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Corrosion-Fatigue Evaluation of Uncoated Weathering Steel Bridges

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Corrosion-Fatigue Evaluation of Uncoated Weathering Steel Bridges applied sciences Article Corrosion-Fatigue Evaluation of Uncoated Weathering Steel Bridges Yu Zhang, Kaifeng Zheng, Junlin Heng * and Jin Zhu Department of Bridge Engineering, School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China * Correspondence: [email protected]; Tel.: +86-182-8017-6652 Received: 19 July 2019; Accepted: 19 August 2019; Published: 22 August 2019 Featured Application: The new findings highlight the enhancement in corrosion-fatigue performance of steel bridges by using the uncoated weathering steel. Besides, an innovative approach has been established to simulate the corrosion-fatigue process in uncoated weathering steel bridges, providing deep insights into the service life of the bridges. The approaches suggested in the article can be used (not limited to) as a reference for the research and design of uncoated weathering steel bridges. Abstract: Uncoated weathering steel (UWS) bridges have been extensively used to reduce the lifecycle cost since they are maintenance-free and eco-friendly. However, the fatigue issue becomes significant in UWS bridges due to the intended corrosion process utilized to form the corrodent-proof rust layer instead of the coating process. In this paper, an innovative model is proposed to simulate the corrosion-fatigue (C-F) process in UWS bridges. Generally, the C-F process could be considered as two relatively independent stages in a time series, including the pitting process of flaw-initiation and the fatigue crack propagation of the critical pitting flaw. In the proposed C-F model, Faraday’s law has been employed at the critical flaw-initiation stage to describe the pitting process, in which the pitting current is applied to reflect the pitting rate in different corrosive environments. At the crack propagation stage, the influence of pitting corrosion is so small that it can be safely ignored. In simulating the crack propagation stage, the advanced NASGRO equation proposed by the NASA is employed instead of the classic Paris’ law, in which a modified fatigue limit is adopted. The fatigue limit is then used to determine the critical size of pitting flaws, above which the fatigue effect joins as a parallel driving force in crack propagation. The model is then validated through the experimental data from published articles at the initiation stage as well as the whole C-F process. Two types of structural steel, i.e., HPS 70W and 14MnNbq steel, have been selected to carry out a case study. The result shows that the C-F life can be notably prolonged in the HPS 70W due to the enhancement in fatigue strength and corrosion resistance. Besides, a sensitivity analysis has been made on the crucial parameters, including the stress range, stress ratio, corrosive environment and average daily truck traffic (ADTT). The result has revealed the different influence of the above parameters on the initiation life and propagation life. Keywords: corrosion-fatigue; pitting corrosion; critical pitting size; fracture mechanics; uncoated weathering steel 1. Introduction Weathering steel has been widely used in bridge engineering in the U.S., Europe and Japan since half a century ago. Due to the excellent corrosion resistance of weathering steel, it can be applied in the corrosive environment without coating. Various grades of weathering steel have already been Appl. Sci. 2019, 9, 3461; doi:10.3390/app9173461 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, x 3461 FOR PEER REVIEW 2 of 24 already been incorporated in the codes of practice, such as American grades A242, A588, A606 and incorporatedA709, Japanese in thegrades codes JIS of SMA practice, and suchthe British as American S355J2G1W grades [1,2]. A242, Since A588, 2017, A606 over and 50% A709, of highway Japanese gradessteel bridges JIS SMA in andthe theUS Britishwere constructed S355J2G1W with [1,2]. weathering Since 2017, oversteel. 50% In Japan, of highway 75% steelof the bridges weathering in the USsteels were were constructed used in with bridge weathering engineering steel. Inin Japan,2008, 75%and of80% the weatheringof newly built steels steel were usedbridges in bridgewere engineeringconstructed inwith 2008, weathering and 80% ofsteel newly in the built past steel 25 bridges years [3,4]. were constructedIn China, the with first weathering weathering steel steel in thebridge past was 25 yearsconstructed [3,4]. In in China, 1991 [5], the followed first weathering by the massive steel bridge application was constructed in the 2010s. in 1991 [5], followed by theA massivegreat advantage application of uncoated in the 2010s. weathering steel (UWS) bridges is the reduction of cost. Dolling et al. A[1] great claimed advantage that