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Concrete has become the most used material on Earth over the 200 years following the invention of modern cement. The design concept has undergone a transition from the allowable-stress design method, limit-state design method, to the performancebased design method, in response to the evolution of materials, sophistication of experimental facilities, and advancement of computation skills. From the issues on resources and energy depletion, global warming, and resilience etc., it is necessary to create a new design framework taking into consideration the required performance beyond the conventional concept, in order to construct infrastructure and buildings in a more rational way.In other words, we should construct a design system that sets the continued existence of the diverse and rich global environment as its most important criterion of value. In this paper, we review the design and technology system developed in the past and discuss it based on the above-mentioned new viewpoint, while constructing and presenting a new design system for concrete structures, focusing mainly on the concept of sustainability, which is regarded as the most important factor in achieving conservation of Earth's rich resources as well as sound socio-economic activities of humankind in the future, and we examine its feasibility.

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A new type of bridge called "butterfly web bridge" has been constructed in Japan. In a butterfly web bridge, the panels used as the web are cut so as to appear pinched in the center, giving a butterfly-wing shape. For the butterfly-shaped web made of precast panels with a thickness of 150 mm, 80 MPa steel fiber-reinforced concrete is used. The design method was proposed after the shear tests of butterfly webs. In this paper, four projects of expressway bridges using this new technology will be shown. It has been shown that by a simplified construction process, construction time can be reduced. Then, future development is proposed in the last part of this paper by considering a 500-m-span extradosed bridge. The butterfly web technology will greatly affect bridge design and construction in the near future. K E Y W O R D Sbutterfly web, extradosed bridge, fiber-reinforced concrete | INTRODUCTIONOne of the recent innovations in bridge technology is the composite bridge. A variety of ideas have been applied in this area, including the use of steel members in the web, and attempts to find an effective method for utilizing the prestressed forces in the concrete members used for the deck slab and bottom slab. Examples include corrugated steel web bridges and composite truss bridges. In Japan, over 150 corrugated steel web bridges have been constructed since the first one to be built in 1993. The composite truss approach was first adopted in 2003, and there are now eight composite truss bridges in service. These composite bridges achieve reductions of 10-15% in girder weight compared with conventional concrete bridges, and the weight reduction has given them an advantage in Japan, where earthquakes are frequent.In a corrugated steel web bridge, the joints between the web and the concrete slabs run continuously along the longitudinal direction of the bridge, enabling the structural details of the joint to be simplified. However, fabricating the corrugated steel web requires folding of the steel sheets using a press, and the individual corrugated steel webs need to be welded together at the construction site. These processes can affect the economy and ease of construction. In contrast, composite truss bridges use conventional materials such as steel pipes that do not need to be joined on site, but because nodes are used for the joints with the concrete slabs, substantial forces concentrate at the nodes. Moreover, joint details become more complex for longer spans. These factors make it more difficult to achieve economy and ease of construction, and that is probably why there are only few examples of composite truss bridges around the world.Being involved in the design and construction of such bridges, the author considered the potential for structures that combine the benefits of these two types of composite bridges, and eventually developed the "butterfly web bridge" design 1 ( Figure 1) described in this paper. A butterfly web bridge, which uses butterfly-shaped panels instead of a double Warren truss, is a new structure...

Concrete engineers and researchers have been developed durable reinforce concrete technologies for long time. However, we have not reached the goal which gives us a perfect technology against deterioration of reinforced concrete. Basically concrete itself is high durable material. And we recognize this fact when we see Roman concrete structures are still working now. The technologies described in this paper are the challenge to derive the solution against deterioration of reinforced concrete. This research and development has been taking for about 30 years. Then a non-metallic highway bridge is under design and will be built in 2020 with the key technologies of aramid fiber tendons, fiber reinforced concrete and butterfly web.