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, an essential part of our infrastructure that links us between cities and changes the 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, advanced technology 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 near the bridge site for strength, depth, land layout and other elements to ensure the safety and durability of the final structure. Using the results of these tests and with the help of computer-aided design, engineers can picture the bridge’s behavior under different weights and weather conditions to determine the type of bridge to build and how to build it.
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 (known as piers) that will later support the rest of the bridge. These piers are typically made 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. Once the piers get installed, it’s time to add supportive structures like the abutments, which are located at each end of the bridge and created to withstand horizontal force. Other support features might include beams, bridge bearings and retaining walls. These components all make up the substructure, ensuring proper reinforcements to support the superstructure.
These supports can consist entirely of concrete or use a combination of steel or other materials, depending on the bridge’s type and size.
Step 4: Completing the Superstructure
The superstructure includes all components that directly receive the load, including girders, arches or suspension cables, depending on the bridge type. Then it’s time to build the bridge deck and roadway, incorporating appropriate materials like concrete, asphalt and rebar. Crews will also Install safety features such as guardrails, lighting and signage during this step.
To install the superstructure, engineers must harness various materials and assemble structures that maintain support when exposed to wind, gravity and other natural forces present in the area.
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 the 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.
- Beam bridges: Also known as girder bridges, these bridges consist of horizontal beams supported by vertical columns or piers made of reinforced concrete or steel.
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.
What are the Structures of a Bridge Called?
Bridges are made up of various structural elements that keep the bridges functional and safe for long-term use. While not every bridge is built the same, these general components make up a basic bridge structure.
- Deck: The deck is the roadway surface of the bridge, where vehicles, pedestrians or other forms of traffic travel.
- Superstructure: The superstructure refers to the portion of the bridge above the piers or abutments and includes the deck, beams, girders, arches, trusses or other load-bearing elements that support the bridge deck.
- Substructure: The substructure consists of the components that support the superstructure. It includes piers, abutments, foundations and other elements that transfer the loads from the superstructure to the ground.
- Piers: Piers are vertical support structures built to withstand and distribute the loads from the bridge deck and superstructure. They are usually constructed in a series along the length of the bridge to provide intermediate support.
- Abutments: Abutments are support structures located at the ends of a bridge. They are designed to withstand the horizontal forces and moments exerted by the superstructure and transfer those forces to the ground. Abutments often incorporate retaining walls to hold back the earth and provide stability.
- Bearings: Bearings are devices between the superstructure and substructure to allow for controlled movement and rotation. They accommodate thermal expansion, contraction and other forces that can induce bridge movements.
- Girders: Girders are horizontal beams that span between piers or abutments and support the bridge deck. They are typically made of steel, concrete or a combination of both.
- Arch: An arch is a curved structural element that carries loads primarily by compression and transfers them to the abutments or piers. Arches can be made of masonry, concrete or steel.
- Trusses: Trusses are frameworks made of interconnected members that form triangles or other geometric shapes. They are often used for longer spans and can be made of steel or timber.
- Cables: Cable-supported bridges use cables as the primary load-bearing elements. These cables are typically made of steel and can be arranged in various configurations, such as suspension or cable-stayed bridges.
What is the Simplest Bridge to Build?
The simplest bridge to build is typically a beam bridge. Beam bridges consist of horizontal beams supported by vertical columns or piers. A big part of their simplicity is their use of common, easy-to-source materials like reinforced concrete or steel.
The construction process of a beam bridge generally involves the following steps:
- Site preparation: Clear the area where the bridge will be constructed and level the ground.
- Foundation construction: Construct the foundations or piers that will support the bridge.
- Beam placement: Install the horizontal beams across the supports.
- Deck installation: Place the bridge deck on the beams. The deck is often made of concrete, asphalt or other materials suitable for travel.
- Finishing touches: Add necessary safety features such as guardrails and barriers. Conduct inspections and ensure the bridge meets the required standards and regulations.
It’s important to note that while a certain type of bridge is easy to build or efficient for everyday travel, it’s not always the best bridge for every situation. A tremendous amount of science, engineering and planning goes into designing each unique bridge.
The Best Bridges Are Built With the Best Equipment
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Sources:
Business Insider | Engineering Insider | Explain That Stuff | Britannica | MadeHow | How Stuff Works | Engineering Feed | PDH Bridges | Bright Hub Engineering
