197

Urban Habitat Constructions under Wind Catastrophic Events
Ted STATHOPOULOS1*, Charalambos C. BANIOTOPOULOS2 and Ioannis ZISIS1
1

Centre for Building Studies
Dept. of Building, Civil & Environmental Engineering, Concordia University
1455 de Maisonneuve Blvd. West, Montreal, QC, H3G1M8, Canada
2
Dept. of Civil Engineering, University of Thessaloniki
Institute of Steel Structures, 54124, Thessaloniki, Greece*e-mail: statho@bcee.concordia.ca

Abstract
The paper discusses the implications of natural disasters due to extreme wind events on urban habitat
construction and introduces Action-C26, a joint effort among European academic institutions under theEuropean Cooperation in Science and Technology (COST) program. With several activities, Action-C26
aims at assessing the risk for catastrophic events in urban areas. In this context, a proposed framework forrisk-based decision making is presented and used to physically model the case of a typhoon. Furthermore,critical components of such models are discussed in detail, including particularly the case of a full-scale
study that involves wind and structural monitoring of a low building. Typical results from this study are presented and their integration with the risk assessment model is discussed.
Key words: habitat construction, risk assessment, wind extreme events, wind load paths

1. Introduction
Increased public concern regarding global environmental change in the past decade made researchers fromvarious disciplines to become aware of their social
responsibility. Unfortunately, the scientific community
realized in a rather tragic way the severity of the situation in the aftermath of several catastrophic natural
disasters occurred in the recent past. Some of the mostfatal and costly of these events were the result of
extreme wind incidents. Hurricanes, typhoons and tornadoes were reported and tracked around the globe. The
social and economic impact associated to these natural
disasters initiated a drastic response from a number ofpolitical and academic institutions.

2. European Cooperation in Science andTechnology (COST)
The European Cooperation in Science and Technology (COST) is a joint European research initiative with
36 participating countries. This program has as main
objective to advance scientific technical research in theEuropean domain and support cooperation among
participating countries. Moreover the access to institutions from non-members countries encourages aninternational research interaction between Europe andother scientifically developed regions. The COST program consists of nine key domains but Transport &Global Environmental Research
13/2009: 197-202
printed in Japan

Urban Development (TUD) is of particular interest
given that is dedicated to research activities related totransport systems and infrastructures, urban land use anddevelopment, architecture and design, as well as othercivil engineering issues. Among the several activities
within the TUD domain is Action-C26 entitled “Urban
Habitat Constructions under Catastrophic Events”. The
main objective of the Action-C26 is to advance research
related to the behaviour of constructions under catastrophic events (i.e. earthquakes, fire, wind etc.). The principle behind this Action is that urban habitat constructions
can be exposed to unforeseen extreme loading events
such as severe weather conditions and natural or
man-made hazards. The response of constructions tosuch extreme conditions is a major concern andAction-C26 participating members have as main focus
to increase the knowledge from the carried out researchon this particular matter. There are four distinct technical working groups within the action assigned to study
the following subjects: fire resistance (Working Group1), earthquake resistance (Working Group 2), impact
and explosion resistance (Working Group 3) and risk
assessment for catastrophic scenarios in urban areas(Working Group 4). The first three working groups havebeen assigned specific catastrophic scenarios whereas
the fourth group aims at developing a common methodology for decision making based on risk assessment thatwould be also applicable as a procedural guideline to theother groups. The suggested methodology can be©2009 AIRIES198

T. STATHOPOULOS et al.

applied to any natural catastrophic events and a casestudy of extreme wind events such as hurricanes,
typhoons and tornadoes is demonstrated briefly herein.

