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A longitudinal eld study of the effects of wind-induced building motion on occupant wellbeing and work performance S. Lamb a,n , K.C.S. Kwok a,1 , D. Walton b,c,2 a Institute for Infrastructure Engineering, University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751, Australia b Health Promotion Agency, Level 4, ASB House,101 The Terrace, PO Box 2142, Wellington 6140, New Zealand c University of Canterbury, Adjunct Fellow Univ. of Canterbury, Department of Psychology, Private Bag 4800, Christchurch 8140, New Zealand article info Article history: Received 8 December 2013 Received in revised form 8 July 2014 Accepted 20 July 2014 Keywords: Wind-excitation Tall building Low frequency vibration Motion sickness Sopite syndrome Occupant comfort work performance abstract The current study uses a longitudinal within-subjects design to investigate the effects of wind-induced tall building motion on occupant wellbeing and work performance. 47 ofce workers on high oors of wind-sensitive buildings and 53 control participants completed 1909 surveys across 8 months and over a range of wind conditions. The results show that the effects of building motion are emergent, as motion sickness develops after a duration of exposure to motion, which mostly manifest as symptoms of sopite syndrome, or low-dose motion sickness (tiredness, low motivation, distraction from work activities, and low mood), which occur at 23 times baseline rates. As motion sickness increases, work performance signicantly decreases by 0.760.90 standard deviations below baseline. Affected individuals attempt to manage their own discomfort, and indicate a preference to work a different location during motion, take 3040% longer breaks, and attempt to self-medicate using analgesics. Humans are adaptable, allowing most occupants to continue their work activities, but at reduced levels of performance and comfort. Design criteria for tall buildings should attempt to minimise the environmental stress of building motion on work performance and wellbeing rather than motion tolerance or formal complaint to building owners. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Despite their rigid appearance, tall buildings possess elastic properties allowing them to ex in response to external forces. Strong winds can cause buildings to vibrate, or sway, at low frequencies below 1 Hz, and at low accelerations up to approxi- mately 40 mg (1 mg is equal to 1/1000th of gravity or 0.0098 m/s 2 ). Tall buildings sway in the predominant wind direction and also the perpendicular direction, producing an elliptical motion. Bursts of motion occur at random intervals at the natural frequency of the building, causing an unpredictable pattern of motion. Studies have shown that building motion can be perceptible to occupants, cause fear, and induce motion sickness in some occupants (Hansen et al., 1973; Goto, 1983; Burton, 2006; Lamb et al., 2013). While researchers can predict accelerations that occupants will perceive (e.g. Tamura et al., 2006), researchers do not clearly understand the frequencies and accelerations required to induce motion sickness and other adverse effects, or understand the inuence of individual differences, such as susceptibility to motion sickness. Further, researchers do not understand how building motion affects occupant wellbeing and work performance. Current build- ing guidelines specify acceptablebuilding accelerations, but these may not be adequate to ensure a healthy work environment. Yet building motion will likely be a more common problem for design professionals and building occupants in the future due to trends toward urban densication (World Health Organization, 2010), higher levels of tall building construction (Council on Tall Building and Urban Habitat, 2013), and global warming-induced changes in weather patterns. 1.1. Previous building motion studies Relying mostly on motion simulator studies, building designers may contend that building motion has a minimal effect on the wellbeing of occupants, except perhaps during rare events at very high accelerations over about 3035 mg (Chen and Robertson, 1972; Isyumov and Kilpatrick, 1996; Denoon et al., 2000; Burton et al., 2005; Tamura et al., 2006; Denoon and Kwok, 2011). Researchers have limited opportunity to study actual building occupants. Building owners rarely permit the measurement of Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jweia Journal of Wind Engineering and Industrial Aerodynamics http://dx.doi.org/10.1016/j.jweia.2014.07.008 0167-6105/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. Tel.: þ64 27 421 9061. E-mail addresses: [email protected], [email protected] (S. Lamb), [email protected] (K.C.S. Kwok), [email protected] (D. Walton). 1 Tel.: þ61 2 4736 0444. 2 Tel.: þ64 4 917 0060. J. Wind Eng. Ind. Aerodyn. 133 (2014) 3951

A longitudinal field study of the effects of wind-induced building motion on occupant wellbeing and work performance

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Page 1: A longitudinal field study of the effects of wind-induced building motion on occupant wellbeing and work performance

A longitudinal field study of the effects of wind-induced buildingmotion on occupant wellbeing and work performance

S. Lamb a,n, K.C.S. Kwok a,1, D. Walton b,c,2

a Institute for Infrastructure Engineering, University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751, Australiab Health Promotion Agency, Level 4, ASB House, 101 The Terrace, PO Box 2142, Wellington 6140, New Zealandc University of Canterbury, Adjunct Fellow Univ. of Canterbury, Department of Psychology, Private Bag 4800, Christchurch 8140, New Zealand

a r t i c l e i n f o

Article history:Received 8 December 2013Received in revised form8 July 2014Accepted 20 July 2014

Keywords:Wind-excitationTall buildingLow frequency vibrationMotion sicknessSopite syndromeOccupant comfort work performance

a b s t r a c t

The current study uses a longitudinal within-subjects design to investigate the effects of wind-inducedtall building motion on occupant wellbeing and work performance. 47 office workers on high floors ofwind-sensitive buildings and 53 control participants completed 1909 surveys across 8 months and over arange of wind conditions. The results show that the effects of building motion are emergent, as motionsickness develops after a duration of exposure to motion, which mostly manifest as symptoms of sopitesyndrome, or low-dose motion sickness (tiredness, low motivation, distraction from work activities, andlow mood), which occur at 2–3 times baseline rates. As motion sickness increases, work performancesignificantly decreases by 0.76–0.90 standard deviations below baseline. Affected individuals attempt tomanage their own discomfort, and indicate a preference to work a different location during motion, take30–40% longer breaks, and attempt to self-medicate using analgesics. Humans are adaptable, allowingmost occupants to continue their work activities, but at reduced levels of performance and comfort.Design criteria for tall buildings should attempt to minimise the environmental stress of building motionon work performance and wellbeing rather than motion tolerance or formal complaint to buildingowners.

& 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Despite their rigid appearance, tall buildings possess elasticproperties allowing them to flex in response to external forces.Strong winds can cause buildings to vibrate, or sway, at lowfrequencies below 1 Hz, and at low accelerations up to approxi-mately 40 mg (1 mg is equal to 1/1000th of gravity or 0.0098 m/s2).Tall buildings sway in the predominant wind direction and alsothe perpendicular direction, producing an elliptical motion. Burstsof motion occur at random intervals at the natural frequency of thebuilding, causing an unpredictable pattern of motion. Studies haveshown that building motion can be perceptible to occupants, causefear, and induce motion sickness in some occupants (Hansenet al., 1973; Goto, 1983; Burton, 2006; Lamb et al., 2013). Whileresearchers can predict accelerations that occupants will perceive(e.g. Tamura et al., 2006), researchers do not clearly understandthe frequencies and accelerations required to induce motion

sickness and other adverse effects, or understand the influenceof individual differences, such as susceptibility to motion sickness.Further, researchers do not understand how building motionaffects occupant wellbeing and work performance. Current build-ing guidelines specify ‘acceptable’ building accelerations, but thesemay not be adequate to ensure a healthy work environment. Yetbuilding motion will likely be a more common problem for designprofessionals and building occupants in the future due to trendstoward urban densification (World Health Organization, 2010),higher levels of tall building construction (Council on Tall Buildingand Urban Habitat, 2013), and global warming-induced changes inweather patterns.

1.1. Previous building motion studies

Relying mostly on motion simulator studies, building designersmay contend that building motion has a minimal effect on thewellbeing of occupants, except perhaps during rare events at veryhigh accelerations over about 30–35 mg (Chen and Robertson,1972; Isyumov and Kilpatrick, 1996; Denoon et al., 2000; Burtonet al., 2005; Tamura et al., 2006; Denoon and Kwok, 2011).Researchers have limited opportunity to study actual buildingoccupants. Building owners rarely permit the measurement of

Contents lists available at ScienceDirect

journal homepage: www.elsevier.com/locate/jweia

Journal of Wind Engineeringand Industrial Aerodynamics

http://dx.doi.org/10.1016/j.jweia.2014.07.0080167-6105/& 2014 Elsevier Ltd. All rights reserved.

n Corresponding author. Tel.: þ64 27 421 9061.E-mail addresses: [email protected],

[email protected] (S. Lamb), [email protected] (K.C.S. Kwok),[email protected] (D. Walton).

