Transportation Defined: Pier caps cap piers

Pier Caps

Pier Caps

By David Rookhuyzen / ADOT Communications

If you’ve driven Interstate 10 in Casa Grande recently, then you probably noticed work going on to expand the freeway to three lanes in each direction near Interstate 8. That includes expanding bridges carrying I-10 over Jimmie Kerr Boulevard and the Union Pacific Railroad tracks.

Next year cars will use the larger bridge on a wider I-10 without giving much thought to the engineering behind it. But for now they can see the new vertical supports known as piers capped by what are known as – wait for it – pier caps. Pier caps creating the horizontal section in the picture above will eventually support bridge girders.

Erin Kline, an engineer on the project, explained the role these vertical concrete beams will eventually play.

“Pier caps transfer the loads from the superstructure to the piers. They hold the bridge girders on bearing pads and disperse the loads from the bearings to the piers. Bridges with piers will all have pier caps to transfer the load from the superstructure. I would say majority of the bridges in Arizona are like this,” Kline said.

We’ll have more to say about the anatomy of this project moving forward. For now you can read more about the coming improvements at the project's website.


Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained...leave a comment here on the blog or over on our Facebook page!