1,721,025 research outputs found
Assessment of design mechanical parameters and partial safety factors for Wire-and-Arc Additive Manufactured stainless steel
Get PDFEarly investigations suggest that the use of Additive Manufacturing (AM) technologies for construction has the potential to decrease labor costs, reduce material waste, and create customized complex geometries that are difficult to be manufactured using conventional construction techniques. Nevertheless, the full exploitation of AM technologies requires data on the material mechanical properties so that reliable and safety design requirements can be developed. Among different metal AM techniques, the so-called Wire-and-Arc Additive Manufacturing (WAAM) results to be potentially suitable to realize large-scale structural elements of any shape and size. However, the results of early experimental tests on WAAM-produced alloys suggest the need of ad-hoc considerations to properly interpret the geometrical and mechanical features of the printed outcomes. The present study analyzes the data obtained from the experimental results of tensile tests carried out on WAAM-produced 308LSi stainless steel elements with the purpose of calibrating design values and partial safety factors. In order to account for the anisotropic behavior proper of WAAM-produced elements, the design values of the main mechanical parameters have been calibrated for the three main orientations of the specimens with respect to the deposition layer. The calibrated design values and partial safety factors for the yielding and ultimate tensile strength are compared with recommended values for stainless steel structures as provided by EN1993:1-4 - Eurocode 3 (EC3). Additional considerations upon the Young's modulus values, highly influenced by the anisotropic behavior of WAAM-produced stainless steel, are presented as well
Demontabele verbinding met injectiebouten
No full textDuurzaamheid wordt steeds belangrijker in de bouwsector. Demontabel en herbruikbaar bouwen vermindert het gebruik en verbruik van natuurlijke grondstoffen en minimaliseert afval en uitstoot van schadelijke stoffen. Binnen de sectie Steel and Composite Structures van de TU Delft is ontwikkeling van technische oplossingen voor duurzame staal-beton liggers één van de hoofdonderzoekslijnen. De crux zit – zoals praktisch altijd – in een ontkoppelbare, maar effectieve verbinding tussen vloer en constructie.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Steel & Composite Structure
A static and free vibration analysis method for non-prismatic composite beams with a non-uniform flexible shear connection
No full textSteel-concrete composite beams are widely used in practice because of their economic cross-section design. As sustainability becomes more and more important in the construction industry, the design of composite beams must be adapted to meet the requirements of the circular economy. This calls for demountability and reusability of the structural components, as well as optimized use of materials, for example by using non-prismatic beams. Linear-elastic design and the (optimized) use of demountable shear connectors are key in the design of reusable composite structures. In this paper, analytical prediction models for the elastic behaviour and the first eigenfrequency of non-prismatic composite beams with non-uniform shear connector arrangements are derived. The approach is based on 6th and 2nd order differential equations used to define matrix equations for a finite number of linearized composite beam segments. The analytical models are validated using experimental and numerical results obtained with a simply supported tapered composite beam. The analytical models are suitable for comprehensive structural analysis of non-prismatic composite beams with non-uniform shear connection.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Steel & Composite Structure
Lifting Gantries: A Study On The Structural Behaviour & Design Method
No full textSeveral topics related to lifting gantries have been studied. These are the modelling of the structure, the structural behaviour of the gantry, the input parameters of the model and the standards used for the design. A hand calculation model, based on the analysis of built-up compression members in EN 1993-1-1, has been developed that describes the behaviour of a portal like gantry structure. The model executes geometrically non-linear calculations, that take into account the second order effects from the deformation of the gantry, and determines the resistance of the gantry based on the axial forces in its chords and on stability checks. Three different mast sections, out of which the gantry columns are made, have been investigated: MSG, DS and NYW. The latter is currently under developed by Mammoet and is called a New York Wheel mast section. The focus is on the application of this section type. The gantry in the model is subject to a vertical load from the self-weight of the mast sections, a vertical load from the weight of the payload and a horizontal point load at the top of the gantry. The latter accounts for operational loads and wind loads on both the structure and the payload. In the model the horizontal load is expressed as a percentage of the weight of the payload. The resistances obtained from the hand calculation model are within 5% of the resistances obtained from a numerical benchmark model, for the gantry configurations considered. Therefore, the model is considered accurate enough for a preliminary design. It is able to represent a rigid and a flexible foundations, as well as a hinged and a rigid connection between the columns and beam(s) of the gantry. From the calculations with the hand calculation model several conclusions were drawn. The horizontal load is of large influence for the maximum payload, much larger than the influence of the global imperfection. The difference can easily be between 10-to-30% for the NYW mast sections, between 2% and 4% horizontal load. Also, the influence is larger for a gantry with a rigid beam-column connection than for a hinged connection. Calculating with a different imperfection, for example no imperfection instead of 1/250 of the gantry height, result in a 6-to-10% resistance difference. The resistance of a gantry with a rigid connection at the top is considerably larger than for a hinged connection, for an asymmetric section like the NYW mast sections. A rigid connection yields a 1.5 to 4 times higher resistance than a hinged connection, when NYW sections are used on a rigid foundation. The resistance for the three mast section types under consideration has been compared for a rigid foundation. It turns