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Types of bridges: classification and characteristics

Discover how many and what types of bridges exist, how they are classified, and what are the peculiar characteristics of each type

Bridges are a fundamental element in construction, useful as a connection from one side to the other, in the presence of otherwise insurmountable obstacles. Bridges connect territories separated by rivers, valleys, and other natural and man-made impediments.

These majestic works of engineering art not only facilitate the passage of people and goods but are also a symbol of comprehensive connection and progress.

Given the importance and widespread use of bridges, it is necessary to identify advanced tools for the proper management of bridges, timely inspection of bridges, and constant monitoring of the structural health of bridges to ensure safety, sustainability, and efficiency of connection infrastructures.

What are the structural elements of a bridge?

A bridge is a majestic engineering work. But what are its main components? There is not just one type of bridge, as we will see later, but despite this, we can list some common components, each playing a unique role in ensuring the bridge’s stability, load-bearing capacity, and functionality:

  1. Main beams: they are the main components of a bridge, extending between piles and abutments and supporting the superstructure elements. Depending on the type of bridge, they can be called longitudinal beams, transverse beams, or arch bridges. They can be made of steel, reinforced concrete, or a combination of different materials;
  2. Deck: it is the road surface of the bridge on which vehicles, pedestrians, or other forms of traffic travel. Different materials can be used, such as concrete, steel, or wood, and it is supported by the main beams;
  3. Abutments: they are support structures positioned at the ends of the bridge, essential to ensure the stability and safety of the entire structure;
  4. Foundations: they are the basic structures that transfer the weight of the bridge to the underlying ground. Foundations can consist of piles, footings, or other similar structures;
  5. Piles or piers: they are vertical elements that, together with the abutments, support the loads coming from the bridge superstructure. Usually, they are arranged in series along the length of the bridge to provide intermediate supports;

Structural components of a bridge

Structural components of a bridge

Types of bridges: what are they and how are they classified

Bridges can be classified based on a series of variable elements:

  • the materials used for their construction;
  • their intended use;
  • the static scheme;
  • obstacle to overcome;

Let’s analyze them in detail.

Types of bridge

Types of bridge

Classification of bridges according to materials

Based on the materials used for the superstructure, we can distinguish between bridges:

  • made of wood, mostly used for pedestrian traffic, but also possibly for road bridges and which can be weather-protected or unprotected;
  • made of stone or brick masonry: a material resistant only to compression, especially suitable for the arch scheme;
  • made of reinforced concrete and pre-stressed concrete;
  • made of steel and steel-concrete;
  • made of composite materials (fiberglass or carbon fiber).

Classification of bridges based on materials

Classification of bridges according to materials

Classification of bridges based on intended use

Another criterion to distinguish between bridges is their intended use. They are outlined as:

  • road bridges, distinguished into I, II, and III category bridges depending on the traffic volume affecting the bridge;
  • pedestrian bridges;
  • railway bridges, categorized as A and B, depending on the served line;
  • channel bridges, supporting pipelines or constituting the waterway themselves;
  • mixed-use bridges.

Classification of bridges based on intended use

Classification of bridges based on intended use

Classification of bridges based on the static scheme

Based on the static scheme, we can distinguish:

  • beam bridges, either statically determinate (simply supported beam) or statically indeterminate (such as Gerber or continuous beams). They are characterized by the presence of one or more longitudinal beams that constitute the main structure, supported by substructures like piers and abutments. These beams are mainly subjected to shear forces and bending moments. The beams can take different forms, such as solid or truss, depending on the structural and functional requirements of the bridge. For materials used, road and railway bridges usually employ precast beams in pre-stressed concrete or steel, with a composite concrete deck. In rare cases, cast-in-place concrete beams are used. For walkways, laminated wooden beams are common, appreciated for their aesthetic qualities. Beam bridges are classified as:
    • truss bridges;
    • box girder bridges;
    • truss-box girder bridges.
  • arch bridges: distinguished by their main load-bearing structure, which is formed by a curved arch mainly subjected to compression forces. This arch usually extends in the upper part of the bridge deck, which is supported by the arch itself through vertical tension elements, known as hangers. In this case, the main structure has a curved axis. They are further divided into:
    • pure arch bridges;
    • arch-truss systems;
    • stiffened arch-truss bridges.
  • truss bridges, characterized by an intermediate operation between an arch and a beam if equipped with inclined piers compared to the vertical. They can be further classified as:
    • truss bridges with vertical piers;
    • truss bridges with vertical piers and buffer beams;
    • truss bridges with inclined piers.
  • suspension bridges, distinguished by the presence of straight cables connecting a main pylon, called a mast, to the bridge deck. Due to the inclination of the cables, the deck is subject to horizontal compression or tension forces, so it is designed with a girder capable of withstanding such forces. They consist of a beam supported by a limited number of almost straight cables. The cables, anchored to a pylon or mast, can be anchored to the ground or to the deck itself;
  • cable-stayed bridges, characterized by cables with low flexural rigidity, allowing them to assume a stable curved shape. These cables, through suspension elements, support the bridge deck. Loads are partially carried by the cables and partially by the stiffening girder. They are generally made of steel.

What is a Gerber saddle?

The Gerber saddle is a structural element widely used in bridges and industrial buildings that offers an effective and economical connection between elements, improving overall constructability. This structure involves a reduction in the depth of the end section (notch) of a beam or deck, creating a corresponding protrusion (shelf). However, this geometric modification leads to the formation of a discontinuity region within the reduced section, where stress distribution is disturbed and concentrated. This area may be subject to damage and a reduction in the ultimate capacity of the saddle itself due to aggressive environmental and chemical factors.

Classification of bridges based on the static scheme

Classification of bridges according to the static scheme

Classification of bridges according to the obstacles to overcome

Based on the obstacles to overcome, we can distinguish between:

  • bridge: developed to cross and overcome a watercourse;
  • viaduct: in the presence of valleys or mountain gorges, often with beams in succession;
  • flyover: crosses at a higher level a secondary road of importance.
  • overpass flyover: falls under viaducts, built in urban centers as a fast-flowing road;

Classification of bridges based on the obstacle to overcome

Classification of bridges based on the obstacle to overcome

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