FCT: DEC - Artigos em revista internacional com arbitragem científica
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- Instability of Vibrations of Mass(es) Moving Uniformly on a Two-Layer Track ModelPublication . Dimitrovová, Zuzana; DEC - Departamento de Engenharia Civil; MDPI - Multidisciplinary Digital Publishing InstituteBallasted railway tracks can be modeled using reduced/simplified models composed of several layers of discrete components. This paper deals with the two-layer model, which is very popular due to its computational efficiency. In order to provide some recommendations for track design, it is necessary to identify which set of parameters leads to some irregular/unexpected behavior. In this paper, irregularities are investigated at three levels, namely, (i) the critical velocity of a moving constant force, (ii) the instability of one moving mass, and (iii) the instability of two moving masses. All results are presented in a dimensionless form to cover a wide range of real parameters. Irregular cases are identified by sets of parameters leading to them, which is the main finding of this paper; then, general conclusions are drawn. Regarding the method, all results are obtained analytically or semi-analytically, where “semi” refers to solving the roots of a given polynomial using predefined numerical procedures in symbolic software. No numerical integration is involved in any of the results presented. This means that the results are highly accurate and refer to exact values, so any kind of parametric or sensitivity analyses is readily possible.
- Study of Natural Ventilation Strategies in the São Cristóvão Church in Lisbon Using a Multizone Airflow ModelPublication . Baltazar, Luis G.; Alcobia, João; Silva, Hugo Entradas; DEC - Departamento de Engenharia Civil; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); CERIS - Polo NOVA; MDPI - Multidisciplinary Digital Publishing InstituteVisitors have a significant impact on the indoor climate of buildings housing works of art, and the relationship between the number of visitors, the indoor air quality and the protection of exposed works of art is an important factor in the overall study of the indoor climate of heritage buildings without mechanical ventilation and/or air-conditioning systems. In view of these concerns and the lack of studies on natural ventilation in heritage buildings, this study aims to analyse the performance of natural ventilation in the São Cristóvão Church in Lisbon, Portugal. For the preparation of this study, an analysis of the natural ventilation of this church was carried out by creating a model in the CONTAM software, and the indoor air quality was analysed based on different international standards and guidelines for carbon dioxide levels and air flow rates (ACH). Estimating the current ventilation strategy, an average ACH of 0.75 h−1 was estimated during the time the church is open, and an ACH of 0.15 h−1 was estimated during the time the doors were closed. In a yearly analysis, an average ACH of 0.30 h−1 was obtained. These air exchange values guarantee EN 16798-1 category I air quality for 72% of the year and category II air quality for 18% of the year. Different natural ventilation strategies were analysed: (a) three scenarios exploring different cross ventilation scenarios; (b) a scenario assuming that the church is closed all year round; and (c) a scenario estimating an increase in the number of visitors, giving an idea of the variations in human pollutants and possible consequences. Taking into account the air infiltration and the fact that masses, an occasional situation with a high number of visitors, are always held just before the church closes, it is guaranteed that carbon dioxide levels will never exceed the limit of 350 ppm above the outdoor values imposed by EN-13779, registering a maximum of 291 ppm.
- Bio-based boards made of hazelnut shell and A. donax for indoor applicationsPublication . Cintura, Eleonora; Faria, Paulina; Molari, Luisa; Mazzocchetti, Laura; Dalle Donne, Matteo; Giorgini, Loris; Nunes, Lina; DEC - Departamento de Engenharia Civil; CERIS - Polo NOVA; Elsevier BVThe present study investigated the reaction to fire of bio-based boards for indoor applications made of A. donax and hazelnut shells as aggregates. A sodium silicate solution was employed as the adhesive due to its several advantages. Among others, the possibility of moderating some of the main drawbacks of bio-based building composites, such as the resistance to fire. The considered materials were analysed both individually, to test their inherent properties, and when integrated into the composites, ensuring considerations about materials' influence on the final products’ properties. Two different test methods, using a cone calorimeter, were considered and performed. The results showed that the sodium silicate solution avoided flaming and smoking, in case of a constant heat application with and without an igniter (spark), demonstrating the benefit of its use in this type of bio-based composites. Overall, the particleboards demonstrated their ability to comply with fire behaviour consistent with the Class A1 requirements, while the bio-components on themselves were characterized by an intermediate fire risk propensity. Thus, the present study provided an effective solution to avoid one of the main drawbacks of bio-based composites. It demonstrated the feasibility of employing the proposed bio-based boards as indoor coating, with no risk to human life in case of fire.
