The calculation of the reinforced-concrete rectangular box sections according to ultimate strength method

METHOD: The calculation of sections are of great importance for designing the reinforced-concrete structures. Dimensioning the reinforced-concrete sections according to their limit conditions require long and tiresome calculations. Assisting tables and abac charts reduce these calculations a great deal. Nowadays, once the problem is programmed with the computer, the result is obtained without any further need for tables and abac charts. However, as this opportunity is not always reachable, the assisting tables and abac charts are still required. Because of this; in application. the calculation of sections are made according to the tables and abac charts prepared previously. fitting the aim. It is clear that allowable section calculations can only be obtained when they are done according to the principles corforming the said regulations of the above mentioned tables and abac charts. In this study, the calculation bases of the reinforced-concrete rectangular box sections loaded with bending moment and axial force are explained according to their breaking limit conditions. In constructions, the rectangular box sections member loaded with bending moment and axial force are generally faces in columns and big viaduct pillars. For calculation this kind of members according to their breaking limit conditions, it is necessary to know the following: a) Mechanical characteristics of the material, that is stress (strain)- deformation (σ-ε) diagrams and. b) The changes in the shape of the section(deformation). Since the application of reinforced concrete in the buildings, the theory of elasticity has lost its varidity. The ultimate state is today a real method and it enables us to give dimensions of the sections and provides stress control. In the second chapter of this study some assumptions are assested: Since the wall thickness is thin center of gravity of the reinforcement is assumed to pass from the middle. the condition of equal reinforcements on parallel walls is examined. The assumptions in the computations done according to the carrying capacity (Ultimate strength design): a) The sections that are plane before changing their form, get also plane after deformation, b) Tensile strength in concrete is neglected in sections subject to bending, c) The adherence between concrete and steel is complate d) At ultimate strength, stresses and strains are not proportional. The diagram of compressive concrete stress distribution may be assumed a rectangle, trapezoid, parabola or any other shape which results in ultimate strength in reasonable agreement with comprehensive tests. e) Maximum fiber stress in concrete does not exceed 0.85 fcd f) The stress-strain relation of steel elasto-plastic, g) When reaching carrying capacity, the distribution of concrete stress in the pressure zone is like stress-strain curve obtained from samples experienced under axial compression.