Reliability Analysis of an Underground Reinforced Concrete Rectangular Water Tank

Abstract

The failure of reinforced concrete rectangular underground water tank designed according to 1 has been analyzed using the First Order Reliability Method. In doing this, the limit state functions were defined for both the ultimate state conditions (flexure, shear and torsion) and serviceability limit state (cracking) for both the tank wall and floor slab. Some basic variables present in the limit state function are used to study their variation with the reliability index and hence their significance in order to ensure safe design. The results obtained revealed that the design requirement for floor slab in tension yields the lowest performance level and as such the requirement becomes the principal factor to be considered when alternative technique suggested by 2 is not employed in the design of the wall and floor slab. It was also shown that increase in the span of the slab leads to the decrease in the performance of the tank or leads to the decrease in the reliability index making the tank on safe. It may be suggested that for the purpose of suitability and economy, the span should be between 5000mm to 7000mm. The result also shows that as reinforcement ratio increases safety index increases and a reinforcement ratio of 0.01 to 0.02 is recommended for economic design.