Trivia Tuesday, July 8

Question: What is the main purpose of an expansion joint in bridge construction?

C. To accomodate thermal movement

Expansion joints are a critical component in bridge construction, designed to absorb the thermal movement of materials caused by seasonal temperature changes.

As bridges are exposed to heat in the summer and cold in the winter, the steel and concrete used in their construction naturally expand and contract. Without expansion joints to accommodate this movement, structural elements could crack, deform or experience premature wear.

According to a Bridge Preservation report from the Federal Highway Administration (FHWA), temperature changes can result in length variations of several inches in longer bridges. Expansion joints are installed at strategic points—typically between spans or between the bridge deck and abutments—to absorb these movements without compromising the structure’s performance.

These joints are designed to allow movement in multiple directions, including longitudinal, transverse and sometimes vertical motion. This flexibility helps prevent internal stress buildup that could otherwise transfer to critical bridge elements such as beams, piers and bearings.

The FHWA identifies several common types of expansion joints, including strip seals, modular joints and finger joints. Each type accommodates a specific range of movement and traffic loads.

For example, modular joints are used on long-span bridges with large, expected movements, while strip seals are more common on shorter spans with moderate movement needs.

Beyond accommodating thermal expansion, expansion joints also serve to protect the bridge’s substructure. Properly sealed joints prevent water, dirt and road salt from infiltrating the structure—reducing the risk of corrosion and degradation.

In northern climates especially, freeze-thaw cycles and deicing chemicals can accelerate deterioration if joints are not functioning properly.

When expansion joints are neglected, the consequences can be severe, according to the FHWA’s report. Improper joint function can result in deck cracking, pothole formation and water damage to reinforcing steel. FHWA guidance emphasizes the importance of regular inspection and maintenance, including cleaning, resealing and timely replacement of worn or damaged components.

Recent advancements in expansion joint materials and design are improving durability and reducing long-term maintenance needs. Newer joint systems incorporate flexible elastomers, corrosion-resistant steel and prefabricated elements to speed installation and extend service life. These improvements are increasingly important as bridges across the U.S. age and undergo rehabilitation.

Ultimately, expansion joints are far more than a design detail—they are essential to the safety, performance and longevity of modern bridges. By accommodating natural thermal movement and shielding internal components from damage, they help ensure that bridges remain reliable and cost-effective throughout their service lives.

Have a question you'd like featured in our weekly Trivia Tuesday series? Email Harlee Hewitt, Associate Editor of R&B at [email protected].