Column Design by P Delta Method

Generally, the analyses used to determine the distribution of bending moments and internal forces in a structure are first-order analyses. Such analyses neglect the so called P-Δ effects: (the effects produced by the vertical forces acting through the laterally deflected position of the structure). Thus, the stiffness and strength of the structure is overestimated. In an attempt to compensate for these shortcomings, the present design procedure requires increases in the column sizes in a sway permitted structure. As an alternative, a method for directly including the P-Δ moments in the analysis of the structure is presented. It is shown that if such an analysis is used, the members in both braced and unbraced structures may be designed as sway prevented.