Concrete Box Sections under Biaxial Bending and Axial Load

Abstract

A computer program is developed for ultimate strength design of concrete box sections subjected to biaxial bending and axial load. The distribution of steel reinforcement is assumed to be symmetric in the section. In the analysis the equilibrium equations are expressed in terms of the three unknowns describing the location of the modified axis and the total reinforcement area within the cross section, which leads to three simultaneous nonlinear algebraic equations that are solved by a procedure based on the Newton-Raphson method. It is observed that the iterative algorithm used in the program converges rapidly for many different problem tested, and execution time of the program is small; hence the program can be run many times with different reinforcement arrangements and the most suitable reinforcement pattern among them can be chosen.