A method to evaluate the punching shear strength of reinforced concrete (RC) flat slabs without shear reinforcement at the connection to interior columns is proposed. The method is based on the assumption that the punching shear strength is controlled by the inclination of a unique punching shear crack that produces a conical failure surface.The inclination angle of the crack is variable. It follows that the location of the critical section is not established in advance, but changes with crack angle. Its location depends on the reinforcement ratio, material strengths and effective depth. According to the proposed method, the punching shear strength is a function of the inclination angle of the governing crack that controls the amount of shear carried by the compression zone and the flexural reinforcement crossing the potential punching cone by accounting for its slenderness and concrete size effect. The method describes the behaviour observed in tests and numerical and analytical investigations. The novel premise that the punching shear strength of flat slabs at connections to interior columns is controlled by the inclination of the failure surface shows remarkable agreement with the results of 209 tests on isolated specimens reported in the literature. This paper also assesses the adequacy of strength predictions obtained using the proposed method and the methods adopted in the codified provisions.

This paper summarizes the results of an experimental study on local bond stressslip relationship of deformed reinforcing bars embedded in self-compacting concrete, considering the effect of concrete confinement by transverse reinforcement. In this study were cast 104 specimens by using self-compacting concrete and vibrated concrete. Pull-out tests were performed on deformed bars with short anchorage length (ld ≤ 5∅). The parameters analyzed were the concrete type, the confining reinforcement, the bar diameter and the anchorage length of bar. The results of this study showed that the ultimate bond strength was higher for self-compacting concrete compared to vibrated concrete, and the slip corresponding to the ultimate bond strength was higher for vibrated concrete. Also, it has been observed higher ultimate bond strength for smaller bar diameter. In general a decreasing tendency of the ultimate bond strength with increased anchorage length of bar was found, yet with some exceptions. All the specimens confined with transverse reinforcement had a pull-out failure, while the unconfined specimens had a splitting failure, hence the presence of transverse reinforcement changed the type of bond failure from unfavorable (splitting), to a favorable one (pull-out). A new bond model for pull-out failure based on regression analysis of the experimental data from this study was proposed, considering the favorable effects that the confining reinforcement and relative rib area have on bond strength.

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This paper is concerned with the ultimate behaviour of isolated flat slab members at the connection to interiorcolumns. An experimental programme that focuses on the response of two-way members with various material and geometric configurations is presented. A full account of the results of ten scale tests comprising members with and without transverse reinforcement as double-headed shear studs is given. After describing the experimental arrangement and specimen details, the results and observations obtained from tests are provided and discussed.Particular attention is given to the influence of a number of key parameters that characterise the behaviour at the ultimate state such as slab thickness, layout and amount of the flexural and transverse reinforcement. The test results enable direct assessment of the governing factors that affect the behaviour and failure mode of flat slab members at the connection to interior columns. Finally, experimental results and observations are used to assess the adequacy of strength predictions obtained from analytical models currently adopted in design.

Abstract. The nanometric scale researches results can be found, in present, in every industry domains, due to the effects of the new products, obtained on the basis of this researches. In the concrete industry, the research goal at this level is to obtain, finally, a material with new features, whose structural behavior to be considerably better than of the current one. Basically, it aims to achieve, using nanotechnologies, a new structural material for constructions, starting from the current concrete advantages (good compressive strength, durability, etc.), eliminating the disadvantages (low tensile resistance, cracks, etc.), and controlling, in the same time, the costs. Thus, in this paper are presented the required parameters in order to obtain this kind of material, by highlighting the nanocomponents characteristics and the quantities that are used to achieve the expected quality requirements. The real time influence of these nanocomponents on the quality of the studied material can be observed using a dedicated software, specially developed for this purpose.