1 Tel.: þ61 2 4736 0444.2 Tel.: þ64 4 917 0060.

J. Wind Eng. Ind. Aerodyn. 133 (2014) 39–51

Page 2: A longitudinal field study of the effects of wind-induced building motion on occupant wellbeing and work performance

building accelerations or allow researchers to approach buildingoccupants and commercial organisations are also hesitant tocommit staff resources to research. Some studies have measuredactual responses to motion following severe wind events (Hansenet al., 1973; Goto, 1983; Denoon and Kwok, 2011; Lamb et al.,2013). These studies rely on occupants' retrospective assessmentsand single-sample measures that cannot establish motion-inducedchanges in wellbeing or work performance. Most research, andindeed building standards, have focused on the threshold ofmotion perception (e.g. Chen and Robertson, 1972; Tamura, et al.,2006; Denoon and Kwok, 2011). While a valid design criterion,wellbeing and work performance are more relevant to the qualityof the indoor office environment. Building designers consider alow rate of occupant complaint to buildings owners evidence thatbuilding accelerations are within an acceptable range (Hansen etal., 1973; Isyumov and Kilpatrick, 1996). However, recent evidenceshows that office workers informally complain to colleagues andfamily rather than to building owners (Lamb et al., 2013).

Simulator studies show motion to have a negligible effect ontask and cognitive performance (Jeary et al., 1988; Morris et al.,1979; Denoon et al., 2000; Burton et al., 2004, 2011). These studiesare limited because they use task performance measures that maybe too simple to detect true performance differences, and oftenreport ceiling effects (high baseline scores that have insufficientvariability to detect actual changes in performance). Further, thesestudies expose participants to high acceleration motion for shortdurations (usually less than one hour), which may not provoke thetypes of symptoms that affect actual building occupants. Studiesrarely consider how occupants may attempt to adapt to or com-pensate for building motion. Controlled motion simulator studiescannot measure unprompted behaviours that might occur in realoffice buildings, for example, break-taking behaviour, changing taskdemands and taking medication. While Denoon and Kwok (2011)examined control tower workers over the course of approximatelyone year, the study focused mostly on the perception of motion, butdid not examine the effect of motion on work performance oroccupant wellbeing. Further, airport control towers are not repre-sentative of a typical office building. Only a longitudinal study, afield study repeatedly measuring the responses of actual officebuilding occupants over a long period, can provide convincingevidence of the real effect of building motion.

1.2. Motion sickness

Those occupants susceptible to motion sickness are most likelyto report adverse effects of building motion (Lamb et al., 2013).Since the ancient Greeks discovered ‘seasickness’, humans haveknown that unusual motion causes a physiological disturbancecharacterised by nausea, dizziness and vomiting (Reason andBrand, 1975). Only in the last 40 years, NASA scientists discoveredthat sustained exposure to gentle accelerations can cause subtleearly onset symptoms of motion sickness, called sopite syndrome(Graybiel and Knepton, 1976). Symptoms include sleepiness, diffi-culty concentrating, low mood, and decreased motivation, whichmay persist but never develop into nausea. Within a dose-response model, low-dose symptoms of motion sickness, particu-larly sopite syndrome, are more likely to occur in the accelerationrange of tall buildings than classic high-dose symptoms of nauseaand dizziness (Walton et al., 2011). Recent evidence lends supportto this hypothesis, as Lamb et al. (2013) report that buildingoccupants most frequently report difficulty concentrating duringbuilding motion, a cardinal symptom of sopite syndrome. Waltonet al. (2011) argue that symptoms of low-dose motion sickness arecommon and can occur for reasons other than building motion,and occupants may misattribute these symptoms to normal workstress and fatigue.

1.3. The current study

This study aims to understand the effects of wind-inducedbuilding motion on occupant wellbeing and work performance,particularly in terms of low-dose motion sickness. Low-dosesymptoms of motion sickness, tiredness, distractibility, low-mood and low-motivation, can occur for reasons other wind-induced building motion. The challenge for building motionresearch is to delineate the symptoms that occur with somebaseline incidence in the workplace, from those that occur withgreater incidence because of building motion, requiring both asophisticated experimental design and complex statistical techni-ques. Some of the terms and techniques are likely to be unfamiliarto an engineering audience, and we attempt to explain thesethroughout.

The current study uses a longitudinal within-subjects design, atechnique that examines how the normal response of an indivi-dual changes in response to an environmental variable (ormanipulated variable) over a long period of time. Wellington,New Zealand, is one of the windiest cities in the world due to itsunique geography, caused by mountain ranges that channelprevailing winds, creating a consistently high wind climate (seeLamb et al., 2013). Forty-seven office workers in 22 wind-sensitiveWellington buildings, and a control condition of 53 office workerson near-ground floors, completed a total of 1909 online surveysover 231 days (8 months). A control condition allows us toinvestigate the baseline incidence of symptoms that may appearlike low-dose motion sickness and to establish normal level ofwork performance in an office environment not subject to buildingmotion. The study used online surveys to unobtrusively measurethe occupant response to motion during work hours over a rangeof wind conditions from calm (1.2 m/s) to near gale (29.0 m/s)allowing us to examine how wellbeing and work performancechange in response to building motion. The survey measured fourmain responses to building motion: (1) the perception of buildingmotion, (2) low- and high-dose symptoms of motion sickness, (3)self-reported work performance and objectively measured taskperformance, and (4) compensatory or adaptive behaviours. Thehuman vestibular system, located in the inner ear, is sensitive tochanges in environmental accelerations, capable of detectingaccelerations of 2–5 mg in the frequency range of tall buildingmotion (Tamura et al., 2006; Denoon and Kwok, 2011). Therefore,occupant reports of motion, supported by objectively measuredwind speeds and predicted building accelerations, provided theindependent measure of building motion. A sample of buildingaccelerations supplements these analyses.

2. Method

2.1. Participants

Respondents who work in wind-sensitive buildings and com-pleted the survey reported in Lamb et al. (2013) received aninvitation to participate in the current study. Participants recruitedfrom the survey distributed additional study invitations to theirwork colleagues. All participants gave their informed consent. Thestudy recruited 108 participants in total. The analysis excluded oneparticipant who reported she became pregnant during the study,because morning sickness may be confused with motion sickness.The analysis excluded 7 further participants from the experimentalcondition as they reported no instances of building motion duringthe duration of the study. The experimental condition comprised47 individuals who worked in the top third of tall buildings, orabove the 10th floor who reported perceptible wind-inducedmotion in that building. 53 participants worked on the 3rd floor

S. Lamb et al. / J. Wind Eng. Ind. Aerodyn. 133 (2014) 39–5140

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or lower formed the control condition, as they were unlikely toperceive building motion during any wind conditions.

Participants in the experimental condition worked on a meanfloor of 15.8 (SD¼6.0) and control participants on a mean floor of 1.8(SD¼0.96). The sample was biased towards females (73%, N¼73;Males¼27%, N¼27), though the bias was evenly represented acrossconditions, X2(1, N¼100)¼0.1, n.s. Age (M¼39.6 years), U (1)¼1218.5, Z¼�0.004, n.s, and occupation, X2(4, N¼91)¼3.2, n.s, werealso evenly represented across condition. The majority of participantsreported a ‘professional/managerial’ occupation (67%, N¼61), fol-lowed by ‘clerical/administration’ (28.6%, N¼26). The Motion Sick-ness Susceptibility Questionnaire (MSSQ) (Golding, 2006) providesan estimate of an individuals' likelihood of suffering motion sicknesswhen exposed to real or apparent motion. The MSSQ estimatessusceptibility based on the rate of reported motion environments(e.g. ships, cars, roller coasters) as both a child and an adult. Themean MSSQ score (M¼17.9, SD¼10.2) of the entire sample was1.5 points higher than the mean reported in a large sample ofindividuals in Wellington, New Zealand (Lamb et al., 2013) of 16.4(SD¼11.6, N¼994). The difference was small, equating to 0.14standard deviations, likely accounted for the over representation offemales in the sample, who have higher MSSQ scores on averagethan males (Golding, 2006). MSSQ scores did not differ by condition,U (1)¼1116.5, Z¼�0.72, n.s. Across the 231 study days (8 months),the 100 remaining participants completed 892 usable surveys in theexperimental condition and 1017 in the control condition. 69 wereexcluded because they were not completed on the assigned day, 35because of a change in employment/work floor, and 20 becauseparticipants were outside of the office for longer than 3 h. Partici-pants in the experimental condition completed an average of 18.9(SD¼4.5) surveys in the experimental condition, and 19.2 (SD¼4.6)in the control. The survey took a mean of 5.3 min to complete(SD¼2.0). Participants reported ‘personal issues’ outside of work inapproximately 20% of all surveys. The proportion was too large toexclude, therefore all analyses controlled for personal issues.

