What is the difference between a suspension bridge and a cable-stayed bridge

A suspension bridge is a type of bridge structure that uses the main cable (usually steel cable) and sling as a stiffened beam suspension system to transfer the load to the pylon and anchor. This bridge design is known for its large span capacity, reasonable force, full use of material strength, and relatively low construction costs2. Suspension Bridges are mainly composed of main cable, tower, anchor, sling and stiffened beam, which can be distinguished according to different classification criteria such as main cable anchoring mode, line shape, number of suspension spans, etc.

Suspension bridges and cable-stayed bridges are two common types of bridges that exhibit notable differences in their structures, load-bearing mechanisms, material usage, appearances, as well as their applicability and stability.

Structural Composition:

Suspension Bridges: Primarily consist of steel cables, towers, and anchorages. The steel cables serve as the primary load-bearing element, while the towers support the steel cables, and the anchorages secure the ends of the steel cables.

steel cable-Stayed Bridges: Comprise steel cable towers, main beams, and stay steel cables. The stay steel cables are directly connected to the towers and suspend the deck. The main beams of steel cable-stayed bridges are often made of steel, concrete, or a steel-concrete composite.

Load-Bearing Structures:

Suspension Bridges: Rely primarily on the steel cables to bear loads, which transmit tension forces to the anchorage system. The stiffening girder, or truss, locally bears and transfers loads, but in earth-anchored systems, it does not experience significant axial forces due to its self-weight, resulting in relatively low dead load internal forces.

Cable-Stayed Bridges: Share the load between the stay cables and the main beam. The horizontal component of the stay cables' tension induces significant axial forces in the main beam, with dead load internal forces accounting for a large proportion. The tension in the stay cables can be adjusted directly to manage the dead load internal forces in both the cables and the beam.

Material Usage:

Suspension Bridges: Tend to employ steel for their stiffening girders due to its light weight, helping to reduce the overall bridge mass.

Cable-Stayed Bridges: Offer greater design flexibility in material choice for the main beam, which can be steel, concrete, or a steel-concrete composite.

Appearance and Applications:

Suspension Bridges: Feature main cables stretched between towers, sagging into an arc shape, with vertical suspender cables supporting the deck at intervals. This configuration lends a distinctive aesthetic and iconic status to suspension bridges, particularly in long spans.

Cable-Stayed Bridges: Have stay cables originating from the top of a single or multiple towers, radiating towards the deck in one or both directions, with the angle of inclination increasing with distance from the tower. Cable-stayed bridges are widely used in urban settings and where large spans are required.

Span Length and Stability:

Suspension Bridges: Can achieve longer spans than cable-stayed bridges because the steel cables bear vertical loads, and the force on the steel cables does not increase with span length.

Cable-Stayed Bridges: Have limitations on span length due to the increasing tension in the stay cables and axial compression in the deck as the span increases. However, cable-stayed bridges are generally more stable, as the stay cables, towers, and deck form a statically determinate system (based on the three-hinged arch principle), whereas suspension bridges constitute a statically indeterminate system.

In summary, suspension bridges and cable-stayed bridges differ significantly in their structural configurations, load-bearing mechanisms, material utilization, visual appearances, and their suitability for various spans and stability requirements. The choice between the two depends on specific engineering needs and design criteria.