A Multi-Segment Beam Approach for Capturing Member Buckling in Seismic Stability Analysis of Space Truss Structures

This study addresses a fundamental shortcoming in conventional dynamic stability analyses of space trusses: traditional rod elements or unsegmented beam models fail to capture member buckling under severe seismic excitation, often mischaracterizing structural failure modes, namely mistaking collapse due to instability for mere loss of loadbearing capacity. To overcome this limitation, we propose a multi-segment beam numerical method that discretizes each member into multiple segments enhanced with high order shape functions. Validation through modal analyses of simply supported beams, isolated space trusses, and space truss–frame systems reveals that while conventional unsegmented beam models accurately predict low order vibration frequencies, they entirely neglect member buckling in higher modes. Under strong earthquake loading, these models misleadingly indicate global stability accompanied by gradual degradation of load capacity. In contrast, the multi-segment beam model simultaneously resolves low order global vibrations and high order local buckling phenomena, unveiling progressive seismic instabilities triggered by member buckling. Dynamic stability analyses confirm that the multi-segment approach reliably identifies the true critical failure mode. This paper recommends that in the modal analysis and seismic stability analysis of space trusses, the space truss members should be divided into three segments with cubic shape functions selected for the analysis. This methodology thus provides precise predictions of failure mechanisms and critical seismic thresholds, enabling dependable safety evaluations for long-span spatial structures in seismic regions.