Análise não-linear de estruturas reticuladas espaciais de concreto armado

Present an automatic program for non-linear analysis of spacial frames of reinforced concrete, including verification of structures under definite loading and research on its load-bearing capacity for a given disposition of loads. On its development are considered both the non-linearity of the stress-strain diagrams of the materials (physical non-linearity) and the second order effects of the axialflexural interaction (geometrical non-linearity). ln the case of structure loaded by torsion, combined or not with others efforts, the effects of torsion are considered on an approximative way, based on the spacial truss model, adopted by the C.E.B. The final part presents some examples of application of the automatic program and some comparisons with others methods of analysis and experimental investigations. Some comments about the results obtained and suggestions for more advanced studies in the future are also included.Apresenta um programa automático para a análise não-linear de estruturas reticuladas espaciais de concreto armado, compreendendo tanto a verificação de uma estrutura sob a ação de um carregamento definido, como a pesquisa de sua capacidade de carga para uma dada disposição de cargas. Em sua elaboração foram levados em conta além da não-linearidade dos diagramas tensão-deformação dos materiais (não-linearidade física), os efeitos de segunda ordem decorrentes da interação axial flexão (não-linearidade geométrica). No caso de estruturas solicitadas à torção, combinada ou não com outros esforços, são considerados os efeitos da torção de maneira aproximada, tendo por base o modelo da treliça espacial, adotado pelo C.E.B. Em sua parte final o trabalho apresenta exemplos de aplicação do programa e comparações com outros métodos de análise e pesquisas experimentais. Estão incluídos, também, comentários sobre os resultados obtidos e sugestões para aprimoramento deste trabalho

Influência da velocidade de concretagem sobre a pressão lateral do concreto fresco no dimensionamento de fôrmas

A pressão lateral do concreto fresco gera uma carga que possui grande influência no dimensionamento das fôrmas de pilares, paredes e faces laterais das vigas. Sua previsão deve ser realizada de modo que se aproxime bem dos valores suportados pelas fôrmas, evitando-se, assim, o superdimensionamento ou subdimensionamento dessas estruturas provisórias que representam até 12% do custo total da obra. O cálculo da pressão lateral que o concreto fresco exerce sobre as fôrmas envolve diversas variáveis, sendo uma delas a velocidade de concretagem. O principal objetivo deste trabalho foi estudar a influência da velocidade de concretagem sobre a pressão lateral do concreto fresco calculada a partir de modelos teóricos apresentados por normas e referências internacionais. Para isso, foram realizadas medições da velocidade de concretagem em pilares de cinco obras de Goiânia e calculadas as pressões máximas suportadas por suas respectivas fôrmas, a partir das dimensões e dos vãos entre os apoios dos elementos que as constituíam. Os resultados obtidos apontam que as velocidades de concretagem em campo chegam a 248,57 m/h, superando os valores limitados pelos métodos teóricos de cálculo, e que as estimativas da pressão realizadas a partir das velocidades medidas in loco ultrapassam os valores máximos suportados pelas fôrmas em até 603,75 vezes. Assim, concluiu-se que é necessária a formulação de equações para estimar a pressão lateral do concreto fresco a altas velocidades de concretagem, conforme as atuais práticas no mercado da construção civil.The fresh concrete lateral pressure generates a load that has great influence in the design of the formworks of columns, walls and lateral faces of the beams.Its prediction must be performed in such a way in order to approach precisely well over the rate values supported by the formworks, avoiding, therefore, the oversizing or undersizing of these temporary structures which represent up to 12% of the total cost of the construction. The calculation of the lateral pressure that fresh concrete exerts on the formworks involves several variables; one of them is the placement rate. The main objective of this work was to study the influence of the placement rate, in situ, on the lateral pressure of fresh concrete calculated from theoretical models presented by norms and international references. For this purpose, measurements of the placement rate were conducted on columns of five building work places at Goiânia city, Goiás, Brazil and it was calculated the maximum pressure supported by their respective formworks from the dimensions and spans between the supports of the components that constituted them. The obtained results indicate that the placement rate in the field observations reach 249 m/h, exceeding the values limited by the theoretical methods of calculation, and that the lateral pressure estimation produced from the placement rate measured in situ exceed the maximum values supported by the formworks up to 604 times. Thus, it was concluded that it is necessary to adjust equations to estimate the lateral pressure of fresh concrete at high rate of concrete placement, according to the current practices in the construction market

Comparison between concrete stress diagrams according to the Brazilian standard ABNT NBR 6118: 2014

This study aims to compare methods for the determination of concrete properties by means of the stress diagrams present in the Brazilian standard ABNT NBR 6118: 2014. The area under the stress diagram, the internal reactions, and the application point of the resulting reactions for the parabola-rectangle and rectangular block diagrams are present in order to compare them. Deductions and numerical examples were used, and different results were obtained for each formulation. This is due to non-consideration of the relationship between stress and strain in the simplified rectangular block. The rectangular block is applicable only for cases in which the concrete reaches the ultimate strain. These cases are those that concrete crushing determines the section failure in compression with steel yielding in tension (domain 3) or without steel yielding (domain 4)

Structural flexural strengthening through material bonded to the concrete substrate