- Effects of post-fracture repeated impacts and short-term temperature gradients on monolithic glass elements bonded by safety filmsPublication . Bedon, Chiara; Santos, Filipe A.; CERIS - Polo NOVA; DEC - Departamento de Engenharia Civil; ElsevierWeathering and operational conditions, as known, have significant impact on typical constituent materials which are used for many construction applications. Among others, structural glass solutions can suffer for these effects in terms of major modification of material properties of interlayers, bonds, connections, gaskets and polymeric components in general. In this paper, the attention is given to the effects of repeated low-amplitude impacts and short-term temperature gradients for the characterization of load-bearing capacity in monolithic glass elements retrofitted by safety films. Especially for existing glass systems which are made of monolithic glass with limited strength and resistance capacity against ordinary and accidental mechanical loads, safety films are commercially available for retrofit interventions. They are primarily expected to keep together glass fragments in case of breakage, and thus minimize possible injuries. Besides, after first fracture, the so obtained glass-film composite elements have uncertain residual mechanical capacity against ordinary loads, given that it mostly depends on thin films composed of Polyethylene terephthalate (PET)-layers and pressure sensitive adhesives (PSAs). To this aim, a set of experiments (for a total of 950 configurations) is carried out in laboratory conditions (30 °C) on small-scale samples of fractured annealed monolithic glass elements bonded by commercial safety films, under repeated low-amplitude impacts / vibrations (S1-TR series), or additionally subjected to preliminary short-term thermal gradients (S2-TC1 series cooled at +5 °C and S3-TC2 series at −20 °C). Localized impacts are quantified in acceleration peaks in the range of 2 ÷ 14 m/s2 and rotations at supports in the order of 15 ÷ 20°. The interpretation of dynamic experimental results is carried out in terms of post-fracture vibration frequency (based on classical operational modal analysis techniques) and used, with the support of simplified analytical models or Finite Element (FE) numerical simulations, to characterize the response of cracked glass-film samples. Most importantly, the vibration frequency decrease is used to quantify their residual load-bearing capacity under unfavourable conditions, and to quantify the post-critical benefit of thin bonding safety films under unfavourable conditions.
- Testing of a full-scale flat slab building for gravity and lateral loadsPublication . Coronelli, Dario; Lamperti Tornaghi, Marco; Martinelli, Luca; Molina, Francisco Javier; Muttoni, Aurelio; Pascu, Ion Radu; Pegon, Pierre; Peroni, Marco; Ramos, António Pinho; Tsionis, Georgios; Netti, Teresa; DEC - Departamento de Engenharia Civil; ElsevierFull-scale testing of a two-storey flat slab structure is reported, undertaken in the SlabSTRESS research project; the construction and testing were planned and carried out at the ELSA laboratory of the European Commission's Joint Research Centre. The dimensions are three bays by two, spans 4.5 and 5 m, slab thickness 0.2 m, interstorey height 3.2 m. Two different longitudinal reinforcement details were considered; welded studs shear reinforcement was provided only in the second floor slab. The testing program included seismic tests for service and ultimate actions, using the pseudodynamic technique with virtual walls. To this aim a building structure was designed with primary walls and the flat slab frame as secondary element. Cyclic loading tests followed up to ultimate drift capacity of the structure. The sequence of tests included strengthening of a set of damaged connections using bolted bars in holes drilled through the slab, followed by cyclic testing to failure. The instrumentation was provided for the global response and the connections with local rotations in the columns and slab; cracking around the columns was measured with through-crack sensors; a measurement system for internal forces and moments was included within the columns. The results show the response with deformations and damage for the different loading conditions up to failure. The results obtained on a full-scale structure extend and confirm the knowledge in the literature, mainly based on isolated connections and/or small-scale samples.
