The building materials branch of the construction industry is continuously developing due to occurrence of new products which seek to improve the “green” character of buildings by using different types of wastes. Prefabricated products of different sizes such as blocks, panels, beams and other spatial elements can now be obtained with eco-materials. Concrete is the most used material in the building industry and thus it is necessary to diminish its environmental pollution. There are different ways for improving the “green” character of concrete, such as the addition of waste products of different types (fly ash, silica fume, slag, shredded tyre rubber, agricultural powder wastes, etc.) or by replacing some of the components (i.e. cement, aggregates) with eco-materials. Materials with pozzolanic properties (fly ash, silica fume, banana leaves powder, volcanic tuff, etc.) can, in certain proportions, replace the cement. In order to replace the aggregates, the substitution materials are obtained with sizes which are corresponding to the aggregate sort (polystyrene granules, shredded plastic recipients, agricultural wastes, etc). In the current article, the experimental results obtained on types of eco-concrete used for producing reinforced concrete beams are presented. The eco-concrete used for pouring the reinforced concrete beams contains the following materials: fly ash as replacement for the cement, metalic fibers, polyester fibers and hemp fibers. The beams models were tested in two point bending. The strength capacity and type of failure were analysed and compared as a function of the type of eco-concrete.
In the first part of the current study, the effectiveness of the transversal cross-section reduction method for RC beams in marginal areas (by means of mechanical drilling) was validated. The said method “encourages” the formation of plastic hinges at the beam ends and, at the same time, allows for taking into account the bending stiffness of RC slabs, which is exerted upon the RC beams. In these conditions, the second part of the current research study (i.e., the current manuscript) highlights the real mode of reducing the lateral stiffness of the slabs upon the RC beams. These elements form a common body, together with the beam–column frame node. The same method as in the first part of the study—“weakening” the plates in the corner area through vertical drilling, without affecting the integrity of the reinforcing elements—was used. The analytical MR RC frame model, studied by means of the comparative method, highlights the efficiency of the transversal cross-section reduction method for RC slabs. Basically, the directing of the plastic deformations from the weakened slab areas towards the marginal areas of the reinforced concrete beams takes place. The beams rotate as far as the weakened slab areas allow its plastic deformation, thus being possible to observe the partial conservation effect of the beam–column frame joint. Furthermore, for the analytical model with the maximum number of vertical holes in the corner areas of the concrete plate, minimal plastic deformations are recorded for the marginal areas of the concrete columns. A partial conservation of the formation mechanism of the “beam-slab-frame node” common rigid block is also noted. Consequently, the dissipation of the seismic energy is made in a partially controlled and directed manner, in the “desired” areas, according to the “Strong Columns—Weak Beams” (SCWB) ductile mechanism of the lateral behavior to seismic actions for reinforced concrete frame structures. The mechanism is specified in current design norms for RC frame systems. The effectiveness of the method for reducing the transversal section of the RC plates in the corner areas by means of transversal drilling is highlighted and validated from the perspective of the local and global ductile seismic response of reinforced concrete frame structures. A significant reduction in the bending stiffness of the slabs upon the beams and a real development of the plastic hinges in the marginal areas of the beams (together with partial implications and plastic deformations) were observed.
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