No abstract

This paper describes an experimental study of the punching resistance of unbonded post tensioned flat slabs supported on edge columns. Fifteen slabs rectangular in plain, with sides of 2 m by 1.2 m and 120 mm thick were tested, supported on square columns with sides of 200 mm and with length of 600 mm at the top and at the bottom. The main variables are the eccentricity (Mu/Vu) of the shear force, which is obtained varying the relation between loads parallel and perpendicular to the free edge; the amount of unbonded tendons (4 or 6 tendons perpendicular to the free edge and 3 or 2 tendons parallel to the free edge with the column); and the non‐prestressed flexural reinforcement detailing. The behavior of slabs is discussed in terms of vertical displacements, strains on concrete and on non‐prestressed rebars, forces on the unbonded tendons, cracking pattern and ultimate shear forces. The increase of the eccentricity (Mu/Vu) changes the failure mode from punching to flexure and torsion associated to punching.

Beams are structural elements commonly used in structure for construction designs. Usually wood is applied as structural elements and its use is very important because it is a material of renewable source, low density and satisfactory mechanical performance. When the wood surface is not properly treated, the structure can be destroyed not only by environmental conditions but also the attack of insects, compromising the structural design. This research presents the use of a particulate composite material of epoxy resin reinforced with white Portland cement in order to be applied as repair in timber columns. The mechanical performance of this material is essentially numerical, based on the Finite Element Method. The wood used in the simulation was the Eucalyptus grandis. The elastic properties were obtained from the specialist literature in the field of timber structures. The results of numerical simulations in terms of tension and buckling loads, the inclusion of the composite in the damaged regions (for all dimensions of the defects studied) provided buckling load results significantly higher than the buckling load values for the conditions without composite, and near to the values of the buckling loads without defect, highlighting the good performance of the particulate composite material in the repair of timber columns.

Resumo This paper presents the results of reinforced concrete columns strengthened by addition of a self-compacting concrete overlay at the compressed and at the tensioned face of the member, with and without addition of longitudinal steel bars. Eight columns were submitted to loading with an initial eccentricity of 60 mm. These columns had 120 mm x 250 mm of rectangular cross section, 2000 mm in length and four longitudinal reinforcement steel bars with 10 mm in diameter. Reference columns P1 and P2 were tested to failure without any type of rehabilitation. Columns P3 to P8 were loaded to a predefined load (close to the initial yield point of tension reinforcement), then unloaded and strengthened for a subsequent test until failure. Results showed that the method of rehabilitation used was effective, increasing the loading capacity of the strengthened pieces by 2 to 5 times the ultimate load of the reference column. Este artigo apresenta os resultados de pilares de concreto armado reforçados por meio da adição de camadas de concreto auto-adensável, tanto na face tracionada quanto na face comprimida, com ou sem adição de barras de aço longitudinais. Oito pilares foram submetidos a um carregamento com excentricidade inicial de 60mm. Estes pilares possuíam seção transversal retangular de 120 mm x 250 mm, comprimento de 2000 mm, e armadura longitudinal constituída por quatro barras de 10 mm de diâmetro. Os pilares de refer-ência, P1 e P2, foram ensaiados até a ruptura sem nenhum tipo de reabilitação. Os pilares P3 à P8 foram inicialmente submetidos a um pré-carregamento que provocava na armadura longitudinal, tensões próximas a do escoamento do aço. Em seguida, estas peças foram descarregadas e reforçadas. Após o concreto do reforço atingir resistência adequada, estes pilares foram ensaiados até a ruptura. Os resultados mostraram que o método de reforço estudado foi eficiente, pois dependendo da face do pilar em que se aplicava a camada de reforço, as peças reabilitadas apresentaram uma capacidade de carga de 2 a 5 vezes maior que a dos pilares não reforçados. Palavras-chave: pilar; concreto armado; reforço; excentricidade; concreto auto-adensável.

ResumoThis article presents the study of reinforced concrete columns strengthened using a partial jacket consisting of a 35mm self-compacting concrete layer added to its most compressed face and tested in combined compression and uniaxial bending until rupture. Wedge bolt connectors were used to increase bond at the interface between the two concrete layers of different ages. Seven 2000 mm long columns were tested. Two columns were cast monolithically and named PO (original column) e PR (reference column). The other five columns were strengthened using a new 35 mm thick self-compacting concrete layer attached to the column face subjected to highest compressive stresses. Column PO had a 120mm by 250 mm rectangular cross section and other columns had a 155 mm by 250mm cross section after the strengthening procedure. Results show that the ultimate resistance of the strengthened columns was more than three times the ultimate resistance of the original column PO, indicating the effectiveness of the strengthening procedure. Detachment of the new concrete layer with concrete crushing and steel yielding occurred in the strengthened columns.Este artigo apresenta um estudo do comportamento de pilares de concreto armado reforçados por encamisamento parcial, com o uso de uma camada de 35 mm de concreto auto adensável na face mais comprimida submetidos à flexo-compressão até à ruptura. Foram utilizados parafusos conectores como armadura de ligação entre as duas camadas de concreto de diferentes idades. Foram ensaiados 7 pilares de 2000 mm de altura, sendo 2 peças concretadas monoliticamente nomeadas de PO (pilar original) e PR (pilar de referência). Os outros 5 pilares foram reforçados utilizando uma camada de 35 mm de concreto moldada na face submetida a maior compressão. O pilar PO tinha uma seção transversal retangular de 120x 250 mm e as demais colunas 155 x 250 mm após executado o reforço. Os resultados alcançados mostram que os pilares reforçados atingiram uma resistência de aproximadamente três vezes maior com relação ao pilar PO, demostrando eficiência da técnica utilizada. Os pilares apresentaram o desplacamento da camada de reforço nas cargas finais, com tendências ao esmagamento do concreto e escoamento do aço.Palavras-chave: pilares, reforço, concreto, parafusos.