Analysis of Strength and Ductility of High-Strength Concrete Columns with Random Properties

Concrete is currently the most widely used construction material in the world. However, its mechanical properties when suffering damages have not been fully understood which may be the reason that no generally accepted nonlinear theory had been available for the analysis and design of concrete structures. In fact, the complexity of concrete material originated from two essential characteristics, that is, nonlinearity and randomness. In the past 25 years, there have been significant developments in the production and use of high strength concrete HSC. During this period, experimental research related to the behavior of high strength concrete members has increased significantly. However, with the availability of data on higher strength concretes, the applicability of the code equations need to be reevaluated and the extrapolation of equation from lower strength to high-strength concretes needs more experimental verification. The experimental data on HSC columns still remains limited and the applicability of code equations to members mad of HSC needs more experimental verification. The ductility of reinforced concrete columns is an important factor for the strength and stability of reinforced concrete structures. The ductility of columns can be achieved by the confinement of the core concrete. Recently, concrete strengths much higher than 60 MPa have been used in the construction industry. However, the behavior of high strength concrete columns is not adequately known, yet. As a result, the design provisions of current building codes related to strength and ductility of high strength concrete columns cannot be not satisfactory. This paper presents the results of a research project in which the available test data on high strength concrete columns have been evaluated in terms of strength, ductility, and drift ratios. The relationships between confinement parameters and column performance are illustrated. A number of different formulas have been proposed for predicting the strength and ductility of high-strength concrete columns by various researchers. In the present study, models and experimental results collected from the literature are evaluated. The investigations show that the uncertainties of effective factors on strength and ductility of such columns must be considered. A probabilistic analysis is needed to evaluate the uncertainty in the design process. In this paper, the mechanical properties of steel and concrete are supposed that to be uncertain and have normal and lognormal distributions with different coefficient of variations, changing from 10% to 25%. The Monte Carlo method is used to generate random variables. The strength and ductility parameters for generated variables are calculated and compared with the experimental data. By using the results, the reliability and the safety level of the formulas are determined. It is shown that the proposed model by the authors has a very good agreement with experimental results with minimum errors and sufficient reliability as well.