- RILEM TC 277-LHS reportPublication . Maravelaki, Pagona Noni; Kapetanaki, Kali; Papayianni, Ioanna; Ioannou, Ioannis; Faria, Paulina; Alvarez, Jose; Stefanidou, Maria; Nunes, Cristiana; Theodoridou, Magdalini; Ferrara, Liberato; Toniolo, Lucia; DEC - Departamento de Engenharia Civil; Springer VerlagThe scope of this collective paper produced in the frame of RILEM TC 277-LHS is to provide sound knowledge on the use of additives/admixtures in lime-based mortars, based on literature and practice. The most widely known additives/admixtures are systematically presented. Their main effects and testing of their performance have been properly tabulated. It is well known that a plethora of additives/admixtures are produced every year by chemical industries. However, when using them in lime-based mortars, compatibility and durability aspects are of primary importance. The introduction of additives/admixtures in lime mortars was imposed by the need to improve important properties of these composites in the fresh and hardened state, namely, workability, durability, early-age and long-term strength and to reduce defects, such as shrinkage and long setting time. In this review paper, the terminology proposed by EN 16572 is followed, designating additive as a constituent added in small quantity to the binder, and admixture as a substance in quantities at least 1% w/w added to the mix. The additives/admixtures are classified according to their action and their validation with specific testing methodologies highlights the dosage sensitivity and the need to develop further standardization. The combination of different additives proposed in several studies resulted as the most promising strategy to enhance the performance of lime mortars. However, recently developed additives and admixtures need to be further evaluated with reference to their compatibility with other mortar constituents, and their effects on the overall mortar and render durability need to be studied. Finally, adopting similar terminology for additives/admixtures in lime and cement-based mortars will facilitate better comparison and assessment issues.
- Numerical Evaluation of Transverse Steel Connector Strengthening Effect on the Behavior of Rubble Stone Masonry Walls under Compression Using a Particle ModelPublication . Cismaşiu, Ildi; Azevedo, Nuno Monteiro; Pinho, Fernando F. S.; DEC - Departamento de Engenharia Civil; CERIS - Polo NOVA; MDPI - Multidisciplinary Digital Publishing InstituteThe structural rehabilitation of historic/traditional rubble masonry wall constructions requires consolidation and retrofitting solutions to be employed in order to withstand dynamic loads, high vertical loads, and differential settlements. One of these strengthening techniques is based on the use of steel bar connectors perpendicular to the wall, considered individually or integrated into more complex strengthening techniques. The aim of this study is to evaluate numerically the strengthening effect of transverse steel connectors on rubble masonry walls. With this purpose, a 2D particle-reinforced model (2D-PMR) was devised and applied to model uniaxial compression tests. The results presented show that predictions calculated using the proposed 2D-PMR model are very close to known experimental results, particularly in the corresponding failure modes, the increase of the maximum uniaxial compression value, and ductility. Parametric studies are also conducted by varying the diameter of the steel bars and the level of strengthening to assess the influence of the bar-bond effect and lateral plates. The presented parametric numerical studies show that (i) a two-level strengthening solution guarantees a similar response to the three-level strengthening solution adopted in the experiments; (ii) it is not relevant to apply a grout injection during the application process of the steel connectors if lateral plates are adopted; and (iii) the 2D-PMR model can be used in the definition of the steel bar diameter and properties; as shown, a smaller (8 mm) bar diameter predicts a similar strengthening effect to the (12 mm) bar size adopted in the experiments. Given the performance of the proposed 2D-PMR model, further work is underway that will allow the 2D-PMR model to numerically assess other reinforcement techniques, namely, reinforced micro-concrete layers and textile reinforced mortar.
