Figure 13. Frequency responses of Branch A, C, and F (Table 2) in Case E (Table 1) when the base acceleration is 10 m/s 2 . (a,b) Show sweep responses, stroboscopic points, and HBA solutions of Beam 1 and Beam 2, respectively. Stable and unstable HBA solutions are plotted by the solid line and dot-dashed line, respectively. In (a,b) , Zone C means that the branch belongs to Zone C in Fig. 11. The triangle markers indicate the bifurcation points as follows: sn saddle-node bifurcation, pd period-doubling bifurcation, ns Neimark–Sacker