Steel structure fatigue

Many steel structures - like bridges, storage tanks, and ships - are held together by welds. And when incidents arise from fast fractures or fatigue failures they can often be traced to weaknesses in the welds. The sinking of the Alexander Keilland oil platform in 1980 is an example. 

The toughness of wood is important in design for exactly the same reasons that that of steel is it determines whether a structure (a frame building, a pit prop, the mast of a yacht) will fail suddenly and unexpectedly by the propagation of a fast crack. In a steel structure the initial crack is that of a defective weld, or is formed by corrosion or fatigue in a wooden structure the initial defect may be a knot, or a saw cut, or cell damage caused by severe mishandling. 

High strength low alloy steels (line pipe, structural) and steels for fatigue intensive applications (axles, bearings, rail steels)... 

To find out possible reasons for the mechanical fatigue, measurements inside the pipe (noise) as well as in pipework and steel structure have verified the vibrations to be very low. Finally to avoid any risk of fatigue, grids supporting the candles have been installed. However, since the installation of this grid a tendency of bridging has been observed, which we did not experience earlier. 

Govindaraju, M. R., Strom, A., files, D. C., Biner, S. B. Chen, Z-J. (1993). Evaluation of fatigue damage in steel structural components by magnetoelastic Barkhausen signal analysis. Journal of Applied Physics, 73, 6165-7. 

Since the use of FRP in steel structures is not as developed as in the case of concrete, attention is mainly focused on several issues. We distinguish flie following main areas of interest related to many aspects that characterize metal structures the intervention on nodes that can significantly reduce the growth of injury due to fatigue, the intervention of tended elements, and compression that allows to greatly decrease the tension in the original structure. 

Bassetti, A., Nussbaumer, A. and Hirt, A. (2000a), Fatigue life extension of riveted bridge members using pre-stress carbon fibre composites , in Steel Structures of the 2000s, ECCS, Istanbul, pp. 375-380. 

Yu. Y. and Chiew, S. P. (2007), Fatigue behaviour of CFRP bonded steel plates . Proceedings of the 5th International Conference on Advances in Steel Structures — ICASS, Singapore, 2007. 

ECCS recommendations for the fatigue design of steel structure. European convention for constructional steel works. Technical committee fatigue. First Edition, No. 1985, 34. 

Krejsa, M. 2014. Probabilistic fadure analysis of steel structures exposed to fatigue. Key Engineering Materials 577-578 101-104. doi 10.4028/www.scientific.net/ KEM.577-578.101. 

The occurrence, type, and progress of damage must be defined (e.g. the progress of fatigue fracture of a steel structure). 

Code of practice of fatigue design and assessment of steel structures, BS 7608, British Standard Institution, London (1993)... 

The second failure mode to consider is fatigue. The drum will revolve about once every second, and each part of the shaft surface will go alternately into tension and compression. The maximum fatigue stress range (of 2 x 56 = 112 MPa) is, however, only a quarter of the fatigue limit for structural steel (Fig. 28.5) and the shaft should therefore last indefinitely. But what about the welds There are in fact a number of reasons for expecting them to have fatigue properties that are poorer than those of the parent steel (see Table 28.1). 

Figure 28.6 shows the fatigue properties of structural steel welds. The fatigue limit stress range of 120 MPa for the best class of weld is a good deal less than the limiting range of 440 MPa for the parent steel (Fig. 28.5). And the worst class of weld has a limiting range of only 32 MPa ...

Fig. 28.5. Fatigue data for a typical structural steel in dry air. Note that, if the fatigue stress range is less than 440 MPa (the fatigue limit] the component should last indefinitely. The data relate to a fatigue stress cycle with a zero mean stress, which is what we have in the case of our tail drum.

Fig. 8.65 Corrosion fatigue crack growth data for structural steel in seawater at 0.1 Hz, / = -I to 0.85 and -1.10 V (Ag/AgCI) (after Scott...

Thorpe, T. W., Ranee, A., Silvester, D. R. V., Scott, P. M. and Morgan, H. G., The effect of North Sea service conditions on fatigue crack growth in structural steel . Fatigue in offshore structural steels, Thomas Telford Ltd., London, pp. 35-46 (1981)... 

Turnbull, A., Review of the electrochemical conditions in cracks with particular reference to corrosion fatigue of structural steel in seawater . Reviews in Coatings and Corrosion, 5, Nos. 1-4, 43-160 (1982)... 

---