Design S-N curves for old Portuguese and French riveted bridges connection based on statistical analyses

Maintenance of ancient road and railway metallic bridges has become a major concern for governmental agencies in the past few decades. Indeed, since the construction of these structures, between the end of the 19th century and the beginning of the 20th century, traffic conditions have evolved, both in weight and frequency. In the purpose to assess the remaining life of old metallic bridges, some critical structural details have been identified and associated to S-N curves in order to be used in damage estimation (using Palmgren-Miner’s rule for cumulative damage, for example). These constructional details are described by design rules of several European and North American standards, such as the Eurocode 3, BS 5400 and AASHTO standards. The particularity of ancient bridges is that hot riveted assemblies, commonly used for their construction, are not represented in most construction standards. Further experiences on the matter by numerous research teams have suggested detail category C71 from the Eurocode 3 as appropriate. In this paper, experimental data from double shear assemblies manufactures from three different metallic ancient bridges is used to identify, through a statistical analysis, the S-N curves that best fit this constructional detail. Portuguese and French puddled iron bridges were considered.The authors of this paper thank the National Society of French Railways and the SciTech - Science and Technology for Competitive and Sustainable Industries, R&D project NORTE-01-0145-FEDER-000022 cofinanced by Programa Operacional Regional do Norte ("NORTE2020"), through Fundo Europeu de Desenvolvimento Regional (FEDER) for their collaboration and support during this research works. The authors also acknowledge the Portuguese Science Foundation (FCT) for the financial support through the post-doctoral grant SFRH/BPD/107825/2015

A self-heating approach to characterize anisotropy effects in fatigue behaviour: application to a nineteenth century puddle iron from a French railway bridge

International audienc

Optimization of the palindromic order of the TtgR operator enhances binding cooperativity

TtgR is the specific transcriptional repressor of the TtgABC efflux pump. TtgR and the TtgB efflux pump proteins possess multidrug-binding capacity, and their concerted action is responsible for the multidrug resistance phenotype of Pseudomonas putida DOT-T1E. TtgR binds to a pseudo-palindromic site that overlaps the ttgR/ttgA promoters. Dimethylsulfate footprint assays reveal a close interaction between TtgR and the central region of this operator. The results of analytical ultracentrifugation demonstrate that TtgR forms stable dimers in solution, and that two dimers bind to the operator. Microcalorimetric analysis of the binding of the two TtgR dimers to the cognate operator showed biphasic behavior, and an interaction model was developed for the cooperative binding of two TtgR dimers to their target operators. The binding of the two TtgR dimers to the operator was characterized by a Hill coefficient of 1.63 ± 0.13 (kD = 18.2( ± 6.3) μM, kD′ = 0.91( ± 0.49) μM), indicating positive cooperativity. These data are in close agreement with the results of sedimentation equilibrium studies of TtgR–DNA complexes. A series of oligonucleotides were generated in which the imperfect palindrome of the TtgR operator was empirically optimized. Optimization of the palindrome did not significantly alter the binding of the initial TtgR dimer to the operator, but increased the cooperativity of binding and consequently the overall affinity. The minimal fragment for TtgR binding was a 30-mer DNA duplex, and analysis of its sequence revealed two partially overlapping inverted repeats co-existing within the large pseudo-palindrome operator. Based on the architecture of the operator, the thermodynamics of the process, and the TtgR–operator interactions we propose a model for the binding of TtgR to its target sequence.This study was supported by grants BIO2003-00515 and BIO2006-05668 from the CICYT, and by grants CVI-344 and CVI-1912 from Junta de Andalucía.Peer reviewe

Contribution to the study of the influence of the stress ratio on the high cycle fatigue behaviour of riveted joints

International audienc