STRUCTURAL FRAME VIBRATION ANALYSIS BASED ON MEASURED SUPPORT MOBILITIES

摘要

A standard rolled steel beam of rectangular hollow section 60×40×3.2 mm and length 1700 mm was vertically supported at both ends on the heavy concrete floor in a laboratory hall. A uniform sandwich damping (resulting in a composite loss factor in beam bending of about 0.030) had earlier been applied to the upper and lower surfaces (width 60 mm) of the beam. The vertical translational mobilities (direct and cross) at two stations along the span of the beam were measured (impact testing), curve-fitted (complex modal analysis) and inverted (in matrix form). The vertical translational stiffnesses so obtained were used as input data in the numerical analysis of the superstructure introduced below. An upper beam having the same cross-sectional properties as the lower beam just described but of the length 700 mm was connected at its ends, over welded transverse thin plates, to the two stations on the lower beam. Thus a resiliency supported plane frame superstructure was constructed. The dynamic properties of this superstructure were calculated by use of the exact displacement finite element method as implemented in the computer program SFVIBAT-DAMP. Measured and calculated data for the separate lower beam and for the resiliently supported superstructure showed a reasonable agreement in the frequency range studied (0-400 Hz) except for the dampings at the four resonance frequencies of the superstructure.