Push-out tests on demountable shear connectors of steel-concrete composite structures

The deconstruction of steel-concrete composite structures in buildings and the later separation of the materials is a labour- and cost intensive work. The shear studs are welded on the steel beam and imbedded in the concrete deck and a large amount of cutting work becomes necessary. As a result, recycling is difficult and the potential for reusing entire elements is lost. The carbon footprint of composite structures could be decreased by application of the principles of “design for deconstruction and reuse”. This paper presents a desk top study and corresponding laboratory experiments on demountable shear connectors that facilitate recyclability and even provide the potential for reusing complete structural elements. In the Laboratory of Steel and Composite Structures of the University of Luxembourg 15 push-out tests have been carried out using different bolted connection systems suitable for multiple uses in order to verify their performance focusing on shear strength, stiffness, slip capacity, ductility and ability of demounting. The investigated systems included pre-stressed and epoxy resin injection bolts, solid slabs and composite slabs with profiled decking. The results showed that the tested demountable shear connections could provide higher shear resistance than conventional shear connections. The critical failure mode is shear failure of the bolts, while there was no visible damage observed on the connected members. Most of the tested connections could fulfil the ductility requirement according to by Eurocode 4. The application of epoxy resin in the hole clearance resulted in lower slip capacity. The outcome provides an important basis for the justification of the forthcoming enhancement and validation of numerical models of the demountable shear connections. The failure behaviour, the observed damages and the resulting ability of the elements for re-use are discussed in detail

Meltdose tacrolimus population pharmacokinetics and limited sampling strategy evaluation in elderly kidney transplant recipients

Background: Meltdose tacrolimus (Envarsus (R)) has been marketed as a formulation achieving a more consistent tacrolimus exposure. Due to the narrow therapeutic window of tacrolimus, dose individualization is essential. Relaxation of the upper age limits for kidney transplantations has resulted in larger numbers of elderly patients receiving tacrolimus. However, due to the physiological changes caused by aging, the tacrolimus pharmacokinetics (PK) might be altered. The primary aim was to develop a population PK model in elderly kidney transplant recipients. Secondary aims were the development and evaluation of a limited sampling strategy (LSS) for AUC estimation. Methods: A total of 34 kidney transplant recipients aged >= 65 years, starting on meltdose tacrolimus directly after transplantation, were included. An eight-point whole blood AUC0-24h and an abbreviated dried blood spot (DBS) AUC0-24h were obtained. The PK data were analyzed using nonlinear mixed effect modeling methods. Results: The PK data were best described using a two-compartment model, including three transit compartments and a mixture model for oral absorption. The best three-sample LSS was T = 0, 2, 6 h. The best four-sample LSSs were T = 0, 2, 6, 8 h and T = 0, 1, 6, 8 h. Conclusions: The developed population PK model adequately described the tacrolimus PK data in a population of elderly kidney transplant recipients. In addition, the developed population PK model and LSS showed an adequate estimation of tacrolimus exposure, and may therefore be used to aid in tacrolimus dose individualization.Nephrolog

Post-COVID-19 patients in geriatric rehabilitation substantially recover in daily functioning and quality of life

BackgroundAfter an acute infection, older persons may benefit from geriatric rehabilitation (GR).ObjectivesThis study describes the recovery trajectories of post-COVID-19 patients undergoing GR and explores whether frailty is associated with recovery.DesignMulticentre prospective cohort study.Setting59 GR facilities in 10 European countries.ParticipantsPost-COVID-19 patients admitted to GR between October 2020 and October 2021.MethodsPatients’ characteristics, daily functioning (Barthel index; BI), quality of life (QoL; EQ-5D-5L) and frailty (Clinical Frailty Scale; CFS) were collected at admission, discharge, 6 weeks and 6 months after discharge. We used linear mixed models to examine the trajectories of daily functioning and QoL.Results723 participants were included with a mean age of 75 (SD: 9.91) years. Most participants were pre-frail to frail (median [interquartile range] CFS 6.0 [5.0–7.0]) at admission. After admission, the BI first steeply increased from 11.31 with 2.51 (SE 0.15, P P P P ConclusionsPost-COVID-19 patients admitted to GR showed substantial recovery in daily functioning and QoL. Frailty at GR admission was not associated with recovery and should not be a reason to exclude patients from GR.Public Health and primary careGeriatrics in primary car

Two-scale modelling of composite 'steel-reinforced resin' interaction (INTERMOD): Towards reusable and demountable structures & infrastructure

Steel-concrete composite beams are widely used in practice because of the simple construction sequence and the economic cross-section design. The application of welded headed studs in composite beams prevents the non-destructive separation of the composite beam, which leads to a very low scoring in the sustainability assessment in terms of the reuse of structural components. A demountable connection between the steel beam and concrete deck must be made to allow for reusability and adaptability of the structure, which maximizes its functional lifetime and minimizes itsenvironmental footprint

