Papers by Keyword: Reinforced Concrete Structure

Abstract: This paper considers the basic methods of physical-mathematical modeling that are used to describe the processes of non-stationary mass transfer of "free calcium hydroxide" in concrete structures placed in a liquid environment with a defined flow rate. The boundary value problem of "free calcium hydroxide" mass conductivity in dimensionless variables is obtained. To demonstrate the possibilities of the obtained solution, we will carry out a numerical experiment: in which the fluctuation in the field of dimensionless concentrations by the different values of the Fourier number, in accordance with the theory of similarity, will be considered as an indicator of the process time. The study indicated the results of calculating the concentration distributions "free calcium hydroxide" over the dimensionless thickness of the concrete structure at Fourier numbers 0.01; 0.1; 0.2; 0.5 and 1. The study also provides an example of determining the time of reaching the coastal structure surface critical concentration "of free calcium hydroxide" leading to the beginning of high-basic cement concrete. Analysis of the solution also makes it possible to determine the duration of the service life of a reinforced concrete structure, which is determined by the processes occurring at the interface: in concrete - mass conductivity (k), and in the liquid phase - mass transfer (β).

Abstract: The paper considers methods of physical and mathematical modeling that can be used to describe the processes of non-stationary mass transfer of free calcium hydroxide in buried concrete and reinforced concrete structures of coastal zones. The authors proposed a mathematical model of mass transfer in an unrestricted two-layer plate in the form of a system of parabolic partial differential equations with boundary conditions of the second kind at the "concrete-liquid" interface and of the fourth kind at the "concrete-soil" interface. In terms of the results of experimental studies of the mechanisms for reducing the quality of concrete due to exposure to sulfate and acidic environments, using the obtained solutions of the mathematical model, it becomes possible to select the optimal composition of concrete with high anticorrosion properties.

Abstract: The article deals with the analysis of the problem of the load-bearing capacity of reinforcing bars placed above the columns in slab-column connections of reinforced concrete structures. Failure of the support zone by punching and lack of proper structural integrity reinforcement can lead to a progressive collapse. The EC2 standard guidelines recommend the use of integrity reinforcement, however, they lack any instructions concerning the amount of necessary reinforcement. The article presents a theoretical calculation model that permits a more detailed analysis of internal forces in reinforcing bars located directly above the column. Adopting a solution in the form of exact equations makes it possible to take into account the influence of a non-linear change of the bar stiffness and considerable deflections. The calculation model is based on the results of experimental investigations. On the basis of a theoretical model it is possible to estimate the tensile force of the bar at which the bars located directly in the support zone are ruptured.

Abstract: In the paper the results of laboratory tests performed on a simplified model of a slab-column connection were presented. The aim of investigations was to find out at which value of the load the destruction of such a connection occurs due to a rupture of the bars above the column. In respective models the column was situated axially or eccentrically with respect to span of bars. In each case the reinforcement passing above the column consisted of bars with a diameter of ø8 mm, ø12 mm or ø16 mm. The obtained results of laboratory tests and calculations permitted to determine the relations between the exerted load and the displacement of the column in time and also were compared with the guidelines contained in the standards CSA A23.3 and ACI 352R. Based on the results, the reduction of the load bearing capacity of the reinforcement bars due to bending was determined.

Abstract: In a properly designed slab-column structure the failure of the floor should be signalled by cracks and significant and visible deflections of the floor in the spans. The paper presents two proposed ways of calculating a uniform loading causing the destruction of the central field of a typical slab-column structure. The values obtained in the limit state were compared with the value of the load obtained during the experimental research.

Abstract: A great advantage of computer calculations is the opportunity to map the whole floor, including the supporting beams, columns and walls, in one model, with the members fully cooperating with one another. In this way the need for strenuous compiling of the loads on supporting members and independent searching for extreme values becomes eliminated. As a separate part of a floor, in this case a beam appears occasionally. The mapping of a beam in a model can have various forms. The paper presents a comparison of the influence of the way in which a rib is modelled on the results of statistical calculations. As a reference point for substitute shell models a solid spatial model was adopted.

Abstract: The behaviour of reinforced concrete slab-column structures under the impact of accidental loading is very significant due to safety reasons. The failure of the support zone by punching and lack of proper structural integrity reinforcement can lead to a progressive collapse. However, the instructions on how to prevent such situations are not very detailed. According to the guidelines of standard EC2, the structural integrity reinforcement should be continuous throughout the length and consist of at least two bars above the column in every perpendicular direction. EC2 does not state the amount of necessary reinforcement. The article presents a theoretical model of calculation that permits a more detailed analysis of internal forces in reinforcing bars located directly above the column. Adopting a solution in the form of exact equations makes it possible to take into account the influence of a non-linear change of the bar rigidity and considerable deflections. The calculation model was verified on the basis of the results of experimental investigations. It enables to estimate the tensile force of the bar at which it is ruptured during the destruction of the support zone.

Abstract: Abstract. After recent earthquakes in the majority of seismic areas around the world including our country Iran and considering the irretrievable casualties and economic lost due to these earthquakes, natural catastrophic mitigation committees, research and scientific centers that are responsible for providing structural and seismic codes presented the concept of performance design, study of lifelines and retrofit and rehabilitation of existing and vital structures and the majority of researches in the field of earthquake engineering and structural engineering is focused on retrofit of structures considering economic and feasibility problems. Considering the increasing use of concrete structures in Iran and their substituting for steel structures ( due to weaknesses, constructional problems and defects) and considering the internal defects and failure modes, these structures should be retrofitted against earthquakes or preparations should be provided to decrease and minimize failure modes. concrete frames that consist of beam, column and connection is a essential part of concrete structures. Internal defect of concrete frame results in failure modes such as debonding and delamination in beams, buckling and torsion in column, local crashing in connection. Considering the several benefits of FRP sheets and their increasing use during years, these composites can be used for compressive-tensile, shear, bending, torsional retrofitting as well as for ductility increasing. In this study different types of failure modes of concrete frames and internal defects of them that lead to collapse are investigated. In addition different cases of retrofitting by FRP sheets to prevent failure modes and exciting defect are presented and these cases are compared.

Abstract: The paper presents the results of calculations, taking into account a material model (isotropic reinforcement according to Misses), representing laboratory tests of additional reinforcement. Complying with PN-EN 1991-1-7:2008 (EC1) and PN-EN 1992-1:2004 (EC2) this reinforcement is applied in reinforced concrete slab-column structures in order to protect them against progressive collapses. Additionally, an analysis was carried out, considering, the effect of applying in the material model the true stress-strain curve. In the course of these experimental investigations the values of displacements caused by the exerted load were compared with the values of numerical calculations.

Abstract: This paper presents the results of laboratory tests concerning the central connection of the slab with the column, in which an additional reinforcement ensuring the structure against a progressive collapse was applied as to recommended in the standard PN-EN 1991-1-7:2008 as well as in PN-EN 1992-1-1:2008. Regulations concerning the necessity of such a reinforcement are also contained in the American and Australian standard as well as in the Bulletin FIB. The obtained results of investigations have been compared with calculations based on a spatial numerical model representing the analyzed phenomenon. The numerical model bases on predefined material models of steel and concrete, taking into account non-linear dependences of the strength of these materials. The values of displacements of the upper surface of the slab depending on the exerted load were compared with the values of numerical calculations.