Issue 9

Z.H. Qian et alii, Frattura ed Integrità Strutturale, 9 (2009) 105 - 112; DOI: 10.3221/IGF-ESIS.09.11 111 Figure 9 : Fatigue improvement techniques. Figure 10 : Surface properties after FBM treatment at different temperature (Barletta, 2007). Novel techniques Ultrasonic impact treatment (UIT) and laser shock peening are two new techniques to improve the fatigue life for steel structure. It is revealed by Lehigh University that the peak compressive residual stress induced UIT exceeded the yield stress of the base material near the sample surface [24] . The depth of compressive stress layer in base metal was 1.5-1.7 mm for UIT. The induced compressive residual stresses benefit to increase the threshold value of stress intensity factor range, th K  , for fatigue crack initiation and early propagation. Laser peening is an emerging surface treatment technology that is an extension of shot peening. Compared to shot peening, laser peening indicates a significant increase in fatigue life based on the laboratory tests to the native welded specimens [25]. C ONCLUSIONS his paper reviewed the fatigue failures at welded connections of orthotropic deck, and presented several improvement techniques. Stress performance of orthotropic deck is complex due to high concentrated stress, residual stress and out-of-plane stress. The fatigue behaviors of some welded connections are still in the dark, and T