- 3D DEM model simulation of asphalt mastics with sunflower oilPublication . Câmara, Gustavo; Micaelo, Rui; Monteiro Azevedo, Nuno; DEC - Departamento de Engenharia Civil; CERIS - Polo NOVA; Springer International Publishing AGA three-dimensional particle model, based on the asphalt mastic micro-structure representation following a discrete element model framework, was developed to investigate the influence of sunflower oil (rejuvenator) on the rheological properties of asphalt mastic. Dynamic shear rheometer tests in laboratory, for a frequency range of 0.1–20 Hz and temperatures in a range between 20 and 80 ∘C, were carried out in order to assess the viscoelastic behaviour of asphalt mastics containing different oil-to-bitumen content by mass proportions (2.5–20%). Master curves were constructed for two reference temperatures (30 ∘C and 50 ∘C). Experimental results showed that the increase in sunflower oil content resulted in a progressive decrease in viscosity. However, the rheological behaviour of the mastic containing the highest oil amount could not be properly represented in master curves, indicating that the specimen had a different rheological behaviour when compared with the lower oil contents responses. Numerical simulations of rheometer tests were carried out with an asphalt mastic particle assembly that emulated the experimental procedure. The viscoelastic contacts within the asphalt mastic assembly were simulated with a generalized Kelvin contact model. A calibration procedure was derived based on the fitting of laboratory data. The simulations were shown to have a good agreement with laboratory values. The average errors for the dynamic shear modulus and phase angle were 3.4% and 4.0%, respectively, considering both temperatures of analysis. Finally, a considerable improvement was accomplished in comparison with the numerical response obtained with the often-used Burgers model.
- Experimental Validation and Numerical Analysis of a High-Performance Blast Energy-Absorbing System for Building StructuresPublication . Gomes, Gabriel de Jesus; Lúcio, Valter José da Guia; Cismaşiu, Corneliu; Mingote, José Luis; CERIS - Polo NOVA; DEC - Departamento de Engenharia Civil; MDPI - Multidisciplinary Digital Publishing InstituteThe paper presents a full-scale blast testing experimental campaign conducted on an energyabsorbing connector comprising thin-walled inversion tubes as kernel elements mounted in a façade protective panel. LS-DYNA finite element predictions of the global and local deformation/inversion of the panel/connectors compared reasonably well with the experimental observations. After validation, the numerical model was used to analyze the response of a simple idealized reinforced concrete structure under three blast-loading scenarios: the first two scenarios produce, approximately, the same impulse but are significantly different in terms of load duration and overpressures, and represent a far-field and a near-field scenario (1600 kg TNT at 20 m (i) and 150 kg TNT at 5 m (ii), respectively); the third scenario is more demanding, and consists in a half standoff distance of the second (150 kg TNT at 2.5 m (iii)). These numerical simulations allow to assess the effect of standoff distance and blast loading on the effectiveness of the protective system. One may conclude that the introduction of EACs strongly limits the forces imparted to the protected structure, reducing significantly the corresponding energy absorption demand. Comparing the energy absorbed by the structure in different scenarios, with and without the protective system (8 × ϕ64 × 2 mm), one can see that these reductions can reach, respectively 67%, 72% and 68% in the far-field, near-field and very near-field explosions.
- Retrofitting Historic Buildings for Future Climatic Conditions and Consequences in Terms of Artifacts Conservation Using Hygrothermal Building SimulationPublication . Coelho, Guilherme B. A.; de Freitas, Vasco Peixoto; Henriques, Fernando M. A.; Silva, Hugo Entradas; CERIS - Polo NOVA; DEC - Departamento de Engenharia Civil; MDPI - Multidisciplinary Digital Publishing InstituteClimate change will greatly influence the world at several levels and will have consequences on the interior climate of historic buildings and artifacts conservation. Buildings are responsible for a large slice of the overall emissions, which is due both to the greenhouse gases that are released during their construction as well as the activities that are performed therewithin. One way of counteracting this trend is to design more efficient retrofit buildings and predict their behavior using simulation software, which can thoroughly assess the performance of new buildings or the impact of each retrofit measure for existing buildings. In this study, a calibrated computational model of high thermal inertia building was used to assess the performance of passive retrofits in mitigating the effects of climate change concerning artifact decay mechanisms. In addition, a methodology that aims to reduce the amount of time spent to perform these studies is also presented, in which time savings reach up to 63%.