2.2. Materials

The 55-item online survey included seven sections. Ten itemsinvestigated characteristics of building motion. Four itemsrequested information about perceptible building motion, thecause, severity and duration of building motion. Two items askedwhen and how participants sensed motion. Four items askedparticipants to judge building motion on 11-point scales regard-ing: the unpleasantness of motion, the effect on work perfor-mance, preference to leave the building and work somewhere else,and the acceptability of motion.

Six items requested information about work breaks, includingthe length, frequency and purpose of breaks.

Fourteen items investigated participant wellbeing, includingtiredness (Akerstedt and Gillberg, 1990), mood, motivation and8 potential symptoms associated with motion sickness (‘yes’ or‘no’): nausea, headache, upset stomach, cold/flu, dizziness, poorcoordination (i.e. clumsy), difficulty concentrating, generally feel abit “off” (not feeling quite normal). Participants also rated theseverity of each symptom. Two items examined mediation taken,including analgesics, motion sickness tablets and cold/flu pills.Participants also reported recent absences from work.

Work performance is difficult to define and complex to measure(Pransky et al., 2006; Ryan and Tipu, 2009). Work performance ismore than simple productivity, or a ratio of objectively measuredinputs to outputs (Tangen, 2005). Criteria that define high workperformance differ between jobs and are not directly comparable(Viswesvaran, 2001). Objective measures, such as task performanceor cognitive performance, are only indicators of work performance.For example, an individual may show high scores on short tasks and

cognitive tests, but perform poorly at work because of low mood andmotivation. Researchers consider subjective ratings a more accurateindicator of ‘true’ work performance (Pransky et al., 2006; Ryan andTipu, 2009). In applied research, self-reported measures are often theonly practically available measure (Pransky et al., 2006). Self-reportedmeasures are appropriate for this study, as the aim is to detectchanges in work performance across environmental influences, notthe quantification of absolute performance. Self-reported workperformance ratings correlate well with supervisor ratings, atr¼0.64 (Higgins et al., 2007) and can also correlate well withobjective measures (Ryan and Tipu, 2009). Work performancemeasures ideally include both subjective and objective components.

Fourteen items examined self-reported work performance.Three items asked participants to rate their work performanceon 11-point scales. First, relative to their average work perfor-mance (0¼ ‘much less productive than average’, 5¼ ‘about aver-age’, 10¼ ‘much more productive than average’). Second,performance compared to their colleagues. Third, performancecompared to their perception of their maximum possible perfor-mance. Participants rated their agreement with 10 statementsabout their performance on 5-point Likert scales, including oneitem from Endicott and Nee (1997), “I have done everything thatmy manager expects of me”.

Seven items assessed work activities on the survey day anddynamic characteristics of the participants' workspace, e.g. tem-perature, light, and noise. Participants reported particulars aboutthe workday, including their arrival time, time out of the office,time at their desk, and work stress.

Participants completed the Stroop Test (Stroop, 1935), consist-ing of 26 trials with an inter-trial period of 700 ms. The maindependent measures recorded were average reaction time and thepercentage of correct responses.

The final section included four items, location of surveycompletion, personal stress, and general comments.

A 43-item exit survey asked about the participant's workenvironment, current employment, job satisfaction and job stress.The survey also collected MSSQ scores (see Golding, 2006) anddemographic information.

2.3. Wind data

The New Zealand National Institute of Water and AtmosphericResearch (NIWA) climate database provided wind data from theWellington airport station (3445) at sea level. Wind speed wasmeasured as the maximum hourly gust speed (m/s) corrected fromthe airport at 5.8 m (terrain category 2) to a reference height of150 m in the Wellington CBD (terrain category 4), using a terrainheight multiplier of 1.15 (Australia Standard/New ZealandStandard 1170.2., 2011).

2.4. Building accelerations

Participants who were permitted to place accelerometers intheir building received the accelerometers via mail, and wereinstructed to place the accelerometer box on a level surfaceunlikely to be bumped, preferably a window ledge. Calibrated GulfCoast Data Concepts (GCDC) X6-1A tri-axial accelerometers, set at20 Hz, high gain (72 g), and 16-bit resolution recorded buildingaccelerations continuously for a period of 3–4 weeks. 6 usableacceleration records were collected. A Butterworth filter post-processed the acceleration data, set at 5 Hz.

Across the 8-month study period, we estimated buildingaccelerations using a formula devised by Carpenter et al. (2013).The formula estimates accelerations fromwind speeds, taking intoaccount the natural frequency, density and floor plan area of abuilding (Appendix A).

S. Lamb et al. / J. Wind Eng. Ind. Aerodyn. 133 (2014) 39–51 41

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2.5. Procedure

Participants received online surveys across 8 months from the23rd of April 2012. The study aimed to collect approximately 20surveys per participant, spread evenly across ‘low’ (calm breeze,0–8.9 m/s), ‘medium’ (moderate breeze, 9–18.4 m/s) and ‘high’wind categories (strong breeze and higher, 18.5þ m/s). The survey,called the “Work Environment Survey” included general itemsabout the general work environment to mask the purpose of thesurvey. No study materials indicated the hypotheses of the study,in order to reduce the likelihood of demand characteristics(erroneous participant reports based on the expectation of theexperimenter). We selected survey days according to a series ofrules designed to balanced sample sizes across wind categoriesover the survey period and to minimise potential priming (expec-tancy) effects. Participants received survey invitations between2:30 and 3:00 pm. Participants received surveys in the late after-noon to ensure that potential exposure to motion was sufficient toproduce a physiological response to motion, a survey sent too earlymay produce an erroneous report of no experience symptomswhich may later develop. Participants completed the survey attheir convenience given their work commitments. The softwaretime stamped each survey, and showed that participants almost allcompleted surveys with two hours of the survey request. Thesurvey presented the six main survey pages in random order.In the Stroop Test, participants indicate the colour of a target wordby clicking on one of two options, receiving feedback after eachtrial. The survey always concluded with the closing questions andcomments section. ‘Motion perception category’ (no buildingmotion reported, ‘possible’ motion, and ‘definite’ motion) andscores on the Combined Motion Sickness Scale (CMSS) are themain independent measures in the analysis. CMSS scores are acomposite measure of both low-dose and classic symptoms ofmotion sickness taking into account the reported severity of eachsymptom. The main dependent measures are work performance(e.g. self-reported work performance), comfort (e.g. objection tomotion) and wellbeing (e.g. nausea and tiredness). Most analysesuse Multi-level Modelling (MLM) and Mixed Model Binary Logisticregression. The 1909 surveys in the current study are not inde-pendent because 100 different participants completed them.Therefore, surveys completed by the same person are likely to bemore similar than surveys completed by another individual. MLMsaccount for this problem by giving each individual their ownregression line, and comparing the slopes of the regression linesrather than creating one regression line for all data. From apractical perspective, one can largely ignore the technicality andinterpret the results like a normal regression or Analysis ofVariance (ANOVA) using the technique to demonstrate significant,or statistically reliable, differences between groups. MLMs arerobust to non-normality, data points with unbalanced samplesizes, and automatically account for missing data (Heck et al.,2010). Mixed Model Binary Logistic regression analyses assess theinfluence of one variable on a dichotomous outcome. The currentstudy uses the technique to examine the influence of buildingmotion on reported symptoms of motion sickness (“Yes”/“No”).Like MLMs, the mixed model component accounts for the cluster-ing of surveys within each study participant. All categorical dataare weighted to control for differential response rates (the numberof completed surveys), which usually resulted in small corrections.All analyses used unweighted data as MLMs automatically accountfor unbalanced data.

The analysis effectively uses two control conditions; the “con-trol condition” including 53 participants on low floors, and “base-line” (no wind/no building motion) in the experimental condition.The control condition (low floors) is primarily to establish theeffect of unpleasant weather conditions on building occupant

wellbeing and work performance. High-wind days might beassociated bad weather, or general annoyance, so participantsmight be distracted and unhappy on windy days, which we wouldotherwise misattribute to building motion. Further, without acontrol condition it is impossible to establish whether the experi-mental condition at baseline is unusual in any regard. For all otheranalyses to establish the effect of building motion of occupants,the analysis compares wellbeing and performance during baseline(no building motion/low wind) and building motion. Comparingoccupant responses from baseline to building motion is a “withinsubjects” comparison (a comparison over time), and is statisticallymore powerful than “between subjects”, or between groups(between the experimental and control conditions). Thereforethe majority of the analyses prefer the within subjects compar-isons within the experimental condition.

