Load-bearing capacity of cold-formed sinusoidal steel sheets

Currently, corrugated cold-formed steel sheets are widely used as parts of cladding panels and roof envelopes in public and residential buildings. However, the design of corrugated sheets is weakly covered by the current building codes. This paper investigates the load-bearing capacity of corrugated steel sheets with the sinusoidal profile, presenting the results of the experimental research that was performed in the GRISPE project at the Research Center for Steel, Timber and Masonry, Karlsruhe Institute of Technology (KIT). Three types of tests were carried out: (1) single span tests under downward loading, (2) internal support tests under downward and upward loading to investigate the moment-support interaction and (3) end support tests under downward loading to determine the local resistance of the profiles. The obtained results are used to validate the design methods for bending moment resistance of sinusoidal sheets. The validation demonstrated that the conventional design method and the Swedish code for light-gauge structures StBK-N5 provide a safe and accurate prediction of the resistance and can be recommended as simple design rules for sinusoidal sheets. The Eurocode for silos, EN 1993-4-1:2007, was found to provide a simplified solution for calculating the section properties of the sinusoidal profile. In addition, the obtained experimental results showed that internal supports can considerably reduce the bending moment capacity in the span of the sheet. Some conclusions are made on the dependency of M / R -interaction on the direction of loading, the fixing type and the support width

Caractérisation des alliages d'aluminium après refusion in situ (application au soudage)

Les domaines d application du soudage à l arc électrique sous protection gazeuse des alliages d aluminium se sont diversifiés en particulier dans le secteur des industries du transport. Les effets des paramètres opératoires restent cependant à parfaire tant leur détermination expérimentale demeure incomplète. Cette étude porte sur le développement d un protocole expérimental et numérique apte à reproduire les conditions d élaboration d un joint soudé. La complémentarité de ces deux aspects permet l interprétation à l échelle locale et globale des phénomènes constatés. L essai, qui s appuie sur les différents tests à chaud développés au laboratoire, est complété par un dispositif restituant des vitesses de refroidissement comparables à celles observées en soudage. Les caractéristiques mécaniques en traction des alliages étudiés sont déterminées par méthode inverse et implantées au sein de la représentation éléments finis de l essai. L objectif des présents travaux est de répondre aux problèmes liés au mode d élaboration du joint et d aborder les effets du bridage en cours de refroidissement. Les résultats sont étayés par l approche numérique. Les influences des paramètres de préparation, du flux protecteur et du préchauffage sont quantifiées en comparaison d un assemblage obtenu sous conditions normales. Des pièces non préchauffées ou insuffisamment décapées dans les zones à assembler, pénalisent la résistance en traction du joint soudé. La résistance mécanique de l assemblage est exprimée en fonction des variations de la vitesse de chauffage et du temps de maintien à fusion de l apport. L analyse de ces deux facteurs révèle qu ils ne sont pas déterminants quant à l optimisation de la tenue du joint soudé. Cette résistance est en effet davantage affectée par le mode de refroidissement de l assemblage et peut être améliorée par élévation du débit de projection d argon refroidi. Les effets du bridage sont chiffrés en comparaison des contraintes internes globales des assemblages. Ils participent majoritairement à l évolution des contraintes internes observées lors du refroidissementAluminium alloys arc welding under gas protection diversified in particular for transport industries applications. The effects of welding parameters could be achieved so much experimental determination remains incomplete. This study deals with the development of an experimental and numerical protocol able to reproduce the processing conditions of the welded joint. The complementarity of these two aspects allows interpretation to local and global scale of the noted phenomena. The test, based on various hot trials developed in the laboratory, is supplemented by a device restoring cooling speeds comparable with those observed in welding. The tensile mechanical characteristics of the studied alloys are determined by reverse method and implemented within the finite elements representation of the test. The objective of present works is to answer to the problems linked on the processing mode of the joint and to approach the clamping effects during cooling. The results are braced by the numerical approach. The influences of the parameters of preparation, protective flow and pre-heating are quantified in glance of an assembly obtained under normal conditions. Not preheated specimens, or not pickled surfaces, penalize the tensile strength of the welded joint. Mechanical strength of the assembly is expressed according to the variations of the heating rate and of the holding period to weld metal melting. The analysis of these two aspects reveals that they aren t determining as for the optimization of the strength of the welded joint. This strength is indeed more affected by the cooling mode and can be improved by rising the cooled argon flow. Clamping effects are quantified to comparison of the global internal stresses of assemblies. They take part mainly in the evolution of internal stresses observed during coolingVALENCIENNES-BU Sciences Lettres (596062101) / SudocSudocFranceF

Extracorporeal membrane oxygenation network organisation and clinical outcomes during the COVID-19 pandemic in Greater Paris, France: a multicentre cohort study

Erratum inCorrection to Lancet Respir Med 2021; published online April 19. https://doi.org/10.1016/S2213-2600(21)00096-5.International audienceBackground: In the Île-de-France region (henceforth termed Greater Paris), extracorporeal membrane oxygenation (ECMO) for severe acute respiratory distress syndrome (ARDS) was considered early in the COVID-19 pandemic. We report ECMO network organisation and outcomes during the first wave of the pandemic.Methods: In this multicentre cohort study, we present an analysis of all adult patients with laboratory-confirmed SARS-CoV-2 infection and severe ARDS requiring ECMO who were admitted to 17 Greater Paris intensive care units between March 8 and June 3, 2020. Central regulation for ECMO indications and pooling of resources were organised for the Greater Paris intensive care units, with six mobile ECMO teams available for the region. Details of complications (including ECMO-related complications, renal replacement therapy, and pulmonary embolism), clinical outcomes, survival status at 90 days after ECMO initiation, and causes of death are reported. Multivariable analysis was used to identify pre-ECMO variables independently associated with 90-day survival after ECMO.Findings: The 302 patients included who underwent ECMO had a median age of 52 years (IQR 45-58) and Simplified Acute Physiology Score-II of 40 (31-56), and 235 (78%) of whom were men. 165 (55%) were transferred after cannulation by a mobile ECMO team. Before ECMO, 285 (94%) patients were prone positioned, median driving pressure was 18 cm H2O (14-21), and median ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen was 61 mm Hg (IQR 54-70). During ECMO, 115 (43%) of 270 patients had a major bleeding event, 27 of whom had intracranial haemorrhage; 130 (43%) of 301 patients received renal replacement therapy; and 53 (18%) of 294 had a pulmonary embolism. 138 (46%) patients were alive 90 days after ECMO. The most common causes of death were multiorgan failure (53 [18%] patients) and septic shock (47 [16%] patients). Shorter time between intubation and ECMO (odds ratio 0·91 [95% CI 0·84-0·99] per day decrease), younger age (2·89 [1·41-5·93] for ≤48 years and 2·01 [1·01-3·99] for 49-56 years vs ≥57 years), lower pre-ECMO renal component of the Sequential Organ Failure Assessment score (0·67, 0·55-0·83 per point increase), and treatment in centres managing at least 30 venovenous ECMO cases annually (2·98 [1·46-6·04]) were independently associated with improved 90-day survival. There was no significant difference in survival between patients who had mobile and on-site ECMO initiation.Interpretation: Beyond associations with similar factors to those reported on ECMO for non-COVID-19 ARDS, 90-day survival among ECMO-assisted patients with COVID-19 was strongly associated with a centre's experience in venovenous ECMO during the previous year. Early ECMO management in centres with a high venovenous ECMO case volume should be advocated, by applying centralisation and regulation of ECMO indications, which should also help to prevent a shortage of resources