Advanced Steel Construction

Vol. 11, No. 3, pp. 269-282 (2015)



Chun-sheng Wang 1,*, Ben T. Yen 2, Hai-ting Li 3 and Lan Duan1

1 Engineering Research Center for Large Highway Structure Safety of Ministry of Education, College of Highways, Chang'an University, Xi'an, Shaanxi Province, China
2Department of Civil and Environmental Engineering, Lehigh University, Bethlehem, PA 18015-4729, USA
3Department of Civil Engineering, The Univers
ity of Hong Kong , Hong Kong, China
*(Corresponding author: E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.


DOI 10.18057/IJASC.2015.11.3.2



The in-service steel bridges are often required to carry increasing volume of traffic and heavier trucks or freight trains. More attention should be paid to possible fatigue damages of such structures. It has been reported that for many structure details with an equivalent stress range below the constant amplitude fatigue limit (CAFL) and free of fatigue cracks, calculations show that the remaining fatigue life has been exhausted. This condition indicates that it could be too conservative to predict the remaining fatigue life of in-service steel bridges by utilizing the equivalent constant amplitude stress ranges with the direct extension of S-N curves of AASHTO specifications with a slope of -3 to below the CAFL. This over-prediction of fatigue damage may lead to unnecessary rehabilitation and maintenance actions. For a better fatigue life evaluation and prediction, a set of bi-linear S-N curves with a break at the CAFL for the AASHTO fatigue strength categories and with a slope of -4 below, has been proposed for fatigue life evaluation of in-service structures. This paper applies the concept of the equivalent constant amplitude stress range for bi-linear curves to AASHTO specifications and Eurocode. Cases of fatigue evaluation of in-service steel bridge components are studied by correlating the field-measured live-load stresses with the bi-linear S-N curves. Comparative results from the bi-linear S-N curve approach, the current AASHTO specifications and Eurocode approach are presented.


Keywords:Steel bridges, Fatigue life evaluation, Bi-linear S-N curve, Constant amplitude fatigue limit, Equivalent stress range


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