Nitsch Engineering is providing structural engineering services associated with the load rating of a built-up steel girder bridge with an open deck of timber railroad ties. The existing bridge is located on private property and does not carry vehicular traffic. The owner, Seaboard Solar, intends to construct a solar farm on the property, and the bridge is being evaluated to determine its ability to provide access for emergency vehicles. Due to the poor condition of the existing timber decking, it is assumed that for load rating purposes, a new reinforced concrete deck would be constructed prior to the bridge’s use for vehicular access.
Since no plans/surveys exist for the bridge, Nitsch Engineering’s survey team used laser scanning to perform a bridge survey. The scan data was used to prepare AutoCAD drawings that detail structural components and dimensions for use in the load rating. Using these drawings and noted existing conditions identified and measured during a site visit, the load rating of the superstructure is being prepared for statutory and HL-93 vehicle loads using Massachusetts Department of Transportation Load and Resistance Factor Design (LRFD) standards. Special care is taken to account for capacity reductions due to section losses and ineffective structural components caused by deteriorated rivets. After using the AASHTOWare Bridge Rating (BrR) software to model the bridge, a load rating report will be compiled and submitted to Seaboard Solar. The findings of the load rating report will be used to determine the scope of the rehabilitation design during the deck replacement project.