On the thermo-mechanical characterization of cement mortars exosed to high temperature

Some recent technical documents on fire-resistant walls made of either cementitious blocks or clay bricks are bringing onto the stage the thermo-mechanical behavior of the mortars. Information on mortars decay at high temperature, however, is either contradictory or can hardly be found in the technical-scientific literature. This study aims to provide information on the thermo-mechanical behaviour of mortars in residual conditions. Three mortars are investigated (a reference mortar, cube strength fcc » 5 MPa, and two higher-grade mortars, fcc » 10 MPa and fcc » 15 MPa, respectively). All mortars are tested past a high-temperature cycle at 200, 400 and 600°C. On the whole, the mechanical decay turns out to be very close to that of typical ordinary concretes, while the thermal diffusivity is markedly lower. A worked example about a concrete-block fire-resistant wall ends the paper

Finite Approximations to Quantum Physics: Quantum Points and their Bundles

There exists a physically well motivated method for approximating manifolds by certain topological spaces with a finite or a countable set of points. These spaces, which are partially ordered sets (posets) have the power to effectively reproduce important topological features of continuum physics like winding numbers and fractional statistics, and that too often with just a few points. In this work, we develop the essential tools for doing quantum physics on posets. The poset approach to covering space quantization, soliton physics, gauge theories and the Dirac equation are discussed with emphasis on physically important topological aspects. These ideas are illustrated by simple examples like the covering space quantization of a particle on a circle, and the sine-Gordon solitons.Comment: 24 pages, 8 figures on a uuencoded postscript file, DSF-T-29/93, INFN-NA-IV-29/93 and SU-4240-55

Deformation capacity evaluation for flat slab seismic design

The authors acknowledge the dedicated and careful work carried out by the Associate Editor and Reviewers whose constructive criticism contributed to a very significant improvement of the quality of the paper. Authors wish to dedicate this work to the memory of their co-author Prof. Ion Radu Pascu, UTCB Bucharest, who passed away on June 10, 2021. Publisher Copyright: © 2021, The Author(s).In flat-slab frames, which are typically designed as secondary seismic structures, the shear failure of the slab around the column (punching failure) is typically the governing failure mode which limits the deformation capacity and can potentially lead to a progressive collapse of the structure. Existing rules to predict the capacity of flat slab frames to resist imposed lateral displacements without losing the capability to bear gravity loads have been derived empirically from the results of cyclic tests on thin members. These rules account explicitly only for the ratio between acting gravity loads and resistance against concentric punching shear (so-called Gravity Shear Ratio). Recent rational models to estimate the deformation capacity of flat slabs show that other parameters can play a major role and predict a significant size effect (reduced deformation for thick slabs). In this paper, a closed-form expression to predict the deformation capacity of internal slab-column connections as a function of the main parameters is derived from the same model that has been used to develop the punching shear formulae for the second generation of Eurocode 2 for concrete structures. This expression is compared to an existing database of isolated internal slab-column connections showing fine accuracy and allowing to resolve the shortcomings of existing rules. In addition, the results of a testing programme on a full-scale flat-slab frame with two stories and 12 columns are described. The differences between measured interstorey drifts and local slab rotations influencing their capacity to resist shear forces are presented and discussed. With respect to the observed deformation capacities, similar values are obtained as in the isolated specimens and the predictions are confirmed for the internal columns, but significant differences are observed between internal, edge and corner slab-column connections. The effects of punching shear reinforcement and of integrity reinforcement (required according to Eurocode 2 to prevent progressive collapse after punching) are also discussed.publishersversionpublishe

La puesta en juego de la cultura física en programas socioeducativos del partido de Luján

Este escrito sintetiza algunos hallazgos de una investigación, realizada en el período 2008-2009 en el partido de Luján, que se propuso indagar algunas políticas públicas educativas, sociales y de salud en el ámbito del Estado. El objetivo general fue describir cómo son los programas y proyectos sociales, educativos y de salud implementados por el Estado (nacional, provincial y local), radicados en el Partido de Luján que incluyen contenidos de la cultura física; en tanto uno de los objetivos específicos del estudio se centró en conocer los perfiles del personal a cargo de las acciones; esto es ¿qué conocimientos y habilidades necesitan quienes intervienen en la planificación, implementación, desarrollo, conducción y evaluación de estas acciones?; ¿cómo es la formación, reconocimiento institucional y la supervisión de ese personal? y ¿qué significados otorgan a las acciones y prácticas que tienen a cargo? La presentación de este resumen en esta área y mesa de trabajo, es pertinente a la hora de compartir y/o reflexionar sobre las diferentes concepciones de ocio, tiempo libre y recreación que poseen quiénes practican la enseñanza en estos programas.Facultad de Humanidades y Ciencias de la Educació

