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)

This paper presents the results of seven experimental tests in reinforced concrete wide beams, aiming to investigate their performance when subjected to shear, using prefabricated truss stirrups as shear reinforcement, as well as a supplementary reinforcement to control cracks by delamination. The main analysed variables were: position of the supplementary reinforcement, inclination of the shear reinforcement, and spacing between stirrups. Results showed that strength increments of up to 142% were obtained using the prefabricated truss stirrups. Furthermore, the experimental results were compared with the theoretical shear strength estimates of the tested beams, following the recommendations of NBR 6118 (2014), Eurocode 2 (2004), and ACI 318 (2014), in order to evaluate the safety level of these codes when designing concrete elements subjected to shear with the reinforcement used in this paper.

This paper presents results of eight experimental tests carried to evaluate the mechanical performance of unconnected "W" stirrups.Reinforced concrete wide beams were tested and their characteristics were idealized to represent column strips in flat slab buildings. The main variables were: the type of shear reinforcement; the shear span to effective depth ratio (av/d); and the flexural (ρl) and shear (ρw) reinforcement ratios. In general, both the response and the shear resistance of the structural elements with unconnected "W" stirrups was similar to those elements with vertical closed stirrups. Increments of shear resistance of up to 84% were achieved, indicating that they have high potential for use as shear reinforcement in slab-column connections.

This paper presents and discusses the procedures adopted for repairing and strengthening a damaged reinforced concrete corbel of an industrial biomass boiler. The reinforced concrete corbel was subjected to concrete spalling, favoring the risk of the main tie reinforcement slip in the anchorage zone. The proposed solution involved a local repair with a polymeric mortar and subsequent strengthening using carbon fiber reinforced polymer (FRP) sheets, attending the requirements imposed by the in site conditions and the design plans. The intervention allowed the confinement of the concrete zone subjected to spalling and provided additional safety for the main tie reinforcement of the corbel. The applied technique was demonstrated to be fast, reliable, practical, and cheaper than other available solutions, such as section enlargements with concrete jacketing.

No abstract

PBuscando avaliar a influência da ancoragem na resistência à flexão de vigas reforçadas com mantas de Polímero Reforçado com Fibra de Carbono (PRFC), foram analisados os resultados experimentais de 126 ensaios presentes na literatura e de uma série inédita, ensaiada pelos autores, com 4 vigas de concreto armado. São avaliados os parâmetros que afetam o desempenho e a resistência das vigas, e discutidos os critérios de dimensionamento do fib Bulletin 14 (2001) e ACI 440-2R (2008). Observou-se que, mesmo com dispositivos auxiliares na ancoragem do PRFC, falhas prematuras são possíveis, e também que ambas as recomendações teóricas conduzem a estimativas a favor da segurança, porém excessivamente conservadoras nos casos onde a ancoragem da manta de PRFC é feita adequadamente.

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.

This research evaluates the influence of the replacement of natural coarse aggregates (NCA) by recycled concrete aggregates (RCA) on the shear strength of reinforced concrete beams. Experimental tests on six reinforced concrete beams with RCA replacement ratios of 0%, 30%, and 100% are presented. Furthermore, a database with results of 170 tests on beams with RCA is used to discuss adjustments in the recommendations presented by ABNT NBR 6118 to estimate the shear strength of reinforced concrete beams. According to the Demerit Points Classification (DPC) proposed by Collins, 80% of the theoretical results obtained using models I and II from the Brazilian code fall in an appropriate safety condition range, showing that the substitution of NCA by RCA has a low impact on the shear strength reinforced concrete beams.