Kelly A. Salyards

Experimental Evaluation of the Influence of Human-Structure Interaction for Vibration Serviceability

AbstractThe effects of human-structure interaction on the dynamic performance of occupied structures have long been observed. The inclusion of the effects of human-structure interaction is important to ensure that the dynamic response of a structure is not overestimated. Previous observations, both in service and in the laboratory, have yielded results indicating that the effects are dependent on the natural frequency of the structure, the posture of the occupants, and the mass ratio of the occupants to the structure. These results are noteworthy, but are limited in their application,because the data are sparse and are only pertinent to a specific set of characteristics identified in a given study. To examine these characteristics simultaneously and consistently, an experimental test structure was designed with variable properties to replicate a variety of configurations within a controlled setting focusing on the effects of passive occupants. Experimental modal analysis techniques were employed to both t...

Detection of Internal Defects in Concrete Members Using Global Vibration Characteristics

Rock-pocket and honeycomb defects impair overall stiffness, accelerate aging, reduce service life, and cause structural problems in hardened concrete members. Traditional methods for detecting such deficient volumes involve visual observations or localized nondestructive methods, which are labor-intensive, time consuming, highly sensitive to test conditions, and require knowledge of and accessibility to defect locations. The authors propose a vibration response-based nondestructive technique that combines experimental and numerical methodologies for use in identifying the location and severity of internal defects of concrete members. The experimental component entails collecting mode shape curvatures from laboratory beam specimens with size-controlled rock pocket and honeycomb defects, and the numerical component entails simulating beam vibration response through a finite element (FE) model parameterized with three defect-identifying variables indicating location (x, coordinate along the beam length) and severity of damage (a, stiffness reduction and b, mass reduction). Defects are detected by comparing the FE model predictions to experimental measurements and inferring the low number of defect- identifying variables. This method is particularly well-suited for rapid and cost-effective quality assurance for precast concrete members and for inspecting concrete members with simple geometric forms.

Experimental Results from a Laboratory Test Program to Examine Human-Structure Interaction

Assembly-type structures, subjected to crowd-induced rhythmic excitation, are typically designed to avoid excessive vibration. Most current design guidance recommends using the dynamic properties of the empty structure to assess the susceptibility of a given design to vibration. This recommendation does not incorporate the effects of human-structure interaction where the dynamic properties of the combined system are different from that of the empty structure. To assess the consequences of this recommendation, an experimental study was completed to identify the effects of human-structure interaction on the dynamic properties of the empty structure. The study investigated the influence of posture, mass ratio, and natural frequency of the structure when considering human-structure interaction of a passive crowd. The results of this study are presented and discussed with respect to the prediction of the dynamic response of a structure when the human-structure interaction effects are incorporated or neglected. Because it is likely that the dynamic response of the structure will be overestimated when utilizing the properties of the empty structure, a method for appropriately incorporating the effects of human-structure interaction is needed. An overview of the methods utilized in the study is presented and the results are examined to improve the understanding of the influential factors involved in human-structure interaction.

Development of a Laboratory Test Program to Examine Human-Structure Interaction

Vibration serviceability is a widely recognized design criterion for assembly-type structures likely subjected to rhythmic human-induced excitation. Current design guidance is based on the natural frequency of the structure. However, a phenomenon known as human-structure interaction suggests that there is a dynamic interaction between the structure and the occupants, altering the natural frequency of the system. It is unknown if this shift in natural frequency is significant enough to warrant consideration in the design process. Therefore, there is a need to identify the circumstances under which human-structure interaction should be considered because of its potential impact on serviceability assessment. Because the influence of the structural properties on human-structure interaction cannot be separated from the influence of the crowd characteristics, this study explores the interface of both factors through experimental testing. To do so, a laboratory test structure is designed, constructed, and operated based on particular design criteria selected with knowledge from previous human-structure interaction studies. This study provides a review of the design and construction of the test structure, methods used to validate a finite element computer model to the as-built structure, and the experimental testing procedure for testing with occupants.

