Floor vibration serviceability is a primary design consideration for steel framed floors. Designers in North America typically use the AISC Design Guide 11 methods to check this limit state, but its methods are difficult to apply to atypical floor framing. Finite element analysis is a logical choice for predicting vibration response to walking, but simplified designer-friendly procedures are not available. Three relatively simple, experimentally verified methods of predicting low frequency floor vibration due to walking are presented in this dissertation. The methods are based on finite element analysis of the floor system, are applicable to a wide range of situations, and are intended to be no more complicated than is justified by the current ability to predict modal properties. The first method is to predict the acceleration response using response history analysis with individual footstep forces as the loading function. The second method also uses response history analysis to predict the acceleration waveform, but with a Fourier series representation of the load. The third method is a simplified frequency domain method in which the predicted accelerance frequency response function is used to predict the steady-state response to walking which is reduced to account for incomplete resonant build-up. A two year experimental program including three laboratory specimens, a four bay full-scale mockup, and two steel-framed building floors, was completed at Virginia Tech. These floor systems represent a wide cross-section of the steel framed floor systems used in North America. Modal tests were performed using an electrodynamic shaker and experimental modal analysis techniques were used to estimate the modal properties: natural frequencies, mode shapes, and damping ratios. Responses to walking excitation were measured several times in each tested bay for individuals walking at subharmonics of natural frequencies. During each test, the walker crossed the middle of the bay using a metronome to help maintain the intended cadence. The test with maximum response represents the maximum peak acceleration that can be reasonably expected to occur due to a single walker. The proposed methods were used, with measured damping ratios and walker weights, to predict the modal properties and responses to walking for comparison with measured values. The methods were found to be reasonably accurate, contain significant data dispersion, and be on the conservative side. The results of these comparisons were used to develop design recommendations, including reduction factors to account for the conservatism. The design methods were used to predict the modal properties and responses to walking in a "blind" manner using only information that would be available to a designer. Comparisons of measurements and predictions were used to determine the accuracy of the proposed prediction methods, which were found to be sufficiently accurate for design usage. / Ph. D.

The presented research examined three areas: best practices in high quality dynamic testing of in-situ floor systems, extensive dynamic testing of three bare (non-fit out) in-situ multi-bay steel composite floors to estimate their dynamic parameters/response and to identify trends in dynamic behavior, and development of a set of fundamental finite element (FE) modeling techniques to adequately represent the dynamic response of steel composite floors for the purpose of evaluating vibration serviceability. The measurement, analysis, and computation of a floor's accelerance frequency response function (FRF) is the core premise linking all areas of the presented research. The burst chirp signal using an electrodynamic shaker is recommended as the most accurate and consistent source of excitation for acquiring high quality measurements suitable for use in parameter estimation, operating deflection shape animation, and calibration/validation of FE models. A reduced mid-bay testing scheme is recommended as a time-saving alternative to modal testing over a full coverage area, provided the only desired estimated parameters are frequencies, damping, and mid-bay acceleration response. Accelerance FRFs were measured with an electrodynamic shaker located within 23 unique bays on the three tested floors. Dominant frequencies ranged from 4.85 Hz to 9 Hz and measured estimates of damping varied considerably, ranging from 0.44% to 2.4% of critical (0.5%-1.15% was typical). Testing showed several mode shapes were localized to just a few bays and not all modes were adequately excited by forcing at a single location. The quality of the estimated mode shapes was significantly improved using multi-reference modal testing. FE models for the tested floors were developed based on high quality measured data and were shown to provide adequate representations of measured floor behavior. Fundamental techniques are presented for modeling mass, stiffness, boundary conditions, and performing dynamic analysis. A method of evaluating vibration serviceability was proposed using the FE model's computed accelerance FRF for comparison with a design accelerance curve that represents an acceleration response threshold in the frequency domain. An example design accelerance curve is presented based on current serviceability guidelines for acceleration tolerance and effective harmonic forces due to human activities such as walking. / Ph. D.

The purpose of this study was to examine the effect of bottom chord extensions on deflections and vibration characteristics of joist supported floor systems when joist bottom chord extensions are installed. To understand the effect of bottom chord extensions on deflections, natural frequency, damping, mode shape and effective mass, extensive analytical and experimental studies were conducted on single span and three span joist supported laboratory footbridges with different bottom chord extension configurations. Finite element computer models were created to simulate and compare the results of stiffness and vibration tests. Testing was done with a) the bottom chord extensions in-place before the concrete was placed, b) with all or part of the bottom chord extensions removed, and c) after the bottom chord extensions had been reinstalled with jacking for the single span footbridge and without jacking for the three-span footbridge. Results from the stiffness tests indicate that re-installing the bottom chord extensions to the joists of the single span footbridge with cured concrete with the center of the span raised helps to reduce the uniform load deflections to some extent, but not as much as placing the bottom chord extensions before the concrete placement. Likewise, for the three span footbridge, placing the bottom chord extensions before the concrete placement is observed to be a better solution. Results from the dynamic tests indicate that the effect of bottom chord extensions on the single span footbridge is consistent for natural frequency, 20 psf live load deflections, sinusoidal excitations with high amplitudes, quarter point heel drop excitations, walking excitations, and effective mass values. The effect of bottom chord extensions on the three span footbridge is consistent for the natural frequency and 20 psf deflections. However, the FRF (Frequency Response Function) peaks of chirp, heel drop, sinusoidal excitations, accelerations from walking data, and the MEScope and Finite Element model effective mass results do not follow a common trend. It can be concluded that even though the footbridge was stiffened by the bottom chord extensions, that does not necessarily mean that the acceleration levels, and hence the frequency response function peaks, decrease. However, bottom chord extensions do increase the natural frequencies for all the three governing bending modes. / Ph. D.