A multi-scale approach towards reusable steel-concrete composite floor systems

Traditionally welded headed studs have been used to generate composite interaction between a steel beam and a (cast in-situ) concrete floor. This permanent connection impairs the demountability of the structural components and therefore demolition of the composite floor system is inevitable at the end of the functional service life. The demolition of functionally obsolete but technically sound building components is in contradiction with the globally prevailing ambition of more sustainable development of the built environment through reduced demand for primary resources and reduced emissions of harmful substances. This dissertation aims to overcome the need for demolition of composite floor systems by developing methods, tools and recommendations to enable easy demountability of the structural components. The recommendations are both based on practical experience obtained by full-scale laboratory experiments on a demountable composite floor system consisting of large prefabricated concrete floor elements (2.6 × 7.2 m), and on the (analytical) methods and tools developed to predict the response of the floor system during execution (e.g. instability) and service life (e.g. deflection and stresses).Steel & Composite Structure

Two-scale modelling of composite 'steel-reinforced resin' interaction (INTERMOD): Towards reusable and demountable structures & infrastructure

Steel-concrete composite beams are widely used in practice because of the simple construction sequence and the economic cross-section design. The application of welded headed studs in composite beams prevents the non-destructive separation of the composite beam, which leads to a very low scoring in the sustainability assessment in terms of the reuse of structural components. A demountable connection between the steel beam and concrete deck must be made to allow for reusability and adaptability of the structure, which maximizes its functional lifetime and minimizes itsenvironmental footprint.Steel & Composite Structure

New Materials for Injected Bolted Connections: A Feasibility Study for Demountable Connections

The purpose of this thesis is to investigate the short- and long-term behaviour of injected bolted connections (IBCs) with oversize holes for various injection materials. A central theme in this thesis the demountability of IBCs, as a result of which several release agents are tested for their suitability in and effects on IBCs. Injection bolts have been used successfully in engineering practice using epoxy resin to limit the amount of slip in bolted shear connections with normal clearance holes, but no explicit results are available for connections with oversize or slotted holes. The use of oversize or slotted holes may be beneficial for the (re-)erection process of structures, and thus it is investigated what the effects of such oversize or slotted holes are on the connection behaviour. First, it is examined if grout is suitable as an injection material in injected bolted connections (IBCs), as well as what precautions are necessary to ensure proper demountability of grout and(epoxy) resin-injected bolted connections. Secondly, the connection behaviour under short-term loading is determined, on the basis of which long-term creep tests are carried out. Finally, a new injection material is developed based on the preliminary conclusions drawn from the short- and long-term tests. It is concluded that IBCs can be demounted by treating the connection members with a release agent. The results of the experiments show that the long-term behaviour of resin-injected connections is governing the design, but that modelling of this time-dependent behaviour requires additional testing. The short and long-term performance of the newly developed material (resin reinforced with steel shot) in IBCs with oversize holes is significantly better than that of only resin, on the basis of which it is recommended to further investigate the potential and behaviour of this material in engineering applications

Loss of preload in pretensioned bolts

Minor thesis --- Preload loss in pretensioned bolts is an inevitable phenomenon. This thesis focuses on the different causes for bolt relaxation and their relation to joint design. Investigating bolt relaxation is relevant because there is a direct relation between the bolt preload and the resistance of the connection. In order to assess the loss of preload in pretensioned bolts, test results of extended creep tests (cf. EN 1090-2) have been used. It was found that bolt relaxation is mainly a function of coating thickness of the joint members. The larger the coating thickness, the more bolt relaxation occurs. The influence of bolt relaxation due to flattening of surface roughness could not be quantified due to the governing influence of coating thickness, but the surface roughness is of large importance for the slip resistance. External static loading has an influence on short-term bolt relaxation which can be modelled using an equation derived in this thesis. Proper joint design is key to achieving a high strength friction grip connection with a high preload level and thus a high slip resistance over the entire service lifetime. Higher ratios of clamping length over bolt diameter lead to less bolt relaxation. The results of this thesis can be used to gain insight in the behaviour of preloaded connections, as well as to have an indication on how to achieve a preloaded connection with relatively small preload losses.Civil Engineering and GeosciencesStructural Engineerin

Dubbele Buiging in Betonnen Kolommen: Analyse van het werkelijk doorsnedegedrag en sterktevergelijking met het Eurocodevoorschrift in de Ultimate Limit State

Analysis of the strength of concrete columns subjected to bi-axial bending. Comparison of the true strength with the strength according to the design rules from the Eurocode.Materials and EnvironmentConcrete StructuresCivil Engineering and Geoscience