The service combination analysis in RAM Frame Analysis Load Combination mode is an elastic 2nd order analysis that scales the cracked factors assigned in RAM Modeler by the service multiplier in the Advanced Analysis Criteria dialog. The service analysis in the ACI Alternative Method for Out-of-Plane Slender Wall Analysis is an iterative bilinear interpolation that considers the displacement at the cracking moment with the gross moment of inertia and the displacement at the nominal moment with the cracked moment of inertia. The out-of-plane displacements in RAM Frame will be larger than displacements calculated using ACI slender wall for practical moments. If the maximum nodal displacement in RAM Frame for the service combination exceeds displacement limits, a more detailed analysis should be performed prior to changing wall stiffness.

First, rerun the service analysis using the gross moment of inertia. To force the service analysis to use the gross moment of inertia, the service modifier in the advanced analysis criteria should be larger than 1 divided by the bending cracked factor assigned in RAM Modeler. The program will cap the stiffness at 1.0 times the gross moment of inertia in the analysis. If the maximum service moment in the wall considering 2nd order effects is below 2/3 the cracking moment, then the wall remains uncracked for the service combination per ACI slender wall. The assumption to use the gross moment of inertia was valid.

If walls are cracked, rerun the service analysis with a service modifier that brings the cracked factor assigned in RAM Modeler to a service state (e.g. 1.4). If the cracked factor in RAM Modeler represents a fully cracked section, the RAM Frame results are conservative and can used directly if desired. If displacements are exceeding deflection limits, the service modifier typically can be increased because the service moments are less than the moment that reduces stiffness to fully cracked. However, this is decision that requires engineering judgment.

The DA Tilt-Up Tools spreadsheet can be used to help investigate the service analysis.