繊細な構造材がつくる木細工のような木造ブリッジ

中国の農村活性化の一環としてLUOスタジオが設計した〈ティンバーブリッジ〉

CULTURE2022.07.11

〈ティンバーブリッジ（Timber Bridge in Gulou Waterfront）〉は、中国の江門市鼓楼（ころう）における、池で分断された集落をつなぐ木造の橋です。

建築のサステナビリティに注目し、自然素材を用いた建築に重点を置く中国の設計事務所LUOスタジオ（LUO studio）が設計しました。海外でさまざまな取り組みがなされる農村活性化プロジェクトの1つ、「鼓楼ウォーターフロント・リゾート」の一環となる橋です。

（以下、LUO studioから提供されたプレスキットのテキストの抄訳）

鼓楼は干潟という特殊な環境にあるため、この水のシステムを活用した池や塚を形成し、漁業や農業を行うという伝統が根付いている。

広東・香港・マカオ湾岸地域の急速な都市化に伴い、多くの村人が伝統的な漁村生活を捨て、都会的な生活を送るようになった。そのため、漁業を生業とする水の村は次第に姿を消しつつある。

廃れゆく村を再開発する「鼓楼ウォーターフロント・リゾート」

鼓楼ウォーターフロント・リゾートは、OCT（Overseas Chinese Town）が農村活性化の一環として開発したエコ文化観光リゾートで、塚や池を中心とした独特の空間構造を保存するとともに、農村開発と地元集落の文化的背景との融合を目指したものである。このリゾートは、地域の水のシステムを維持しながら、自然学習、親子向けのレクリエーション、漁業文化などのアクティビティを統合している。

このリゾートにおける人や漁船の移動を容易にするための橋が必要とされた。

木によるアーチ橋

漁業文明期には道路は整備されていなかったため、水路が交通や物流の重要なルートとなっていた。橋の上は歩きやすく、下には船が通れるスペースを確保するとともに、構造の効率性を高めるため、中国では伝統的に「アーチ」が採用されていた。特に中国南部は木材が豊富なため、木材を利用した橋梁の伝統がある。

このプロジェクトは、鼓楼ウォーターフロント・リゾートの数ある橋のうちの1つである。都市における建築との差別化を図り、伝統的な農村文化を再生するために、LUOスタジオは天然の木材を用いたアーチ橋を採用した。

このリゾートには、小型の漁船から大型の観光船までが出入りする。

さまざまな大きさの船がスムーズに橋の下を通過できるよう、通常の水位より1.35mの高さに位に位置する基部から2.8mの高さのアーチ構造を組み合わせて、4m以上の高さを確保した。これは、大型観光船が通過できる条件を満たしている。

25.2mというスパンを実現するため、3本のカーブした大きな梁を主要構造部材として配置した。また、製造・輸送コストを考慮し、各主梁は適切な位置で3分割し、現場で鉄筋ボルトにより連結・組み立てるという工法を採用した。

「屋根付き」回廊を備えた橋

この橋は、伝統的な商業地区と子供たちの憩いの場とのジョイントエリアに位置する。「現実的な」商業エリアから「夢のある」子供のためのレクリエーションエリアへの移行を強調するため、閉じた回廊空間を橋の上に作成した。

また、このプロジェクトは古くからある屋根付き橋の建設の知恵を受け継いでいる。橋の上に屋根付き通路を設けるという形式は、橋の構造を強化し、雨や湿気に強く、木材を乾燥させ、腐食を防ぐため古くから行われてきた伝統的な方法である。

この木造橋のある地域は降雨量が多いため、廊下空間の外側は何層もの金属板で覆われ、雨から効果的に保護するとともに、空間のまとまりを演出している。

アーチの下部も「見せる」小断面の構造部材

屋根の高さは一定とすることで、廊下空間の天井高さは両側が高く、中央が低いというバリエーションが生まれた。また、中間部に設置された展望台により、構造的安定性を確保している。

橋の主要構造である3本の梁以外の木製部材は、100mm×100mmや100mm×50mmといった小断面のものが採用されている。

この小断面の構造システムは、回廊内の空間だけでなく、橋の下を通るゲストにも精巧な職人技とディテールによるユニークな視覚体験を提供するものである。

以下、LUO studioのリリース（英文）です。

Timber Bridge in Gulou Waterfront by LUO studio

Background: rural revitalization

Due to the unique tidal flat landform, Gulou in Jiangmen City established the tradition of making use of the water system to dig ponds and form mounds for fishing and farming. As the water system and fish ponds occupy a large area and form a fragmented spatial pattern in local villages, many bridges have been built to connect the areas segmented by water. With rapid urbanization in the Guangdong-Hong Kong-Macao Greater Bay Area, many local villagers have abandoned the traditional fishing lifestyle in favor of living a more urban life. For this reason, water villages in which people make a living by fishing have been gradually disappearing.

Gulou Waterfront is an eco-cultural tourism resort developed by OCT in the context of rural revitalization, aiming to combine rural development with the cultural background of local villages on the premise of preserving the unique spatial fabrics featuring mounds and ponds. The resort maintains the form of the basic local water system while organically integrating nature education, parent-child recreation, and fishing & husbandry activities.

Those operations in the resort require several bridges in certain areas, to facilitate the movement of people and fishing boats.

Arched wooden bridge

During the fishing civilization period, roads were poorly developed, so water systems became the key route for transportation and logistics. Since bridges need to be walkable while also ensuring more space for boats underneath to pass through, traditional bridge construction techniques in China adopted “arches” to create space for the passage of boats under bridges, and enhance the effectiveness of the structure. Due to the abundance of woods, Southern China has the tradition of applying timber to build bridges.

