Multi‐Year Off‐System Bridge Load Rating Program

To meet the Federal Highway Administration’s (FHWA) National Bridge Inspection Standards, the Kansas Department of Transportation (KDOT) has commenced a $75,000,000 multi‐year initiative to load rate each of the 19,200 non‐fracture critical bridges owned by local public authorities across the state. Lochner, which completed the load rating of approximately 600 locally owned fracture critical bridges under a similar initiative, is a member of the consultant team responsible for the load ratings contract covering the southern half of the state. Lochner will load rate close to 3,500 non‐fracture critical bridges over the ten‐year contract.

As an initial task, Lochner assisted in the development of procedures that will guide all load ratings performed under the project. For each allocated bridge, Lochner first collects office data, comprising design plans and prior load ratings, then conducts a field visit to determine the accuracy of that data. Lochner then performs special inspections of each bridge and uses the results to calculate load ratings with American Association of State Highway and Transportation Officials (AASHTO) BrR software. Special haul vehicles—the new standard set in the FHWA Memo HIBT 10—are used to calculate the load ratings, which may be allowable stress ratings, load factor ratings, or load and resistance factor ratings depending on the age and type of the bridge.

Lochner’s designated bridges include a significant number of arch bridges for which no accurate load rating procedure exists. Therefore, Lochner proposed a procedure that based its load rating on a method called the Modified MEXE. The method was originally developed circa World War II by the United Kingdom’s Military Engineering Research and Development unit, which was also responsible for developing the portable, pre‐fabricated, truss bridge known as the Bailey Bridge. Currently in use by the United Kingdom, Lochner studied the method to assure its compatibility with AASHTO’s Manual for Bridge Evaluation. The project team then developed conversions to the US system including nine load rating trucks, created an Excel spreadsheet for the empirical load rating, and developed field investigation forms for collecting arch data and measurements. After beta testing the field forms and office evaluations on a sample of arch bridges, the method was submitted to KDOT and FHWA for approval and the eventual adoption of the method throughout the Kansas by all program consultants. FHWA has called the bridge load rating method promising and commented that other states may be looking to use this method on arch bridges throughout the country.