Analysis results related to a dynamic load case (i.e., response spectra analysis) are obtained after modal contributions from each dynamic mode are combined according to CQC or SRSS. Thus, all results (displacements, reactions or member forces etc...) have always the positive sign.

In some cases, the sign of analysis results is required (examples are for design of foundations, load combinations with dynamic load cases, etc...). Therefore, an option is provided in General Criteria dialog, so that analysis results for a dynamic load case are adjusted with a sign. The following equation is used so that the sign from the most predominant modes for each dynamic analysis results is used as the sign of the response. In the following equation, the computation is carried out for “N” mode shapes, and ∅_i is the i^th mode shape value of any dynamic quantities (member force, displacement, etc…).

Note that once this option is checked, it is applied to all dynamic analysis load cases.