PSI - Issue 5

Hołowaty J. et al. / Procedia Structural Integrity 5 (2017) 1035 – 1042 Wichtowski and Hołowaty. / Structural Integrity Procedia 00 ( 2017) 000 – 000

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1036

Nomenclature B, C, D quality levels for weld imperfections D damage index f y yield strength f u ultimate strength N number of cycles n i actual number of cycles at stress range i N i theoretical fatigue life at stress range i NDT non-destructive testing R

ratio of the minimum to maximum applied stress

T fat

fatigue life in years

t

plate thickness applied stress



nominal stress range



reference value of fatigue strength at 2·10 equivalent constant amplitude stress range at 2·10 6 cycles

 c

6 cycles

 E,2

partial factor for fatigue action partial factor for fatigue strength infinite life fatigue strength

 Ff  Mf Z rj

2. Procedures for assessment

The growing importance of adequate safety and resistance assessment in steel bridge structures has resulted in both improvements and refinements in assessment methods [SB-LRA (2007)], and the publication of new recommendations for the safety and durability assessment of existing structures (Kühn et al., 2008), leading to further harmonization of the design rules and the Eurocodes. New information is now included on materials and riveted structures to comply with modern standards. The possibility of using plastic deformation capacity in the analysis is explained. The high reserve of strength in riveted connections is also calculated according to EC3 but there is still some information required on the clamping effects in riveted connections. The necessity to keep many old bridges in operation has required reliable and safe procedures with practical applications. The new European recommendations were drawn up within the framework of cooperation between the Joint Research Centre of the European Commission (the JRC) and the European Convention for Structural Steelwork (ECCS). They were published as a JRC scientific and technical report, regarded as part of the Eurocode background documents. The recommendations gives the general procedure for the assessment of existing structures (Kühn et al., 2008). The procedure uses the safe life method in accordance with nominal stresses. The analysis takes into account all the factors which may influence the reliability and safety of existing steel bridges. It allows, as the need arises, a more precise and more reliable calculation of the structure’s resistance, since assessment is divided into four levels: preliminary, detailed, expert and remedial. The assessment of old bridges is usually initiated following doubts arising from changes in operating conditions, a long service period, and deterioration. The new European recommendations for resistance assessment in existing bridges have been accepted internationally, including in Canada, the UK, Denmark and Switzerland. The implementation design methodology in these countries is described in detail by Wiśniewski et al. ( 2012, 2013), who give the results of material testing, data on real loadings, load tests and the behaviour of the structures tested, along with redundancy effects in the probabilistic assessment of existing bridges. Reliable assessment of existing structures provides for their safe operation over a specified residual service life with an adequate balance between profit and risk. 2.1. General assessment procedure