Ultimate strength design of reinforced concrete members by computers

Abstract

The Ultimate Strength design formulas of the "Building Code Requirements for Reinforced Concrete (ACI 318-63) are transformed into such a form that, the reinforcement can be directly computed,once the basic loads, geometrical data, and material properties are known. At first, the stress resultants of each member for different load cases are combined in any prescribed way, in order to obtain the critical condition.However, the members are designed for each case of the combined stress resultants. In beams, both the flexural and the shear reinforcements are calculated, not only at the ends of the member but also at midpoints and quarter points. In case the beam section is found to be inadequate to carry the bending moment, the depth of the section is increased to a minimum satisfactory value, and a new reinforcement is computed.The dimensions of the cross-section are not altered if the section is inadequate against the shear. However, a warning message is printed out to this effect. Web reinforcement is calculated for an inch length of the beam. This allows the designer to choose the spacing of stirrups and/or bent-up bars in accordance with the common practice. Columns are designed for both uniaxial and biaxial bending cases. In the formulation phase of columns subject to uniaxial bending three kinds of formulas are studied: 1-Exact formulation recommended by the Code ACI 318-63 ; 2-Empirical equations of ACI 318-63 ; 3-Equations derived by considering strain compatibility ( ACI Publication SP-7,"Ultimate Strength Design of Reinforced.Concrete Columns." All of the above formulas are transformed into a form most suitable for the straightforward computation of reinforcement areas. After a comparative test of these different formulas in the computer, it has been found that they produce almost identical results for a wide range of data variation. Therefore, the empirical column formulas of the Code (ACI 318-63) are adapted for use in the programming as they are the simplest. For biaxial gending, the approximate method,in which the biaxial bending of a column is related to its uniaxial resistance through a factor is used. A comprehensive Fortran program for the automatic design of retnforced concrete beams and columns is developed in a way that,"Building Code Requirements for Reinforced Concrete (ACI 318-63)" Ultimate Strength Design requirements are completely satisfied. The IBM 1620 machine of the Computer Center of Robert College has been used.