Bridges are some of the most ancient structures invented by man. From simple logs placed across a river to modern cable slayed bridges connecting to cities, bridges have been key to the growth of human civilization. For a bridge to be successful, it needs to be designed. Bridge design requires that bridges are safe and comfortable with sufficient capacity to carry any anticipated load.

Even with the complex bridges of today, the technology used in bridges keeps evolving to achieve safer , economical and more durable bridges. As a result, a number of bridge types have been developed to fit different situations.

Types of Bridges

There are several different types of bridges, each with its own unique features and characteristics. Here are some common types of bridges:

1. Beam bridges: Beam bridges are the most common type of bridge, and they are characterized by horizontal beams that support the roadway. They are simple and economical to build, and they are normally used for shorter spans.

Bridge design
Gerber beam Bridge. Source: Katorisi, CC BY-SA 3.0, via Wikimedia Commons

2. Arch bridges: Arch bridges are formed from a curved arch that spans a distance between the two supports. They are strong and aesthetically pleasing. They are suitable for longer spans.

Bridge design
Arch bridge in Tartu. Source: Iridescent, CC BY-SA 3.0, via Wikimedia Commons

3. Truss bridges: Truss bridges are a framework of diagonal beams that create a truss-like structure. They are strong and efficient which makes them suitable for long spans.

Bridge design
Truss bridge. Source: Beyond My Ken, CC BY-SA 4.0, via Wikimedia Commons

4. Suspension bridges: Suspension bridges consist of a roadway suspended from cables anchored to towers. They are normally used for long spans and provide a graceful and elegant appearance.

Bridge design
Clifton suspension bridge. Source: WFan, CC BY-SA 4.0, via Wikimedia Commons

5. Cable-stayed bridges: Similar to suspension bridges, cable-stayed bridges are more efficient design with a smaller number of cables to support the roadway. They are normally adopted for medium to long spans.

Bridge design
The Ben van Berkel cable stayed bridge. Source: Henk Monster, CC BY 3.0, via Wikimedia Commons

6. Floating bridges: Floating bridges have their roadway supported by pontoons or floating platforms. Floating bridges are suitable for areas with soft or unstable ground as well as places with a high water level.

Bridge design
Evergreen Point Floating Bridge. Source: SounderBruce, CC BY-SA 4.0, via Wikimedia Commons

Basics of bridge design

In terms of design, bridges have to be made to safe, functional and aesthetically pleasing. To achieve this, structural design is done for bridges as discussed below:

1. Determination of a design criteria: The first step in designing a bridge is to develop a design criteria which includes; the anticipated loads, span length, and materials to be used as well as any constraints to be considered.

2. Selection of a bridge type: In order to proceed further with bridge design, a selection of the type of bridge has to be made. This selection depends on; the design criteria, the site conditions (such as water levels and soil conditions), and the specific needs of the project.

3. Load analysis: The next step is to analyze the loads anticipated on the bridge, including live loads (such as vehicles and pedestrians), wind loads, and earthquake loads. The results of this analysis can then be used to determine the required strength and stiffness of the bridge.

4. Selection of materials: The materials to be used in construction normally depend on the design criteria, the available resources, and the specific needs of the project. Common materials used in bridge construction include; concrete, steel, and timber.

5. Design of the structural system: In the design of the bridge structural system, different components (such as beams, girders and foundations) of the bridge are arranged and designed such that each component is strong enough to withstand the expected loads while also ensuring efficiency and cost-effectiveness. This process in particular might involve the use of the computer models and simulations to test the performance of the different design options for the bridge.

6. Preparation of construction drawings: Once the structural design is complete, the next step is to prepare the construction drawings, which detail the dimensions and specifications of the various components of the bridge. These drawings are used to guide the construction process and ensure that the as-built condition of the bridge is as per the design.

7. Review and approval: Before construction can begin,, the structural design and construction drawings of any bridge project have to be reviewed and approved by the appropriate authorities, such as a local building authority.

8. Construction: Depending on the type and size of the bridge, the construction of a bridge can be complex involving a combination of in-house construction and subcontracting, and may also involve partnering with multiple contractors and suppliers.

10. Testing and inspection: Once a bridge is constructed, it is subject to a series of tests and inspections intended to ensure that it meets the required standards and safety needs before use. This stage may include load testing, visual inspections and others types of tests.


In conclusion, it is important to note that bridges are complex structures, and their design can involve a number of the experts such as structural engineers, architects and mechanical engineers. These experts are required to ensure that the design process is a success, and that the bridge is built to safe and functional.

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