The flexural and shear seismic demand for single column piers or hammerhead piers is based only on the analysis results of seismic combinations. For single column piers the plastic hinging is not considered because cap capacity is unaffected by the column response.

For multiple column piers, program first analyzes the entire pier as a frame and solves for moments and forces in the cap. Then it carries out the analysis of pier cap as a continuous beam model. For this continuous model, pin supports are modeled at column locations and the 1.2 times plastic hinge moments applied to the cap and column locations. The dead load is also applied to this model and solved. Program then determines the cap demand at check points along the length of the cap. These responses are compared to a second response. The second response is determined based on seismic loads applied to the pier and solved as a frame. The smaller of the two is considered as the controlling response and becomes the seismic demand for the cap.