Tornadoes in Urban Areas Indonesia
LH ATMOSPHERIC
ENGINEERING
Effects of Tornadoes on Urban Areas and Allowance
for in Structural Design
Mohammed Fahad Ashfaq
1243955
University of Birmingham
College of Engineering and Physical Sciences
School of Civil Engineering
Edgbaston
Birmingham
B15 2TT
United Kingdom
Submission Date: 10/03/15
CONTENTS
1.0.
Introduction ............................................................................................................................................... 1
2.0.
General Formation of Tornadoes .............................................................................................................. 1
3.0.
USA – Prime Location for Tornadoes ......................................................................................................... 2
3.1.
Tornado Effects on Urban Areas – Joplin Tornado................................................................................ 2
4.0.
Allowance for Tornadoes in Structural Design .......................................................................................... 3
5.0.
Conclusion ................................................................................................................................................. 4
6.0.
References ................................................................................................................................................. 4
Figure 1 - Tornadoes in USA, 2014 (Spc.noaa.gov, 2015) ....................................................................................... 2
Figure 2 - Track and magnitude of Joplin Tornado (U.S. DEPARTMENT OF COMMERCE, 2011) ............................ 2
1.0.
INTRODUCTION
Tornadoes are columns of air that rotate due to differences in wind velocities and temperatures, forming
below cumulonimbus clouds, which make contact with ground level (Met Office News Blog, 2013). There are
locations across the globe more prone to tornado formation due to factors such as humidity, temperature and
geographical location (LiveScience.com, 2015).
20° to 50° from both sides of the equator locate zones, around which tornadoes are concentrated. These zones
provide optimum conditions of differing air masses and high velocity air (jet stream) moving west to east; path
differs during the year, both satisfying conditions for tornado production (Eagleman, Muirhead and Willems,
1975). The devastation and magnitude of tornadoes varies significantly. Wind speeds, temperature differences
and geographical location all simultaneously affect the level of devastation that can occur. If a tornado is
formed in an area of high-speed winds, where there are large temperature differences between air masses,
whist being located in an area of high population density, the aftermath is clear to be devastation. Although
computer programs can detect tornadoes from Doppler radar data (Nssl.noaa.gov, 2015). There may also be a
need for protecting the built-environment and more importantly lives against these natural phenomena. It is
crucial for structural designs in locations known to tornado hotspots to implement methods for resistance
against such powerful wind vortices with tangential and vertical velocity components, without making designs
too costly (Haan, Balaramudu and Sarkar, 2010).
2.0.
GENERAL FORMATION OF TORNADOES
General formation occurs when humid, warm air accumulates due to solar heating of the ground. This buoyant
air rises upwards forming large cumulonimbus clouds, thus giving rise to a thunderstorm where the internal
structure develops of updrafts and circulation (Eagleman, Muirhead and Willems, 1975). Meanwhile wind
shear occurs, due to the difference in wind speeds at different altitudes. Thus causing the wind to spin in a
horizontal motion (Met Office News Blog, 2013). When this air is caught in an updraft from a thunderstorm,
enough energy is provided for the circular vortices to enhance the wind speed greatly forming a tornado; the
funnel cloud from the base of the cumulonimbus cloud moves towards the ground. Interestingly, stronger
tornadoes are formed when the base of the thunderstorm is closer to ground level, whilst it is also possible for
multiple funnels to stem from the same updraft (Eagleman, Muirhead and Willems, 1975).
1
3.0.
USA – PRIME LOCATION FOR TORNADOES
Formation can also relate specifically to geographical location. Figure 1 maps out the occurrence of tornadoes
within the USA. The Central- Eastern regions are a target to numerous tornadoes, due to the rise to conditions
suited for tornado generation. Cool, dry air moves westwards over the Rocky Mountains, simultaneously
warm, moist air heads northwards from the Gulf of Mexico. The tornado activity occurs when the cool and
warm air mix, giving rise to instable atmospheric conditions (thunderstorms) (Eagleman, Muirhead and
Willems, 1975). The tornado then forms as in the general case.
Figure 1 - Tornadoes in USA, 2014 (Spc.noaa.gov, 2015)
3.1.
TORNADO EFFECTS ON U RBAN AREAS – JOPLIN TORNADO
The average number of deaths yearly caused by tornadoes fluctuates massively, due to the unpredictability of
magnitude and whereabouts a tornado may strike. In USA, between years 2012-2014, number of deaths
occurring from tornadoes averaged only 57 yearly (Spc.noaa.gov, 2015). Whilst the year 2011 had inflicted 553
deaths to the country.
