When Analysis is performed with at least one Seismic load group (in LFD) or one Extreme Event Seismic limit state (in LRFD), program carries out the analysis for the seismic load combinations and determines the internal responses in cap and column elements. By default the EQ loads in seismic groups are reversible. However, user has the option to change that. Depending upon the load groups defined, the EQ force may be either for uniaxial or a reversible EQ loads.

Plastic hinging moments in columns are determined when columns are designed. Therefore, if plastic hinging moments in columns are to be considered in design, it is required that all the columns be designed before the design of cap or footings.

When a column is designed, program carries out three sets of calculations for it. First it carries out the design of column for elastic loads. This is explained in more detail in the Column Design Section of this chapter. Second set of calculations are done for seismic load groups. For that program determine the column seismic demand. It divides the analysis response by the response modification factor and obtains the column demand for each combination. Once the seismic demand is determined, program checks it against the biaxial capacity of the column. If the capacity is not adequate, it is flagged in the report. The third calculation is done to determine the plastic hinge moments for each column. This is explained in more detail below.