This article proposes an alternative method for the structural design of reinforced concrete elements strengthened in bending by metallic plates or fiber-reinforced polymer (FRP) bonded to the concrete substrate. It is proposed a new calculation procedure for the strengthening using thin adhered material bonded to the element surface that dispenses the iterative process generally used in the design. The proposed routine is validated by comparison with other methods. A practical example is also presented, applying the procedure to an element of a building where a load change was foreseen. As result, it was verified that the proposed procedure provides values similar to the trial-and-error method used in the FRP strengthening design. Results are also coherent with other methods available in the literature for metallic plates. Therefore, since this routine obtains similar values without using an iterative method, its applicability in the design becomes advantageous

Rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART): Study protocol for a randomized controlled trial

Background: Acute respiratory distress syndrome (ARDS) is associated with high in-hospital mortality. Alveolar recruitment followed by ventilation at optimal titrated PEEP may reduce ventilator-induced lung injury and improve oxygenation in patients with ARDS, but the effects on mortality and other clinical outcomes remain unknown. This article reports the rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART). Methods/Design: ART is a pragmatic, multicenter, randomized (concealed), controlled trial, which aims to determine if maximum stepwise alveolar recruitment associated with PEEP titration is able to increase 28-day survival in patients with ARDS compared to conventional treatment (ARDSNet strategy). We will enroll adult patients with ARDS of less than 72 h duration. The intervention group will receive an alveolar recruitment maneuver, with stepwise increases of PEEP achieving 45 cmH(2)O and peak pressure of 60 cmH2O, followed by ventilation with optimal PEEP titrated according to the static compliance of the respiratory system. In the control group, mechanical ventilation will follow a conventional protocol (ARDSNet). In both groups, we will use controlled volume mode with low tidal volumes (4 to 6 mL/kg of predicted body weight) and targeting plateau pressure <= 30 cmH2O. The primary outcome is 28-day survival, and the secondary outcomes are: length of ICU stay; length of hospital stay; pneumothorax requiring chest tube during first 7 days; barotrauma during first 7 days; mechanical ventilation-free days from days 1 to 28; ICU, in-hospital, and 6-month survival. ART is an event-guided trial planned to last until 520 events (deaths within 28 days) are observed. These events allow detection of a hazard ratio of 0.75, with 90% power and two-tailed type I error of 5%. All analysis will follow the intention-to-treat principle. Discussion: If the ART strategy with maximum recruitment and PEEP titration improves 28-day survival, this will represent a notable advance to the care of ARDS patients. Conversely, if the ART strategy is similar or inferior to the current evidence-based strategy (ARDSNet), this should also change current practice as many institutions routinely employ recruitment maneuvers and set PEEP levels according to some titration method.Hospital do Coracao (HCor) as part of the Program 'Hospitais de Excelencia a Servico do SUS (PROADI-SUS)'Brazilian Ministry of Healt

Modelisation du comportement jusqu'a rupture en flexion de poutres en beton a precontrainte exterieure ou mixte

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Recomendações sobre procedimentos invasivos em pacientes com doenças do fígado e do trato biliar : relatório de reunião conjunta da Sociedade Brasileira de Hepatologia (SBH), Sociedade Brasileira de Endoscopia Digestiva (SOBED) e Sociedade Brasileira de Radiologia Intervencionista e Cirurgia Endovascular (SOBRICE)

As doenças do fígado e das vias biliares são causas comuns de morbidade e mortalidade. Procedimentos invasivos com finalidade diagnóstica e terapêutica são frequentemente recomendados nos casos de doenças hepatobiliares. O reconhecimento das indicações e limitações das técnicas comumente empregadas é crucial para uma adequada seleção dos pacientes, maximizando os resultados positivos e reduzindo o risco de complicações. Em 2018, a Sociedade Brasileira de Hepatologia (SBH), em colaboração com a Sociedade Brasileira de Radiologia Intervencionista e Cirurgia Endovascular (SOBRICE) e a Sociedade Brasileira de Endoscopia Digestiva (SOBED) realizaram um encontro exclusivamente voltado para a discussão dos procedimentos invasivos nas doenças hepatobiliares. Este texto resume as principais recomendações discutidas durante o evento, e tem a intenção de auxiliar clínicos, gastroenterologistas, hepatologistas, radiologistas e endoscopistas no uso adequado dos procedimentos invasivos para manejo de pacientes com doenças hepatobiliares.Liver and biliary tract diseases are common causes of morbidity and mortality worldwide. Invasive procedures are usually performed in those patients with hepatobiliary diseases for both diagnostic and therapeutic purposes. Defining proper indications and restraints of commonly used techniques is crucial for proper patient selection, maximizing positive results and limiting complications. In 2018, the Brazilian Society of Hepato­logy (SBH) in cooperation with the Brazilian Society of Interventional Radiology and Endovascular surgery (SOBRICE) and the Brazilian Society of Digestive Endoscopy (SOBED) sponsored a joint single-topic meeting on invasive procedures in patients with hepatobiliary diseases. This paper summarizes the proceedings of the aforementioned meeting. It is intended to guide clinicians, gastroenterologists, hepatologists, radiologists, and endoscopists for the proper use of invasive procedures for management of patients with hepatobiliary diseases