Department of Civil, Construction, and Environmental Engineering

Our structural engineering faculty and staff working with the Bridge Engineering Center (BEC) have been helping Iowans—and getting national attention for it.

Four projects in particular stand out:

• protecting the bridges of Madison County
• building the latest technology into I-235 bridges
• using decommissioned railroad flatcars for low-volume road bridges
• testing ultra-high performance concrete

Protecting the Bridges of Madison County

Madison County's historic covered bridges—made famous by Robert James Waller's 1992 novel "The Bridges of Madison County" and the 1995 movie directed by Clint Eastwood—have been arson targets in recent years. A September 2002 fire destroyed the 1883 Cedar Bridge. A year later the 1884 Hogback Bridge was damaged by an arson fire.

Our structural engineers are developing round-the-clock monitoring technology to help protect these historic bridges. Brent Phares, the associate director of the BEC and an adjunct assistant professor of structural engineering in CCEE, said the equipment includes:

Flame detection devices. The devices detect infrared light, ultraviolet light and the flicker rate as the light frequencies change. Phares said flames emit a unique light signature the devices will recognize.

Infrared cameras. The cameras record heat rather than light. They'll "photograph" people at the bridge—even on the darkest night. And they'll detect the heat flash if a fire is ignited.

Fiber-optic strain gages. The gages will be attached to the bridge and will measure changes in temperature.

Data from the monitoring equipment will be collected and processed by a computer at the bridge, Phares said. If the equipment detects something suspicious, emergency crews will be notified. Dispatchers will also have access to video images from the monitoring equipment so they can determine whether there's an emergency.

The project is supported by a $126,000 cooperative agreement with the U.S. Department of Agriculture Forest Service's Forest Products Laboratory in Madison, Wisconsin. The laboratory and the center have cooperated for more than 20 years on transportation research projects.

"I believe this will help more than anything we've done," said Todd Hagan, the Madison County engineer. "Our other forms of protection are all after-the-fact. This is hopefully something that will get us there before it's too late."

The project was covered in Good Morning, America; ASCE's Civil Engineering magazine; and USA Today, to name a few.

But the technology isn't limited to just these bridges. It could be adapted to any bridge where security is an issue, said Terry Wipf, Pitt-Des Moines Professor in Civil Engineering and the director of the BEC.

Building the Latest Technology into I-235 Bridges

Our engineers have helped the Iowa Department of Transportation (DOT) monitor and evaluate four bridges as part of the Interstate 235 (I-235) reconstruction project in Des Moines.

"This work that we're doing is going to help build more durable bridges," said Wipf. "They'll last longer and they'll save the state money."

Here are just a couple of examples of how they've helping the state build better bridges over I-235:

Fiber Optic Sensors

They installed fiber optic strain gages in the East 12th Street bridge and the pedestrian bridges at 40th and 44th streets. The gages work by transmitting light through glass fibers. Strain on the fibers changes the light that's reflected back. A black box records the changes and therefore the strains. The system can take up to 250 measurements every second. That strain history is recorded by computers and can tell engineers how a bridge is performing.

High Performance Steel

The East 12th Street bridge was the first—and only—Iowa bridge made with high performance steel. The steel is designed to be stronger and tougher. That means it takes longer for cracks to develop. And when cracks develop, they spread much slower.

Phares said researchers have built fiber optic strain gages into the bridge to continuously measure how the bridge and its new steel perform over time.

The Federal Highway Administration supported the monitoring research with a $155,000 grant from the Innovative Bridge Research and Construction program.

Pedestrian Bridges

To overcome difficulties encountered during construction of the first pedestrian bridge over I-235 at East Sixth Street, the Iowa DOT asked them to install strain gages on the project's other two pedestrian bridges.

Mike LaViolette, a bridge research specialist with the BEC and lecturer in CCEE, said the gages were installed on the hangers supporting the bridges' concrete walking surfaces. The gages measured the forces on the bridges when crews installed the walking surfaces. We also installed accelerometers on the bridges as another way to measure the forces during construction. The instruments helped crews prevent cracking by keeping the forces balanced and within the bridge's design capabilities.

The Iowa DOT supported the monitoring project with about $50,000.

Reusing Decommissioned Railroad Flatcars for Low-Volume Road Bridges

Iowa has the sixth largest number of bridges in the nation. Approximately 80 percent of the 25,000 bridges in Iowa are on secondary roads and are the counties' responsibility. To provide Iowa county engineers with low-cost bridges, the BEC, through research sponsored by the Iowa DOT, investigated the feasibility of using railroad flatcars (RRFC) as the superstructure for low-volume road (LVR) bridges.

Several characteristics make decommissioned RRFCs desirable for use in LVR bridges: they are easy to install, can be used on current or new abutments, are available in various lengths, and are relatively inexpensive.

Based on the results of the feasibility study and a consequent demonstrative project in which two RRFCs were constructed (one in Buchanan County and one in Winnebago County), it was determined that properly engineered RRFC bridges can support Iowa legal loads.

Since completion of the first two phases of the RRFC bridge research (Phase III is currently in progress) close to 20 such bridges have been constructed in Iowa alone. According to Buchanan County Engineer Brian Keierleber, Buchanan County now has 10 RRFC bridges and plans on constructing three more a year for an indefinite period of time.

Research has shown that by selecting the proper RRFCs and engineering the connection between them, they become viable, economical replacement bridges. Keierleber estimates that RRFC bridges require less construction time—approximately one-half to two-thirds the time required to construct a similar-sized slab bridge and at approximately one-quarter to one-half the cost of a slab bridge.

Testing Ultra-High Performance Concrete

Ultra-high performance concrete is made from sand, cement, water and small steel fibers. It does not contain the coarse aggregate found in standard concrete. Because the ultra-high performance concrete is engineered to include finer materials and steel fibers, it's denser and stronger than standard concrete.

Phares estimated a beam of ultra-high performance concrete can hold twice the load of a similar beam made of standard concrete.

The capacity test of the 71-foot beam was part of a $450,000 project to study the innovative concrete. The project was funded by the Federal Highway Administration and the Iowa Highway Research Board.

The researchers spent a June morning applying more and more hydraulic pressure to the top of the beam. They wanted to see how much it could take before breaking. And it took a lot: 595,000 pounds of load. That's more than the weight of seven semi trucks.

Brian Degen, a graduate student in civil engineering, said researchers had predicted the beam would break under 640,000 pounds of load.

It couldn't hold that much. But Phares said a similar beam isn't going to have any problems holding up 100th Avenue over Little Soap Creek in southeast Iowa's Wapello County. When that bridge is built this fall, it will be the first time engineers will use ultra-high performance concrete in an American bridge.

For More Information

To learn more about these and other projects, contact Terry Wipf, 515-294-6979, tjwipf@iastate.edu; Wayne Klaiber, 515-294-8763, klaiber@iastate.edu; or Brent Phares, 515-294-5879, bphares@iastate.edu.