Human Footfall Research Articles

Acoustic and vibratory characterization of in‐room footfall noise: Part 2.

Prior to Phase I of this study [ J. Acoust. Soc. Am. 22], existing footfall literature was primarily focused on transmission between spaces, i.e., IIC. This study measured the sound power and vibratory spectra produced by footfalls using both human subjects and standard tapping machines. One tapper had rubber‐tipped drop weights and the other had cored samples of shoe soles used by human participants. Within a reverberation room, 12 floor profiles were tested with the tapping machines. Human subjects were tested with three previously tested floors and a new floor profile. Fourteen male and female subjects walked on the floor surfaces while wearing three different types of footwear: leather‐soled shoes (hard), rubber‐soled shoes (medium), and sneakers (soft). Sound power spectra and vibratory signatures for each condition were measured using the procedures of ISO 3741. The current study verified repeatability from Phase I to Phase II, produced sound power footfall data for vinyl flooring applied directly to concrete, and developed improved correction curves to model tapping machines as human footfalls. Similarities between the rubber‐tipped tapper and women's leather shoes and a comparison of sound power and corresponding vibratory signatures are discussed. [Worked supported by The Paul S. Veneklasen Research Foundation.]

Seismic/acoustic detection of ground and air traffic for unattended ground sensor technology

Human footfall and vehicle traffic create surface waves in soil media that can easily be detected by seismic sensors. Field measurement data have been acquired with a triaxial geophone at several experimental sites. The in-plane-surface wave components dominate the response and decay at a rate of approximately 1/R, where R is distance. This decay rate is due to the combined effect of spreading (1/sqrt(R)) and damping losses in the soil. Further, the detection range is dependent upon the level of environmental noise, soil compliance, moisture content, and topography. Human detection was achieved in rural environments at distances up to ∼30–40 m, and vehicle detection was possible at much greater distances. Seismic signals due to aircraft are small when compared to the acoustic signature. Ground-based microphone measurements clearly show the blade passage frequency tones of propeller airplanes and the broader band signature of turbojet aircraft. Time- and frequency-domain signal-processing methods for the detection and identification will also be introduced. These experimental results will be discussed with particular emphasis placed on wave phenomenon, detection and identification algorithms, and the related physics.

An investigation of the characteristics of impact sound sources for impact sound insulation measurement

At the assessment of the impact sound insulation of a construction, a standard tapping machine is used as sound source. However, the current standard tapping machine has been criticised especially for measurement of wooden joist floors since the sounds generated by a tapping machine differ from those generated by actual footfall. This study has investigated the waveform and frequency spectra of human footfall (walking, running and jumping), of sand balls, sand bags and dropped tires, and of the standard tapping machine. It is shown that the frequency spectra differ between the standard tapping machine and actual footfall, especially at low frequencies. Results from other excitation sources such as a sand ball falling from a certain height showed concordance with actual footfall. This means that a sand ball drop as an impact source provides a better representation of actual human footfall than the standard tapping machine.

Identification and correlation of human footfall load parameters using multivariate analysis.

This research had two main objectives: to identify and quantify the multiple reaction parameters of human footfall load histories for 24 subjects; and to seek statistical correlations of the reaction parameters with two gaits: fitness walking and running, with two footfall surfaces: rigid and mat, and with two subject attributes: gender and arch index. These reaction parameters, measured with a force plate, include the subjects' foot reaction forces in the three orthogonal directions and the particular features of these forces such as their duration, average values, peak values, and rates of loading. An automated data retrieval-software system evaluated these reaction parameters. The statistical correlations were made using principal component analysis (PCA), a method that projected the 13 identified footfall reaction parameters onto subsets of three or four parameters called principal components that contained most of the variance of the original thirteen. The results, among others, show couplings between the vertical and the peak medial load, but an uncoupling of the posterior-anterior loads with the loads in the other two directions.

Stimulus-response measurement of floor impact sound

In the area of floor impact testing, a number of excitation techniques have been used for evaluating the degree of sound transmission. The ultimate goal of the excitation is to replicate the force and time duration of a human footfall so one can reliably rank the acoustical quality of the floor/ceiling system. The most common excitation methods involve dropping some object from a known height so the kinetic energy delivered to the floor is consistent. The limitation of the energy method is that the force spectrum imparted to the floor can vary if the floor finish has unstable or nonlinear characteristics (e.g., a thick carpet). In order to control this parameter, research laboratories have occasionally used a force sensor to help calibrate the impact forces from dropped objects. This paper will discuss the concept of using a force sensor as one component of a stimulus–response impact sound measurement in the field. A unique 13-kg force transducer ‘‘platform’’ was constructed in order to perform the field experiments. The platform is capable of measuring large dynamic forces at frequencies up to 100 Hz. Some examples of two-channel field data (force versus sound pressure) will be presented to demonstrate the technique.

