桁 = 木 + 行
The bridge design concept is originated from the hat graphic pattern and features of their traditional costume. We have obviated the use of bamboo as the main structural elements due to its short lifespan of ~1-2 years. Instead, we adopt a timber structure added with bamboo façade and straw cover at bridgeends, mimicking the hat fringe features and their traditional mushroom dwellings. With an arch truss bridge form, we no longer need any central support in river so the risk of support damage by river downwash vanishes. In addition, use of natural construction materials, user-safety, ease of maintenance, environmental friendliness, durability, ease of construction, etc. are also emphases in our bridge design.
Design Concept Closer relationship – Truss to trust! Most of the people in Mixia Village are “Hani” (哈尼人), one of the many ethnic groups in China. Their living environment and lifestyle are simple and natural. To be simple and natural, we choose to build our bridge with timber, bamboo and straw. We also bring in features of their traditional costume and houses to our design to build a closer relationship between the bridge and the Mixia People.
Site Plan (1:250)
Existing bridge location
Existing bridge to be demolished
Key Engineering Considerations i)
Choice of Materials
Delete Intermediate Pier Eliminate potential destroy by river downwash in wet seasons
ii) i) is achieved by slightly relocating the bridge to shorter route across the river. Also help reduce construction materials req’d iii) End supports and main members above highest water level Avoid impact by soil loss at supports and damages of main members by river downwash
Timber logs eg 雲南鐵杉 Tsuga dumosa (Pinaceae) available at Yunnan for Main Structural Members
Natural Locally available Readily available for future maintenance Harmonizing with adjacent environment Durable & Maintenance-friendly
We use timber logs, not sawn planks more natural form of wood, keeping the barks, more intact against cracking
Local Bamboo for Deck Plank, Side Fence and Top Shade
Bridge Plan (1:50)
Key adv of chosen materials
Direction of river flow
New bridge location
~2m Masonry for foundation
Straw for Top Shade
Main truss members in same size & length
≤200mmφ timber log of ~1.5m long (or even shorter!)
• Lighter-weight members Easier transportation • Promote forest sustainability (avoid felling old trees)
Simple construction sequence : (i) Construct foundation blocks + erect temporary bamboo platform (TBP) (ii) Assemble truss arch structure on TBP (iii) Install bamboo deck plank (iv) Fix bamboo facade & install straw cover
Main Structural Member : Plug-&-socket connection Minimal skills req’d for on-site assemble Suitable for Local involvement All truss main members are of same dia & length Obviate problem of fixing wrong members Bridge deck : Bamboo plank Villagers already with certain (or even Simple & standard type connection : very good) skills! Each end of the log member is
Need to walk along a steep footpath to bridge site!
Use Small Members
rounded over a short length for slidefitting into pipe sockets!
Maintenance Aspects Timber parts: Good Durability Improved life span (>10yr c.f. 1-2yr for bamboo) Further enhanced life span with pre-treatment (using natural method e.g. mud / heat treatment done) Minimal maintenance Bamboo & Straw parts: Easy to obtain material & replace Steel connectors : Will provide some spare parts for maintenance Galvanized to achieve minimal maintenance
Though timber members are durable & maintenance-minimal with pre-treatment, possibility of damage e.g. by accidental impact can’t be totally obviated; Replacem’t work may be req’d. Will provide spare connectors & teach villagers how to do Slide-fit 2 half-members into replacement Member extg joints, connect Damaged member
Design with Community features Local-style : bamboo environment, mushroom dwelling, straw roof. Local-feature : fence-cum-shade symbolizing fringes of local costume, truss matching with their hat pattern
The smaller the better! So, we avoid large member size
Reuse of construction materials : Bamboo from temp. platform reused as deck plank Timber-cum-bamboo bridge visually fully-blending with environment No mid-pier No obstruction to river flow Use of local material Min. transportation ∴Low embodied energy/carbon emission to promote sustainability No paint applied No risk of river contamination
Temp. Bamboo Platform
User Safety + Friendliness
Shading at each end against heavy rain & hot sunshine
With side fence against falling into river
Cover high enough to allow material at back basket
Side fence for the elderly…
Reuse 2. Trim and 1. Fix temp. remove damaged timber member w/ spare connectors. member.
3. Replace with new timber member.
4. Remove temp. member; Replacem’t completed.
Wide enough to allow 2 ppl walking together (even with livestock)
Wider deck for mom with kid…
1b Highest water level
• • • •
Further Engineering Considerations Truss form to fit Single-span Design Timber better in compression than tension Arch shape helps reduce tensile force in timber members Bridge-shape haunched to avoid deck-flooding / hit by river downwash Bridge ends also above high water to avoid flooding / hit by river flow
To eliminate the potential impact of support erosion at bridge ends, the following foundation detail is proposed: Foundation block formed by stones joined with cement
Drain tubes to avoid water accumulation at roller recess
Sectional Elevation Y (1:50)
Timber roller support at one end of truss (fixed at the other end)