3. Framework for Risk-Based Decision
Making
The process of risk-based decision making using anengineering modelling approach includes the following
five fundamental stages (Faber, 2008): preferences (aimand purpose), consequences (states of marginal utility),
uncertainties (aleatory and epistemic), temporal andspatial variations/dependencies and options for decision
making. An unexpected catastrophic event will have anumber of consequences that are generated as thesystem changes and as the society reacts to the new
system conditions. The uncertainties involved in such
events reflect directly on the process of decision making
and need to be considered. A generic risk assessment
Bayesian framework proposed by Nishijima and Faber(2007) considers the exposure, the vulnerability and therobustness to generate risk indicators for the risk-based
decision making. The Bayesian approach allows realtime updating of the model using information extracted
during the development of, say a typhoon event. In moredetail, there are three separate phases involved in suchrisk management frameworks: before, during and after.
The first phase uses information available prior to theevent, whereas the other two phases incorporate more
precise knowledge derived for the specific event. A
graphical example of these three phases is presented inFig. 1 where the different level of information is used torefine the risk management model.
The physical modeling of the typhoon event in the
proposed model involves five separate sub-models thatinteract with the previously mentioned information extracted during the typhoon phases (Fig. 2). The typhoon
model is based on several sub-models related to occurrence, transition, wind field, surface friction andvulnerability. The initial development of these models isbased on knowledge available prior to the catastrophic
wind event and as the hazard starts to develop, themodels are updated with additional information.

4. Structural Failure and Prevention during
Catastrophic Wind Events
Urban habitat constructions (e.g. low-, medium- andhigh-rise buildings) are prone to excessive damage during extreme wind events. Rapid climatic changes are
sometimes accountable for some of these destructive
natural phenomena. The proposed risk assessment andFig. 1 Risk management model refinement during typhoon phases (after Nishijima and Faber, 2007).

Fig. 2 Representing the event of typhoon using the generic risk assessment framework(after Graf et al., 2008 and Nishijima and Faber, 2009).

Urban Habitat Constructions under Wind Catastrophic Eventsdecision making models need to be integrated andadjusted to the specific characteristics of both the structure and the wind event.
4.1 Wind nature and climatology
A motion of an air mass is well known as wind. Of
greater interest for engineers are wind characteristics
within the atmospheric boundary layer, which is actuallyextended up to a few kilometres over the surface ofearth. Current wind building codes and standards (e.g.
ASCE/SEI 2005) have adopted the so called power law
or log law to describe the wind velocity profile within
the boundary layer which for structural engineering
applications is assumed to be extended only up to a few
hundred meters above the ground.
Primary circulations are fundamental air mass flows
due to changes of radiation, rotation of the earth andcomplex water/land distribution. Secondary circulations
are atmospheric flows due to thermal variation over the
lower atmosphere. This category includes the tropical
cyclones, which are also known as hurricanes andtyphoons in different places of the earth. The classification of the various types of tropical cyclones is based on
maximum sustained winds. The lower intensity tropicaldepressions and tropical storms occur for wind speeds
up to 17 m/s (39 mph) and 33 m/s (74 mph) respectively.
For maximum sustained winds over 33 m/s the tropical
cyclone is considered to be a hurricane (or typhoon,
severe tropical cyclone). Local winds, which havenegligible effect on primary and secondary circulations,are of smaller scale but in some cases, may be equallydestructive. Tornados are the most catastrophic among
local winds with Chinooks (North America) and thunderstorms to occur on a more frequent basis. Tornado’s
tangential wind speeds can exceed in extreme cases
108 m/s (250 mph).
4.2 Structural damage and building codes
Building codes are supposed to assist designers tomake buildings resist high wind effects. In some cases,
excessive damage is noticed during hurricane events,
even if the recorded wind speeds were lower than the
maximum recommended by the code design value(Kareem, 1984). Local, national and international building codes have been revised several times over the lastfew decades but the losses and damages due to wind arestill considerably high (ABI, 2003, Munchener Ruck,2006). These facts indicate the necessity of advanced
research in the area of extreme wind action and building
interaction.
The nature of extreme wind phenomena is very complex and researchers must focus on the understanding ofsuch events. If the design wind speed is not exceeded,
could it be that the pressure coefficients or perhaps the
exposure factors have been miscalculated? Alternatively,
could it be that design parameters are appropriate but
the buildings have been constructed poorly in terms ofmaterials, connections and workmanship? Notwithstanding the relevance of these questions, the structural