This project is a timber bridge, which is one of the many in Gulou Waterfront Resort. To differentiate it from urban constructions and revitalize traditional rural culture, LUO studio adopted natural wooden materials to construct an arched bridge. The resort provides access for small fishing vessels, as well as large tour ships. To enable boats of various sizes to pass under the bridge smoothly, the load-bearing platform at the bottom of the arch which is 1.35m higher than the normal water level, combined with the 2.8m arched structure, forms a space more than 4m higher than the normal water level. This meets the clearance requirements for large tour boats to pass through. Based on geological surveys, the span of the bridge is set at 25.2m. Through structural calculation and construction analysis, LUO studio utilized 3 large curved beams as main structural components, which are arranged in a parallel manner with a 2.8 spacing between each other. With full consideration of manufacturing and transportation costs, each main beam was divided into three sections at appropriate positions, connected and assembled by steel-strengthened bolts on the site, to form the complete wooden beam.

Set covered corridor on the bridge

The ridge is located in the joint area between a dense traditional commercial street area and a children’s recreation area. LUO studio created a relatively “closed” corridor space on the timber bridge, which is different from other open landscape bridges in the resort. The aims were to accentuate the transition from the “practical” commercial street area to the relatively “dreamy” children’s recreation area, allowing visitors to feel a sense of ceremony in the moving process.

Constructing a covered corridor on bridges has been an old tradition that dates back to the Spring and Autumn Period and the Warring States Period. The initial intention was to strengthen the bridge structure, resist rain and moisture, keep the wood dry and prevent it from corrosion.

This project also inherits the construction wisdom of ancient covered bridges. The covered corridor enhances the overall structural stability and protects the arched wooden structure beneath from exposure to sun and rain.

The west area of the Pearl River Delta where the timber bridge is located has abundant rainfall, so the corridor was constructed in a relatively closed form. The exterior of the corridor space is covered by layers of metal plates, which effectively protect it from rain and also create a sense of cohesion for the space.

Covered corridor construction

1. Sub-structural system formed by wooden components with small sections

Apart from the three large wooden arched beams that bear the main load of the bridge body having a section size of 600mm*300mm, other wooden components adopt small sections. They are either 100mm*100mm or 100mm*50mm. Small wooden components are interlocked and anchored to the three main arched beams, functioning as sub-beams on upper and lower levels. In addition, the two ends of these sub-beams are combined with upward components to form a stable triangle of forces.

The plane of the bridge’s roof is a complete rectangle. The top, left, right edges of the bridge’s side facades also consist of rectangular silhouettes, while only the lower edge is a natural curve. This generates height variations of the corridor space that is higher on the two sides and lower in the middle. To ensure the structural stability of the covered corridor space, the design team set horizontal connecting rods in the middle section and added two viewing platforms on either side, which also avoid the monotonous feeling when viewing the corridor space from the entrance and exit.

The small-section sub-structural system not only enhances the sense of structure in the corridor space but also reveals the elaborate craftsmanship and details to visitors on tour boats and offers them a unique visual experience.

2. Construction modules & material specifications

The small-scale wooden components are arranged with small spacing in between. The spacing between neighboring substructures is set at 1,000mm equally. This perfectly matches the scales of the steps and metal exteriors. Between neighboring sub-beams, three steps are set at the steep sections of the arch, while two steps are set at the gentle sections. The length of each external metal plate is controlled at about 900mm, which is appropriate for manufacturing, transporting, and installation. The 900mm length of timber frames also provides a suitable space for a single person to stand, lean, and rest.

3. Top light, side and bottom gaps

The neighboring upper and lower steps of the corridor have a clearance of 70mm. A gap of about 200mm is set in between layered metal plates on the exteriors of the corridor space. A 1,500mm-wide daylighting belt is set at the middle of the corridor roof. When walking slowly into the corridor space from the entrances at both ends, visitors can catch the sparkling water under the bridge through the narrow gaps between steps.

As they continue to climb the bridge, the bright light refracted by the upper and lower metal plates attract them to look out through the side gaps. Such a special “collected” viewing experience distinguishes this timber bridge from other open bridges. While passing through the platforms from two ends to reach the center of the bridge corridor, visitors can fully experience the light and shadows from the top, feeling calmness and openness in the mind. Such design forms a continuous spatial rhythm that gradually reaches the climax.

Industrialization and handwork

The materials utilized were manufactured and processed by factories based on industrialization standards, and all the necessary timber and metal components were treated by modern industrial technology and methods. During the installation and construction, only the three main beams were hoisted by large machinery. All other follow-up construction steps were fully adaptable and transportable through the hands of the workers in response to the local context. The whole construction process not only effectively harmonized with the surrounding construction sites and took advantage of efficient industrialized methods, but also conveyed rural warmth as well as the “localization” of construction.

Project information:
Project name: Timber Bridge in Gulou Waterfront
Client: Jiangmen OCT Co., Ltd.
Design studio: LUO studio
Design / construction instruction: Luo Yujie, Lu Zhuojian, Wang Beilei
Structural consulting: LaLu Structural Consulting
Construction firm: Shenzhen Zhenhui Architectural Engineering Co., Ltd.
Wood material suppliers: SHENGTEHAOSEN, KINGSPINE-HOUSE
Lighting fixture supplier: Meteor Shower
Location: Gulou Waterfront, Jiangmen, Guangdong, China
Photography: Jin Weiqi
Video production: Jin Weiqi, Xiao Shiming
Total spatial area: 166 square meters
Wooden bridge body size: 25.2m*7.3m*8.6m
Main materials: pine wood, concrete, aluminum plate, glass
Start time: March 2021
Completion time: January 2022

LUO studio 公式サイト

http://www.luostudio.cn

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繊細な構造材がつくる木細工のような木造ブリッジ