Investigating the reliability of RC beams of tall buildings designed based on the new ACI 318-05/ASCE 7-05

The level of safety achievable in reinforced concrete (RC) beams designed based on the new ACI 318-05/ ASCE 7-05 is investigated in this study. The study makes use of the more recent statistical data on fl exure and shear provided by Szerszen and Nowak. Due to the importance of using real ratios of lateral/gravity loads in any such reliability analysis, a set of RC buildings was chosen, loaded and designed and the actual nominal wind-to-dead load ratios were derived. Using these and the statistical data mentioned above, reliability indices for moment and shear were calculated. The resulting reliability indices for moment and shear are then presented in comparison. In addition, the reliability index variations along the beam at the controlling stations are compared to each other. The results of the study indicate that reliability indices at the controlling stations obtained for different limit states are not consistent for low values of nominal windto-dead load ratios, but converge consistently for high ratios. It seems that the use of older shear strength factors provides a reliable safety margin and that the use of the more recent statistical data for material combined with the older shear strength factors leads to more consistency.