Unified Spectro-Geometric Framework for Multi-Span Beam Vibrations under Arbitrary Boundary and Coupling Conditions. - Guo, Yan-yu; Wang, Hao; Guo, Xiang-ying; Hao, Rong-biao; Zhu, Yu-nan; Yang, Xiao-dong (International Journal of Structural Stability & Dynamics, 2026)