3. Results

On days classified as ‘high’ wind (gust speeds over 18.5 m/s),13.7% (N¼63) of participants in the experimental condition (highfloors of wind-sensitive buildings) reported ‘possible’ buildingmotion, and 23.2% (N¼107) reported ‘definite’ motion. Thus,36.8% of participants indicated perceptible wind-induced buildingmotion on high wind days. Of the participants who reportedmotion, the majority reported motion as ‘definite’, or ‘obviouslyperceptible’ (62.8%). The remainder of participants reportedmotion to be ‘possible’ or ‘barely perceptible’. The latter indicatingbuilding movement was at or near participants' threshold ofmotion perception.

Daily average gust speeds are the mean of hourly maximumgust speeds between 8 am and 6 pm for each day, which producesan estimate of the likely exposure to motion across the hours keptby most office workers. A daily average of the maximum hourlygust speeds then takes into account the distribution of motionover the whole day, which is necessary given that participantscompleted the survey late in the day in response to their overallexposure to motion. Fig. 1 shows that participants reportedperceptible building motion at significantly higher wind speeds,F (2, 802)¼72.1, po0.001, and predicted building accelerations(see Appendix A), F (2, 614.7)¼77.9, po0.001, than during base-line (no-motion conditions). Both wind speeds and predictedbuilding accelerations were significantly higher during ‘definite’than ‘possible’ building motion. Further, increases in participants'judgments of motion severity significantly correspond to increasesin wind speeds, F (1, 805)¼150.0, po0.001, and predicted accel-erations, F (1, 632)¼193.0, po0.001. Wind speeds alone do notpredict adverse occupant responses, because directional windeffects and shielding mean a high wind speed does not cause allbuildings to vibrate with equal probability. The above method,using occupant reports of motion supported by objectively mea-sured wind speeds provides the best alternative. The perception ofmotion is frequency dependent, so changes in accelerations acrossdifferent building are not directly comparable in a traditionalsingle analysis. Multilevel models control for the effects of fre-quency dependence, because all comparisons are made within-subjects (or across time), holding frequency constant. Thus, themean values are uninformative as they are values averaged acrossdifferent buildings, individuals and different frequencies. The meandifferences, however, reveal a significant and consistent trendshowing that significantly higher accelerations cause participantreports of motion compared with baseline. Together, these analysesshow that participant reports of motion are credible.

Participants rated just over a fifth of motion as ‘strong’ or ‘verystrong’, see Table 1. The reported duration of motion was onaverage longer on ‘definite’ motion days than ‘possible’ motion

S. Lamb et al. / J. Wind Eng. Ind. Aerodyn. 133 (2014) 39–5142

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days. Participants most frequently detected building motion byvestibular or proprioceptive cues (i.e. felt the sensation of motion).Auditory cues accounted for a third of reported ‘definite’ motion,and visual cues accounted for only about 10% of reported motion.

3.1. Building accelerations

Fig. 2 shows an example peak acceleration of 6.7 mg measuredin one tall building; a magnitude most occupants would likely feel.Acceleration data collected in the current study largely support theestimated accelerations calculated using Carpenter et al.'s (2013)equation, described in Appendix A. The equation provided esti-mated building accelerations as a function of wind speed acrossthe entire period of data collection.

Fig. 3 shows the maximum predicted acceleration for eachbuilding, for each survey day where participants reported ‘definite’building motion. For each of the 11 buildings, Fig. 3 shows theaccelerations plotted against the natural frequency of each build-ing, compared with the Architectural Institute of Japan (2004)curves for motion perception. 9 of the 11 predicted peak accelera-tions are clearly in a range perceptible to building occupants. Peakaccelerations in 2 buildings have an estimated magnitude wherehalf of the building occupants are likely to perceive motion. Fiveare at accelerations where approximately 30% of occupantsare likely to feel motion. In 3 cases, predicted peak accelerationsare likely to be felt by less than 10% of occupants. The majority ofstudy buildings approximated the H-30 curve, in reasonableagreement with proportion of occupants who, on average,reported ‘definite’ perceptible motion across all ‘high’ wind days(23.2%).

3.2. Symptoms of motion sickness

A series of mixed-effects binary logistic regression analyses onsymptoms of motion sickness show that at baseline, participantson high floors were no more likely to report nausea, dizziness andfeeling ‘off’ (feeling slightly unwell) than participants working onlow floors, shown in Fig. 4. This indicates that experimentalparticipants were not predisposed to any conditions associatedwith building motion, and that calm conditions in the experi-mental condition are a reliable baseline to compare acrossincreases in building motion. In the experimental condition, aMLM showed that significantly higher rates of nausea occurred

during ‘possible’ and ‘definite’ building motion than at baseline.At baseline, occupants reports of nausea were rare at 2.2% (N¼13),but increased significantly by 10% during reported buildingmotion. Of the 47 experimental participants, 25.5% (N¼12)reported nausea on at least one occasion. Dizziness was also rareat baseline, but increased significantly by 16% during ‘definite’building motion. Participants were 10% more likely to reportfeeling ‘off’ during ‘possible’ or ‘definite’ building motion than atbaseline. Note, error bar are included in all figures as they providean indication of the relative error between groups, but because thestudy used a repeated-measures design, there can be significant

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Perception of building motionNo motion Possible Definite

Perception of building motion

Fig. 1. (A) Average daily gust speeds across reported occupant perception of building motion, and (B) predicted building accelerations across occupant perception of motion.Note that predicted accelerations appear low due to the averaging across different buildings, individuals and different frequencies. Error bars represent standard error. Nomotion (N¼595), ‘possible’ motion (N¼90) and ‘definite’ motion (N¼123).

Table 1Reported strength, duration and first mode of perception of wind-induced buildingmotion across ‘possible’ and ‘definite’ motion perception in the experimentalcondition.

Motion perception category

Possiblemotion

Definitemotion

Judged strength of motion % N % N

Very mild (building motion is barely noticeable) 80.2 73 22.3 29Mild (building motion is noticeable) 14.3 13 33.8 44Moderate (building motion is easily perceptible) 4.4 4 22.3 29Strong (building motion is obvious) 1.1 1 13.8 18Very strong (building motion is unmistakable) 0 0 7.7 10Total 100 91 100 130

Reported percentage of the day that motion was reported10% 70.1 61 40.9 5220% 14.9 13 21.3 2730% 9.2 8 13.4 1740% 4.6 4 3.1 450% 1.1 1 9.4 1260% 0 0 4.7 670% 0 0 3.9 580% 0 0 2.4 390% 0 0 0.8 1Total 100 87 100 127

First mode of perceptionHeard 12.2 11 31.8 41Saw 11.1 10 7.0 9People 2.2 2 0.8 1Felt 71.1 64 60.5 78Other 3.3 3 0 0

100 90 100 129

S. Lamb et al. / J. Wind Eng. Ind. Aerodyn. 133 (2014) 39–51 43

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differences between groups despite overlapping error bars in thevarious figures (Cumming and Finch, 2005).

Tall building occupants reported significantly higher levels ofsleepiness on the Karolinska Sleepiness Scale (Akerstedt and

Gillberg, 1990) during ‘definite’ building motion than ‘possible’motion or baseline, F (2, 777.4)¼4.9, po0.001; a 15% increase inthe proportion of occupants feeling sleepy compared with baselinelevels. Participants also reported significantly greater distractionfrom work activities (losing concentration, daydreaming, takingadditional breaks) during ‘definite’ motion, F (2, 778.76)¼4.4,po0.05. Rates of other symptoms, such as headaches and impairedcoordination, were unaffected by reported building motion. Partici-pants in the control condition showed no increases in any measuredsymptoms across increases in wind speeds, therefore higher rates ofmotion sickness cannot be attributed to factors other than wind-induced building motion, for example, distraction due to weatherconditions or mood related responses to unpleasant weather.

