Punching strength is a critical point in the design of flat slabs and due to the lack of a theoretical method capable of explaining this phenomenon, empirical formulations presented by codes of practice are still the most used method to check the bearing capacity of slab-column connections. This paper discusses relevant aspects of the development of flat slabs, the factors that influence the punching resistance of slabs without shear reinforcement and makes comparisons between the experimental results organized in a database with 74 slabs carefully selected with theoretical results using the recommendations of ACI 318, EUROCODE 2 and NBR 6118 and also through the Critical Shear Crack Theory, presented by Muttoni (2008) and incorporated the new fib Model Code (2010).Keywords: flat slab, punching shear, reinforced concrete, codes.O dimensionamento à punção é um ponto crítico no projeto de lajes lisas e devido à falta de um método teórico capaz de explicar este fenômeno a verificação da capacidade resistente de ligações laje-pilar é feita normalmente utilizando-se as recomendações de normas de projeto. Este artigo discute aspectos relevantes do surgimento do sistema de lajes lisas, dos fatores que influenciam na resistência à punção de lajes sem armadura de cisalhamento e faz comparações entre os resultados experimentais de um banco de dados com 74 lajes cuidadosamente selecionadas com resultados teóricos utilizando-se as recomendações das normas ACI 318, EUROCODE 2 e NBR 6118 e também através da Teoria da Fissura Crítica de Cisalhamento, apresentada por Muttoni (2008)

Ribbed slabs have been widely used in buildings due to their many advantages, especially the decrease of concrete below the neutral line. This paper presents an experimental and computational study on ribbed slabs with wide-beam, two one-way slabs and two two-way slabs, with variable depths were tested to evaluate their resistance to punching and shear strength of slabs. Experimental and computational results showed that the wide-beam ribs connection is a critical point in the design of the slabs due to the difference in stiffness in the transition zone. Best results for the ultimate load estimates for ribs were provided by EC 2 (2004), while estimates of ACI 318 (2008) and NBR 6118 (2014) were respectively conservative and unsafe. Test results on slabs also revealed that the Brazilian alternative to analysis ribbed slabs as solid ones failed to give satisfactory results.

ABSTRACT. This paper presents results of tests on 18 one-way reinforced concrete slabs under point loads having as main variable the transverse flexural reinforcement ratio, the loading position and the width of the slab. The response of the slabs is described and discussed in terms of deflections, strains of the concrete and of rebars, cracking pattern, failure modes and failure loads. Experimental results are also used to discuss and evaluate theoretical treatments presented by American Concrete Institute 318 (ACI, 2014) and Eurocode 2 (Comité Européen de Normalisation [CEN], 2005). All slabs failed by punching shear and results indicate that the recommendations presented by the codes are conservative, especially those related to the prediction of one-way shear resistance of reinforced concrete flat slabs.Keywords: one-way slabs, punching, shear, asymmetric loading.Resistência à punção de lajes de concreto armado com cargas concentradas assimétricas RESUMO. Este trabalho apresenta resultados de ensaios em 18 lajes unidirecionais de concreto armado sob carregamento concentrado, tendo como variáveis a taxa de armadura de flexão transversal, a posição de carregamento e a largura da laje. Seu comportamento é descrito e discutido em termos de deslocamentos, deformações do concreto e das armaduras, padrão de fissuração, modos e cargas de ruptura. Os resultados experimentais também são usados para discutir e avaliar as recomendações apresentados pelas normas ACI 318 (2014) e Eurocode 2 (CEN, 2005). Todas as lajes romperam por punção e os resultados indicam que as recomendações normativas são relativamente conservadoras, especialmente aquelas relacionadas com a previsão da resistência ao cisalhamento unidirecional de lajes lisas de concreto armado.Palavras-chave: lajes unidirecionais, punção, cisalhamento, carregamento assimétrico.

WebWorldWind is a 3D virtual globe API for HTML5 and JavaScript developed by NASA with support of the European Space Agency (ESA) and other partners. In this paper, the results of the first year for the on-going collaboration between ESA and NASA on WebWorldWind development are presented, highlighting concrete examples built with the newly introduced features and putting them in relation to possible research and education use cases. Finally, the next steps and roadmap are briefly introduced.

A greater number of structures are being built with flat reinforced concrete slabs because they offer several advantages. However, many designers are still unsure about the type of slab that has the best structural performance and which building codes provide the best strength estimates. This study presents nonlinear computer simulations of 16 flat reinforced concrete slabs under symmetrical punching: 4 solid slabs, 4 waffle slabs with wide beams, and 8 waffle slabs with different numbers of ribs supported in the solid area of the slab. Geometric longitudinal reinforcement ratios ranged from 0.45% to 1.97%. The results showed that solid and beamed slabs are more resistant, and normative estimates overestimate their strengths, while the opposite outcome was found for waffle slabs, whose estimates provided in the codes were rather conservative. The most accurate code was EC2, followed by ACI 318 and NBR 6118.