This paper describes two practical methodologies for modeling the collapse of reinforced concrete structures. They are validated with a real scale test of a two-floor structure which loses a bearing ...column. The objective is to achieve accurate simulations of collapse phenomena with moderate computational cost. Explicit finite element models are used with Lagrangian meshes, modeling concrete, and steel in a segregated manner. The first model uses 3D continuum finite elements for concrete and beams for steel bars, connected for displacement compatibility using a penalty method. The second model uses structural finite elements, shells for concrete, and beams for steel, connected in common nodes with an eccentricity formulation. Both are capable of simulating correctly the global behavior of the structural collapse. The continuum finite element model is more accurate for interpreting local failure but has an excessive computational cost for a complete building. The structural finite element model proposed has a moderate computational cost, yields sufficiently accurate results, and as a result is the recommended methodology.
This research evaluates the performance of different protective solutions for reinforced concrete slabs subjected to blast loading. A series of full-scale blast tests were carried out on concrete ...slabs at scaled distances ranging from 0.20 to 0.83 m/kg1/3. For this purpose, 16 concrete slabs were tested; eight of them were unreinforced as ‘control specimens’, and the other eight were protected with five different protective solutions. After the tests, a damage assessment was conducted based on three different parameters. The results showed that there was no clear improvement in the concrete performance when the charge was located 0.5 m from the slab. Significant local damage that completely perforated the slab occurred. In the tests with the load placed 1 m from the slab, the reinforcements that were used significantly contributed to the retention of some fragments produced in these tests.
•Results of full-scale test of corner column removal carried out on a two storey building.•Finite element modelling and comparison between observed and predicted damage patterns and ...deflections.•Monitoring results including DIC, accelerometers and full characterisation of deflections using laser scan.•Interpretation of results.
This paper presents the results of a full-scale robustness test carried out on a two storey building with two square reinforced concrete slabs (25 cm deep) with a span of 6.6 m, in which a corner column was suddenly removed. Despite the extreme action, and the fact that the slab was not designed for it, only relatively minor damage was observed, with a maximum deflection around 22 cm and apparently controled cracking patterns. The slab started working as a simply supported element along the symmetry axis of the structure supported on only 3 columns. The tests was modeled using Finite Element Analysis. It was observed that the model could capture very well the behaviour of the real structure, predicting very similar cracking patterns and deflections. The structure was shored two hours after the test because deflections were not yet fully stabilized. It is suspected that this increase of deflections could be related to the deterioration by torsional effects of the connection between the slab and columns on the first floor.
Flipped classroom in engineering: The influence of gender Chiquito, María; Castedo, Ricardo; Santos, Anastasio P. ...
Computer applications in engineering education,
January 2020, 2020-01-00, 20200101, Letnik:
28, Številka:
1
Journal Article
Recenzirano
The flipped classroom technique has been applied to a part (“Strength of Materials”) of a second‐year compulsory course called “Technology of Materials.” Due to the number of students, the course is ...divided into two groups – one taught with the traditional methodology (98 students), and the other taught with the flipped one (97 students). In the traditional methodology, the teacher explains the lesson and solves the problems, with students as passive actors in the learning process. In the developed flipped classroom model, the students have edited videos on an institutional online platform, available before each face‐to‐face session. In addition, a linked activity is used to check the students’ knowledge before class. The in‐class time is dedicated to briefly reviewing the concepts explained in the video, with a special emphasis on the errors detected in the link activity, followed by groups of students solving problems. The aim of this study is to present quantitative results of the effect of the flipped classroom in engineering with a focus on the gender of the students. The results show that the flipped classroom model has a direct impact on student grades, especially for female students, which presents significant differences when compared with males of the same group. In addition, the grade standard deviation values were lower, ensuring a better general level. The students of the flipped classroom group also attended the exams in a higher ratio than others, as these students are likely to feel more confident in the knowledge they have acquired.
Within the research project ITSAFE, two full-scale structures were built, one consisting of a single-storey, two-span, 7.00 × 14.00 m2 RC frame with a solid slab and another consisting of a ...two-storey, 7.00 × 7.00 m2 RC frame with solid slabs. In the two-span frame, one of the central supports was first demolished using a pneumatic hammer, resulting in rather limited damage (a 14–15 cm deflection at the removed support location). However, torsional cracks appeared at the interface between a column and slab in one of the outer supports. When the second central support was removed, the structure collapsed with the failure of the support–slab connection. The same type of cracking was observed in the two-storey structure, where the column removal was dynamic, and a 22 cm deflection was measured. These experimental results question current practice in which, for internal supports, alternative load path mobilizing membrane forces in the slab are said to prevent their collapse, or in the cases of edge and corner columns, rupture line analysis is used and suggests that special reinforcement at the column–support connection is also needed to prevent the premature failure of the structure.
The dramatic increase in computation efficiency over the last three decades has made the finite-element simulation approach the dominant tool for investigating blast phenomena and their effects on ...building structures. However, the simulation results depend greatly on the mesh size selected for the numerical model, which may generate an inaccuracy in predicting the phenomena correctly. Thus, mesh size for finite-element simulations, appears to be an epistemic uncertainty that is inherent to the simulation process. This paper investigates the reliability of finite-element simulations of a reinforced concrete slab subjected to a certain level of explosion, in terms of mesh size sensitivity. Full-scale free air blast experiments are performed to monitor the blast-structure interaction phenomenon and help validating the numerical simulations. Fifteen finite-element simulations are evaluated with coarse to fine range mesh sizes, and the effects of mesh resolution on the numerical simulations are analyzed. An optimum mesh size is determined for a given set of loading conditions, and established by the amount of internal energy that gives rise to the expected damage on the slab.
