A New Approach to Bridge Inspection and Safety

Unmanned aerial vehicle – Digital image correlation (UAV-DIC) System

Forest Products Laboratory’s (FPL) researcher James Wacker with collaborators from the Department of Civil Environmental Engineering, South Dakota State University are working on a new approach to inspecting bridges that will allow inspections to one day be more cost-efficient, easier to conduct, more accessible, and safer for motorists and inspectors alike. The journal article, “New Bridge Inspection Approach with Joint UAV and DIC System,” was published in Structures Congress 2020.

Our nation’s bridges have been under an every-two-year mandated inspection for nearly 50 years. The current method of inspecting bridges is accomplished largely by visual assessment often using costly snooper trucks. Wacker describes this approach as “a passive approach that has provided subjective and unreliable data.”

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The Latest and Greatest: FPL's NewsLine Hits the Web!

FPL researchers are hard at work discovering the amazing possibilities wood presents to make our lives safer and better. You can read all about what they’ve been up to in our quarterly newsletter, NewsLine.

newsline-2015-2-thumbIn this issue, you’ll learn about the importance of fasteners in keeping your deck safe, research on wood bridges, a new demonstration house, recycling preservative-treated wood, the amazing things we can do in our new pressure treatment plant, and much more.

Past issues of NewsLine can be found on FPL’s website.

If you’d like to have NewsLine delivered right to your inbox, simply send an email request to mailroom_forest_products_laboratory@fs.fed.us

We hope you enjoy this issue and wish you a wonderful holiday season.

-The Newsline Team

Better Bridges: Considering Wood-Concrete Construction

The United States is facing an infrastructure crisis. According to the American Road & Transportation Builders Association, over 61,000 bridges in America are structurally deficient. Although expensive to maintain, particularly in these tough economic times, when these vital pieces of our transportation system fail, the human toll is incalculable.

One needs to look no further for a reminder than the 2007 collapse of the Interstate 35 bridge near Minneapolis, Minnesota. The steel truss arch bridge suddenly failed under the load of rush hour traffic, plunging into the Mississippi river below. The bridge had consistently ranked near the bottom of nationwide federal inspection ratings, and its collapse claimed 13 lives. In the disaster’s wake, fearing similar incidents, federal and state governments mobilized to assess the condition of their own bridges.

As states continue to evaluate and improve their transportation infrastructure, researchers at the Forest Products Laboratory (FPL) are working hard envisioning the future of durable and cost-effective bridges. They believe that the answer may lie in wood, one of mankind’s oldest construction materials, used in conjunction with another time-tested material, concrete.


An example of a composite timber girder–concrete deck bridge

In cooperation with Iowa State University, Research General Engineer Jim Wacker from the Engineering Properties of Wood, Wood Based Materials, and Structures unit at FPL, has set out to investigate the state-of-the-practice related to the use of concrete decks supported by glued-laminated (glulam) timber girders for highway bridge applications. Glulam timber bridges have already proven themselves in our nation’s National Forests, but the practice of using them in conjunction with concrete decks is relatively scarce across the highways of America. The project, which commenced earlier this year, is expected to be finished June 2017.

A composite timber-concrete bridge consists of a concrete slab rigidly connected to supporting timber sections so that the combination functions as a unit. There are two types of composite timber-concrete bridges: T-beam decks and slab decks.

T-beam decks are constructed by casting a concrete deck, which forms the flange of the T, on a glulam beam, which forms the web of the T. Composite slab decks on the other hand are constructed by casting a concrete layer on a continuous base of longitudinal nail-laminated sawn lumber.

Recent research has found that performance of timber bridges constructed 50 to 70 years ago is above average, but despite this, only a small percentage of new bridges built every year are built with graded and engineered lumber. This project hopes to change that.

Composite slab decks have been used as far back as the 1930s, and Wacker’s reassessment of concrete-timber bridge construction will arm bridge engineers with a wealth of knowledge on the best practices of the past — so that bridges of the future can be as cost-effective, durable, and safe as possible.

For more information, please see the FPL Research in Progress publication Investigation of Glulam Girder Bridges with Composite Concrete Decks.

Taking the Long Road: Studying Timber Bridge Service Life

Timber bridges are a much larger part of the U.S. transportation system than many people realize. In fact, one-third of the states have more than 500 timber bridges in their inventories, and wood continues to be a viable option for modern bridge construction.


Click to enlarge in Flickr.

There is a significant need for more reliable data on the expected service life of highway bridges, as engineers begin to implement life-cycle costs analyses within preliminary bridge designs. Claims are made that the expected longevity of concrete and steel bridges stand at 75 years or more, while timber bridges (which engineers are less familiar with) are estimated to last only 20-30 years. Unfortunately, since little data exists, these claims are not based on actual performance data.

bridgeTo generate more quantitative and unbiased data on timber bridge durability, Forest Products Laboratory (FPL) researchers designed a nationwide study in conjunction with the Federal Highway Administration. The goal of the multi-year team effort was to assess the condition of more than 100 timber bridge superstructures around the U.S. in order to provide a better understanding of their design, performance, and durability characteristics.

Six different inspection teams with members from various organizations conducted field assessments of 132 timber bridges. Selected bridges were required to be along public roadways, be in service for at least 16 years, and have available records regarding inspection, maintenance, and repair. The in-depth inspections included visual, probing, and nondestructive evaluation techniques to characterize the condition of the primary bridge superstructure components.

Results of this study found that timber is a durable option for primary structural members in highway bridges superstructures, and that it can perform adequately for more than 70 years when properly pressure-treated with preservatives.

A comprehensive technical report (currently under review) will include more detailed information about all the timber bridges evaluated in this study, and will provide the basis for the development of life-cycle costs analyses and bridge deterioration rate modeling for timber bridges superstructures in the future.

More information on this study can be found in the Proceedings of the 2015 Structures Congress held April 23-25, 2015, in Portland, Oregon.



Science Olympiads Put Bridges to the Test

Students from the Science Olympiad team at Hamilton Middle School in Madison, Wis. had a unique opportunity to experience the Forest Products Laboratory’s (FPL) testing equipment first hand. FPL’s Engineering Mechanics and Remote Sensing Laboratory is equipped with machines that can perform load tests, including specimen compression, bending, and shear. Such tests can come in handy when one is attempting to design a strong, lightweight structure.


Bridge test in progress.

FPL engineers and technicians have been offering guidance to the team for the bridge building event, one of many events that the students compete in. The goal of the event is to build the lightest wooden bridge that can still hold a maximum weight of 15 kilograms.


Students examine their bridge design after testing.

FPL engineers met with the team before they designed their bridges, explaining stresses within bridges they might want to consider, and then tested one of several designs assembled by the team. Witnessing the testing in person allowed the students to see how their bridge deformed under the load of the testing machine and to make decisions about how they could improve their design.

The four-student team will be competing for the Wisconsin state title on March 14, 2015. Hamilton Middle School has won the state title for the past five years in a row and is hoping for a sixth consecutive victory, sending them to Nationals in May.