Effect of second order analysis on the drift reliability of steel buildings

Serviceability limit state is an important limit state in the reliability analysis of building structures. One of the serviceability limit states to consider in the design is the lateral displacement or drift check. Due to the uncertainties in the cross-sectional dimensions and the mechanical properties of materials, the lateral drift of structures is a random variable. Second order effects also amplify the lateral displacements and are a function of gravity loads and lateral displacements. In this study, the drift reliability of steel frames and the effects of second order analysis are investigated using geometric nonlinear analysis and Monte Carlo Simulation technique. Results show that for the drift limit state that does not include P-Delta effect, reliability indices do not depend on return period of the load cmbination, the wind to gravity load ratio or the drift limits. On the other hands, for the limit state in which P-Delta effect is incorporated, in low wind to gravity range, the reliability indices are sensitive, and could change dramatically. The limit state that does not have the P-Delta effect is the lower bound of load combination with 50 year return period, but is the upper bound for the other load combination with 20 year return period. Furthermore, the value of drift limit affects the reliability indices for the limit states that include P-Delta effect.