There is growing concern about the possibility of a suicide bomber being immolated when the army forces or the law enforcement agencies discover the place where they prepare their material or simply ...find themselves inside a building. To study the possible effects that these improvised explosive devices (IEDs) would have on the structures, eight tests were carried out with various configurations of IEDs with vest bombs inside a reinforced concrete (including walls and roof) building constructed ad hoc for these tests. These vests were made with different explosives (black powder, ANFO, AN/AL, PG2). For the characterization of these tests, a high-speed camera and pressure and acceleration sensors were used. The structure behaved surprisingly well, as it withstood all the first seven detonations without apparent structural damage. In the last detonation, located on the ground and with a significant explosive charge, the structural integrity of the roof and some of the walls was compromised. The simulation of the building was carried out with the LS-DYNA software with a Lagrangian formulation for the walls, using the LBE (based on CONWEP) module for the application of the charge. Despite the difficulty of this simulation, the results obtained, in terms of applied pressures and measured accelerations, are acceptable with differences of about 20%.
Fabry disease (FD) is an X-linked lysosomal storage disorder caused by a deficiency of the lysosomal hydrolase α-galactosidase A (α-GalA) that leads to the intra-lysosomal accumulation of ...globotriaosylceramide (Gb3) in various organ systems. As a consequence, a multisystems disorder develops, culminating in stroke, progressive renal and cardiac dysfunction. Enzyme replacement therapy (ERT) offers a specific treatment for patients affected by FD, though the monitoring of treatment is hindered by a lack of surrogate markers of response. Remarkably, due to the high heterogeneity of the Fabry phenotype, both diagnostic testing and treatment decisions are more challenging in females than in males; thus, reliable biomarkers for Fabry disease are needed, particularly for female patients. Here, we use a proteomic approach for the identification of disease-associated markers that can be used for the early diagnosis of FD as well as for monitoring the effectiveness of ERT. Our data show that the urinary proteome of Fabry naïve patients is different from that of normal subjects. In addition, biological pathways mainly affected by FD are related to immune response, inflammation, and energetic metabolism. In particular, the up-regulation of uromodulin, prostaglandin H2 d-isomerase and prosaposin in the urine of FD patients was demonstrated; these proteins might be involved in kidney damage at the tubular level, inflammation and immune response. Furthermore, comparing the expression of these proteins in Fabry patients before and after ERT treatment, a decrease of their concentration was observed, thus demonstrating the correlation between the identified markers and the effectiveness of the pharmacological treatment.
This work deals with the response of eight reinforced concrete (RC) slabs, made at full-scale, some of them with the addition of externally bonded fibre reinforced polymer (FRP). The reinforcements ...were placed in all cases on the face opposite to the explosive detonation. Three scaled distances have been used from 0.83 m/kg1/3, in one test with no extra reinforcement; four tests were made with a scaled distance of 0.42 m/kg1/3: one without extra reinforcement, two with carbon fibre reinforcement (CFRP) and one with the E-glass fibre reinforcement (GFRP); finally, 0.21 m/kg1/3, in three trials, one without extra reinforcement, one with carbon fibre reinforcement and one with the E-GFRP. The first slab, used for calibration of the numerical models, was instrumented with pressure and acceleration sensors. For the validation of the other seven slabs, the damage surfaces on both sides of the slabs are used. In terms of numerical simulation performed with LS-DYNA, several models covering different solutions such as smooth particle hydrodynamics (SPH) or load blast enhanced have been performed for the description of the explosive, as well as the use of CSCM material models for concrete to analyse the best available solutions. The steel was modelled with the piecewise linear plasticity material, while the material laminated composite fabric was used for the FRP. Reinforcement with CFRP resulted in a generally reduced damage area on both surfaces. All models show a good correlation, including non- spherical charges made with SPH models, with the test results when comparing them with respect to acceleration and surface damage. SPH models work well for the high and medium scaled distance, but not so good for the shorter scaled distance.
The discretization error is not always calculated, even though it is essential for the studies of computational solid mechanics. However, it is well known that an error committed by the mesh used can ...be as large as the measured variable, which greatly invalidates the results obtained. The grid convergence index (GCI) method makes possible to determine on a solid basis, the order of convergence and the asymptotic solution. This method seems to be a suitable estimator despite further research is needed in the context of blast situations and finite element (FE) calculations. For this purpose, field trials were performed consisting in the detonation of a spherical hanging load of homemade explosive. The pressure generated by the shock wave was measured in different positions at two distances. With these data, a TNT equivalent has been obtained and used to calculate the shock propagation with the solvers LS-DYNA and ProsAir. This work aims to verify the GCI method by comparing its results with field data along with the simulations carried out. The comparison also seeks to validate the methodology used to obtain the TNT equivalent.This research shows that the GCI gives good results for both solvers despite the complexity of the physical problem. Besides, LS-DYNA displays better correlation with the experimental data than the ProsAir results, with an error of less than 10% in all values.
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