Wu Zhi Qiao Bridge Design Competition

24/06/2010

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Introduction

In response to an invitation to the design competition for a new footbridge in Mixia, Yunnan Province in China, a design of a

ribbon structure is presented in the following pages.

This proposed footbridge satisfies the environmental, buildability and maintenance criteria, which are indicated in the

design brief. The designer’s intention is to provide an aesthetically attractive solution, which is in harmony with the local

environment. An artist’s impression of the proposed footbridge is presented in Figure 1.

Figure 1 Artist’s impression of a new footbridge in Mixia, Yunnan (China).

Design concept

It is proposed that a new footbridge in Mixia, Yunnan, will be a ribbon structure, as illustrated in Figure 1. The new

footbridge will be located in a slightly different location to the existing bridge, as illustrated in Figure 2.This new location will

help to reduce the span length from 19,8m to 18,4m. In addition to that, the new footbridge will be located at a higher level

in relation to the river water level, so it will be possible to avoid flooding during the monsoon period. The new structure will

also not require intermediate supports in the river bed, so there is no possibility of these failing during flooding. The

structural form of the footbridge, is based on the assumption that two main carrying ropes, which span across the river, will

carry all the vertical loads. The deck will be seated on the ropes and the handrails will be attached to the deck. The new

proposed ribbon footbridge, may be prone to wobbling in a horizontal direction. In order to eliminate this, the additional

stabilising ropes have been included in the design. The stabilising system consists of the main (longitudinal) and the

secondary (transversal) ropes, connecting to the bridge deck as illustrated in Figure 3. The installation sequence of the

secondary ropes is presented in Figure 5. The construction sequence of the footbridge is explained in Figure 4 and the

modification of the steep approaches is presented in Figure 6. All the main structural components of the footbridge will be

made of sustainable materials, such as bamboo or cane rope. These materials can be easily assembled in the nearby

village and then transported on site.

Figure 2 Plan layout.

19503150 3150

Handrail (bamboo)

Vertical post (bamboo)

Main stabilising rope

Secondary (transversal)

stabilising ropes

Main carrying rope

Looped secondary rope Bamboo members;

stabilising vertical post

varies

1750

1200

Deck

(bamboo)

Figure 3 Deck cross section.

Wu Zhi Qiao Bridge Design Competition

24/06/2010

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18400 25002500 500500

4095

Min. water level

Min. water level

Min. water level

Min. water level

Stage 1:

1) Preparation works; removal of the

obstacles, earthworks (soil levelling).

2) Installation of the wooden (or bamboo)

piles, forming the anchorage for the main

ropes.

3) Ground levelling/ profiling at the approach

ramps. Installation of the retaining wall

made of bamboo.

4) Installation of the primary (longitudial)

carrying ropes and the main stabilising

ropes; the stabilising ropes shall be

post-tensioned (stretched).

Stage 2:

5) Installation of the deck, made of bamboo.

The deck shall be built in 2m long intervals.

Each interval consists of the following

sequence:

5a) Installation of the deck elements;

bamboo members shall be placed

transversally on top of the primary ropes.

Each transversal element shall be attached

to the rope by means of installation strings.

5b) After the 2m long deck segment is

complete, the handrail shall be installed.

5c) The secondary stabilising ropes shall be

installed at the position of the handrail

vertical post. The transversal ropes are

attached to the main (longitudinal) stabilising

ropes and a bamboo deck.

Stage 3:

6) Repeat No.5 along the length of the main

ropes.

7) Finishes at the approach ramps.

8) Structure complete.

EarthworksMain stabilising rope

Main carrying rope

Retaining wall (bamboo)

Soil infill Wooden piles

Deck transversal members (bamboo)

Handrail (bamboo)

Vertical posts (bamboo)

Main stabilising rope

Secondary (transversal) stabilising rope

ELEVATION

Figure 4 Construction sequence.

Secondary (transversal)

stabilising ropes

Main stabilising rope

Deck

(bamboo)

1) Deck installation (deck and hanrdails).

2) Secondary stabilising rope, weaved

through the hole in a deck's bamboo.

3) Secondary ropes overhung over the

main stabilising ropes (both sides).

4) Secondary rope, from one side ,

pulled under the bridge deck and

connected (looped) to the transversal

rope on the other side of the deck.

5) The same as No.4, but for the other

side of the deck.

6) Instalation of the secondary

(transversal) stabilising ropes is

completed.

Figure 5 Installation sequence of the secondary (transversal) stabilising ropes.

Horizontal bamboo

forming tread

3x280mm

Bamboo

Existing embankment

Stage 1

Bamboo, approx. 1m long pieces, are

driven vertically into the soil. The

vertical bamboo is installed in line at

different levels of the embankment.

Stage 2

Soil is removed (profiled) and bamboo is

cut-off to its final length. The vertical

bamboo, will form the riser of a step.

Stage 3

Horizontal bamboo is installed between

the vertical bamboo risers, to form the

tread.

Removed soil

Bamboo cut-off to

the final lenght

Figure 6 Stair installation at the footbridge approach.