Presence Of Rebars Research Articles

Modelling a reinforced concrete arch bridge by means of the Discrete Macro-Element Model: the case of Giovanni XXIII bridge in Ragusa

Numerical modelling of reinforced concrete structures in the nonlinear field requires the adoption of sophisticated although robust models. When it comes to bridges, to obtain an accurate numerical model uniaxial elements should not be employed due to geometrical inconsistency. Two- or three-dimensional elements are more appropriate even though the explicit modelling of concrete and steel bars can make the simulations too cumbersome for many practical applications. In this study, the Discrete Macro-Element Model (DMEM), implemented in the software HiStrA, initially introduced for the nonlinear modelling of existing masonry structures and also applied in the case of masonry arch bridges, is extended for modelling reinforced concrete structures. The presence of rebars is explicitly accounted for by introducing their contribution in the interface elements. The original modelling strategy is here applied to the Giovanni XXIII bridge in Ragusa (Italy), a road reinforced concrete supported deck arch bridge located in the city centre. The structure is currently a case study identified within an accurate survey and permanent health monitoring installation designed within the MonVia Project funded by the Italian Ministry of Economic Development. The results reported in this paper are relative to numerical simulations where the mechanical parameters of the linear elastic model are calibrated to match the experimental dynamic properties of the structure while the nonlinear parameters are consistent with those reported in the original design of the bridge. Nonlinear static analyses are performed considering both operational and seismic load configurations. The results could be used to define the threshold levels to be considered for the health monitoring of the bridge.

Crack analysis and modeling in concrete beams reinforced with FRP composite sheets

In this article using the principles and relationships governing fracture mechanics and finite elements cracking in the first mode for reinforced concrete beams reinforced with FRP sheets are analyzed and modeled. In this method to simulate the crack in reinforced beams, the relations for determining the stress intensity coefficients with the presence of rebars and reinforcement sheets are developed. Here, it is assumed that a composite sheet is completely bound to the bottom surface of the beam under pure bending moment. In the proposed method beam components are divided into two categories, including components without cracks and components with cracks. In components without cracks, relations, equations, and the conventional stiffness matrix governing the beam are used, taking into account the changes in the moment of inertia caused by the presence of reinforcements and FRP sheets. In the finite component with a crack, the crack profile is simulated by creating a geometric defect in the beam section. So that the reduction in the hardness of the component with a crack is equivalent to the change in the dimensions of the discontinuity. Here, the changes in the hardness of the cracked component are calculated and presented as a function of the modified stress intensity coefficients. To ensure the correctness and accuracy of the presented method, all the analyzes are implemented in Abaqus software. The comparison of the obtained results shows that the presented method is a suitable method for the analysis of reinforced concrete structures resistant to cracking. So that it can be extended and developed for other models with proper accuracy.

Structural effects of FRC creep

Research studies in the last 20 years allowed to obtain reliable rules for designing structures made of fiber reinforced concrete (FRC). However, design aspects like the long-term behavior of FRC, especially when synthetic fibers are adopted, require further research. Long-term behavior includes aging and creep. Aging represent the change of fiber properties into the concrete environment, which may reduce the structural bearing capacity; when present, it is an important issue for the structural safety, especially when fibers are the only reinforcement. Aging of fibers must be proven by experimental tests. Creep is a complex phenomenon, roughly considered by building codes even for traditional reinforced concrete (RC) structures. The introduction of fibers do not change anything in concrete matrix and, before cracking, in the material concrete creep behavior is not expected any change. After cracking, the structural effect of FRC creep depends on the degree of structural redundancy and on the presence of rebars since creep produces a stress redistribution in the structure or from FRC to the rebars. When FRC post-cracking resistance is necessary for equilibrium requirements, in structures with cracked sections in service conditions the structural deferred response has to be analyzed by considering the FRC creep behavior. When FRC is used for resisting secondary actions and rebars are present for equilibrium requirements, the response of a FRC element (with rebars and fibers) will be identical to a conventional RC; FRC contributes by controlling the crack development under both short and long term loading.

Chloride diffusion analysis of reinforced concrete beam enhanced with externally bonded fibre reinforced polymer considering the presence of rebars and stirrups

Chloride diffusion analysis of reinforced concrete beam enhanced with externally bonded fibre reinforced polymer considering the presence of rebars and stirrups

Effects of lossy background and rebars on antennas embedded in concrete structures

ABSTRACTIn this letter the effects of a lossy background on an antenna for wireless embedded sensors network has been studied. The efficiency of the antenna versus the concrete structure size decreases from 72% down to ∼20%. However, it is shown that the boresight gain is essentially unaffected by the block size. The proposed configuration is robust against concrete permittivity variations, change in block dimension and presence of rebars. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2653–2656, 2016

Influence of the viscosity of self-compacting concrete and the presence of rebars on the formwork pressure while filling bottom-up

Self-compacting concrete (SCC) enables new casting techniques, filling formworks by pumping bottom-up. However, fundamental questions remain concerning the formwork pressure when following this advanced filling procedure. A new series of formwork filling tests, with SCC being pumped from the base of the formwork, have been performed in 2012 at the Magnel Laboratory for Concrete Research of the Ghent University (MLCR). Numerical simulations of these formwork filling tests have also been carried out for validation with the experiments. For the filling process of eight casts in total, the influence of several filling parameters on the resulting formwork pressures were tested, like the casting speed, the presence of steel rebars (leading to a reduction of the flow section inside a formwork) and the rheology of the SCC. The formwork pressures were measured at three different positions on the formwork wall with accurate electronic pressure sensors. These measured formwork pressures were finally compared with the computed formwork pressures. Both the experiments and the simulations performed in this study showed a very good agreement and they revealed that the formwork pressures during the filling tests were higher than the hydrostatic pressure for SCC pumped from the base of the formworks. This was due to the additional occurring hydraulic losses. In our experiments, these additional flow losses represented 7% up to 16% of the total wall pressure for the performed filling tests with steel rebars, depending on the viscosity of the SCC and the casting speed. An analytical calculation model for the formwork pressure has been derived and validated, using the experimental measurements and the numerical simulations of the filling tests performed at the MLCR. Finally, the quality of the cast concrete, investigated through a visual inspection of a series of drilled concrete samples taken at several relevant locations of the casts, revealed to be excellent considering the high casting speeds.