Influence of the supplementary reinforcement on the shear strength of beams with prefabricated truss stirrups

abstract: 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.

Estimate of theoretical shear strength of C60 single crystal by nanoindentation

The onset of plasticity in a single crystal C60 fullerite was investigated by nanoindentation on the (111) crystallographic plane. The transition from elastic to plastic deformation in a contact was observed as pop-in events on loading curves. The respective resolved shear stresses were computed for the octahedral slip systems $$\langle{01}\overline{1}\rangle\left\{ {{111}} \right\}$$ ⟨ 01 1 ¯ ⟩ 111 , supposing that their activation resulted in the onset of plasticity. A finite element analysis was applied, which reproduced the elastic loading until the first pop-in, using a realistic geometry of the Berkovich indenter blunt tip. The obtained estimate of the C60 theoretical shear strength was about $${1}/{11}$$ 1 / 11 of the shear modulus on {111} planes. Graphical abstract

Effect of Dislocation Sources on Slip in Fe2Nb Laves Phase with Ni in Solution

ABSTRACTWe have examined the compression response of a ternary Fe2Nb Laves phase by deforming micropillars with a diameter of ~2 μm produced by focused ion beam milling from a two-phase Fe-15Nb-40Ni (at.%) ternary alloy consisting of the Laves phase and γ-Fe. The Laves phase micropillars exhibit high strength of about 6 GPa (of the order of the theoretical shear strength of the material), followed by a burst of plastic strain and shear failure on the basal plane. If dislocation sources are introduced on a non-basal plane in the micropillars by nanoindentation prior to compression, yielding occurs at a significantly lower stress level of about 3 GPa and plastic deformation by slip proceeds on a pyramidal plane close to (-1-122). Furthermore, if regenerative dislocation sources for basal slip are present in the micropillar, the Laves phase can be continuously plastically deformed in a stable manner to at least 5% strain at a significantly lower stress of 800 MPa. We thus demonstrate the plastic deformation of this ternary Laves phase at the micron-scale at room temperature when sufficient dislocation sources are present.

A Study on the Safety of the Shear Capacity Design of Reinforced Concrete Beam-Column Joints

The shear failure probabilities of reinforced concrete beam-column joints have been investigated by Monte Carlo method. The theoretical shear strength of joints is based on the softened strut-and-tie model proposed by Hwang and Lee (2002). The random variables included in this study are the strengths of concrete, the ultimate compression strain of concrete, the strengths of reinforcement, the dimensions of cross-section, and the model error of theoretical shear strength of joints. The shear failure probabilities of joints with SD 280 flexural reinforcement in the beams designed using the ACI Code are all higher than 0.04. The joints designed according to the softened strut-and-tie model are safer than those designed according to the ACI Code. The shear failure probabilities of exterior joints are higher than those of interior joints. The shear failure probabilities of joints with SD 280 flexural reinforcement in the beams are higher than those of joints with SD 420 flexural reinforcement.