Acceptability Criterion for Occupant-Induced Floor Vibrations

Improved methods of construction and design, which make use of materials with low weight-to strength ratios, may make large floor areas, free of partitions, susceptible to transient vibrations induced by small impacts such as human footfalls. Under certain circumstances these vibrations can be very annoying to occupants of buildings. Since the occupants are both source and sensor, the vibration cannot be isolated as with mechanical equipment and must be controlled by the structural system. In the past, it was possible for the structural designer to safely overlook these vibrations for two reasons. The first and most important is that the vibrations have no effect on the structural integrity of the building. Occupant induced vibrations are so small (initial amplitude from 0.005 to 0.08 in.) they may be ignored structurally. Second, the vibrational response of older floor systems is usually negated by damping in the heavy structural floor system or that associated with closely spaced partitions. If the response of the completed floor system is such that occupants are uneasy or annoyed, the intended use of the building can be radically affected. The writer is aware of the closing of a new department store because of uncomfortable floor motion and of the complete loss of secretarial efficiency in a new office building due to occupant induced floor vibration. Correcting such situations is usually very difficult and expensive, and success has been limited. Equally important is the tremendous waste of material in trying to prevent the problem. Most structural designers are acutely aware of potential floor vibration problems, but, until very recently, guidelines were not available to aid in the determination of the suitability of a proposed floor system. As a consequence, design tends to be overly conservative, resulting in heavier than necessary floor systems. The unneeded material in the floor system causes a pyramiding effect because additional material is required in the remaining structural system and foundations to support the added weight. Various scales for determining the acceptability of steel beam- and steel joist-concrete slab floor systems subject to occupant-induced floor vibrations have been reviewed and compared. The scales were shown to be inconsistent and, in general, to underestimate the strong dependence of acceptability on damping. A new criterion, based on experimental results from 91 floor systems, was presented. The proposed criterion is strongly dependent on damping and is suitable for design office use for evaluating the acceptability of steel beam or joist-concrete slab floor systems subject to occupant-induced vibrations.

End Restraints on Steel Joist Floor Vibrations

The problem of perceptible vibrations in steel joist/concrete slab floor systems has been under investigation for nearly 20 years. The vibrations, which can prove to be annoying to occupants, occur as a result of a human footfall. The floors, although structurally safe, lack the flexural rigidity necessary to prevent noticeable oscillations. Two articles by Lenzen6 and Murray, which have presented detailed methods for attacking the vibrations problem, were the primary sources for the background information presented in this paper. The discussion that follows leads to a new method of controlling the floor vibrations problem by varying the rotational end restraints of the floor.

Design to Prevent Floor Vibrations

Efficiently designed floor systems are occasionally found to be susceptible to annoying vibrations induced by human occupancy. Improved methods of construction and design, which make use of high strength-lightweight concrete and high strength steels resulting in reduced mass and rigidity of the floor systems without loss of structural soundness, may make large floor areas, free of partitions, susceptible to transient vibrations induced by small impacts such as human footfalls. Under certain circumstances these vibrations can be very annoying to occupants of buildings. Since the occupants are both the source and the sensor, the vibration cannot be isolated as with mechanical equipment, and must be controlled by the structural system.

The application of oscillating valve circuits to the precise measurements of certain physical quantities

For low-power applications, piezoelectric transducers are often utilized through direct and vibrational excitation. Mechanical energy exists almost everywhere there is movement—vibrations in bridges, wind spinning turbines and human steps onto the floor—and the direct piezoelectric effect inherent in piezoelectric materials converts the mechanical energy into electrical energy. Piezoelectricity can be advantageous in certain applications due to its chemical stability, scalability, and low dependence on environmental conditions, such as temperature and pressure. In this paper we will discuss two distinct excitation methods for energy harvesting optimization. First, a compressive system was simulated and tested, with the goal of simulating human footfall, and the second utilizing a plucking motion, with the goal of coupling high resonant frequencies inherent in piezoelectrics, to low human scale frequencies. The work performed here is in conjunction with NASA for the development of a novel, piezo-driven, interactive flooring system which will be installed at Kennedy Space Center on Cape Canaveral in the summer 2017.