Fatigue durability of cracked steel beams retrofitted with high-strength materials

Steel structures under dynamic loading are prone to fatigue damage and a considerable number of metallic infrastructure in the world are structurally deficient. The fatigue behavior of defected steel beams mechanically retrofitted by different high-strength materials was experimentally studied in this work. The steel beam was I section with an artificial cut at the mid-span and tested under fatigue loading. The specimens were strengthened on the tension flange by carbon fiber reinforced polymer (CFRP) laminate, high strength steel (HSS) plate or SafStrip (SAF) plate. Three mechanical anchorage schemes were designed to test their efficiencies. The fatigue crack propagation was recorded to explore the crack growth rate. Strain gauges were installed on the strengthening material to monitor the strain development. The stress intensity factor (SIF) at the crack front was calculated based on analytical solution and numerical simulation; then, the results were compared with experimental findings. It was demonstrated that the strengthening significantly increased the fatigue life of the beams. The attached strengthening materials not only globally shared a portion of the far-field load on the cracked steel section but also provided a local constraining effect, both of which reduced the crack mouth opening displacement (CMOD) and SIF. The different CMODs resulted from the different retrofitting configurations indicated significant variation in the crack constraining effect caused by various retrofitting systems, which cannot be neglected in analytical modeling.