3.3. Combined Motion Sickness Scale

The previous analysis established that there is a baselineincidence of low-dose motion sickness-like symptoms, and theseoccur with the same frequency in both the control condition andthe experimental condition during baseline. These analysesexclude the control condition, because baseline in the experimen-tal condition provides a statistically stronger comparison. Thesymptoms of motion sickness from the previous analysis wereaggregated into the ‘Combined Motion Sickness Scale’ (CMSS),reflecting the inclusion of both low-dose (tiredness, distractibility,‘off’) and high-dose symptoms (nausea and dizziness) of motionsickness. The scale weighted each symptom based on participants'judged severity of each symptom. In agreement with the previousanalyses, CMSS scores were significantly higher during perceptiblemotion (‘definite’¼2.1; ‘possible’¼1.75) than at baseline (M¼1.37),F (2, 776.7)¼21.2, po0.001. Moderate to high CMSS scores were2–3 times more likely to occur during building motion than atbaseline, shown in Fig. 5. Low-dose symptoms accounted for 80%of the variation in CMSS scores. In non-statistical terms, theanalysis shows that low-dose motion sickness (CMSS scores)occurs during building motion at a rate 2–3 times that we observeduring no building motion. With 95% certainty, the analysis showsthat the observed difference is sufficiently large that it cannot beattributed to noise, error, or the result of a small sample size.Participants reporting high CMSS scores also reported significantlylower mood, F (3, 775.0)¼36.0, po0.001, and motivation, F (3,773.8)¼39.8, po0.001. Participants considered ‘well’, based on aCMSS score of 0, reported they were moderately happy andmotivated,where participants with moderate to high CMSS scores reportedfeeling mildly unhappy and unmotivated. Mood and motivation wereunaffected by reported building motion alone, indicating that motionsickness caused these psychological effects.

3.4. Work performance

Two MLMs examined each of the three measures of workperformance; one to determine the effects of perceptible building

-8

-6

-4

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0

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4

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8

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

Acc

eler

atio

n (m

illi-g

)

Time (sec)

Fig. 2. An example of a large acceleration trace from a study building showing a peak acceleration of 6.7 mg on one axis of the building at 0.45 Hz.

0.1

1

10

100

10.1

Peak

acc

eler

atio

n (m

illi-g

)

Frequency (Hz)

H-90

H-70H-50H-30

H-10

Fig. 3. Predicted peak accelerations in 11 study buildings compared to theArchitectural Institute of Japan (2004) curves estimating the proportion ofoccupants who will perceive frequency dependent peak accelerations.

0

10

20

30

40

50

60

70

feeling ‘off’Nausea Dizziness Generally Distracted Tired

Perc

enta

ge o

f res

pond

ents

(%)

Symptom of motion sickness

Control

Experimental -No motion perceived

Experimental - 'Possible' motion

Experimental - 'Definite' motion

Fig. 4. The frequency of reported symptoms of motion sickness across reportedperception of motion in the experimental condition compared with the controlcondition. Error bars represent 95% confidence intervals.

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motion, the second to investigate the effects of CMSS scores on workperformance in the experimental condition. In model 1, motionperception category, F (2, 782.2)¼3.1, po0.05, and time in the office,F (1, 705.3)¼15.6, po0.001, both significantly affected self-reportedwork performance, shown in Table 2. Self-reported work perfor-mance was significantly lower during ‘definite’ building motion,compared with ‘possible’ motion and baseline. In Model 2, theinclusion of CMSS scores caused motion perception category tobecome non-significant, because CMSS scores accounted for variancepreviously explained by motion perception. Model 2 thereforeexcluded motion perception. Model 2 showed improved modelcharacteristics over Model 1, indicated by a lower Schwartz Bayesian

Criterion. These analyses indicate that building-motion inducedmotion sickness explains the decrease in work performance.

Fig. 6 shows that as CMSS scores increase, work performancesignificantly decrease, F (3, 802.8)¼32.1, po0.001. Low CMSSscores correspond to above average work performance and higherCMSS correspond to average performance. The effect size of theperformance reduction, comparing the two extreme responses,was large at 0.91 (Cohen's d); indicating a performance reductionof almost one standard deviation. Other measures of work perfor-mance, absolute judgments of work performance and a 10-itemwork performance scale, showed the same significant trends(Table 2), although these models exhibited slightly higher

0

10

20

30

40

50

60

70

No symptoms Low Medium High

Prop

ortio

n of

par

ticip

ants

(%)

CMSS category

No motion perceived

Possible motion

Definite motion

Fig. 5. Combined Motion Sickness Scale (CMSS) scores across category of motionperception in the experimental condition

3

3.5

4

4.5

5

5.5

6

6.5

7

No effects Low Moderate High

Self-

repo

rted

wor

k pe

rfor

man

ce

CMSS score category

Averageperformance

Fig. 6. The effect of CMSS scores on self-reported work performance compared toaverage in the experimental condition. The scale mid-point of 5 reflects ‘average’work performance, with higher scores indicating above average performance. Errorbars represent standard error. No effects (N¼336), low (N¼344), moderate(N¼105), high (N¼20).

Table 2The effect of reported building motion, CMSS scores and time in the office on work performance compared to average, absolute performance and the work performance scalein the experimental condition.

Parameter Work performance compared to average Absolute performance (% effort) Work performance scale (10 items)

Model 1 (Est.) Model 2 (Est.) Model 1 (Est.) Model 2 (Est.) Model 1 (Est.) Model 2 (Est.)

Fixed effectsLevel 1 (within subjects)

Intercept 3.47 (0.17)nnn 2.76 (0.47)nnn 4.38 (0.34)nnn 4.03 (0.40)nnn 46.26 (1.27)nnn 44.22 (1.47)nnn

Motion perception categoryNo motion 0.41 (0.17)n 0.43 (0.15)nn 1.44 (0.54)Possible 0.49 (0.24)n 0.32 (0.20) 0.48 (0.75)nn

Definite 0a 0a 0a

Time in office (hrs) 0.20 (0.05)nnn 0.19 (0.05)nnn 0.20 (0.04)nnn 0.18 (0.04)nnn

CMSS scoresNo symptoms 2.18 (0.38)nnn 1.90 (0.32)nnn 8.14 (1.14)nnn

Low 1.38 (0.37) nnn 1.15 (0.31)nnn 4.80 (1.12)nnn

Medium 0.50 (0.39) 0.11 (0.32) 1.45 (1.17)High 0a 0a 0a

Random parametersLevel 2 (between subjects)

Residual 2.69 (0.14)nnn 2.34 (0.12)nnn 1.90 (0.01)nnn 1.62 (0.08)nnn 25.55 (1.33)nnn 21.20 (1.10)nnn

Intercept 0.26 (0.09)nn 0.36 (0.10)nnn 0.44 (0.12) 0.44 (0.11)nnn 7.70 (1.93)nnn 7.05 (1.74)nnn

Schwartz's Bayesian Criterion 3084.3 2985.0 2839.2 2713.6 4899.7 4742.5Pseudo-R2 0.09nnn 0.16nnn 0.11nnn 0.22nnn 0.11nnn 0.25nnn

Note: Standard Error in parentheses.a 0 estimates represent the reference category.n po0.05.nn po0.01.nnn po0.001.

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pseudo-R2 values, explaining more variation in the data. Partici-pants indicated an awareness of adverse building motion effects.Increases in the judged severity of motion, F (1, 206.0)¼8.2,po0.01, and CMSS scores, F (1, 189.3)¼11.8, po0.001, causedparticipants to report higher levels of building-motion-induceddisruption to their work.

3.5. Task performance

Some participants reported office disruptions during the Strooptest, causing artificially high mean reaction times for some trials. Thelongest 5% (N¼40) of mean reaction times were excluded. Meanaccuracy on the Stroop Test was high at 98.3% correct (SD¼3.63). Tocontrol for the interaction between speed and accuracy scores,reaction times were reverse scored and standardised into z-scoresand combined with standardised accuracy scores. Higher scoresindicate low reaction times and high accuracy. Participants affectedby motion sickness also showed significantly lower standardizedspeed / accuracy scores on the Stroop Test (Stroop, 1935), F (2,724.2)¼3.7, po0.05, shown in Fig. 7. The effect size of the perfor-mance reduction was moderate at 0.34, comparing high CMSS scoresto no symptoms. During perceptible building motion, not accountingfor CMSS scores, participants showed significantly improved perfor-mance during building motion compared with baseline, F (1, 734.5)¼6.1, po0.05.

3.6. Perception of the work environment

At baseline, participants judged their office environment asacceptable, but as CMSS scores increased, F (1, 199.5)¼14.1,po0.001, or the judged severity of building motion increased,F (1, 185.7)¼19.9, po0.001, participants indicated a significantpreference to move to another work location (e.g. work fromhome). During reported motion, 36.1% of participants preferred tomove to a different work location. Participants judged more severemotion as significantly more unpleasantness, F (1, 185.3)¼41.6,po0.001. Participants' objection to building motion also increasedwith motion severity, F (1, 181.3)¼19.2, po0.01, and CMSS scores,F (1, 193.9)¼7.9, po0.001 (see Table 3). Overall, 65.2% of respon-dents rated motion in the ‘acceptable’ half of the scale, 20.5% ratedmotion as ‘not sure/neutral’, and only 14.3% rated it in the‘objectionable’ half of the scale. Despite the aversive effects ofbuilding motion, participants rarely objected to motion, suggesting

that occupants adapt to uncomfortable environmental conditions,and/or underestimate the negative effects of motion.

