Figure 14. Frequency responses of Branch F (Table 2) in Case F (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. Zone D means that the branch belongs to Zone D in Fig. 11. The triangle markers indicate the bifurcation points as follows: sn saddle-node bifurcation, ns Neimark–Sacker