Evaluation of Vibration Assessment Criteria and Their Application to Stadium Serviceability

This paper explores the current recommended measures for assessing vibration serviceability in building structures and the recommendations for relating these vibration measures to levels of perception and expected occupant reactions. Two of these assessment measures, the maximum transient vibration value and vibration dose value, are discussed with respect to serviceability in stadium structures. The results of the monitoring and assessment of three stadium structures during several events are presented and these results indicate that the current recommendations are overly conservative in assessing occupant perception. Recommendations for vibration dose levels that are more consistent with the evaluation of events monitored in stadium structures are proposed.

Human-Structure Interaction: Effects of Crowd Characteristics

Design for vibration serviceability currently relies almost entirely on the estimation of dynamic properties of the empty structure to be utilized for estimating the dynamic response or, at minimum, to avoid resonance with the excitation. However, the use of the empty structure properties has been questioned due to a phenomenon referred to as humanstructure interaction where the dynamic properties of the occupied structure can be significantly different from the properties of the empty structure. General trends include an increase in damping ratio and a decrease in natural frequency (although special cases of increasing frequency or new modes have been documented). These trends seem to be affected by the posture of the crowd occupying the structure, and potentially other crowd characteristics. This study aims to isolate several crowd characteristics including posture, distribution, and crowd size, to determine the relative effect that each has on the overall dynamic properties of the occupied test structure.

A Unique Vibration Serviceability Case Study of a Complex Structure

When several occupants of a newly constructed academic building raised a concern of disturbing vibrations in several of the third floor offices, an investigation ensued that aimed to capture and characterize this disturbing vibration. A remote monitoring system was utilized to monitor the offices of interest and the offending vibration was finally recorded. The recorded data indicated that this vibration was not a typical serviceability issue due to walking. The study that followed examined the dynamic characteristics of the floor structure through dynamic testing and consequently several unusual vibration sources were explored ranging from wind or traffic to mechanical equipment to an often overlooked human excitation best described as leg jiggling. Some of the findings related to this unusual and interesting case study are described in this paper.

Experimental Investigation of Dynamic Load Estimation Using Small-Scale Testing

Vibration serviceability in large assembly-type structures such as stadiums and grandstands has become a design and management concern as crowds continue to impose significant dynamic loads on a structure through synchronized movement. However, there is little guidance on the appropriate dynamic design loading to be anticipated for the design of new structures or the assessment of existing structures. The guidance currently available for human-induced dynamic loading is limited to laboratory experiments and numerical models that fail to take into account the effects that many factors of the event atmosphere may have on the loading models. Because measurement of the forces exerted by a crowd under true event conditions is next to impossible, this project investigates the ability to estimate the dynamic loading with consideration of only the more reasonably obtainable acceleration response of the structure during the event. Experimental testing was performed on a simple floor structure subjected to dynamic forces generated by small groups to investigate the accuracy and sensitivity of the load estimation method for consideration when applying this method to large scale structures.

Effects of Human–Structure Interaction from Seated Occupants on a Cantilevered Laboratory Test Structure

Vibration serviceability is an established design criterion for assembly-type structures to limit the vibration induced such that the structure’s occupants are not disturbed by such movement. Most current design guidance recommends the use of the dynamic properties of the empty structure in the dynamic response prediction. This guidance neglects the effects of human–structure interaction where the dynamic properties of the occupied structure are affected by the occupants. Experimental results from seated occupants on a cantilevered laboratory test structure are compared with analytical results obtained by modeling the occupants as an attached spring–mass–damper system. The cantilevered test structure was designed with variable supports to allow varied configurations with different natural frequencies. The experimental study includes various seated postures and group sizes on the test structure with various frequency configurations. The analytical modeling is performed using the modal parameters recommended by the Joint Working Group for passive occupants. A comparison of the resulting modal parameters of the occupied structure is presented and the results are discussed with respect to the estimation of the dynamic response of a structure for vibration serviceability assessment.