Figure 7. Frequency responses and HBA results of Case C (Table 1) when the base acceleration is 5 m/s 2 . The first row (a,b) and the second row (c,d) are the results of Beam 1 and Beam 2, respectively. The first column (a,c) shows sweep responses, stroboscopic points, and HBA solutions of Branch A, D, and G (Table 2). The second column (b,d) depicts the HBA results of Branch D when the solution truncation order, H , is set to be 1, 3, and 5 (Eqs. (6), (7)). Stable and unstable HBA solutions are plotted by the solid line and dot-dashed line, respectively. In (a,c) , the triangle markers indicate the bifurcation points as follows: sn saddle-node bifurcation, sb symmetry-breaking bifurcation, ns Neimark–Sacker bifurcation.