Tham khảo tài liệu 'inspection, evaluation and repair of hydraulic steel structures episode 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | EM 1110-2-6054 1 Dec 01 Figure 2-3. Typical fatigue cracking of riveted member Figure 2-4. Crack surface at the edge of rivet hole Therefore fatigue cracks would more likely be detected long before the load-carrying capacity of the riveted member is exhausted. d. Fatigue strength of corroded members. For severely corroded members where corrosion notching has occurred Category E or E curves and the corresponding fatigue limits have been suggested for cases. When corrosion is severe and notching occurs a fatigue crack may initiate from the corroded region as shown in Figure 2-5. In cases where corrosion has resulted in loss of more than 20 percent of the cross section the corresponding increase in stress should also be considered. 2-12 EM 1110-2-6054 1 Dec 01 Figure 2-5. Fatigue crack from corrosion notch into rivet hole e. Variable-amplitude fatigue loading. 1 Most of the fatigue test data and the Sr-V curves in Figures 2-1 and 2-2 were established from constant-amplitude cyclic loads. In reality however structural members are subjected to variable-amplitude cyclic loads resulting in a spectrum of various stress ranges. Variable-amplitude fatigue loading may occur on hydraulic steel structures. 2 In order to use the available Sr-V curves for variable-amplitude stress ranges an equivalent constantamplitude stress range Sre can be determined from a histogram of the stress ranges Figure 2-6 . Sre is calculated as the root-mean-cube of the discrete stress ranges Sri Sz iksi Figure 2-6. Sample stress range histogram 2-13 EM 1110-2-6054 1 Dec 01 e Jv n S Sre N N 2-3 where m number of stress range blocks n number of cycles corresponding to Sri Sri magnitude of a stress range block f. Repeated loading for hydraulic steel structures. The general function of hydraulic steel structures is to dam and control the release of water. Sources of repeated loading include changes in load due to pool fluctuations operation of the hydraulic steel structure flow-induced vibration and .
