Additional moments are induced on a structure due to the movement of its mass under lateral loads. This structural phenomenon is called the P-Delta effect. Various codes of practice require that these effects be considered in the analysis and design of building structures.

A theoretically exact approach based on nonlinear stiffness formulations is available in the literature. There are also a number of approximate methods to model these effects. The theoretically exact method involves the use of iterations for convergence and special non-linear solution algorithms to negotiate the non-linear part of the load-deflection curve. At each iteration, the nonlinear stiffness coefficients are evaluated. This tends to be time consuming. On the other hand, the approximate methods are relatively easy to implement and use. Most approximate methods in the literature involve modifying the total stiffness matrix of the structure either by adding fictitious members of negative stiffness or subtracting what is known as a "geometric stiffness matrix".

In RAM Frame, two different methods are implemented to consider P-Delta effects in analysis and they are explained below. Note that either mass loads or gravity loads (DL+LL) can be used in each one of the methods.