ANALYSIS AND EXPERIMENTS ON STRESS WAVES IN PLANAR TRUSSES

The dynamics of planar trusses are investigated in terms of axial (lon gitudinal) stress waves, which propagate along structural members and scatter at the joints. The scattering coefficients representing the re flection and transmission of axial waves at each joint are derived fro m the dynamics and compatibility conditions of the joint. The complex multiple reflections of waves within the structure are evaluated in th e frequency domain with a newly developed reverberation matrix, which is formulated from the scattering coefficients and propagating phase f actors. Transient waves are then derived by Fourier synthesis, and eva luated by a Fast Fourier Transform algorithm. Experimental results of propagating broad band pulses are presented for a truss model excited by a step loading. Comparison between theoretical results and transien t wave records indicate that the axial wave theory is valid only for t he response at the very early time. The discrepancy is much reduced if the scattering coefficients are modified to allow mode conversion fro m axial to flexural waves at the joint.