Recorded Stress Histories in Railroad Bridges

Repeated application of stress resulting from locomotives and cars crossing a bridge may cause certain members of the bridge to become a fatigue subject. However, recorded stresses in railroad bridges conducted since 1940 by the Association of American Railroads have shown that only a small percentage of the actual stresses are near the maximum. Also, there are certain factors which tend to favor the bridge in terms of fatigue whereby the actual stresses are less than calculated. Whether or not a stress cycle is completed depends upon the relationship between the axle spacing and the span length. Continuing careful and close inspection is necessary at those locations where fatigue cracks might develop.