Composite construction of floor systems with steel joist or I-beam stiffeners supporting a concrete slab have a tendency to sustain perceptible vibration due to small impacts. An engineering design aid, utilizing a small micro-computer and a BASIC computer program, was developed to analyze rectangular floor systems for susceptibility to sustain vibrations perceptible to humans. The analytical method for the normal modes of vibration using the Rayleigh-Ritz method and the superposition of the normal mode response is derived. A vibration index is calculated to qualitatively rate the floor. The computer method was validated using published data for an I-beam supported concrete slab and a design application for a steel-joist supported floor is demonstrated using a representative human induced impact load.