Report on Phase 2.3, Investigation of Welded Highway Bridges. Project IHR-64

The object of this investigation was to study the effect of internal flaws on the fatigue behavior of butt-welded connections in mild structural steel, the initiation of fatigue cracks from these flaws and the propagation rates of these cracks in the connections. Since internal flaws occur in many welds it is essential to obtain a better understanding of the behavior of flawed connections so that adequate, yet realistic, code requirements can be established. The study is limited to two major types of defects, porosity and incomplete penetration. The porosity was further subdivided into two categories based on the severity of the defect. The specimens with incomplete penetration were made with an initial 3/16" centrally located crack the full width of the- specimen. The fatigue behavior of the connections with the defects is compared with that of sound welds to observe the effects of the defects on the fatigue strength of the connections. The data are compared with result~ of similar studies found in the literature and also with the AASHO 1970 Specification design requirements. Three of the specimens with incomplete penetration were examined radiographically during the fatigue testing to determine when initiation of the fatigue cracks occurred, and how rapidly they propagated. The results of the crack propagation tests are compared with similar relationships developed for high strength steels. A relationship that better fits the data for mild steel has been developed in a manner similar to that used for the high strength steels.State of Illinois. Department of Transportation. Division of HighwaysU.S. Department of Transportation. Federal Highway Administratio