3.7. Compensatory behaviours

Time spent outside the office was significantly affected byMSSQ scores, F (1, 42.7)¼7.1, po0.05, and CMSS scores, F (1,786.0)¼4.48, po0.05, in the experimental condition. No signifi-cant effect of motion perception category was observed, F (2,773.5)¼1.3, n.s. Individuals with high CMSS scores spent signifi-cantly longer periods outside the building on average (67 min),46% longer than those who reported no symptoms (46 min).However, only participants in about 6% of cases reported highCMSS scores. The mean lunch period was 39.3 min (SD¼24.3),unaffected by any factor. This indicates that the previouslyreported time spent outside of the office building occurred outsideof participants' lunch breaks.

Separate MLMs examined the effect of time outside the officefor each category of motion perception, to examine the potentialeffects of MSSQ scores on break times. No significant relationshipwas found between MSSQ scores and time outside of the buildingat baseline, F (1, 45.3)¼3.9, n.s., or during ‘possible’ buildingmotion, F (1, 31.6)¼2.1, n.s. During ‘definite’ building motion, thosewith higher MSSQ scores spent significantly longer periods outsidetheir building, F (1, 27.3)¼6.2, po0.05. Those in the lowestquartile of MSSQ scores spent an average of 44.6 min (SD¼34.2)outside their building at baseline, unaffected by building motion.Those in the highest quartile of MSSQ scores spent a mean of48.9 min outside their building at baseline, which increasedsignificantly to 63.9 min (SD¼49.1) during ‘definite’ buildingmotion. Therefore, those in the highest quartile of MSSQ scoresspent an additional 15 min (or 31% longer) outside their buildingduring ‘definite’ motion. No significant relationship was foundbetween time outside of the office and MSSQ scores in the controlcondition, F (1, 47.2)¼0.94, n.s.

Only one participant reported motion sickness tablet use,which occurred during ‘possible’ building motion judged ‘mild’.Fig. 8 shows analgesic medication (painkillers) use increasessignificantly as CMSS scores increase (mixed-effects binary logisticregression; estimate¼2.36, po0.001). Nearly 5% of participantsreporting no CMSS symptoms used analgesic medication, increas-ing to 33.3% with high CMSS scores.

3.8. The estimated proportion of adversely affected occupants

The final analysis estimates the proportion of building occupantsthat experience the types of adverse effects reported above. Thefollowing analysis estimates the probability of occurrence and thelikely proportion of occupants affected on a high-wind day in Well-ington, shown in Table 4. On high-wind days, 13.7% of occupantsreport ‘possible’ motion and 23.2% of occupants report ‘definite’motion. On these days, a certain proportion of these occupants willalso report moderate to high CMSS scores. However, a certainproportion of these symptoms will occur on a given days for reasonsother than building motion. As an estimate of the baseline level, weuse reported rates of CMSS scores on low-wind (no motion) days.Almost 80% of all reported wind-induced motion occurred on ‘high’wind days, with mean daily wind speeds over 18.5 m/s. We comparethe expected rate with the actual rate that occurs on high wind days.The adjusted rated, shown in Table 4, shows the residual ratecompared with baseline, which we can attribute to building motion.We can therefore expect a 9.9% increase in moderate to high CMSSscores during ‘possible’ motion and a 17.3% increase during ‘definite’motion. Across all high wind days, we can then expect an overallincrease of 1.4% during ‘possible’ motion (13.7�0.099) and 4.0%during ‘definite’ motion (23.2�0.173), a total increase of 5.4%.

-0.6

-0.4

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0.2

0.4

0.6

No effects Low Medium High

Stan

dard

ised

spe

ed /

accu

racy

Str

oop

sco

res

CMSS score category

0

Fig. 7. Standardised speed/accuracy scores on the Stroop Test across CMSS scorecategory. Error bars represent standard error. No effects (N¼336), low (N¼344),moderate (N¼105), and high (N¼20).

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Based on the Wellington wind record for the last 20 years,high-wind conditions (over 18 m/s) occur on 23% of days (NZMetservice, 2013). Based on the characteristics of the currentsample, and the observed wind speeds, 5.4% of office workersin Wellington would suffer low-dose motion sickness anddisplay a significant performance impairment on 53 work daysa year.

4. Discussion

The current study shows that building motion has a largereffect on occupants than previously understood. Building motioncan significantly reduce work performance by almost one standarddeviation in occupants experiencing motion sickness. Other influ-encing factors cannot explain the observed effects. In the controlcondition, the results showed no variation in the main dependentmeasures across wind conditions. Nor can the observed effects beattributed to sample characteristics, as the experimental andcontrol conditions were matched on susceptibility to motionsickness, and the groups did not significantly differ on anysymptoms at baseline. Therefore the observed reduction in workperformance must be attributed to the effects of building motion.Susceptible occupants attempted to minimise their discomfort bytaking medication and longer breaks. The study shows thatbuilding motion is not a benign environmental factor and canrepresent a significant problem for building owners and designers.

4.1. Low-dose motion sickness

Motion sickness was 2–3 times more likely to occur duringreported motion than at baseline. In the observed range ofaccelerations, the majority of reported symptoms (80%) wereassociated with sopite syndrome, including tiredness, low motiva-tion, low mood, feeling generally unwell, more common thanclassic symptoms of nausea and dizziness. This supports Waltonet al.'s (2011) theory that building motion is more likely to causelow-dose motion sickness than classic motion sickness due to therelatively low accelerations that occur in tall buildings. Individualsymptoms of low-dose motion sickness are common and can occur

0

5

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15

20

25

30

35

40

No effects Low Medium High

Perc

enta

ge o

f par

ticip

ants

(%)

CMSS score category

Fig. 8. The proportion of respondents who reported taking analgesic medicationacross symptoms of low-dose motion sickness in the experimental condition. Errorbars show 95% confidence intervals. No effects (N¼15), low (N¼35), moderate(N¼18), and high (N¼7).

Table 3The effect of strength of motion and CMSS scores on rated unpleasantness of motion, judged effect on work performance, preference to move to another workspace, andobjection to motion in the experimental condition.

Unpleasantness Effect on work Move preference ObjectionParameter Estimate Estimate Estimate Estimate

Fixed effectsLevel 1 (within subjects)

Intercept 4.47 (0.26)nnn 5.35 (0.15)nnn 2.86 (0.38)nnn 1.56 (0.37)nnn

Strength of motion 0.54 (0.08)nnn �0.16 (0.06)nn 0.36 (0.10)nnn 0.48 (0.11)nnn

CMSS score 0.04 (0.07) �0.15 (0.04)nnn 0.53 (0.12)nnn 0.25 (0.09)nn

Random parametersLevel 2 (between subjects)

Residual 1.52 (0.17)nnn 0.76 (0.08)nnn 2.94 (0.32)nnn 2.36 (0.26)nnn

Intercept 1.35 (0.39)nnn 0.10 (0.06)nnn 2.52 (0.70)nnn 2.85 (0.73)nnn

Schwartz's Bayesian Criterion 766.0 575.4 899.2 867.2Pseudo-R2 0.11nnn 0.12nnn 0.12nnn 0.12nnn

Estimated marginal meansStrengtha

Mild 5.25 (0.20) 4.80 (0.12) 4.43 (0.33) 3.01 (0.33)Moderate 6.18 (0.30) 4.32 (0.19) 5.62 (0.47) 4.04 (0.44)Strong 6.59 (0.33) 4.41 (0.20) 5.74 (0.48) 3.84 (0.45)

CMSS scaleb

No effects – 4.81 (0.14) 4.60 (0.37) 3.07 (0.36)Low – 4.72 (0.12) 4.81 (0.33) 3.05 (0.33)Moderate – 4.18 (0.16) 5.63 (0.42) 3.62 (0.40)High – 4.32 (0.34) 6.02 (0.76) 4.79 (0.70)

Note: Standard error in parentheses.npo0.05

a Mild (N¼157), moderate (N¼31), strong (N¼27).b No effects (N¼336), low (N¼344), moderate (N¼31), high (N¼27).nn po0.01.nnn po0.001.

