How Is The World’s Longest Pedestrian Suspension Bridge Designed To Withstand Earthquakes?

Pedestrian suspension bridge, also called suspension footbridge, is a kind of suspension steel bridge. Its main function is to be erected on the two banks that need to be connected for pedestrians to pass.

Pedestrian Suspension Bridge
Pedestrian Suspension Bridge

The World’s Longest Pedestrian Suspension Bridge

As the world’s longest and largest pedestrian suspension bridge, the Tianmeng Mountain pedestrian suspension Bridge is located in Shandong Province, China, with a total length of 505.5 meters, the main span of 420 meters, a height of 143 meters from the valley floor, the main beam of 4 meters wide, and a sidewalk of 2.4 meters wide. 

Why Should We Carry Out a Special Seismic Design for Pedestrian Suspension Bridge?

We all know that, compared with ordinary steel bridges, suspension bridges have stronger wind and seismic functions due to their own structural design. Why did the suspension footbridge between the two peaks of Tianmeng Mountain require an additional special seismic design? Combined with the actual situation of the pedestrian suspension bridge project, the main reasons are as follows.

1. The bridge body itself is narrow and long

From the perspective of the design specifications of the pedestrian suspension bridge, the bridge body appears too narrow and long relative to the width, span, and distance to the bottom of the valley. In addition, the type of the bridge is a suspension structure, which results in the suspension foot bridge hanging between the peaks like a soft rope. Once the bridge body is subjected to a huge external force, such as a strong wind or an earthquake in a valley, the bridge body may become unstable and unsafe due to great deformation.

The bridge body itself is narrow and long
The pedestrian suspension bridge body itself is narrow and long

2. The construction site of pedestrian suspension bridge is close to the fault zone

Tianmeng mountain, where the suspension footbridge is located, is located in the Luxi fault block to the southeast of the North China fault block, close to a wide and gentle fault zone, which is deep to the bottom of the crust. According to historical records, there have been many destructive earthquakes in the surrounding area, which have a great impact on the location of the suspension bridge.

3. The suspension bridge is built on a special terrain

The two peaks of Tianmeng Mountain connected by a pedestrian suspension bridge span a huge V-shaped valley, and the natural conditions in the valley are very complicated. The special terrain not only gathers strong wind but also increases the response to earthquakes. In other words, when the displacements of the peaks at both ends of the bridge are out of sync during the earthquake, the seismic force on the bridge will be much greater than that of buildings built in plain areas.

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Special Seismic Design of Tianmeng Mountain Suspension Pedestrian Bridge

Through the above analysis of the special terrain of Tianmeng Mountain and the condition of the bridge body, it can be seen that the seismic and wind resistance design of the suspension bridge is particularly important to ensure the stability and safety of the bridge body. The designers conducted professional research on the seismic response spectrum at both ends of the bridge and conducted a very strict and conservative design on the seismic performance of the bridge.

Special seismic design drawing of suspension foot bridge
Special seismic design drawing of the suspension foot bridge

In order to keep this “soft rope” in the sense of structural mechanics stable, in addition to the slings of general suspension bridges, engineers also designed downward-drawn wind-resistant cable devices on both sides of the bridge.

The existence of the anti-wind cable device makes the suspension foot bridge structure always in a “tight” state of restraint. When the earthquake lateral force arrives, it can be offset in time, so that the bridge structure will not vibrate greatly along with the repeated application of the lateral force, and it will always remain relatively stable. The anti-wind cable has a good shock absorption effect on the structure under the influence of the earthquake, ensuring the safety of the bridge structure. In other words, the ingenious design of this anti-wind cable device is that when an earthquake comes, it can not only restrain the swing of the bridge but also consume the energy generated by the earthquake, thereby ensuring the safety of the bridge.

Wind-resistant cable devices
Wind-resistant cable devices
X-shaped angle steel
X-shaped angle steel

In addition to the wind-resistant cable design, in order to further improve the stability of the pedestrian suspension bridge structure, measures must be taken to increase the rigidity of the bridge deck structure to ensure safety. The deck stress structure of the pedestrian suspension bridge is composed of cross beams and longitudinal beams made of I-shaped steel, with X-shaped angle steel in the middle for stiffening, and the steel structural longitudinal beams are connected by high-strength bolts. With this structure, the weight of the bridge structure is greatly reduced while ensuring strength, thereby improving the seismic performance of the bridge.

There are many types of suspension Bridges and they are built in different environments. The suspension bridge design needs to be flexibly adjusted in combination with the actual environment, which requires suspension bridge designers to have professional knowledge and a richer design experience. AGICO is an enterprise specializing in the design and manufacture of suspension bridges. Our design team has extensive experience in designing bridges under different geographical conditions. You are always welcome to send inquiries to communicate with our experts.

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