approximately of uncoated 5% weathering of the initial steel cost and (UWS) far in bridges excess isof the 5% reduction on capital of costs cost. Dollingcould be etsaved. al. [1 Moreover,] claimed thatHorii approximately et al. [6] indicate 5%d ofthat the weathering initial cost steels and could far in reduce excess about of the 25% 5% onlifecapital cycle cost costs according could be saved.to recently Moreover, under Horii construction et al. [6] indicatedbridges. In that addition, weathering Dolling steels also could listed reduce the aboutenvironmental 25% life cyclebenefits cost of according UWS bridges to recently arising under from construction avoiding painting bridges. [1]. In It addition, is also worth Dolling noting also listedthat the the fire environmental incident has benefits now become of UWS a bridges very critical arising issue from avoidingin steel bridges painting since [1]. Itit iscan also lead worth to notingextremely that detrimental the fire incident consequences has now become[7]. Wan a et very al. [8] critical claimed issue that in steelthe chemical bridges sinceelement it can Mo lead could to extremelynotably improve detrimental the fire-resistant consequences of steel. [7]. Wan Since et th al.e [element8] claimed Mo thatis generally the chemical included element in making Mo could the notablyhigh-performance improve the weathering fire-resistant steel, of a steel. much Since better the fi elementre-resistant Mo performance is generally included can be expected in making when the high-performancecompared with the weathering common steel,carbon a muchsteel. betterHowever, fire-resistant further performanceinvestigations can are be still expected required when to comparedreveal the actual with the fire common resistance carbon of weathering steel. However, steel. further investigations are still required to reveal the actualIn steel fire resistancebridges, ofthe weathering fatigue steel.issue is of particular concern due to the persistent loading-and-unloadingIn steel bridges, the process fatigue by issue the vehicles. is of particular Similar concernto the degradation due to the of persistent steel bridges loading-and- from the unloadingfire hazard process [7], theby corrosion the vehicles. effect Similar should to be the co degradationnsidered into of the steel design. bridges Nevertheless, from the fire the hazard fatigue [7], theissue corrosion of steel bridges effect should will be be further considered accelerated into the when design. exposed Nevertheless, to the corrosive the fatigue environment. issue of steelThe bridgescorrosion will process be further will accelerated lead to geometric when exposed irregulari to theties corrosive in components, environment. escalating The corrosion the local process stress willconcentration, lead to geometric which serves irregularities the fatigue in components, issue. In UWS escalating bridges, the the local problem stress is concentration, even more serious: which servesThe fatigue the fatigue crack issue.is hard In UWSto be bridges,detected the due problem to the isrust even layer more used serious: to proof The corrodents. fatigue crack Thus, is hard it tois becrucial detected to take due into to the consideration rust layer used the tocoupling proof corrodents. effect of corrosion-fatigue Thus, it is crucial (C-F) to take on intothe service consideration life of theUWS coupling bridges. e ffect of corrosion-fatigue (C-F) on the service life of UWS bridges. Figure1 1shows shows a typicala typical fatigue fatigue crack crack in a UWS in a bridge, UWS whichbridge, is which identified is byidentified the dye penetrationby the dye checkpenetration [9]. It check is worth [9]. statingIt is worth that, stating this type that, of this crack type is of very crack diffi iscult very to difficult be detected to be usingdetected common using approaches,common approaches, especially especially in its early in stage. its early Due stage. to the Due diffi toculty the indifficulty detection, in adetection, considerable a considerable number of unrecognizednumber of unrecognized fatigue cracks fatigue might cracks exist in might the aged exis UWSt in the bridges, agedimposing UWS bridges, high risks imposing on the high durability risks oron eventhe durability safety of the or bridgeeven safety consequently. of the bridge Therefore, consequently. a well-established Therefore, model a well-established is urgently required model for is theurgently evaluation required on thefor servicethe evaluation life of UWS on the bridges servic consideringe life of UWS the bridges C-F process. considering the C-F process. Figure 1. TypicalTypical fatigue crack in uncoated weathering steel bridges. The aim of the present study is to provide a deep insight into the corrosion-fatigue (C-F) performance ofof UWSUWS bridges, bridges, which which can can serve serve as as a
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