Fatigue analysis of strengthened steel beams

Many steel structures around the world occur damage because of cyclic loading. To cope with this situation, It is more advantages to strengthen damaged steel structures than rebuilding damaged steel structures. In this study, The performance on pre-cracked steel beams under cyclic loading was investigated on bolt space of the bolted cover plate to Turkish Steel Structure Code. In addition, The pre-cracked steel beam was strengthened with CFRP and compared fatigue performance. Total six specimens were performed using IPE120 profile made of S275 steel material, two of those experiments were performed using unstrengthened specimens, three of them were performed using specimens strengthened with bolted steel plates, one of them was performed using specimen strengthened with CFRP patches. The four-point bending test installation was performed under cyclic loading. The cyclic loading had a constant amplitude, stress ratio was 0.1 and a loading rate was 2 Hertz. Furthermore, the number of initial crack cycles, the change crack length frequently and stiffness changes until fracture were observed during the experimental tests. Experimental results were analyzed using S-N graphs in AASHTO. The specimens used in the experiments were simulated using the finite element method (ABAQUS Packet Program). In this chapter, stress analysis is controlled stress, strain and displacement for three different cases; analyses of beams with different crack lengths, the pre-cracked beams strengthened with different strengthening methods and the crack geometry was changed. In addition, parametric study was practiced and compared results. At the end of this study, as the distance between the bolts of bolted steel plates increases, the fatigue life increases. The shortest and longest to Turkish Code bolt space of the bolted cover plates were extended fatigue life between 1.5 and 2.1. Pre-cracked steel beam with strengthened with CFRP patches did not perform well due to the problem of debonding between CFRP material and steel surfaces, although it increased the fatigue life 1.5 times.