199

response of structures subjected to extreme wind loads
must be evaluated through model and full-scale studies
in order to be able to consider safe and economical
design parameters. Of particular interest is the case of
low-rise buildings, since the effect of extreme windeffects is much more pronounced and severe comparedto high-rise buildings.
4.3 Load paths: structural aspects & research
activity
Extreme wind event risk management incorporates
precise information regarding both the event and its
effect on the distressed structure. This has been examined extensively through simulated wind tunnel studies
but very limited full-scale efforts have been reported.
The evaluation of load path, i.e. how the wind forces
travel from the envelope to the foundation of a building
is still an open question.
4.3.1 Project description
Lack of intensive full-scale research in the field ofwind-structure interaction led to the project “Load Paths
in Wood Buildings,” in which researchers from four
Canadian Universities have assessed the application ofenvironmental loads and their actual transferring
through the buildings’ elements to their foundation. The
objective of this project is to monitor the response of alight-frame wood structure subjected to high wind loads.
The field facilities include three anemometers and asingle-storey test-house constructed according to theneeds of the particular research project (Fig. 3). The
experimental building is equipped with wall and roofpressure taps and load cells were placed at key points
inside the structural system (foundation and roof level).
The unique characteristic of the building is the fact that
it is completely isolated from the foundation and theonly points of contact with the ground are the 3-D loadcells.
In parallel with the structural monitoring of thisbuilding, wind tunnel tests were conducted in the Building Aerodynamics Laboratory at Concordia University

Fig. 3 Test house and meteorological tower location.

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T. STATHOPOULOS et al.

Power Law Exponent .

and a finite element model of the test building was also
developed. Having obtained both full-scale and windtunnel results, the computer-based analysis provided theopportunity to compare and assess the data of eachindividual approach. Details regarding the wind tunnel
and finite element models are presented by Zisis andStathopoulos (2009).
The risk management model discussed in section 3
involves information related to the wind characteristics
and the structural properties and response of habitat construction. Data from the current project could beincorporated in such risk assessment studies. The risk
identification factors introduced before and during thedecision making process intend to assess basic parameters, such as applied wind loads, material properties,
system redundancies and ductilities and the like. The
availability of full-scale real-time monitoring of suchparameters allows a more precise and prompt input data
generation, which consequently results into immediateand safer decision making.
N

1.0

The full-scale facilities in conjunction with themodel scale testing generated a vast amount of data. In
the subsequent sections some representative comparative results are presented. These results are grouped
under two separate categories i.e. results related to
upstream exposure characteristics and results related towind-induced forces at the foundation of the house.
4.3.2 Full-scale terrain data
The basic exposure characteristics (power law exponent, turbulence intensity and roughness length) were
evaluated using the available field data. Wind data collected from two anemometers (at 6.5 and 10.0-meterheight) during October to December 2008 and April toJune 2009 were analyzed and power law exponent,
turbulence intensity and roughness length values were
calculated and plotted with respect to direction (Figs. 4,
5 and 6). The results are based on 10-minute averaged
statistical values (mean and standard deviation) andwere filtered to retain wind speeds over 10 km/h (at

E

S

W

Mean valueStandard deviation

0.8
0.6
0.4
0.2
0.0
0

30

60

90

120

150
180
210
240
Wind Direction (degrees)

270

300

330

360

Fig. 4 Power law exponent variation with respect to direction.
N

Turbulence Intensity

1.0

E

S

W

Mean valueStandard deviation

0.8
0.6
0.4
0.2
0.0
0

30

60

90

120

150

180

210

240

270

300

330

360

330

360

Wind Direction (degrees)Fig. 5 Turbulence intensity variation with respect to direction.
N

Roughness Length (m)

1.4

E

S

W

1.2
1.0
0.8
0.6
0.4
0.2
0.0
0

30

60

90

120

150
180
210
240
Wind Direction (degrees)

270

300

Fig. 6 Roughness length variation with respect to direction.

Urban Habitat Constructions under Wind Catastrophic Events

6.5-meter height). The power law exponent ranges from0.05 to 0.50, the turbulence intensity from 20% to 50%
and the roughness length from a few millimeters up to
1.2 meters. It is quite interesting how these properties
vary considering that the test house is located in a relatively open area with only few low-rise buildings andmedium height trees in the proximity – see Fig. 3.
Consequently, generating the exposure characteristics ina simplified fashion (e.g. open, suburban etc.) for
simulation studies is a rather generic approach that may
compromise the testing accuracy.
4.3.3 Force coefficients
Data acquired from the foundation load cells wereconsidered and the total uplift force was recorded andnormalized in accordance to the approaching windcharacteristics. Moreover data from the wind tunnel
experiments were used to assess the equivalent total
uplift force coefficient using:c f ,z =

∑c A
p ,i

(1)

eff ,iA

where cp,i: instantaneous pressure coefficient, Aeff,i: effective pressure tap area (m2) and A: building area (m2).

