Figure 15. Frequency responses of Branch C, E, and I (Table 2) in Case C (Table 1) when the base acceleration is 9 m/s 2 . (a,b) Show sweep responses, stroboscopic points, and HBA solutions of Beam 1 and Beam 2, respectively. The inset in (a) displays an enlarged picture to clearly indicate the bifurcation points. The red arrows indicate where Branch C and Branch E coalesce and bifurcate. Stable and unstable HBA solutions are plotted by the solid line and dot-dashed line, respectively. The triangle markers indicate the bifurcation points as follows: sn saddle-node bifurcation, sb symmetry-breaking bifurcation, pd period-doubling bifurcation. The red arrows indicate where Branch C and Branch E coalesce and bifurcate.