Arch Bridges are one of the oldest types of bridges and have great natural strength due to its geometry. Since the weight of arch bridges is carried outward along the curve, from the arch to the supports, they can be the perfect choice for long-span erections. Many new developments and improvisations on the design and construction of arch bridges have taken place in recent years, one such is the utilization of Concrete-Filled Steel Tubular (CFST) structures to arch bridges. This article will mainly focus on the use of CFST structures in arch bridges and some examples of CFST arch bridges in China.
Most Common Types of CFST Arch Bridges:
1. Deck arch bridges
2. Half through arch bridges
3. Through deck-stiffened arch bridges
4. Through rigid-frame tied-arch bridges
5. 'Fly-bird-type' arch bridges
Benefits of CFST Arch Bridges:
1. The in-filled concrete helps delay the local buckling of steel tubes.
2. The steel tube reinforces the concrete in order to resist tensile stresses.
3. The steel tube improves the compressive strength of in-filled concrete.
4. The steel tube improves the ductility of in-filled concrete.
Erection Method:
Most CFST arch bridges are erected using the Cantilever method, Swing method, and Scaffolding method from which the Cantilever method and the Swing method are widely used as shown in the figures below. Firstly, Steel Tubular arches are erected and then concrete is pumped into the steel tubes to form the CFST arch ribs. Furthermore, both the main and auxiliary cables are used to maintain stability during the erection of arch ribs.
Figure 2: Cantilever Erection Method
CFST Deck Arch Bridges
In deck arch bridges, CFST ribs can be used either in vertical dumbbell ribs or as two vertical truss ribs connected by lateral bracing of steel tubes. The true arch CFST bridge has a great crossing capacity of almost 400m. An example of a CFST deck arch bridge is shown in the figure below.
Figure 4: Baipanjiang Railway Bridge in ChinaCFST Half-Through Arch Bridges
Half-through arch bridges are preferred when the rise of the arch bridge is much higher than the road elevation for the long-span bridges. The world’s longest CFST arch bridge is the Wushan Yangtze River Bridge in China, with a main span of 460m as shown in Figure 5.
Figure 5: Wushan Yangtze River Bridge in ChinaCFST Through Deck-Stiffened Arch Bridges
CFST through deck-stiffened arch bridges consist of CFST arch ribs and steel tied or prestressed concrete girders. The hangers are generally made of high-strength steel strands while the deck structure is made out of steel composites or concrete, with cross beams and deck slabs. As the length of the span increases, construction challenges can increase since the horizontal reactions are not present until the tied girder is fully constructed.
Figure 6: Hang-zhou Qian-jiang Bridge in ChinaCFST Through Rigid-Frame Tied-Arch Bridge
In CFST rigid-frame tied-arch bridges, rigid frame action is obtained by fixing the arch ribs to the piers; thereby, the arch rib can be erected similar to true arches using the cantilever cable-stayed method. For a large span bridge, temporarily tied bars can be utilized whereas for a small span bridge the piers can withstand the thrust forces which arise due to the light self-weight of steel tubular arch rib. The construction of this type of bridge is less challenging than that of the tied arch with deck girder stiffened bridges.
CFST 'Fly-Bird-Type' Arch Bridges
These types of bridges generally consist of three spans wherein the two side spans are cantilevered half-arches and the central span is a half-through CFST arch. The main arch ribs and side arch ribs are fixed to the piers. Furthermore, prestressed steel bars are anchored at the ends of the side spans to balance the arch thrust.
Figure 8: Maochaojie Bridge in ChinaOverall, CFST arch bridges are an excellent choice for long-span erection bridges and are recently being widely constructed due to their numerous advantages.
Here’s how an arch bridge could be designed through bridge engineering software like midas Civil.
References:
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"New development of long-span CFST arch bridges in China." (2008). Chen, Baochun.
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“Bridge Engineering Handbook.” Ed. Wai-Fah Chen and Lian Duan.
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