The full-scale force coefficient was based on fieldrecorded data, whereas the wind tunnel force coefficient
was the result of the integration of the verticalcomponent of all forces. The mean and peak uplift force
coefficient comparison of the two experimental approaches is presented in Fig. 7. The field data werecollected during May and June of 2009 and were filtered
to retain only those for wind speeds over 8 m/sec. The
mean values were based on a 10-minute average and thepeaks on a 3-second gust. It should be mentioned thatfor this comparison two different sets of wind tunnel
data were considered i.e. tests conducted under open
(power law exponent equal to 0.16) and suburban
upstream exposure conditions (power law exponent
equal to 0.22).
The effect of adequate upstream simulation in thewind tunnel experiments can be seen in both mean andpeak uplift force coefficient comparisons. The twodifferent wind tunnel tests (open and suburban) resulted
into two discrete trends which for some critical winddirections differ up to 25% for the mean and 40% for the
peak values. Results from both wind tunnel tests arewithin the range of the field data but seem to underestimate the averaged (integration of different full-scale
records) peak component, which can be partially justified by the lower level of turbulence. Higher fluctuations of the wind direction should also be addressed andconsidered accountable for the above mentioned discrepancies.

Wind Tunnel (α=0.16)
Full-Scale (mean)

0.0

201

Wind Tunnel (α=0.22)
Full-Scale (range)

C f , m ea n

-0.2
-0.4
-0.6
-0.8
-1.0
0

30

60

90

120

150

180

210

240

270

300

330

360

Wind Direction (degrees)Wind Tunnel - Cf,min (α=0.16)

Wind Tunnel - Cf,max (α=0.16)

Wind Tunnel - Cf,min (α=0.22)

Wind Tunnel - Cf,max (α=0.22)

Full-Scale (minimum)

Full-Scale (maximum)

Full-Scale (range)

1.0
0.5

Cf,p eak

0.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
0

30

60

90

120

150
180
210
240
Wind Direction (degrees)

270

300

Fig. 7 Mean and peak force coefficient comparison (total uplift).

330

360

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T. STATHOPOULOS et al.

5. Conclusions
The frequency of occurrence and the excessive
losses reported during recent extreme wind events introduced a particular interest on the assessment of suchhazards and the development of efficient risk management and decision making models. Action-C26, one of
the key domains of Transport and Urban Development
under the European COST program, is assigned to
examine the effect of catastrophic events on urban habitat constructions. A generic risk assessment framework
proposed by Nishijima and Faber (2007) was discussed
and evaluated for the case of a typhoon. The refinementof such model includes processes directly related to thespecific characteristics of habitat construction e.g. low
buildings. Field monitoring of extreme wind events andstructural response of buildings are of great importanceand of particular contributions on the development ofprecise and effective risk-based decision models.
References
ABI (2003) The Vulnerability of UK Property to Windstorm
Damage, Association of British Insurers, London, UK
ASCE/SEI 7-05 (2005) Minimum Design Loads for Building andOther Structures, American Society of Civil Engineers, New
York, N.Y.
Faber, M. (2008) Risk Assessment in Engineering: Principles,
System Representation and Risk Criteria, Joint Committee on
Structural Safety, ISBN 978-3-909386-78-9.
Graf, M., K. Nishijima and M.H. Faber (2008) Adaption of
typhoon risk modelling to climate changes. Proceedings to
IDRC International Disaster and Risk Conference, Davos,
Switzerland.
Kareem A. (1984) Wind Speed – Damage Correlation in
Hurricane Alicia, Hurricane Alicia: One Year Later, Specialty
Conference, ASCE – EMD, Galveston, Texas, pp. 81-93.
Munchener Ruck (2006) Knowledge Series, Hurricanes-MoreIntensive, More Frequent, More Expensive: Insurance in a Timeof Changing Risks, 302-04891, Munich Re Group, Germany.
Nishijima, K. and M.H. Faber (2007) A Bayesian framework for
typhoon risk management, Proceedings ICWE 12, 12th International Conference on Wind Engineering, Cairns, Australia, 2:
1959-1966.
Nishijima, K. and M.H. Faber (2009) Development of stochastic
typhoon model in Northwest Pacific region and its application
to portfolio loss estimation, Project Summary 18897, ETH
Research Database, Zurich, Switzerland.
Zisis, I. and T. Stathopoulos (2009) Wind-induced cladding andstructural loads on a low wooden building, Journal of Structural Engineering, ASCE, 135(4): 437-447.

