For both SAP2000 and ETABS the hinge calculations use the LRFD-99 formulas for the calculation of column compressive strength. Understrength factors are ignored and the effective fy is used. Also if a steel design has been run even once or member k factors or unbraced lengths have been overwritten then the program uses the k factors and unbraced lengths that it would have used in design. If this is not the case then k =1 and unbraced length equals clear length.
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