Chronicling Covered Construction : NDE Helps To Record Historic Bridges

Covered bridges are part of the fabric of American history, and several hundred historic covered bridges still exist to this day. Although much effort is expended to preserve these structures, the high cost of restoration, neglect, vandalism, and arson often take their toll. Many are lost forever.

One of the more famous bridges from The Bridges of Madison County movie was burned in 2003, and Hurricane Irene destroyed a number of New England bridges in 2011.

Because we cannot completely prevent these types of incidents from occurring, the National Park Service’s Historic American Engineering Record (HAER), in cooperation with the Forest Products Laboratory (FPL), has efforts under way to document these historic structures.

A single laser scan of the Roseman Bridge, Madison County, Iowa. (NRRI).

With the help of laser imaging technology, these two organizations are ensuring that the construction triumphs of yesterday are recorded and preserved for future generations.

Three-dimensional (3D) laser scanners are nondestructive evaluation (NDE) instruments that record precise and accurate surface data of objects in a nondestructive manner. These instruments use an infrared beam of light to calculate and record the distance to an object, typically as data points with spatial coordinates.

These data are then analyzed using various types of computer software to generate a detailed image of coordinates and dimensions.

Three-dimensional laser scanners have successfully been used to digitize objects of various sizes ranging from small diagnostic artifacts to large, complex sites of monumental architecture — and now, nestled between these two extremes, are some of our country’s historic bridges.

For more information, please see Chapter 13 of the FPL’s publication Nondestructive Evaluation of Wood: Second Edition.