Accurate and Rapid Determination of Fatigue Damage in Bridge Superstructures

629103PDFTech ReportBridge superstructuresTraffic loadsVehicle weightTestsHahin, ChristopherSouth, Jeffrey M,Illinois. Dept. of TransportationUnited States. Federal Highway AdministrationNTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and StructuresUS Transportation CollectionFifteen representative steel bridges throughout the State of Illinois wereinstrumented with foil strain gages to determine their frequencies of loadingand the magnitudes of stresses induced by traffic over a 3 to 8-hour period,depending on traffic volume. Reinforced prestressed or post-tensioned concretebridges were not included in this study. Fatigue prone details, such as coverplated wide flanges, were instrumented. For each stress range incrementgathered by the data acquisition system, the cumulative damage sustained overan extended number of years was compared with the number of available fatiguecycles for that stress range using published S-N data for various details andthe Palmgren Miner linear damage rule. A new equation for factor of safetyfor structural details subject to fatigue is described, taking dead load, liveload, and bridge detail fatigue strengths into account. A new histogram-lineardamage method of assessing future fatigue damage in bridges which takestraffic growth and increased truck weights Into account is also described.Other non-welded designs to main load carrying members were examined forsusceptibility to fatigue effects, including riveted beams, weathering steels,reinforced concrete in air (without severe cracking), and post-tensioned beamsthrough a review and discussion of the literature. The actual effect of anincrease in gross vehicle weight on the measured maximum stress range responseof a particular bridge was measured. The histogram-linear damage methodfavorably compared with the root mean cube-linear damage method and to thefatigue damage procedures given in NCHRP 299