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CONTENTS
Volume 14, Number 6, November 2011
 

Abstract


Key Words


Address
K.C.S. Kwok : Univ. of Western Sydney
Richmond, NSW 2753, Australia
J.D. Holmes: JDH Consulting P.O. Box 269, Mentone
Victoria 3194, Australia

Abstract
Low-frequency building vibration is known to induce symptoms of motion sickness in some occupants. This paper examines how the adoption of a theory of motion sickness, in conjunction with a dose-response model might inform the real-world problem of managing and designing standards for tall building motion sway. Building designers require an understanding of human responses to low-dosage motion that is not adequately considered by research into motion sickness. The traditional framework of Sensory Conflict Theory is contrasted with Postural Instability Theory. The most severe responses to motion (i.e., vomiting) are not experienced by occupants of wind-excited buildings. It is predicted that typical response sets to low-dosage motion (sleepiness and fatigue), which has not previously been measured in occupants of tall-buildings, are experienced by building occupants. These low-dose symptoms may either be masked from observation by the activity of occupants or misattributed to the demands of a typical working day. An investigation of the real-world relationship between building motion and the observation of low-dose motion sickness symptoms and a degradation of workplace performance would quantify these effects and reveal whether a greater focus on designing for occupant comfort is needed.

Key Words
motion sickness; nausea; work performance; ecological psychology.

Address
D. Walton : University of Canterbury, and Health Sponsorship Council, Wellington, New Zealand
S. Lamb and Kenny C.S. Kwok : University of Western Sydney, Sydney, Australia

Abstract
The assessment of wind-induced motion plays an important role in the development and design of the majority of today\'s structures that push the limits of engineering knowledge. A vital part of the design is the prediction of wind-induced tall building motion and the assessment of its effects on occupant comfort. Little of the research that has led to the development of the various international standards for occupant comfort criteria have considered the effects of the low-frequency motion on task performance and interference with building occupants\' daily activities. It has only recently become more widely recognized that it is no longer reasonable to assume that the level of motion that a tall building undergoes in a windstorm will fall below an occupants\' level of perception and little is known about how this motion perception could also impact on task performance. Experimental research was conducted to evaluate the performance of individuals engaged in a manual tracking task while subjected to low level vibration in the frequency range of 0.125 Hz-0.50 Hz. The investigations were carried out under narrowband random vibration with accelerations ranging from 2 milli-g to 30 milli-g (where 1 milli-g = 0.0098 m/s2) and included a control condition. The frequencies and accelerations simulated are representative of the level of motion expected to occur in a tall building (heights in the range of 100 m -350 m) once every few months to once every few years. Performance of the test subjects with and without vibration was determined for 15 separate test conditions and evaluated in terms of time taken to complete a task and accuracy per trial. Overall, the performance under the vibration conditions did not vary significantly from that of the control condition, nor was there a statistically significant degradation or improvement trend in performance ability as a function of increasing frequency or acceleration.

Key Words
tall building; wind-induced motion; manual tracking task; occupant comfort.

Address
Melissa D. Burton : BMT Fluid Mechanics, 20 Broad Street, New York, NY, 10005, USA
Kenny C.S. Kwok : School of Engineering, University of Western Sydney, Penrith, NSW 2751, Australia
Peter A. Hitchcock : CLP Power Wind/Wave Tunnel Facility (WWTF), The Hong Kong University of Science and Technology
(HKUST) Clear Water Bay, Kowloon, HKSAR, China

Abstract
While there are a number of guidelines used throughout the world in the assessment of acceptability of tall building accelerations, none are based on systematically conducted surveys of occupant reaction to wind-induced motion. In this study, occupant response data were gathered by both a self-reporting mechanism and by interviewer-conducted surveys in control tower structures over a period of four years. These two approaches were designed in conjunction with experimental psychologists to ensure unbiased reporting. The data allowed analysis of perception thresholds and tolerability at different building frequencies and in different wind climates. The long-term nature of the studies also allowed an investigation of the causes and effects of adaptation to building motion. As the surveys were designed to allow multiple use during single storms, the effects of exposure duration were investigated. A final exit survey was conducted at the primary survey location to investigate views of the acceptability of windinduced motion and the factors underlying these views. The findings of the field studies indicate that none of the currently used acceleration guidelines address all of the factors that contribute to occupant dissatisfaction. An alternative framework for assessing acceleration acceptability is proposed.

Key Words
building motion; serviceability acceleration; motion perception; occupant comfort.

Address
Roy O. Denoon :CPP, Inc., 1415 Blue Spruce Drive, Fort Collins, CO 80524, USA
Kenny C.S. Kwok : School of Engineering, University of Western Sydney, Penrith South, NSW 1797, Australia

Abstract
This paper presents an integrated wind-induced dynamic analysis and computer-based design optimization technique for minimizing the structural cost of general tall buildings subject to static and dynamic serviceability design criteria. Once the wind-induced dynamic response of a tall building structure is accurately determined and the optimal serviceability design problem is explicitly formulated, a rigorously derived Optimality Criteria (OC) method is to be developed to achieve the optimal distribution of element stiffness of the structural system satisfying the wind-induced drift and acceleration design constraints. The effectiveness and practicality of the optimal design technique are illustrated by a full-scale 60-story building with complex 3D mode shapes. Both peak resultant acceleration criteria and frequency dependent modal acceleration criteria are considered and their influences on the optimization results are highlighted. Results have shown that the use of various acceleration criteria has different implications in the habitability evaluations and subsequently different optimal design solutions. The computer based optimization technique provides a powerful tool for the lateral drift and occupant comfort design of tall building structures.

Key Words
serviceability design; occupant comfort criteria; stiffness optimization; dynamic analysis; optimality criteria method.

Address
M.F. Huang : Institute of Structural Engineering, Zhejiang University, Hangzhou 310058, P.R.China, Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Hong Kong
C.M. Chan : Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology,
Hong Kong
Kenny. C.S. Kwok : School of Engineering, University of Western Sydney, NSW, Australia


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