Drones as Damage Detectors? Researchers Consider Remote Aircraft as Bridge Inspection Tool

According to the American Society of Civil Engineers, nearly one quarter of bridges across the country are structurally obsolete and 11 percent are structurally flawed.

Timber bridges in Pennington County, South Dakota.

Timber bridges in Pennington County, South Dakota.

Researchers from the Forest Products Laboratory (FPL) and South Dakota State University are on a mission to identify effective inspection methods, especially where there are accessibility challenges for inspectors, in an attempt to improve this statistic. The team is posing an interesting question as part of their search: Can drones help detect bridge damage? FPL Research General Engineer James Wacker is taking to the skies to find out.

Wacker and his fellow researchers are investigating whether the use of a remotely piloted aircraft, or drone, is a cost effective solution to help inspectors pinpoint areas of structural decay and degradation. Drones can be armed with high-resolution cameras that allow for recording of highly detailed images and videos, along with other tools such as infrared imaging.

Beginning in early spring 2017, the researchers will team up with the South Dakota Department of Transportation to conduct a drone inspection of two timber bridges in South Dakota. High-quality images from the drone will be evaluated and compared with data from conventional inspections.

The final results of the study will be issued in a report that will document the drone inspections and offer recommendations for drone-based inspection procedures.

To learn more about this study, read the full Research in Progress report.

Blog post by Francesca Yracheta

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.

glulambridge

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.

map

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.

 

 

Durability and Wood Protection for Historic Covered Bridges in the United States

Covered bridges are iconic structures in the United States. Over half of the 16,000 covered bridges found across the globe are located in the US. Most were built in the mid- 19th century and found mostly east of the Mississippi River. The unique cultural and architectural qualities of covered bridges drive efforts to protect them from biological and physical deterioration as well as structural damage by vandalism and arsonists.

Portland Mills Bridge, Parke County, Indiana

Portland Mills Bridge, Parke County, Indiana

The National Historic Covered Bridge Preservation Program, sponsored by the Federal Highway Administration, was established to preserve these unique historic structures through research to restore, rehabilitate, and protect them. Vina Yang and Carol Clausen of the Forest Products Laboratory’s Durability and Wood Protection research group, presented a poster paper for the International Research Group on Wood Protection. Their poster, Durability and Wood Protection for Historic Covered Bridges in the United States, was presented at a spring conference in St. George, Utah.

The Portland Mills bridge was constructed using a Burr Arch truss.

The Portland Mills bridge was constructed using a Burr Arch truss.

Protecting covered bridges from decay and insect damage is a top goal and typically done through in-place remedial treatments. Naturally-durable locally-sourced wood species for above-ground replacement components are suitable alternatives to treated wood during bridge rehabilitation. Likewise, guidance for selection of replacement fasteners is available.

Fire is a leading cause of loss and damage for covered bridges, sometimes accidental but also commonly by arsonists and vandals. Traditional fire prevention measures such as sprinklers, alarms, and fire retardant treatments have been evaluated along with the development of new technologies based on flame detectors, fiber optic sensors, and infra-red camera systems that could be used to alert authorities to possible acts of vandalism.

Three-dimensional laser scanning is being used to document as-built design details to authenticate restoration efforts. A variety of new remote sensing technologies are also under development, focusing on continuous remote monitoring of biological and physical conditions in bridges.

Engineered Wood Products Benefit from Better Adhesives

Wood construction materials like plywood or laminated veneer lumber rely on adhesives for part of their structural integrity. When used in outdoor applications, however, humidity can affect their performance even when the materials are mostly protected from the elements.

Joseph Jakes

Joseph Jakes

FPL researcher Joseph Jakes is taking a closer look at the relationship between moisture, adhesives, and wood, particularly as it relates to historic covered bridges. The roof structures keep the heavy timber trusses dry enough that they have lasted 100 to 200 years. But when historic bridges are repaired using today’s engineered wood products, the swelling and shrinking of wood due to humidity changes can cause wood-adhesive bondline failures that result in further costly repairs.

Jakes is working to develop new, sophisticated techniques to better understand the interactions between wood and adhesives at the cellular level. These techniques can be used to formulate improved adhesives, resulting in more cost-effective methods for preserving historic covered bridges.

The results of this project reach beyond the benefits of historic bridge applications. The development of more durable engineered wood products promotes the forest products industry as a whole by increasing the use of wood in outdoor applications. This study will also add to greater fundamental understanding of how wood cell walls swell with moisture.

This project is being conducted in cooperation with the Argonne National Laboratory and the Oakridge National Laboratory.

Improved adhesives will help reduce costly repairs to historic covered bridges.

Improved adhesives will help reduce costly repairs to historic covered bridges.