PSI - Issue 13

Mihaela Iordachescu et al. / Procedia Structural Integrity 13 (2018) 554–559 M. Iordachescu, A. Valiente, E. Scutelnicu/ Structural Integrity Procedia 00 (2018) 000–000

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The structural role of welded joints is not merely resistant since its deformability is influencing the stress distribution in the joined elements. The technical codes include the joint deformability in the stress calculation by means of the moment-rotation diagram, which can be obtained from elastoplastic models sustained by experimental results. In steel structures, the importance of welded joints makes the design codes maximize the control of the welding procedures and of the weld quality. Only qualified welding procedures and welded joints with detected imperfections/defects, in the mandatory inspections, that do not exceed the specifications limits are accepted. Otherwise, the repair of the rejected welded joints is necessary and a specially designed procedure must be used (EAE, 2011). However, the approval of the repairing procedure is not an easy task, because of the design code requirement that repaired welds should undergo the same inspections and tests as the as-designed welds, and provide comparable performances (EAE, 2011). The rejection of welds, on-site performed, originating from a systematic error happens on few occasions. However, when it does occur it gives rise to a problem of such financial and constructive magnitude that the need to design an effective repairing method becomes imperative. The present paper has emerged from this need and the express requirement of the responsible inspection body responsible to give evidence to support the fact that the repaired welds are not more brittle than the as-designed, new ones. Therefore, precracked compact tensile (CT) specimens with the resistant ligament located in the heat-affected zone (HAZ) were used to perform fracture toughness tests. The specimens’ dimensions were determined by the structural detail configuration and slightly differ from those recommended in the fracture toughness standards. The research objective, namely the analysis of the resistant ligaments as plastic hinges, including and excluding respectively the effects of crack ductile growth and of the yield strength in the joints, is addressed. While Fracture Mechanics is used to assess the structural performance of welded joints, the method employed in this work goes beyond the standardized procedures, since it analyses fracture tests performed with precracked CT specimens when a fully plastic regime prevails, with the cracked ligaments lying on the HAZ of the welded joints. Nomenclature   a relative crack size B thickness of compact tensile specimen BM base metal COD crack opening displacement CT compact tensile specimen F applied load HAZ heat-affected zone M bending moment due to F M(0) bending moment at fully plastic yielding occurrence NW designed weld RW repaired weld W width of compact tensile specimen  x non-dimensional rotation centre coordinate σ Y yield strength    p plastic component of COD Θ rotation angle 2. Structural detail configuration and fracture experiments The welded joint subject of this present research is a junction of H section steel columns made between building floors. Shielded Metal Arc Welding was the welding/repairing technique employed. A reinforcing plate, of S355 steel ensured the connection of the upper column, a HEA-400 profile of S275 steel, to the lower one. The need of repair arose from the erroneous welded joint made between the wings of the HEA-400 profile and the reinforcing plate (Fig.1a): a 90 0 angle weld without edge preparation was performed instead of the designed bilateral butt welding, with