An elastic second order analysis requires consideration for cracked regions on the wall. Stiffness after cracking is a function of internal forces and the placement of reinforcement. Wall reinforcement is not determined until after the analysis is performed and designed in RAM Concrete Wall. Therefore, the RAM Frame analysis relies on a cracked factor assigned to the wall that is applied to all finite elements to approximate the cracking effects. The cracked factor (bending) shown in the Add Concrete Wall dialog above modifies wall out-of-plane stiffness in the RAM Frame analysis.

ACI 318 permits the use of a reduced moment of inertia with an elastic second order analysis to account for cracking. ACI 551.2R states that a panel at ultimate load conditions typically exhibits cracks over most of the height and that testing and analytical studies confirm that assuming Ec Icr over the full panel correlates closely with test results. ACI 318 alternative analysis for slender walls provides an equation for the cracked moment of inertia which is typically less than 0.35 Ig.

The cracked factor (bending) factor requires engineering judgement. It should represent an effective out-of-plane moment of inertia for a factored load analysis (conditions at strength failure) with a reduction for uncertainty. It is recommended that the engineer start with a conservative cracked factor to avoid underestimating the 2^nd order effects and later refine the cracked factor if more accuracy is desired.

The DA Tilt-Up Tools spreadsheet can be used to help determine if the cracked factor assigned in RAM Modeler is consistent with ACI 318 Alternative Method for Slender Walls.