Bearing capacity of damaged flexible reinforced concrete columns
Journal Title: Вісник Одеської державної академії будівництва та архітектури - Year 2018, Vol 1, Issue 72
Abstract
The aim of the study is to develop a calculation model for determining the residual bearing capacity of compressed damaged reinforced concrete elements pre-modeled simulated damage and 1 without damage were manufactured and tested. From the selected factors of variation, the parameters characterizing the damage to the element turned out to be the most influencing on the bearing capacity, the element length is secondary. The column with a height of 1.0 m can be considered short. Samples with a length of 1.75 m and 2.5 m have more flexibility than the limit, and this feature must be taken into account in the calculation. The results of a laboratory experiment showed a scheme of damage to elements and confirmed that the maximum strain and stress occur in the middle of a damaged section. An important factor affecting the carrying capacity is the presence of exposed reinforcing bars in the considered damage. In samples with a high level of damage, destruction occurred in the middle of the element height after maximum bending of the exposed rods. The numerical characteristic of the stability of a rod is the Euler force. Expressions for determining the limiting stresses in exposed rods are proposed. To determine the residual bearing capacity of damaged structures of various flexibility, the calculation model was created. At its core, the model based on the basic premises of the existing building codes. The effect of damage is taken into account by a factor of . In damaged eccentrically compressed columns, it is generally necessary to take into account second-order effects. Damage in the eccentrically compressed elements leads to the rotation of the neutral line and to a change in the stiffness of the cross section along the length of the element, this requires taking into account the effect of damage and makes it possible to find a coefficient η that takes into account the effect of flexibility on the residual load capacity. To determine the coefficient η, a system of homogeneous linear equations is obtained. The article presents two generalized types of damage according to the type of shape: direct damage ‒ when the angle of inclination of damage is zero, and oblique damage ‒ when the angle of inclination of damage is not zero. In the direct damage type, the neutral line runs parallel to the damage front line. The obtained two equilibrium equations and an additional dependence make it possible to obtain values of unknown quantities for determining stresses in individual bars of the reinforcement. In an oblique type of damage (with angle γ), the main axes of the damaged section do not coincide with any axis of the intact section, and therefore, the neutral line is not parallel to the damage front, but passes at an angle φ. The first equation of equilibrium in reference to the x axis, the second and third equations are the sums of moments in reference to the x and y axes. Other unknowns are calculated from the condition of parallelism of the planes and the action of the moments of external and internal forces. The fourth and fifth equations are the equations of the static moments of the compressed zone of concrete, their preparation is possible due to the accepted hypothesis that the stresses are uniform over the area of the compressed zone. The system of equations was solved by the Newton method. As a result of the calculation, the value of the residual bearing capacity of the reinforced concrete compressed element damaged during operation (taking into account its actual flexibility) was obtained.
Authors and Affiliations
I. V. , Кlymenko, Ž. , Коs
Keywords
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