained over a longer span of time. The development of skeletons that especially would ensure longevity called for advances in multiple durability- related element technologies and the utilization of sophisticated building construction designing technology concurrently with high-precision construction capabilities. In general, the skeletons of Japanese apartment houses employ rigid frame structure incorporating structural walls. Infills for this type of dwelling houses are subject to various restrictions on degrees of freedom and flexibility, arising from the existence of beams and structural walls. Such restrictions include a) difficulties in flexible planning due to the segmentation of the space by beams; b) limitations in the positioning of ducts according to the locations of sleeves through the beams; and c) difficulties in expanding the accommodation unit space because of structural walls integrated into the construction. All these factors work to hamper the renewal/modification of infills during the reforming of dwellings. The difficulty of effectively utilizing the space due to the height from the beam to the floor which is limited to approx. 2 meters is also a problem. Thus now in great demand are the developments of skeletons ensuring the basic performance capable of addressing these drawbacks flexibly and new system/element technologies of M&E equipment and infills that can match them.

2. Outline of Project In the Project, the flat slab frame structure was adopted as the “Skeleton” for SI apartment houses in order to resolve the problems stated above. In Japan where seismic risks are essential factors to be considered in the design process, it is generally difficult to build flat-slab apartment houses. Therefore, a flat slab structure was achieved by combining the flat slab with high-performance base isolators. The development of this structure and M&E/infill systems to match the structure was verified by designing and constructing a full- scale experimental building. Six member companies of the House Japan Association participated in this project: a)Takenaka Corporation was responsible for the research and technical development of skeleton, as well as the design and construction of the experimental skeleton; b)Takenaka Corporation, Matsushita Electric Works, Ltd., INAX Corporation, Corporation, Tokyo Gas Co., Ltd., and Toho Gas Co., Ltd. undertook the research and technical development of infill, and the design and construction of the experimental infill.

Figure 1 External view of experimental building

Figure 2 Evening view from north The 2005 World Sustainable Building Conference, Tokyo, 27-29 September 2005 (SB05Tokyo)

2.1 Outline of Experimental Building - Scale: Three-storied (of 9-storied model building in design), five spans - Total floor area: 1,254 sq. meters - Span: 7.2 meters by 11.6 meters - Story height: Ground floor = 3.55 meters Standard floor = 3.25 meters - Basic unit area: 80 sq. meters - Maximum unit area: 240 sq. meters

Figure 3 Floor plan, 3rd level of experimental building

3. Main Element Technologies for Support Including Skeleton 3.1 Development of Flexible, High-durability Skeleton The innovative structure system with the combination of flat slab frame structure, long-term base isolators, and high-durability concrete can provide up to approximately 240 sq. meters of space.

Figure 4 Main element technologies applied to experimental building’s Support

The 2005 World Sustainable Building Conference, Tokyo, 27-29 September 2005 (SB05Tokyo)

3.1.1 Flat slab frame structure Conventional structure systems require structural walls and beams, where structural verification and reinforcement are inevitable for expanding/reducing dwelling unit spaces and/or changing the openings. In reality, such renovations have not been conducted. On the other hand, a flat slab structure is very excellent in terms of flexibility of infill. This is also a system durable over a 100 year period of time with several times of remodeling, intended for long-term stockable apartment houses. A durable flat slab frame structure was achieved through the designing method of combining long-term base isolators with high-durability concrete. The experimental building used in the technology demonstration consists of the bottom three stories of a nine-storied model building incorporating the adopted structure, in view of versatility. The thickness of the flat slab was set at 250 mm, with 600 by 1,200 mm columns. For the standard type, a wall-shaped column 450 by 2,000 mm was integrated in the mid-section of the span. By prestressing the slabs and increasing the thickness to 350 mm to keep the strength, the central column may be eliminated, providing for a maximum of 240 sq. meters of interior space, thus enhancing the space flexibility. In case of the actual nine- story building, mega beams shall be incorporated at an interval of four to five stories.

Figure 5 Nine-storied model Figure 6 High-performance base isolators

3.1.2 Long-term base isolators Since the Great Hanshin-Awaji Earthquake in 1995, base isolators have gained popularity as safety installations effective against the earthquake. Conventional base isolators consist of rubber alternated with iron plates and have a base shear coefficient of approximately 0.15, with about one-second period of buildings’ natural vibration. The new base isolator was developed to enable the placement of smooth bodies on smooth surfaces, without using rubber. Specifically, the new isolators use coated stainless-steel plates mounted on Teflon-coated stainless-steel plates, which have realized the friction coefficient of 0.02 and base shear coefficient of less than 0.1. The isolators are capable of prolonging the natural vibration period of a building to about 4 to 6 seconds, thereby significantly reducing the influence of the seismic force on buildings incorporating the system to about one-fourth. Even in earthquake-ridden regions including Japan, the introduction of this technology will enable supple superstructures like those constructed in countries free of seismic activities, and also improve safety against earthquakes. Thus this technology can guarantee long usable life.

