Arch Bridge



ARch Bridge Station SImulation

How Do the Abutments Support an Arch Bridge?

Resources needed - at least 4 pieces of cardboard, cut into 1” x 11” strips (Please prepare the materials ahead of time).

Instructions - Cut a strip of cardboard that's about one inch by 11 inches. Gently bend the strip so that it has a curve.

Bixby Creek Bridge, Monterey, CA Photo credit: © Jay Spooner/iStockphoto

Step 1

Position the cardboard on a table so that it resembles an arch. Press down on the center of the arch. What happens to the ends of the cardboard?

Step 2

Next, place a stack of books at each end of the arch. Press again. Now what happens? Notice how the stacks of books act as abutments, keeping the ends of the arch from spreading outward.

More Background Information

This is more for the teachers and facilitators to acquire more background knowledge of each type of bridges in order to facilitate this session.

Arch bridges are one of the oldest types of bridges. Arch bridges have great natural strength. Instead of pushing straight down, the weight of an arch bridge is carried outward along the curve of the arch to the supports at each end. These supports, called the abutments, carry the load and keep the ends of the bridge from spreading outward.

When supporting its own weight and the weight of crossing traffic, every part of the arch is under compression. For this reason, arch bridges must be made of materials that are strong under compression.

Today, materials like steel and prestressed concrete have made it possible to build longer and more elegant arches, including a spectacular 1,700-foot span in New River Gorge, West Virginia. (More typically, modern arch bridges span between 200 and 800 feet.)

One of the most revolutionary arch bridges in recent years is the Natchez Trace Parkway Bridge in Franklin, Tennessee, which was opened to traffic in 1994. It's the first American arch bridge to be constructed from segments of precast concrete, a highly economical material. Two graceful arches support the roadway above. Usually arch bridges employ vertical supports called spandrels to distribute the weight of the roadway to the arch below, but the Natchez Trace Parkway Bridge was designed without spandrels to create a more open and aesthetically pleasing appearance. As a result, most of the live load is resting on the crowns of the two arches, which have been slightly flattened to better carry it. Already the winner of many awards, the bridge is expected to influence bridge design for years to come.

The Pont du Gard aqueduct Photo credit: © Agnieszka Gaul/iStockphoto

The New River Gorge Bridge Photo credit: © John Brueske/iStockphoto