How Are Bridges Built? A Visual Guide

As human beings started to expand across lands and territories, we needed a structure to overcome natural barriers and obstacles. Engineers harnessed their resources to create bridges, linking us between cities and changing the entire landscape.

How are bridges built? Bridge construction has undergone an immense transformation since the beginning of time, including new sturdier materials, heavy machinery and new construction techniques. Although building bridges is much easier in modern times, bridge engineering involves precise physics, vast resources and thorough planning prior to and during construction.

While bridges require precise and careful work, the basic fundamentals of bridge construction are simple once broken down. Read on or skip to the infographic below to learn more about the basics of bridge building.

Bridge Construction Process

Most bridge construction projects use a similar timeline, beginning with the planning stage and ending with final testing and inspections. While larger projects may require specialized processes, most projects follow these five steps:

Step 1: Site Inspection and Planning

Before construction begins, planners must test the site for soil strength, depth, land layout and other elements. Using computer-aided design, engineers can picture the bridge’s behavior under different weights and weather conditions and determine the correct structure.

Step 2: Setting the Foundation

After planning is complete, workers break ground on the job site and begin installing the bridge’s foundation. To do this, builders choose a stable location or drive supporting piles into the ground and install solid pillars that will later support the rest of the bridge. These pillars are typically made out of concrete and can support immense amounts of weight.

Step 3: Installing Piers and Bridge Supports

Once the bottoms of the bridge piers are in place, crews build upward until each pier has reached its predetermined height. Depending on the size and type of bridge, supports can consist entirely of concrete or use a combination of steel or other materials.

Step 4: Adding the Superstructure

The superstructure includes all components that directly receive the load, including cables, support beams and latticework. To install the superstructure, engineers must harness various materials and assemble structures that maintain support when exposed to wind, gravity and other natural forces.

Step 5: Final Quality and Safety Inspections

Once construction is complete, crews perform safety tests using cranes and bridge booms to ensure that the structure meets all quality standards. These tests allow engineers to rule out or address any structural flaws and move forward with installing final paving and electrical systems.

How Are Bridges Built Over Water?

Bridges built over water use the same construction process as any other bridge, but there are a few extra factors to consider during the planning and construction phases.

For most bridges built over deep water, construction crews must build cofferdams or lower caissons into the water to create a dam and platform for the concrete towers to stand on. Lakes and riverbeds can be unstable, so crews may need to drive piles deep into the earth to achieve stability.

If a stretch of water is wide enough, bridge builders may need to bring in specialized construction equipment like floating cranes, bridge booms and hydro platforms capable of operating over water. These machines allow workers to perform safety inspections and work in areas that they can’t access from the ground.

Bridge Designs

Bridges are designed to handle tension and compression in a variety of ways depending on their use and location. The most common bridge designs include:

Suspension bridges: Cables hung from vertical suspenders support the bridge deck while piers balance compression.
Truss bridges: The superstructure consists of diagonal chords or beams that carry tension and compression throughout the structure.
Arch bridges: A steel, stone or concrete arch balances compression and serves as a wind bracer.
Cantilever bridges: Cantilever bridges use sets of upper chords to carry tension and lower chords to handle compression.

Engineers invest a lot of time and resources in constructing a bridge that achieves its purpose, facing similar challenges as those attempting to build underwater. Although there are different types of bridges, they all employ engineering principles to act as standing structures that people use every day for transporting and commuting. Bridges are both functional in their purpose and elegant in design, reflecting the harmony engineers and builders strive to achieve.

For more information on how bridges work and the construction process, check out the infographic below.