3.1.3 High-durability concrete The selected concrete is densely packed concrete that delays the progress of carbonation and is highly durable with a service life of up to 200 years. The concrete was cast under the strict management of construction in order to ensure its high performance. The 2005 World Sustainable Building Conference, Tokyo, 27-29 September 2005 (SB05Tokyo)

3.2 Highly Durable Finishing Material Support element technologies for longer life of the skeleton, including skeleton waterproofing, improved asphalt membrane waterproofing, stainproof concrete, and highly durable tile finishing system were developed and adopted to the demonstration structure.

3.3 Plumbing Unit Provided for Flexible Positioning In order to allow flexible floor planning of dwellings, it was considered important to flexibly position the water plumbing. In the service life of a highly durable skeleton, several times of overall renewal of M&E installations will have to be considered. For that purpose, pipe shafts were not integrated into the dwelling unit structure of this building, but were laid down along the external corridors. The entire dwellings including the common-use corridors and balconies were provided with double floors, setting the horizontal plumbing on the concrete sub base surface. The standard double-floor height is 250 mm, but if such systems as the limited plumbing and pressurized drain systems are used, the infill designer can flexibly define the dimension as long as the basic functions are ensured. In case of the standard type, “drainage header system” facilitating the drainage in gently inclined pipes was adopted as one of the support technologies. As a result, a ceiling height exceeding 2.60 meters was achieved even in the standard type while maintaining a story height of 3.25 meters.

Figure 7 Drainage header system Figure 8 Inside of pipe shaft

The 2005 World Sustainable Building Conference, Tokyo, 27-29 September 2005 (SB05Tokyo)

4. Interfacing Technology between Building Frame and Dwelling Unit In the experimental building, the separate member companies of the Association constructed the skeleton and the infill and verified the progress of design and construction on the assumption of the actual project, where it became necessary to establish the minimum required rules for a group of dwelling units. Takenaka Corporation which was responsible for the skeleton played a leading role in documenting the basic rule book to ensure the basic performance of apartment houses and efficiently manage the works while ensuring the infill’s flexibility, thus increasing the awareness shared by the participants. This book also can serve as a reference in case of future renovation.

Figure 9 Example of infill rules

5. Infill Technology In the demonstration building, 11 dwelling units were installed with infills, respectively designed and constructed by the six participating companies according to their individual concepts. The infills were characterized by five main concepts, namely, a) dwellings providing for reduction/expansion of dwelling unit area; b) dwellings allowing for flexible modification of the floor plan; c) dwellings designed for effective utilization of the available space, both vertically and horizontally; d) dwellings allowing for alteration of the intended use to other than dwelling; and e) dwellings designed to minimize the environmental load. Some cases of the dwelling units are as follows, the infills of which were designed and constructed by Takenaka Corporation.

The 2005 World Sustainable Building Conference, Tokyo, 27-29 September 2005 (SB05Tokyo)

5.1 Dwelling Unit Type T-1 (Multilevel Dwelling Designed for Effective Utilization of Available Space) A two-by-four maisonnette dwelling unit was installed within a two-layer open skeleton. The infill for a two- story wooden structure was arranged like a nest of boxes. This type realized a multilevel space expansion of a two-story timber floor and a large atrium space in an apartment house. The current Japanese law, however, does not allow use of timber floor in an apartment house yet from the viewpoint of fire prevention. Therefore this dwelling unit type is in an experimental stage. The cost was reduced by using the interior construction material imported from North America, although it remains to be seen whether the rough finish of imported materials is acceptable considering the delicate sensitivity of the Japanese. This dwelling unit was highly appraised in the survey conducted on the occasion of the exhibition of the experimental building.

Figure 10 Dwelling unit type T-1

5.2 Dwelling Unit Type T-2 (Dwelling Designed for Reduction/Expansion of Unit Area) The party wall was relocated in this dwelling unit, utilizing a flat slab frame. The element technologies incorporated in the infill of this unit for flexibility included: a) double floor/ceiling system providing good serviceability of the M&E installations and allowing for flexible positioning of partitions; b) wiring system enabling flexible positioning of outlets (door/skirting caseway); and c) various types of movable furniture and partitions. They were experimentally installed for demonstration.

Figure 11 Dwelling unit type T-2

The 2005 World Sustainable Building Conference, Tokyo, 27-29 September 2005 (SB05Tokyo)

5.3 Dwelling Unit Type T-3 (Dwelling Available for Altered Purpose) This unit was so designed to enable conversion of the intended use from a residence to a SOHO by taking advantage of the extra story-height of the ground floor. The design of this unit included the entranceways incorporated in the balcony, the verified floor material for slab on grade, and the accommodation of information equipment for office use.

Figure 12 Dwelling unit type T-3

6. Conclusion This project has enabled us to present a case study on the whole process ranging from planning and design through construction and renovation of SI housing. The result of the survey conducted during the exhibition of the experimental building has indicated that the flat slab frame system was credited with availability as a skeleton for SI apartment house, and it also has become evident that there are potential needs for this frame. Through the realization of flexible infills, we were able to obtain the exterior skin via which the building varies and expands as if it were breathing over an extended period of time, instead of the landscape of a stereotyped apartment house. This presented building is expected to serve as a benchmark that actually triggers future increase of SI housings and consequently change in people’s sense of values about urban landscape and housings.