Effect of Loading Sequence in Fatigue Life Prediction of a 130 Years Old Railway Bridge

The Miner’s rule is the simplest and the most commonly used fatigue life estimation technique for railway bridges [1]. One of its salient features is that life calculation is simpler and reliable when the detailed loading history is unknown. Further, it has been recognized for fatigue damage estimation in various codes of practices. However, in the case of existing railway bridges where the detailed loading history is known, Miner’s rule might provide incorrect results because it does not not properly take account the loading sequence effect. In the light of this fundamental deficiency, a new damage indicator has been proposed to capture the load sequence effect more precisely by Mesmacque et al. (Int J Fatigue 27:461–467 [2]). The new damage indicator has successfully been applied by Siriwardane et al. in 2008 for fatigue damage estimation of a major bridge in Sri Lanka. From 2012 onwards, Sri Lankan Railways has introduced heavier class of locomotives and some of these new loco’s have more than 40% heavier engine weights than previously used locomotives. The major objective of this study is to estimate the remaining fatigue life of above railway bridge using the sequential law under increased live loads. The bridge is one of the longest railway bridges in Sri Lanka, constructed in 1885, which is still in operation. A Finite Element model of the bridge was developed using SAP2000 V.14 general purpose software package and the fatigue damage estimation is performed by using a Mathlab code. The obtained fatigue lives are compared with commonly used Miner’s estimations. The obtained results verify the effectiveness of the proposed model over commonly used Miner’s rule for life prediction of steel bridges. Hence it could be concluded that it is advisable to apply the sequential law for assessment of remaining fatigue lives of riveted railway bridges, where the detailed stress histories are known. The results further strengthen the idea that necessity of sustainable asset management of civil infrastructures.