Cement-

sand-large

stones

gabion as

end supports

Bridge Concept Design for Mixia Village

Objective: Construct a bridge (for villagers and livestocks crossing)

over river Mixia.

Limitations:

• No assistance by machinery;

• Construction by non-skillful labors;

• Construction period 5 -7 days only;

• Transportation of massive materials is difficult;

• Mostly locally available materials: sands, stones, timbers &

bamboos; and

• Free from maintenance or villagers can manage to carry out long

term maintenance works.

Design considerations:

Bridge geometry & foundation

• Reconstruction of bridge at the same location may involve

demolition of the existing bridge. During the construction period,

villagers cannot cross the river;

• The width of river at the current bridge is about 20m. Based on the

given plan, the river width is about 16m at about 12m

downstream. The proposed bridge shall be built at where as

narrow as possible along the river bank.

• Long span with large mid span bending moment is the major

challenge of the proposed bridge. The attached bridge geometry

makes use of a short mid span which minimizes the mid span

bending moment. This part can either be made by galvanized steel

tubes or even timbers/ bamboos as villagers are able to replace it

when necessary;

• To reduce span bending moment, the existing large boulder being

used as central pier can be considered. However, according to the

villagers, high water flow may even strong enough to push large

boulders forward, thus the boulder may not be a reliable

foundation.

• End supports can be countered balanced by makinguse the weight of the mixture of cements, sand andlarge stones by gabion with limited excavation works;and

• The foundation of piers can be constructed by mixingcement, sand and stones at a certain depth into riverbed to prevent from being flowed away.

Choose of building materials

• Structural elements must be long lasting, timbers andbamboos shall not be considered;

• Steel scaffolding is commonly used as temporaryworks in Hong Kong. In fact, if it is properlymaintained, it can last long comparing with timber andbamboos;

• Galvanized steel tubes are chosen as the majorstructural components as they are relatively lightweight and easily transported comparing with heavyduty steels. It reduces the risk in handling heavymaterials. They also resist corrosion from river waterand can be cut to desired length even on site to suitactual conditions;

• Galvanized steel tubes shall be connected by swivelcouplers as this system is simple to construct andeasily handle even by non-skill labors within limitedconstruction period;

• The number of structural elements can be added up iffinds necessary; and

• Timbers and bamboos are used as non-structuralcomponents like floor panels and hand railings asvillagers are able to replace when necessary.

Min water level

0m 5m

3.36m

Max water level

~16m span

5m10m 10m

Galvanized steel tubes as

main structural elements

& connected by swivel

couplersCement-sand-

large stones

gabion as end

supports

Cement -sand-stones

foundation

Bamboo hand

railing

Mid span can either be made by

galvanized steels or bamboo

(villagers can replaced when

necessary by themselves)Bamboo/timber

floor

(can be replaced

when necessary)

Bridge Concept Design for Mixia Village