A contribution to the thermo-mechanical characterization of cement mortars at high temperature

The association of cement mortars with fibers, textiles and FRP reinforcement is keeping interest high for both high/ultra-high performance mortars and ordinary/bed-fixing mortars, as these composite materials can effectively contribute to structural safety and durability. Since structural safety comprises fire safety, having further information on mortar behavior at high temperatures and in fire is welcome. The thermo-mechanical behavior of a bed-fixing reference mortar (cube strength Rc = 5 MPa), and of two higher-grade mortars (Rc = 10 and 15 MPa) is investigated in this project past a high-temperature cycle at 200, 400 and 600°C. On the whole, the heat-induced mechanical decay turns out to be fairly close to that of ordinary concrete. The mortars, however, exhibit a greater mass loss and a greater insulating capability at any temperature, the latter being related to the markedly lower thermal conductivity and diffusivity compared with ordinary concrete

Hypotony after 25-gauge vitrectomy

Purpose To describe the incidence of hypotony after 25-gauge vitrectomy and to identify preoperative and intraoperative factors that influence the occurrence of hypotony. Design Retrospective, nonrandomized, interventional case series. Methods We reviewed 122 consecutive cases of 25-gauge vitrectomy for all surgical indications. The primary outcome measure was intraocular pressure (IOP) at postoperative day 1, measured with Goldmann tonometry. Secondary outcome measures were clinical signs of hypotony and other complications. Results Hypotony, defined as an IOP of 5 mm Hg or less, was found in 13.1% of cases on postoperative day 1. Clinical signs of hypotony were encountered in 7 eyes (5.7%). The risk of hypotony was significantly lower in cases with air or gas tamponade (3.3%) than in cases without tamponade (22.4%). Hypotony was encountered more often in reoperations (29.9%) than in primary operations (9.2%; statistically significant difference). In cases in which intravitreal triamcinolone was used, the risk of hypotony was significantly higher (35.3%) than in cases without triamcinolone (10.3%). Phakic eyes had significantly less chance of hypotony (6.7%) than pseudophakic eyes (15.6%) and eyes undergoing combined phacoemulsification and vitrectomy (25.0%). At postoperative day 7, all cases of hypotony recovered spontaneously. None of our cases developed endophthalmitis. Conclusion Our results show that a transient hypotony occurs commonly after 25-gauge vitrectomy. Hypotony was significantly influenced by tamponade, reoperation, intraoperative lens status, and use of intravitreal triamcinolone. Although all cases of hypotony recovered spontaneously without permanent damage, the high frequency of hypotony does impose potential risks. Increased vigilance with focus on perioperative antisepsis and low tolerance of sclerotomy leakage are important for the prevention of endophthalmitis. Strategies aimed at lowering the risk of hypotony are needed to improve the safety of this promising technique

Ultimate Capacity of Undercut Fasteners Installed in Heat-Damaged Concrete

The ultimate behavior and bearing capacity of undercut fasteners installed in heat-damaged concrete are investigated in this paper in which the results of a rather comprehensive research project are presented. Sixty-one fasteners (shank diameter ØN=10  mmØN=10  mm) are tested under a pull-out force after being installed in as many preheated and postdrilled slabs made of three different concretes: (1) a low-strength concrete (LSC), f20c=20  MPafc20=20  MPa; (2) a normal-strength concrete (NSC), f20c=52  MPafc20=52  MPa; and (3) a high-performance concrete (HPC), f20c=63  MPafc20=63  MPa. Besides room temperature, five reference temperatures (between 200°C and 450°C at a prefixed distance from the heated surface) are considered to represent as many values of the fire duration prior to the instalment of the fastener. Four values of the embedment depth (45%, 60%, 80%, and 100% of the embedment suggested by the producer=10ØNproducer=10ØN) are investigated. In all cases, except in the virgin unheated specimens, the failure is caused by the thermally-damaged concrete, with the formation of a conical crack. Two finite-element (FE) models are formulated, based on linear-elastic fracture mechanics (LEFM) and on nonlinear fracture mechanics (NLFM), respectively, and their results are shown to envelop the test results. A third simple model based on linear fracture mechanics is also developed to quantify the extra loss of capacity induced by real fires in which the heating rate is one order of magnitude higher than in the electric furnaces generally used in the labs. Last but not least, to have information on the ultimate load associated with the possible formation of a conical crack, even in those cases in which the collapse due to shank yielding precedes concrete-cone failure (typically in high-grade virgin or undamaged specimens), the well-known concrete capacity method (CC-method) is modified to incorporate the maximum aggregate size, which plays a substantial role in crack mechanics