out that for both a hinged and a rigid beam-column connection the NYW sections can bear the highest payload, by far. The resistance to tensile forces, mostly governed by the strength of the connections, is much lower for the MSG sections than for the DS sections. Also, a rigid connection significantly improves the asymmetrical DS sections. For relevant gantry heights the MSG sections can bear a payload that is roughly 50% of the payload that the DS sections can carry, for a hinged top connection. For a rigid connection it is around 30%. The DS sections can carry 15-to-25% of the load the NYW sections can carry, for a hinged connection. For a rigid connection it is 25-to-35%. The stiffness of the foundation has been modelled with the method of Pais and Kausel (1988). It appeared that the stiffness of the foundation can have a significant influence on the resistance of the gantry. The MSG sections are more susceptible to a flexible foundation, because of their relatively small base frame. This results in a much smaller rotational stiffness at the bottom of the gantry columns. A foundation on dense sand leads to a resistance decrease around 5% for the NYW sections and around 35% for the MSG sections. One of the goals of this thesis was to incorporate the use of guy lines into the model and to investigate their influence on stability, stiffness and ultimately resistance. A preliminary study showed great potential for the use of guy lines. The buckling length can be reduced by around 50%, almost to the point where a column with a fixed end at the top is resembled. Also, the first order deflection can be reduced significantly, as over 75% of the horizontal load is taken by the guy lines. This means that the second order effects are drastically reduced. The reduction also has a positive effect on the first order bending moments in the column. A guy line that is installed under a 60 degree angle with the foundation turns out to be effective in both supporting the column and minimizing the gantry footprint. The behaviour of guy lines is highly non-linear. Therefore, it was found challenging to incorporate them in the final hand calculation model accurately. However, the evidence from the preliminary design leads to the recommendation to further investigate the application of guy lines. Several standards have been studied for the design of the gantry. It was concluded that the European crane standard EN 13001-1 is best suited to take into account the loads on the structure and that the structural behaviour of the gantry is best described using the European building standard EN 1993-1-1. The global imperfection of the gantry is a parameter of interest. Mammoet wants to calculate with an imperfection that equals one thousandth of the height of the gantry, since they believe their gantries can be erected with such high precision. The standards under consideration prescribe a larger imperfection, typically 1/500. The fabrication and erection tolerances are however much tighter for the mast sections than provided by the standards. Therefore, a smaller imperfection (1/1000) can be justified, except for very tall gantries and gantries in storm conditions. The horizontal load on the gantry varies between 2.5% and 4% of the weight of the payload, depending on the direction, the weight of the payload and whether or not skidding of the load is involved. A larger portion of the horizontal load comes from wind loads, of which the load on the object to be lifted is a substantial part. It is therefore recommended to further investigate the wind load.Civil Engineering and GeosciencesStructural and Building Engineerin
Fatigue crack initiation prediction using phantom nodes-based extended finite element method for S355 and S690 steel grades
No full textThe assessment of fatigue crack initiation behavior of steel structures is essential and important especially to improve the application of high strength steel in construction. For a complete understanding of fatigue endurance, it is necessary to combine the phenomenological damage model with finite element numerical approach. In this paper, phantom nodes-based extended finite element method is used to predict the fatigue crack initiation of steel material, considering a prediction by XFEM of coupon tests made of steel grades S355 and S690. A user-defined fatigue damage initiation subroutine based on Smith, Watson, and Topper (SWT) damage model combined with non-linear isotropic/kinematic cyclic hardening model is implemented to predict fatigue crack initiation. The proposed method is successfully validated based on fatigue coupon test results of both steel grades, S355 and S690.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Steel & Composite Structure
Requirements for oversized holes for reusable steel-concrete composite floor systems
No full textThe design of sustainable structures is increasingly gaining attention in the construction sector as a societal and technological challenge. Demountability and reuse of structures contributes to the reduction of the environmental impact of the built environment. Welded headed studs used in traditional steel-concrete composite floor systems need to be replaced by demountable shear connectors to enable the transition of the construction sector to a circular business model. The demountable shear connectors are embedded in large prefabricated concrete floor elements and connected to steel beams by bolts. The holes in the beam flange are oversized to account for geometrical and dimensional deviations of all members and to facilitate rapid execution and easy demounting. The goal of this paper is to present a methodology that quantifies the required nominal hole clearance for reusable composite floor systems. Statistical characteristics of dimensional and geometrical deviations serve as input for Monte-Carlo simulations. The aggregated results of the Monte Carlo simulations are used to determine the required nominal hole clearance for a specified probability of successful installation of the demountable shear connectors. The proposed methodology is applied to the composite floor system of a demountable and reusable car park building. The contradicting requirement of oversized holes and composite interaction is solved by injecting the hole clearance with a (steel-reinforced) epoxy resin. The bearing resistance of the (steel-reinforced) epoxy resin is addressed based on preliminary results of creep experiments on resin-injected bolted connections.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Steel & Composite Structure
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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