Developed reliability-based interaction curves for design of reinforced concrete columns

The provision of a safe structural system is a major object of structural designs. Due to uncertainties of varying magnitudes associated with loadings, the material and geometrical properties, current design methods that are not fully based on the probability concept are not able to yield a constant reliability level. This paper examined the criteria of British Standard Code of Practice (BS 8110, 1997) currently in use in Nigeria, for the design of reinforced concrete columns subjected to axial and bending loads using the probability-based concept. In order to offer designs capable of maintaining a predefined safety level, a computer program in FORTRAN language was developed. The modules in the program were based on BS 8110 (1997) design requirements and the First Order Reliability Method. Individual parameters were considered random with practical probability distributions. The program starts with a preliminary design and iteratively selects values of the design va riables that lead to the predefined safety level. Interaction curves were plotted for varying safety indices. On the curves, design decisions relating to ratios of dead to live loads, effective to the gross depth of a section and reinforcement can be made. In contrast to the current method of BS 8110 (1997), the proposed design curves guide the designer to the knowledge of the expected level of safety of the section being designed.