Investigation of several aspects of the vibration characteristics of steel member-supported floors

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Virginia Tech

Four aspects influencing the vibration characteristics of steel member supported floors were investigated. The four aspects are: 1) the number of tee-beams effective in resisting a heel-drop impact for steel joist and steel beam-concrete slab floors, 2) the effective moment of inertia of steel joist and joist-girder members, 3) the ability of joist seats to provide composite behavior between the supporting member and overlying slab, and 4) the effects of extending and restraining the bottom chords of joist members.

A new equation was developed to predict the number of effective tee-beams. The proposed equation is recommended to replace the two current equations. The proposed equation is a regression equation based on the results of a finite element analysis of 240 floor systems and is considered to be more accurate than the current equations.

Next, a study was undertaken to determine the relationship between the span-to depth ratio of a joist or joist-girder member and it's effective moment of inertia. Twenty five joists and joist-girders were modeled and analyzed using the finite element method and their effective stiffnesses calculated. The effective stiffness of each member was plotted against the respective span-to-depth ratio. A linear regression line was then fit to the data to mathematically represent the trend.

Finally, a vibration test floor was constructed to investigate the joist seat behavior and extended bottom chords. Finite element models were developed and analyzed and frequency and stiffness tests were performed to evaluate the floor's behavior. Conclusions were then drawn and recommendations made concerning the joist seat behavior and the effects of extending joist bottom chords.