This report describes the procedure developed and being employed to determine and assess live-load stresses in structural members of welded steel bridges on extended· weight coal haul routes. Those bridges are routinely subjected to loads from coal trucks in excess of those permitted on other routes. Those elevated loads may result in high stresses in bridge members. Of principal concern are certain weld details on steel bridges that are susceptible to fatigue cracking when subject to high live-load stresses. Seventeen welded steel bridges on extended-weight coal haul routes have been identified for investigation under this study.

The study test procedure consists of 1) a review of coal-haul data and plans to identify lanes of a bridge subject to greatest coal-truck loading, 2) identification of weld details of interest for analysis on portions of the bridge superstructure subject to high live-load stresses, 3) field application of strain gages to measure live-load stresses at locations of interest on a bridge, 4) continuous monitoring of live stresses from routine traffic for an extended period and 5) data retrieval and reduction and fatigue analysis.

Fatigue analysis is based on the number of stress cycles measured during the field test and the equivalent resolved live-load stress. That is compared to the 1992 AASHTO fatigue performance data for applicable structural details (e.g. welded connections). An exemplary use of the study test procedure is given for the KY 15 bridge over the North Fork of the Kentucky River and KY SO in Perry Co. This report describes the test locations, test procedures and results of the derived test data.

The field tests will indicate the level of live-load stresses to which the bridges are exposed. Additionally, the fatigue analyses may indicate whether welded steel bridges on extended-weight coal haul routes are susceptible to fatigue damage.

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The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the views or policies of the University of Kentucky, the Kentucky Transportation Cabinet, nor the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. The inclusion of manufacturer names and trade names are for identification purposes and are not to be considered as endorsements.