Ted STATHOPOULOS
Born in Athens, Greece, he received his
Civil Engineering Diploma from the
National Technical University of Athens,
Greece and both his M.E.Sc. and Ph.D.
from the University of Western Ontario.
He is currently Professor at the Department of Building, Civil and Environmental Engineering and Associate Deanof the School of Graduate Studies ofConcordia University, Montreal, Canada.
His research in the area of wind effects onbuildings and their codification has been influential in the development ofcodes and standards around the world. He has an extensive publication
record with more than 125 articles in refereed journals. He has received
several awards and distinctions for his research. Most importantly, hereceived the 2009 Jack E. Cermak Medal of the Engineering Mechanics
Institute of ASCE for his contributions to wind engineering, particularly
his work that has been the key ingredient in the low rise wind provisionsof the Canadian Building Code and the ASCE 7 Standard, affecting thedesign of millions of buildings. He is a member of ASHRAE TechnicalCommittee 4.3 on Infiltration Requirements and Ventilation and of the
ASCE 7 Committee on Minimum Wind Loads. He is currently chairing
the Executive Committee of the ASCE Technical Council of Wind
Engineering. He is a professional engineer registered in Quebec, Ontario
and in Greece; he is a Fellow of the Canadian Academy of Engineeringand a Fellow of the American Society of Civil Engineers. He is the Editorof the Journal of Wind Engineering and Industrial Aerodynamics.

Charalambos C. BANIOTOPOULOS
Professor Dr.-Ing. C.C.Baniotopoulos is
Director of the Institute of Metal Structures and Head of the Civil Engineering
Department, Aristotle University ofThessaloniki in Greece. He has lectured
extensively and has focused his researchon the structural response and the designof metal and wind-sensitive structures.
His recent research activity has centeredon wind energy structures. Having been
awarded an Alexander von Humboldt
Fellowship and later within the framework of an HCM Fellowship, hecarried out research at the RWTH Aachen in Germany, the Joint ResearchCentre of the EU, Ispra site in Italy and the ELSA Laboratory. During thelast 25 years, he delivered lectures as visiting professor in several
universities all over the world. He is member of the Management
Committee of a european COST action dealing with the catastrophic
events in the built environment and the Greek delegate in Eurocode
9-Aluminium structures chairing the mirror national committee. He has
been project leader of more than 50 research projects supported bynational, EU and international funds. Since 2005, he has been chairman of
the Hellenic Scientific Society of Wind Engineering.

Ioannis ZISISMr. Zisis received a Diploma in Civil
Engineering from the Polytechnic
Faculty of Aristotle University ofThessaloniki, Greece and a Masters ofApplied Science in Building Engineeringfrom Concordia University, Montreal,
Canada. He is currently a PhD Candidate
and Graduate Research Assistant in the
Department of Building, Civil and Environmental Engineering at Concordia
University.
His research interests are related towind effects on buildings and specifically on wind-induced loads andresponse of low-rise buildings. The focus of his PhD research is the windload path concept which he studies using both full-scale monitoring andwind tunnel simulation. In addition, a major part of his current work is
aimed at the codification of experimental findings, such as attenuation
effects on low-rise wood buildings and wind-induced loads on patio
covers.
Mr. Zisis has received numerous awards and distinctions during his
graduate studies, including the Catherine Lalonde Memorial Scholarshipfrom Canadian Wood Council. He is a student member of the CanadianSociety of Civil Engineers (CSCE), the American Society of Civil
Engineers (ASCE), the American Association of Wind Engineering(AAWE) and a member of the Structural Wind Engineering Committee of
the Technical Council on Wind Engineering (TCWE) of ASCE.

(Received 7 November 2009, Accepted 16 February 2010)