Risk of utilizing class 2 sections for road bridges

The utilization of Class 2 steel cross-sections for road bridges may result in unwanted stress conditions in the ultimate state analysis. With the proposed global safety factor, the ratio Mpl /Mel=1.1-1.2 and more, is often insufficient protection for maintaining the structure in the elastic range. For serviceability limit states defined with frequent and infrequent loads, which are repeated 120-6240 times, low cycle fatigue criteria may become important. In some cases this will decide the dimensions of cross-sections. The reliability index *bSLS = 1.5 and *bULS = 3.8, mentioned in the EC1 documents, are much too small and with the proposed global safety factor they are actually twice as big. Generally, we can conclude that the risk of utilization of class 2 cross-sections for road bridges does not exclude the problem of low cycle fatigue and therefore additional safety measures are recommended.