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for reasons other than building motion (Graybiel and Knepton,1976) which may lead building occupants to attribute thesesymptoms of motion sickness to factors other than buildingmotion, such as normal work stress and fatigue.

4.2. Work performance

Susceptibility to motion sickness moderates the effect of buildingmotion on reported symptoms of motion sickness (Lamb et al., 2013),and the current study shows that motion sickness mediates the effectof building motion on work performance, shown by both subjectiveand objective measures. Participants' self-reported work performancewas significantly lower during reported building motion than atbaseline. Increases in CMSS scores, or motion sickness, explain thedecrease in performance scores. Non-motion sick participants reportabove average work performance, moderate to high levels of motionsickness cause work performance to drop below average. The 5.8% ofparticipants who report high CMSS scores showed a performancereduction of almost one standard deviation. Moderate CMSS symp-toms occurred more frequently, in 24.8% of cases, causing a smaller,but still large decrease in performance of just over three-quarters of astandard deviation. Taking into account the base-rate of low-dose-likesymptoms of motion sickness, we estimate that on high-wind days inWellington, 5.4% of tall buildings occupants on high floors willexperience low-dose motion sickness, which has a large adverse effecton their work performance. Such a performance deficit is likely tooccur on 53 work days a year. However, other factors were notincluded in the analysis that may underestimate the cost of buildingmotion to organisations. The estimates are based only on perceptiblemotion, and some occupants may be affected by motion below thethreshold of perception. Other factors including lost productive timefrom taking longer breaks, increased turnover, potential long-termeffects, employee dissatisfaction, sick days and other flow-on effectswere not included in the estimates of degraded work performance,which may further increase the cost to organisations. These estimatesare an average effect based on the reported effects of motion across 17different buildings, therefore occupants in more wind-susceptible

buildings might show a relatively larger effect. We argue that thisrepresents a substantial problem for occupants, organisations andbuilding owners/designers. The maximum observed wind speed wasonly 75% of a one-year return period, therefore the observed effectsare likely a conservative estimate of the potential adverse effect ofbuilding motion on occupants. Objective performance measuressupported the participants' self-reported performance. Increases inCMSS scores corresponded to significantly lower speed/accuracyscores. High CMSS scores lowered performance by 0.34 standarddeviations, and moderate CMSS scores by a smaller factor of 0.13standard deviations. Lan et al. (2011) found a similar trend, wherereaction time and accuracy on the Stroop Test decreased whenparticipants felt uncomfortably warm, leading to a 9.5% increase inreaction times. Sleep deprivation can also reduce accuracy andreaction times on the Stroop Test (Cain et al., 2011). Given thatbuilding motion induced higher levels of tiredness in this study,tiredness likely contributes to the performance reduction. Buildingmotion had a larger effect on self-reported work performance than theStroop Test performance. The Stroop Test took less than one minute tocomplete, so participants likely increased their concentration andeffort for that short period. Self-reported performance evaluatedperformance across the whole day, and is likely a more reliablemeasure of ‘true’ performance than simple accuracy and reactionmeasures. Motion sickness caused a decrease in work performance,shown by both objective and subjective measures.

In one of the few field-studies to investigate sopite syndrome,Wright et al. (1995) show that sopite syndrome affects two-thirds ofemergency workers who travel to accident sites by helicopter orambulance; three-quarters of those affected by the syndrome show asignificant reduction in cognitive performance. Environmental stressfactors have been shown to reduce performance, such as thermaldiscomfort (Lan et al., 2010), understood to increase demands onworkers' attention and their ability to concentrate, which subsequentlylowers work performance. Motion sickness is considered a ‘stress’placed on occupants, that likely increases demands on workers'cognitive reserves, attention, or ability to concentrate, which subse-quently can reduce work performance (e.g. Hocking et al., 2001;

Table 4The probability of perceiving building motion across wind speed category, with estimates of the probability of occurrence of each wind speed category and the estimatedproportion of building occupants with reduced work performance.

Wind category

Low (0–8.9 m/s) Medium (9–18.4 m/s) High (18.5þm/s)

% N % N % N

No perceived motion 91.8 146 83.2 158 63.1 291Possible motion 4.4 7 11.1 21 13.7 63Definite motion 3.8 6 5.8 11 23.2 107

100.0 159 100.0 190 100.0 461

Probability of occurrence 0.32 0.46 0.23Estimated days per year (365) 115.3 167.4 82.3Estimated working days per year (236) 74.5 108.2 53.2

Expected rate(low-wind category)

Actual rate(high-wind category)

Adjusted rate(actual – expected)

Perception of motion CMSS scores by motion perception % N % N (%)

Possible motion No symptoms 41.5 31.7Low 46.3 46.0Medium 11.6 22.2 þ10.6High 0.7 0.0 �0.7Total 100.0 100.0 þ9.9

Definite motion No symptoms 41.5 28.6Low 46.3 41.9Medium 11.6 22.9 þ11.3High 0.7 6.7 þ6.0Total 100.0 100.0 þ17.3

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Vischer, 2007; Lan et al., 2010;). Burton et al. (2004) reported increasedtask distraction in a motion simulator study, supporting these findings.

The observed effects show that building motion-inducedmotion sickness causes the reduction in work performance ratherthan other potential causes, such as vibration-induced disruptionto tasks. Building motion did not cause all participants to becomemotion sick, and work performance was undisrupted in those whodid not report motion sickness. At least in the range of observedaccelerations and frequencies, building motion has a smaller directeffect (e.g. vibration interference to tasks) on work performancethan the effects of motion sickness. Although, given the majority ofparticipants reported their occupations as manager or administra-tion, most of their daily tasks involved computer work, meetings,and other typical office activities rather than specialised tasks thatrequired fine motor control such as surgery or assembly tasks.

Drawing on studies of ship motion and performance, Wertheim(1998) suggests that motion-induced performance impairment ismostly due to motion sickness-induced reductions in motivation,balance and fatigue. Wertheim (1998) does suggest that motionmight affect “mental load”, as in stress models such as thermalcomfort (e.g. Lan et al., 2010) or general environmental stressfactors (e.g. Vischer, 2007). Recent studies support this hypothesis,as cognitive performance deteriorates while performing balancetasks, suggesting that balancing may compete with other cognitivetasks, causing a performance reduction (Anderson et al., 1998; Mayet al., 2009; Chong et al., 2010; Mersmann et al., 2013). It isunknown whether low accelerations, characteristic of tall build-ings, are sufficient to present a significant challenge to balance,especially office workers usually sit for the majority of the work-day, reducing demands on posture.

In contrast to the current study, previous research has foundlimited evidence for the adverse effect of motion on performance(Jeary et al., 1988; Morris et al., 1979; Denoon et al., 2000; Burtonet al., 2004, 2011). Experimental studies may inadvertently pro-duce symptoms that are rare in actual buildings. These studiesoften induce high rates of nausea, by exposing participants to highaccelerations for a short period. In one such study, a third ofparticipants asked to leave the simulator at nausea-producingfrequencies (Burton et al., 2005). These studies may induce high-dose symptoms where low-dose symptoms are more common inactual tall buildings undergoing low accelerations. The currentstudy demonstrates that field studies are necessary to ensure thatexperimental studies do not produce misleading results.

Against expectations, participants who reported ‘definite’building motion showed higher accuracy and lower reaction timeson the Stroop Test than at baseline. Burton et al. (2004) also foundthat those who reported motion in a simulator study showedimproved performance on standardised tests. The tempting inter-pretation, as suggested by Burton et al. (2004), is that low-levelmotion can have an enhancing effect on work performance. Underconditions of thermal stress, Lan et al. (2011) found that partici-pants increased their effort to maintain performance. Similarreactions may occur during building motion, as individualsattempt to complete a task quickly so they may then reducedemands on their concentration.

4.3. Tolerance, complaint and wellbeing

Since the 1970s, researchers have adopted a simple model ofoccupant behaviour assuming individuals have a ‘tolerance’ formotion, once exceeded, may result in occupant complaint to buildingowners (Hansen et al., 1973). Reported objection to motion was low inthe current study (in 14.3% of surveys during building motion), andparticipants reported no instances of complaint to owners, supportingother studies showing that complaint is rare (Burton, 2006, Lamb etal., 2013). Some occupants may feel constrained in their ability to

complain to building owners or their employers (Lamb et al., 2013),and/or the adaptability of humans is such that they tolerate environ-mental stressors or use strategies to compensate for those stressors. Inthe current study, occupants took longer breaks, likely an attempt toreduce their exposure to motion. Up to 35% of occupants also self-medicated using analgesics, which are likely to have a minimal effecton symptoms of motion sickness. During the current study period, noparticipants reported leaving their office to work at another location,although a third reported a preference to move to a different worklocation (e.g. work from home) during reported building motion. Thatproportion was 2.5 times the reported level of objection, indicatingoccupants have a high tolerance for motion, or are simply unable toleave their office environment.

