Trunnions have been around since the medieval era, but unless you’re in construction, you may not have heard of them before. They’re used in a variety of different applications, including bridge construction, and allow multiple parts to move at the same time. You have probably used trunnion bearings in your daily life without even realizing it. Trunnions appear in everything from vehicles and trailers to satellites, hydraulic cylinders and even stage lighting.

Here’s a brief overview of what trunnion bearings are and how they’re used in bridge construction.

What is a trunnion bearing?

The word “trunnion” comes from the old French for “trunk,” which refers to the trunnion’s shape. The trunnion is inserted into a full or partial cylinder to create a trunnion bearing. Both the shaft (the trunnion) and the cylinder can rotate, which allows the joint to pivot as necessary.

One easy example of a trunnion bearing is your shoulder joint: your shoulder has a ball-and-socket joint, which allows your arm to move in different directions (including rotating 360 degrees) while still staying attached. Depending on how a trunnion bearing needs to rotate, the design can be different, but the concept is the same.

When designing a trunnion bearing, engineers determine whether the shaft or cylinder (or both) need to rotate, and plan accordingly. They may even use multiple shafts to achieve their goals. While this can be complicated, computer assisted design programs can help them design a part that will get the results they need.

One of the most important considerations is how much stress will be placed on the trunnion bearing. If a trunnion bearing is improperly designed, it will break apart when used. That’s because the motion can “pull” the trunnion in different directions, especially if there are multiple shafts involved.

Obviously, this is a simple overview—trunnion bearings can differ depending on their application, and range in size from small objects to massive pieces that support bridge construction.

How trunnion bearings help bridge construction

Trunnion bearings are used in movable bridges, like drawbridges. For example, trunnion bearings can act as an axle at the top of a bridge to support the weight of the bridge, plus the counterweights. This allows the bearings to raise and lower the lift span.

As you might expect, trunnion bearings for bridge construction aren’t widely available—in many cases, they have to be custom made for the specific bridge. This is where the help of an engineer and their computer assisted design software can help design, plan and execute the bridge construction.

If you have a project that needs a trunnion bearing—particularly a movable bridge—it’s important to partner with the right construction and design firm. ACMS Group has more than two decades of experience overseeing major construction projects, including bridge construction. If you need expert engineering and construction experience for your project, we can help. Reach out to us today to learn more about our services and arrange a consultation. We look forward to discussing your project.