Bridges are structures built over rivers, lakes, and oceans to allow smooth passage for vehicles and pedestrians.
As the transportation industry rapidly evolves, bridges are now designed to span mountain streams, navigate challenging geology, and meet diverse transportation needs.
In classifying bridges based on their structure, a focus on mechanical characteristics is essential for understanding the basic features of various bridge types.
This categorization serves as a critical aspect in the study of bridge engineering. The primary force members, the foundational basis, fall into five categories: beam bridge, arch bridge, steel frame bridge, cable-stayed bridge, and suspension bridge.
1. Beam Bridge:
The main girder is the primary load-bearing component with force characteristics centered on beam bending. Materials like reinforced concrete and prestressed concrete are commonly used for small to medium-span bridges.
Supported beam bridges are suitable for spans up to 20 meters, while cantilever and continuous beam bridges can accommodate spans of 60-70 meters.
Advantages include construction with locally available materials, industrialized construction, durability, adaptability, and a mature design theory.
However, limitations arise due to the structure, accounting for a significant portion of the total design load, thereby restricting its ability to span large distances.
2. Arched Bridge:
The arch rib is the primary load-bearing element, supporting pressure at the base. Materials such as masonry and reinforced concrete are applied, with spans ranging from dozens to 300 meters.
Advantages encompass greater spanning capacity, reduced use of steel and cement, durability, aesthetically pleasing designs, and a more straightforward structure. However, challenges arise in foundation requirements and increased costs for multi-hole continuous arch bridges.
3. Steel Frame Bridge:
This bridge type is a connected structure with rigid connections between pillars and primary beams, sharing joint forces.
The characteristics involve pillar and primary beam rigid connection, reducing positive bending moments and providing vertical force while bearing bending moments.
Reinforced concrete is the primary material suitable for small and medium-sized spans, especially in areas requiring greater clearance under the bridge.
Advantages include small external dimensions, increased headroom under the bridge, expansive views, and reduced concrete usage. However, drawbacks include higher foundation costs, larger steel quantities, and secondary internal forces in super-static structures.
4. Cable-Stayed Bridge:
Prominent load-bearing members include beams, cables, and towers, with wires extending from the building to the shaft for increased elastic support. The load transfer occurs from the post to the wires and the tower. The primary materials are prestressed steel cables, concrete, and steel, making it suitable for medium or large bridges.
Advantages include a smaller girder size, increased spanning capacity, better wind stability than suspension bridges, and simplified construction without a central anchor spindle. However, challenges include complex calculations, intricate rope and beam or tower connection structures, and the requirement to work at heights with strict technical demands.
5. Suspension Bridge:
The main cable acts as the primary load-bearing member, transferring external loads from the beam through the tie to the main cable and then to the anchor spindle ends. Prestressed steel cables, concrete, and steel are the primary materials suitable for large and super-large bridges.
Advantages include uniform force distribution due to high-strength steel cables, resulting in a sizeable spanning capacity. However, disadvantages include low overall steel durability, poor wind stability, and the need for substantial anchor ingots at both ends, leading to higher costs and increased difficulty in construction.