Wind-sensitive buildings do not provide an environment con-ducive to employee wellbeing. Participants judge building motionto be unpleasant, indicate a preference to leave the work environ-ment, take longer breaks and report symptoms of motion sickness.Studies of human factors consistently find that humans adapt topoor design, though inadequate design limits performance poten-tial (Noyes, 2003). Building occupants likely adapt to buildingmotion (not to be confused with habituate), continuing theirresponsibilities in a sub-optimal environment, albeit at lowerlevels of performance. This provides a potential explanation forconsistently low rates of occupant complaint about motion(Burton, 2006; Lamb et al., 2013). These results have broaderimplications for design, as the adaptability of humans in responseto environmental stress may mask general design inadequacies,for example, temperature, noise and poor office layout. From anergonomic perspective, the criteria for optimal design should notbe to maintain environmental stressors within a tolerable range,instead to reduce environmental stressors on performance andwellbeing.

4.4. The perception of motion and sub-perception effects

While studies have proposed that building motion below thethreshold of perception may affect occupants, there has been noevidence to support the hypothesis (Hansen, et al., 1973; Morriset al., 1979; Jeary et al., 1988). Stoffregen et al. (2010) showed thata moving room oscillating at imperceptible accelerations inducesmotion sickness in some individuals, which could plausibly occurin building occupants. In the current study, a high proportion ofmotion was reported as ‘possible’ or ‘barely perceptible’ (42.5%),indicating that accelerations were at or near the threshold ofperception. Rates of nausea (12–13%), feeling dizzy (15–22%) andfeeling ‘off’ (27–30%) did not differ significantly regardless ofwhether motion was reported as ‘possible’ or ‘definite’, all ofwhich were significantly higher than at baseline (2%, 6%, and 18%respectively). This evidence suggests that imperceptible buildingmotion may affect building occupants. Future studies couldaddress the possibility.

4.5. Serviceability criteria/future research

Motion sickness is a normal response to unusual environmentalconditions. With the exception of 5% of individuals, either highlysusceptible or immune, all humans are capable of experiencingmotion sickness. Rough seas can cause even experienced sailors toexperience motion sickness (Reason and Brand, 1975). The pro-blem then for serviceability criteria is to determine the ‘dose’ atwhich occupants become sick, and how individual factors mediatethe dose, such as susceptibility to motion sickness. The dose islikely a complex interaction of the frequency, severity and dura-tion of building motion.

The Architectural Institute of Japan (2004)/ISO/FDIS 10137: 2007(E)(International Organisation for Standardisation, 2007) provide the

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most conservative set of acceleration criteria. Both are based on thelevel at which 90% (H-90; Architectural Institute of Japan, 2004) ofoccupants are likely to perceive motion during a wind event with aone-year return period event, leaving a comfort factor to the discretionof the building designer. Both criteria then base their design standardon the point where most people will perceive motion. However, belowthat the 90% threshold, a significant proportion of occupants will havealready perceived motion and likely suffered the associated effects.Most of the effects observed in the current study occur around ataround H-30 to H-50. Duration effects may partly explain the reportedsymptoms observed at relatively low accelerations. Building motionresearchers have not adequately studied the interaction between thestrength and duration of motion. The current study, and the motionsickness literature generally, would suggest that short durationexposure to high acceleration motion would cause nausea in mostindividuals, but long duration exposure to low acceleration motionwould likely cause low-dose motion sickness in most individuals andonly cause nausea in the most sensitive individuals (e.g. Graybiel andKnepton, 1976; Reason and Brand, 1975). This evidence suggests thatmotion can adversely affect occupants at lower accelerations thanpreviously understood. Future research could determine the doseacross the spectrum of accelerations that are likely to occur in tallbuildings.

While the average floor of participants in the experimentalcondition appears low at 15.8, these are applicable to taller build-ings. Due to Wellington's high earthquake risk, buildings designersallow greater structural flexibility than in other regions of NewZealand. Taller building will show greater deflection than shorterbuildings, so we would expect to observe similar trends in othercountries, and expect the effects to occur on higher floors, holdingall other variables constant. The results presented here are likely aconservative estimate of the occupant response to motion, becausetaller buildings with lower natural frequencies, below about 0.4 Hz,are more likely to induce motion sickness. We might expect toobserve more motion sickness and less sopite syndrome, dependingon building acceleration and the duration of exposure to motion.

4.6. Limitations

Across the study period, the maximum observed wind speedonly reached 75% of the one-year return period for wind speeds inWellington. Wind speeds at or near the one-year return periodoccurred, but outside of standard office hours. These findings thenindicate a conservative estimate of the potential for the adverseeffects of building motion. A future study might measure buildingaccelerations in a small sample over a long period to determinethe motion dose that produces the effects reported in the currentstudy and investigate the effects of imperceptible accelerations.The current sample over-represented females. While, the experi-mental and control conditions were balanced across gender, theimbalance may over-represent susceptibility to motion sickness, asfemales on average have higher MSSQ scores (Golding, 2006). Thebias only influences the proportion of individuals affected, not themagnitude of the effect on wellbeing or work performance.

5. Conclusions

Previous research has focused on the immediate or direct effects ofmotion: perception and task performance. The current research showsthat the effects of building motion are emergent, as motion sicknessdevelops after a duration of exposure to motion, which mostlymanifests as symptoms of sopite syndrome, including tiredness, lowmotivation, distraction from work activities, and low mood. Duringbuilding motion, participants report these symptoms at 2–3 times thebaseline rate. As participants report higher levels of motion sickness,

work performance significantly decreases by 0.76–0.90 standarddeviations below baseline performance. That performance reductionsare limited to those experiencing motion sickness, suggests that director immediate effects of motion, such as vibration interference withtasks, has a minimal effect at low accelerations. Work performancereductions were supported by both subjective measures of self-reported work performance and objective measures of task perfor-mance on the Stroop Test. Participants judgedmost building motion asunpleasant, but despite this and other effects on comfort, only 14% ofparticipants judged motion as objectionable, which suggests that mostoccupants have a reasonably high tolerance for motion. Affectedindividuals attempt to manage their own discomfort, and indicate apreference to work a different location during motion, take 30–40%longer breaks, and attempt to self-medicate using analgesic medica-tion.

The rate of tall building construction is increasing (Council on TallBuilding and Urban Habitat, 2013), and these buildings are inherentlywind-sensitive due to their height, slender designs, and lightweightmaterials. Further, they have low natural frequencies, which are morelikely to provoke motion sickness (Guignard and McCauley, 1990), andare exposed to higher wind speeds due to their height. While buildingoccupants tolerate, or adapt to motion, wind-excited buildings do notprovide a healthy or productive work environment. Humans areadaptable, allowing most occupants to continue their activities, butat reduced levels of work performance and comfort. The designcriteria for tall buildings should be to minimise the environmentalstress of building motion on work performance and wellbeing. Thechallenge for future research is the quantification of the dose ofmotion that causes adverse affects in occupants. Robust designstandards for building motion will reduce the likelihood that futurebuildings undergo unacceptable accelerations adversely affect buildingoccupants.

Acknowledgements

The research reported in this paper was supported underAustralian Research Council's Discovery Projects funding scheme(Project DP1096179). The views expressed herein are those of theauthors and are not necessarily those of the Australian ResearchCouncil. The authors acknowledge the assistance of Prof. VaughanMacefield, Prof. Nigel Bond and Sarah Lamb.

Appendix A

Carpenter et al. (2013) proposed a formula to estimate buildingaccelerations from wind speeds accounting for the natural fre-quency, density and floor plan area of a building. Carpenter et al.'s(2013) equation includes wind speed and structural parameters forbuildings not known to exhibit significant wind-induced motion.Test buildings in the current study are known for their wind-sensitivity, based on known episodes of perceptible wind-inducedmotion. The following equation was found to provide moreaccurate predictions of wind-induced building motion (see Lamb,2014):

a¼ 0:148V3

fm0

where: a¼peak resultant acceleration (m/s2), V¼Maximum hourlygust speed (m/s), f¼fundamental frequency (Hz), m0¼building massper unit height¼ρbA, ρb¼building density (kg/m3), A¼building planarea (m2).

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