1,721,218 research outputs found
Structural response of fire-exposed laminated glass beams under sustained loads; exploratory experiments and FE-Simulations
No full textThis paper investigates the structural response of laminated glass beams under combined fire-exposure and sustained in-plane loading. This is done by means of experimental testing and Finite Element (FE) numerical modelling. Firstly, small-scale (1 m long) laminated glass beams are tested under thermal exposure and in-plane loading on a small fire resistance test furnace. From the test results it can be seen that laminated glass beams are able to sustain an imposed in-plane load for a time of 34–51 min before failing according to the limiting rate of deflection as defined in EN 1363–1:2012. It should be noted, however, that the observed failure times are strictly related to the boundary conditions applied in the test, i.e. the magnitude of mechanical loads (in this study a relatively small load of P = 1.15 kN was applied) and the presence of an inherent top zone protection, which may have positively affected the results. Secondly, additional FE thermo-mechanical simulations are performed to further investigate the mechanical response of the laminated glass beams under thermal exposure, with a focus on the effects of the top zone protection and the load magnitude on the performance of the examined laminated glass beams. From the FE study it can be seen that reducing the top zone protection (from 40 mm to 0 mm) results in a reduction in failure time from 45 min to 20 min, while increasing the load with a factor 5 (taking 30 mm top zone protection as a reference) results in a reduction of failure time from 32 to 18 min
Laminated connections under tensile load at different temperatures and strain rates
No full textIn the last years, a novel typology of adhesive connections for structural glass application has emerged, known as laminated adhesive connections, which makes use of the transparent ionomer SentryGlas® (SG) from Kuraray and the Transparent Structural Silicon Adhesive (TSSA) from Dow Corning. Despite being used in several projects, limited information is available in literature on their mechanical behaviour and on the effects of strain rate and temperature. In this work the behaviour of laminated connections under tensile loading is studied by means of experimental, analytical and numerical analyses. The experimental investigations show that temperature and strain rate variations have important effects on the mechanical response of the connections. Two main interesting phenomena are also observed: the whitening phenomenon in TSSA and the development of bubble within the SG adhesive. The analytical studies of the stress state show that confinement state of the adhesive induces a non-uniform three-dimensional stress distribution in the adhesive with a dominant hydrostatic component of the stress tensor, which is observed to be in agreement with the experimental results. Three-dimensional finite numerical analyses show that the stress field deviates from the uniform distribution with a large gradient of hydrostatic and deviatoric stresses over the adhesive area. The output of the finite numerical model are then compared with the observations of the experimental campaigns. Herein, the full set of numerical results is synthetized by the definition of so-called stress factors. The latter allow to derive the three-dimensional stress state in the adhesive at different temperatures and to compute the stress peak in the non-linear stress field distribution. Finally, prediction models are proposed for the tensile resistance of TSSA and SG laminated connections. A logarithmic law is proposed for the strain rate effects for both TSSA and SG connections. Linear and inverse hyperbolic-tangent-based laws are instead proposed for the TSSA and SG temperature effects, respectively.Accepted Author ManuscriptOLD Structural Desig
Experimental investigation of the cyclic properties of welds in mild structural steels
No full textStructural steels have long been used in construction applications. Their mechanical properties and behavior under seismic loading or under fatigue design are of considerable interest for researchers and engineers. Although extensive studies have been conducted on the cyclic behavior of structural steels, they mostly focus on base material responses. However, base material response can be affected by changes in microstructural properties of steels. In steel construction this situation often arises in welding different components where due to thermal loading certain regions change their crystallographic phases and consequently their mechanical properties. This master's thesis is dedicated to the investigation of the lesser known large amplitude cyclic material behavior of these regions termed Heat Affected Zones (HAZ). The behavior of welded connections is of paramount importance for structural integrity. Their behavior under extreme loading conditions can be the determining factors for the failure of joints and subsequent structural collapse. Field observations following significant earthquake events (e.g. 1994 Northrigde incident) has shown that the assumed ductility of the steel construction can be put into question when poorly executed welded structural joints suffer premature fracture. The head-boomed experience from these suggests that failures often arise from combination of ill-conceived detailing and insufficient weld quality (e.g. large defects on low thoughness). As the understanding of this problem progressed, better detailing properties and quality controls have been proposed to avoid brittle nature of joint failure. In this master’s thesis the author investigates the behavior of S355J2+N structural steel as HAZ of welded material and base material subjected to uniaxial cyclic loading and large inelastic strain demands under seismic loading in the experimental and numerical level. HAZ at welded specimens is obtained through thermal loading in the laboratory environment. Uniaxial cyclic loading tests are performed in the laboratory as well. In addition, comparisons between the base and welded metals for the steel class of S355J2+N are provided as well including material parameters for Voce-Chaboche and Updated Voce-Chaboche models. Results of this study reveal that under cyclic loading welded material hardens more than base material. In addition, plateau region exercised in base material disappears in welded material and welded specimens experience rounding around the yield stress which is not the case for base material. Accuracy of simulation of welded material and correctness of model parameters greatly depend on whether Voce-Chaboche or Updated Voce-Chaboche model is applied to the right material being investigated.SGCRESSLA
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Fatigue Study of the Linthkanal-Brücke
Full text linkAs fatigue cracks were discovered under the bridge deck of the 48 years old railway bridge Linthkanal-Brücke, located near the Ziegelbrücke town in Switzerland, a few studies were conducted to understand the mechanism behind the cracks formation. However, the results of them were not conclusive. The purpose of this Master thesis is to elaborate a deeper understanding of this steel tied-arch bridge behaviour in order to find out the effects causing fatigue cracks to develop at specific locations. To achieve this goal, a complete finite element modelling of the structure was conducted with SCIA software, using a refined plate sub-model inserted in a global bar model, to mimic the structural behaviour of the bridge deck. A distributed train carriage load was set in motion over the bridge deck, and the stresses found under each loads position were used to carry out a fatigue analysis in various elements including the critical details where damages were encountered. As the locations of the cracks were of very complex geometry, the fatigue assessment methods had to be adapted to the detail geometry and the level of modelling enabled by the software chosen to perform the study. Since a detailed sub-model in plate elements was built, a sensible choice of fatigue control was the structural hot-spot method to evaluate the stress range in the weld details at risk. This approach provides a linearized value of the stress peak in the weld toe, thus allowing a more precise analysis of the problematic area. An altered structural hot-spot method was applied to another set of details comparable to a mouse hole. As an additional check, the nominal stress method was used to assess the bridge hangers fatigue life. The results showed that, while the hangers of the bridge are not at risk of fatigue failure, the cracks in the critical details of the transversal stiffeners on top of the crossbeams are explainable. Indeed, the very rigid connection between the crossbeam and the bridge main span deck creates a mixed system behaviour, very similar to an orthotropic deck. Furthermore, the lower welds of the transversal stiffeners were discovered to be the most likely to fail under fatigue. This outcome was supported by the existing crack locations found in the bridge. This understanding back-up the recommendation of loosening the bolts connecting the crossbeams and the deck stiffeners elements. Hence this action would result in reducing the connection between the aforementioned elements and relieve the details under strong fatigue loads. Eventually, this study could also be applicable to bridges built in Switzerland with similar “orthotropic decking”, in addition to helping the increase of the Linthkanal-Brücke bridge service life duration.SGCRESSLA
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