What are the classifications of arch bridges?

Arch bridges can be classified based on the position of the arch relative to the deck. The classifications include deck arch bridges, where the deck is above the arch; through arch bridges, where the deck passes through the arch; and half-through arch bridges, combining elements of both deck and through arch designs.

How is vortex shedding addressed in arch bridge design?

Vortex shedding, a concern for arch bridge design due to potential hanger vibrations, is typically addressed by connecting the hangers, reducing their length, and altering their natural frequency to mitigate vibration issues.

Why is buckling of the arch rib a concern in arch bridge design?

The buckling of the arch rib is a critical concern in arch bridge design due to the high axial forces that the curved rib is subject to. Ensuring the structural stability and integrity of the arch against buckling is essential for the bridge's overall safety.

How has FEM analysis impacted arch bridge design?

Finite Element Method (FEM) analysis has significantly impacted arch bridge design by enabling the exploration and realization of complex arch shapes that were previously unfeasible. Advances in computer technology and software like MIDAS CIVIL have facilitated the design of innovative and aesthetically pleasing arch bridges worldwide.

Design Considerations for Arch Bridges

Q: What factors affect the design of an arch bridge?

The design of an arch bridge is influenced by several factors, including function, cost, safety, aesthetics, traffic demand capacity, foundation conditions, erection procedures, clearance requirements, the arch-to-span ratio, arch and deck slenderness, and the number of hangers or piers.

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1. Arch Bridge Definition and Classifications

An arch bridge is usually defined as a vertically curved and axially compressed structural member spanning an opening and providing support for the moving loads above the opening. The deck can be supported or hung from this main structure, and depending on the position of the arch relative to the deck, arch bridges can be classified as deck arch, through arch, and half-through arch bridges as shown below:

Figure 1. Deck Arch Bridge

Figure 2. Through Arch Bridge

Figure 3. Half-Through Arch Bridge

2. Design Considerations for Arch Bridges

Many factors affect the design of an arch bridge. In general, these factors are related to function, cost, safety, aesthetics, traffic demand capacity, foundation conditions, erection procedure, clearance requirements, and so on. General design recommendations focus mainly on the arch-to-span ratio, the arch and deck slenderness, and the number of hangers or piers.

a. Rise-to-Span Ratio

The rise-to-span ratio for arches may vary widely because an arch can be very shallow or, at the other extreme, could be a half-circle. Most arches would have rise-to-span ratios within the range of 1:4.5 to 1:6.

There are typical spans used for different types of materials. Below are some:

Filled spandrel masonry arch bridges are suitable for spans < 20 m.
Spans of masonry arch bridges range from a few meters to 146 m.
Concrete arch bridges are suitable for spans ranging from 35 m to 200 m, though there are some bridges with spans well over 200 m.
Steel and CFST (concrete-filled steel Tube) arch bridges have a larger capacity than the ones mentioned above, allowing larger spans because of the higher material strength.

3. Vortex Shedding

Vortex shedding should be taken into consideration when designing an arch bridge. There are times when an arch is identified that is having problems with hanger vibrations especially those with I-section hangers. These vibration issues are usually solved by connecting the hangers as shown below, reducing the length of the hangers, and changing their natural frequency.

Figure 4. Horizontal Cable Connecting Hangers (The Bridge Engineering Handbook by Wai-Fah Chen and Lian Duan)

4. Buckling of Arch Rib

Since the curved rib of the arch bridge is subject to a high axial force, the chance of failure due to buckling of the rib must be taken into consideration when designing an arch bridge.

5. FEM Analysis

With the development of computer technology and its applications to structural analysis, various challenging arch shapes have turned up in practice that previously may have been imagined but were impossible to design. MIDAS has played a major role in the infrastructure of the world and MIDAS CIVIL has been used to design some of the most beautiful arch bridges in the world.

As an example, look at some of the MIDAS CIVIL project applications below:

Figure 5. Arch Bridge (Taipei, Taiwan)

Figure 6. Steel Arch Bridge (Nanning, China)

Figure 7. Laguna Española Bridge, Aruba

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