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HAER Surveys

HAER has surveyed 86 covered bridges as part of the National Covered Bridges Recording Project. The archival documentation produced for these surveys is housed at the Library of Congress in the HAER Collection.


Fly-Through Animation

Photograph of West Union Bridge entrance. The text painted on the bridge reads: "1876, J.J. Daniels, West Union. Cross this bridge at a walk."

West Union Bridge (HAER IN-105) is the work of the prolific Indiana covered bridge builder Joseph J. Daniels (1826-1916). It is an excellent example of his use and development of the Burr-Arch Truss. Read more about the bridge and watch the fly-through.


HAER Engineering Studies

The following engineering studies have been carried out or are in progress:

Detail of measured drawing: Gilpin's Falls Bridge's Burr-Arch truss


Detail of measured drawing: Contoocook Railroad Bridge's Town truss


Detail of measured drawing: Eldean Bridge's Long truss


Detail of measured drawing: Pine Bluff Bridge's Howe truss


  • Moose Brook Bridge (HAER NH-48, forthcoming)
  • Pine Bluff Bridge (HAER IN-103)
Detail of measured drawing: Morgan Bridge's Queenpost truss

Other truss types:


Detail of measured drawing: Sulphite Railroad Bridge's deck

Additional studies:

    • Analyzing Covered Bridge Floor Systems (HAER NH-53, in progress)
    • Covered Bridge Educational Models (HAER MD-190, in progress)


Recently Completed Engineering Study: Strength of Burr-Arch Trusses

Photograph of Burr Arch truss model

Significance: Beginning about 1804, Theodore Burr (1771-1822) built wooden covered bridges that combined a multiple-kingpost truss with an arch into one structural form. The Burr arch-truss is now the most common type in the inventory of extant nineteenth-century covered bridges in the United States. However, there is considerable variability in the geometric parameters and details used for actual bridges. Results of a survey of thirty Burr arch-truss bridges were used to design and fabricate a 2/3-scale symmetry model of a Burr arch-truss. This model was load-tested to investigate the behavior of Burr arch-trusses at strength. The overall observations from the tests are that strength is connection-controlled, flaw-controlled, and generally brittle. Some general principles of strength limit state analyses of structural systems are presented in the context of Burr arch-trusses.

Authors: Dario Gasparini, Stacey Hursen, Gregory Willenkin, Kamil Nizamiev, Case Western Reserve University, 2015.

Project Information: The Strength of Burr-Arch Trusses research project was facilitated through Cooperative Agreement No. P10AC00630, between NPS and CWRU. Christopher H. Marston, HAER Architect, served as project leader. Prof. Dario Gasparini developed and led the research, with engineering students Stacey Hursen, Gregory Willenkin, and Kamil Nizamiev, all of Case Western Reserve University. Rudy Christian constructed the truss model, assisted by his wife Laura and Andrew Schaeffer. David Simmons, James Cooper, Campbell Fitzhugh, and Linda Gasparini assisted with the survey of Burr arch-truss bridges in Ohio, Indiana, and Pennsylvania.

Download the Report: The report will be available on the Library of Congress' website next year. Until then, you can download the report here (pdf, 12 MB).

Supplemental Materials: The following files are provided for use in the peer-review process. We will post them in a different format for public use once the study is published. The video and photographs show the load-testing of the Burr arch-truss model on May 21, 2015. Both focus on the moment of failure, when the model was loaded to the maximum load of 68.8 kips.