Thomas Covered Bridge

This project included the total rehabilitation of a 119-year-old historic covered bridge in Armstrong Township, Indiana County. The Thomas Bridge is the only known Town Lattice Truss Bridge with a single bottom chord in the United States. The wooden Town Lattice Truss was modeled and analyzed using WinSTRUDL to determine its capacity for its own dead load as well as AASHTO wind loads and BOCA snow loads. The existing floorbeam and lateral bracing system was replaced with steel beams and diaphragms; including PTFE coated stainless steel plates attached at the interface of the truss bottom chord and the diaphragms to allow vertical and horizontal translation while providing lateral/torsional stability. The structural decking became glued-laminated panels with longitudinal deck planks to maintain the historic appearance. Of outstanding significance on this project was the coordination between the Pennsylvania Department of Transportation, the Pennsylvania Department of Environmental Protection and the Pennsylvania Historical and Museum Commission. Maintaining each entity’s standards was critical, however, the need for the design exceptions did not stop the project from being completely designed and approved on schedule.


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Gibson-Thomas Engineering Co., Inc. is a multi-discipline consulting engineering firm established in 1916 in Latrobe, Pennsylvania. Our past experience, key staff and commitment to total client satisfaction are the major factors that our clients consider when contracting with Gibson-Thomas Engineering.

724-539-8562
Corporate Office
  • Corporate Office
    • 1004 Ligonier Street
      Latrobe, PA 15650
    • P: 724-539-8562
Pennsylvania Offices
  • Clarion Area Regional Office
    • East Brady, PA
    • P: 724-526-2190
  • Harrisburg Area Regional Office
    • Camp Hill, PA
    • P: 717-612-9880
  • Indiana Area Regional Office
    • Indiana, PA
    • P: 724-471-2246
  • Pittsburgh Area Regional Office
    • Wexford, PA
    • P: 724-935-8188
Florida Office
  • Fort Myers Area Regional Office
    • Ft. Myers, FL
    • P: 239-776-2908
Virginia Office
  • Virginia Office
    • Richmond, VA
    • P: 804-672-4221