Woods of Net Sunshine falls into the deep forest, filtered through foliage and landing on cobwebs. Woods of Net is a gentle field made to contain a net artwork by Toshiko Horiuchi. Woods of Net uses 589 wooden members weighing a total of 320 tones. Absolutely no metal components were used in its assembly. This is a fusion of the lost traditional construction methods of Japan and world-leading structural analysis techniques. Like the temples of Nara and Kyoto, which have lasted for hundreds of years, we expect it to blend into the scenery while being inherited as cultural heritage for the future. Hakone is part of Fuji-Hakone-Izu National Park, less than 100 kilometers from Tokyo. It is one of the most popular destinations among Japanese and international tourists looking for a scenery. The Hakone Open-Air Museum is opened in 1969 as the first open-air museum in Japan. The museum exhibits more than hundreds of modern and contemporary art on its spacious grounds of 70,000m2 set against the stunning natural backdrop of the surrounding valley and mountains. We undertook the maintenance of the entire Hakone Open-Air Museum. Naturally, many problems will appear in a museum that has been established for 40 years. Dead-end circulation routes and steep slopes up which is difficult to push wheelchairs. Overgrown garden trees. Obsolete equipment. Groups of disused temporary buildings. Arriving at the architecture by traversing the vast landscape, covering 7 hectares, all the many tiny problems accumulate into a huge pile. Woods of Net was implemented as a part of the master plan. An Area Like a Campfire Toshiko Horiuchi's artwork is more beautiful outside. When one see her artwork, it is easy to arose in one’s mind the image of a colorful net floating like a huge cobweb among the trees, with children romping about in it. Because the pavilion is in a forest, a deep, soft place is wanted rather than a box. There are no walls in Woods of Net. Instead, the area is shaped by piling up wood. There are no precise boundaries between inside and outside. The concept for shaping an area in Woods of Net is similar to an open-air campfire. Approaching from a distance, one’s body gradually begins to feel the light and warmth, then enters a circle of people. Instead of a campfire, lighting up the center of Woods of Net are children jumping about in Toshiko Horiuchi's vivid net. Making a circle around them are the parents who brought along the children. Structure Analysis of the Wooden Dome Assemblage While interlocked dowels and wooden members fixed by wedges is the single jointing method in the wooden dome assemblage, all have differing angles. Safety was examined by modeling the joints and treating the horizontal members of the 598-member dome as linear elements, modeling each individual interlocking condition as a linear element jointed with dowels. The analysis results were visualized as a flow of forces in the assemblage, using rainbow colors to clearly and understandably indicates the forces generated. Structural Analysis of the Net The net is composed of a nylon rope that is an extremely soft substance (a nonlinear material), so increasing the loads will give rise to localized deformations. Accordingly, the flow of forces in the net was examined using an analytical computer program specifically intended for nonlinear materials. The analysis results were visualized as a flow of forces similar to that in the wooden dome assembly, and the critical parts could be identified at a glance. In making these examinations, the presence of 80 children (about 30kg each) was hypothesized, then nine cases for the distribution of 80 children were hypothesized and the safety of each confirmed. The Newest Old Structure Woods of Net is a fusion of the lost traditional construction methods of Japan and world-leading structural analysis techniques. Today, Japan’s traditional construction methods of wood are being lost. Despite the fact that the temples of Nara and Kyoto have stood for more than a millennium, modern building codes disallow those original wood-assembly methods that do not use metal hardware. The reason for this is that ordinary structural analysis techniques cannot deal with the unpredictable movements of wood. In this case, our team made use of state-of-the-art structural analysis computer programs, and succeeded in reviving traditional techniques through a rationalized method only possible in the present day. Each of the 598 timber members has a different length and thickness. That is because in any timber that is rationally and correctly treated, the forces will diffuse throughout the structure. A wooden structure with large cross-sections will not easily decay or burn. It takes hundred of years for deterioration to reach the point where it will affect the structure. In addition, by giving it a coating of oil once each year, a layer of resin will form inside the fibers, further extending their longevity. The wedges have a small cross-section by comparison with the main structure, and are scheduled for inspection and replacement every thirty years. Even if the wood gets wet in the rain, water will not collect in the joints. This is old wisdom learned from the structure of Kiyomizu Temple in Kyoto. Water cannot easily enter the joints, and water that does enter is promptly expelled. The upper surfaces of the wood are sloped to prevent water from collecting.