Engineers must consider many factors when designing a bridge. The purpose of this article is to educate you on the eight areas that are required when developing a bridge. Continue reading to learn more about what the Areté Engineers team considers when designing a bridge.

8 Factors Engineers Consider When Designing a Bridge 

As engineers, we are commonly asked, “what factors do you consider when designing a bridge?” To accurately answer that question, you need to understand all the pieces that go into a bridge project. 

The following eight areas (or disciplines) are necessary when first beginning a bridge project:

  • Survey
  • Geotechnical Engineering
  • Civil Engineering 
  • FEMA Permitting (Hydrology and Hydraulics) and Environmental
  • Traffic Engineering
  • Right of Way
  • Utility Coordination
  • Bridge Engineering

1. Survey

Developing a detailed survey of the existing topography is essential to all the engineers involved in the project. Engineers require a completed study before any preliminary engineering work can begin. 

2. Geotechnical Engineering

Once establishing the bridge location, the geotechnical engineer will locate where they take the subsurface soil borings. Then a drill rig will go to the site and auger into the soil to a predefined depth (or bedrock). The purpose is to obtain the required primary soil data for the geotechnical engineer to determine the type of bridge foundation required. 

3. Civil Engineering

The civil engineer is responsible for designing the roadway. They will provide the roadway elevations along with the horizontal and vertical curve information. Then the civil engineer prepares a cross-section of the road, so the contractor will understand how much fill is necessary to build the roadway approaches for the bridge.  

4. FEMA Permitting & Environmental 

When the bridge crosses a significant waterway, the Department of Homeland Security’s (DHS) Federal Emergency Management Agency (FEMA) will complete a detailed flood study at the proposed bridge site. 

There are two potential scenarios FEMA will follow.

The First Scenario: If the proposed bridge replaces an existing bridge, the hydraulic engineer will determine if they can obtain a “No Impact.” To achieve a “No Impact,” the hydraulic engineer must prove that the proposed bridge does not increase the 100-year floodplain by using the FEMA model. 

The Second Scenario: If a “No Impact ” is not obtainable, they will need to acquire a Letter of Map Revision (LOMR). LOMR is the process of changing the FEMA flood maps and can become expensive and lengthy. 

5. Traffic Engineering

For a bridge going over a public road, the engineer will need to study and evaluate current and future traffic. They will also need to assess the roadway geometry to design the bridge accordingly. This part is usually not necessary for smaller or private bridges. 

6. Right of Way

In some situations, the roadway width or the alignment may change due to the proposed construction. If this occurs, acquiring property may be necessary to complete the project.

7. Utility Coordination

An engineer may sometimes need to relocate utilities to make way for the proposed construction. 

8. Bridge Engineering

The bridge engineer is responsible for the design of the bridge. They will consider several factors during this step.

  • Foundation type
  • Substructure type
  • Superstructure type
  • Bearing type
  • Deck type
  • Bridge rail type

Conclusion: The Factors Engineers Consider When Designing a Bridge

Along with evaluating the above eight areas of bridge design, the engineer will need to consider the following questions.

  • Should a multi-span bridge have simple spans, or should it be continuous?
  • Is it possible to make the beams inter-gray with the substructure?
  • How to deal with thermal expansion?
  • What should the maximum design load (truck) be?

Ultimately, the engineer reviews all the information discussed above, analyzes the bridge concerning the dead loads (the weight of the bridge), the live loads (traffic), and the environmental loads (snow loads and wind loads) when designing a bridge. Then all of the noted factors will be developed into a model to size all the bridge elements. 

Areté Engineers Can Be Part of Your Next Bridge Project!

Now that you know the factors engineers consider when designing a bridge, it’s time for you to get started! At Areté Engineers, we regularly provide bridge engineering services for DOT, municipal, and private clients, so we are ready to design your next bridge! Contact us to get started.