Figure 2 - Track and magnitude of Joplin Tornado (U.S. DEPARTMENT OF COMMERCE, 2011)
The major incident of that year in the USA that lead to such devastation occurred in Joplin, Missouri on May
22nd, which according to National Weather Service killed 158 directly (U.S. DEPARTMENT OF COMMERCE,
2011). The population of Joplin city at 2010 consensus equated to 50,150 people with population density of
approximately 580 people per km2 (Quickfacts.census.gov, 2015). Even though less than 0.5% of the
population were killed, over 1,000 people were injured and displaced from their homes (U.S. DEPARTMENT OF
COMMERCE, 2011). Without the ability of detecting the formation of the Joplin Tornado, it is clear that the
2
death toll would have risen. All of this damage had been caused within only 40 minutes of tornado formation
(Wheatley, 2013). Alongside such an unusually high death toll for the modern era, the costs incurred through
damages to properties (commercial and residential) equated to more than $2 billion (Joplin, Missouri hit by EF5 Tornado on May 22, 2011, 2013). The tornado had a stem of 1.6km and path length of 35.6km, rated at EF-5
on the Enhanced-Fujita Scale, with wind speeds exceeding 322km/h (U.S. DEPARTMENT OF COMMERCE,
2011).
Figure 2 shows the path Joplin Tornado had taken. A major reason for the unusual high death toll and
destruction was due to the width of the stem, allowing coverage of a larger land mass and the tornado’s ability
to reach higher speeds closer to the centre of the urban city. As the path came closer to the inner city, the
tornado levelled up further on the Enhanced-Fujita scale until it reached level 5, where it impacted city
inflicting huge damages to public facilities, such as schools, hospitals, domestic and commercial property. Eyewittness accounts confirmed steel roof trusses were rolled up like paper and extreme twisting of main
suppport beams in medium rise steel structures (Crh.noaa.gov, 2015). The impact to the extent of damage
didn’t end there, the loss of life ripped open the heart of the community. Whilst due to the destruction of
numerous workplaces, unemployment increased as a result; Work Investment Board showed an increase in
unemployment rate of 8.9% in 2011, which decreased as the recoveration process went underway to 6.9% in
2012 (Joplin, Missouri hit by EF-5 Tornado on May 22, 2011, 2013). Huge disruptions was apparent to the
general living of all, as schools were forced to close, with re-construction of some schools in Joplin taking 3
years for completion (Joplinschools.org, 2015). Whilst the impact on the transport infrastructure was further
felt due to the masses of debris that lay on roads and severe turning over of approximately 15,000 vehicles
(Crh.noaa.gov, 2015). It is evident that the simultaneous effect of high-speed tornadoes and coincidental
occurrence in urban cities is the result of such devastation.
4.0.
ALLOWANCE FOR TORNADOES IN STRUCTURAL DESIGN
It is of utmost importance for the designer to consider designing a structure to withstand load effects from
tornadoes in tornado prone areas in a cost-effective manner. Whilst also noting probability of occurrence of
tornadoes within the region and having an appreciation of the duration of these extreme events, as they only
last for a few hours at most (Wheatley, 2013).
ASCE 7-05 provisions provides designers in USA with methods for resisting loadings induced by tornadoes in
employing a 3-s gust velocity e.g. 40m/s in “Tornado Alley” region (Haan, Balaramudu and Sarkar, 2010).
However, these provisions assume flow in 1-D of straight-lined winds in conventional atmospheric boundary
layer (ABL) conditions, the reality of tornadoes is much more complex, as they are devised from horizontal
wind forces, tangential velocity components and uplift forces, all acting simultaneously with each other.
Thus, methods for allowance have stemmed from wind tunnel modelling to simulate the extreme case of the
three components that make up a tornado. Haan, Balaramudu and Sarkar, 2010 have modelled the impact of
changing tornado stem diameters, alongside different orientations of building faces whilst increasing velocity
speeds on a one-storey building with a gable roof. Case, Sarkar and Sritharan, 2014 went further to assess
required changes in structural design that need further strengthening, by wind tunnel modelling; replicating a
real tornado to model scale and utilising various different structural models with slight variations in geometry.
The use of wind tunnel testing has allowed for investigations into the tornado skeleton and structure-tornado
interaction. Bluestein and Golden, 1993 cited by Haan, Balaramudu and Sarkar, 2010 showed 90% of all
tornadoes had maximum wind speeds of smaller than 72m/s. Results from Haan, Balaramudu and Sarkar, 2010
displayed slower moving tornadoes with smaller stem diameters caused greater damage to structures then
faster moving tornadoes with larger stem diameters. It was apparent that a greater time for interaction
between structure and tornado was available, whilst a greater uplift force was generated by the slower and
smaller stemmed tornadoes. Largest generation of lateral loading occurred from the edges of the tornado-like
3
vortices. These results were obtained from wind tunnel testing, hence up-sizing the outcomes for such results
doesn’t necessarily reflect actual results from tornadoes in reality, due to effects e.g. debris impact on
structures that can accumulate with time.
For application in design, from wind tunnel modelling, sensors initiated to detect the surface pressures acting
on the walls and roof of the building. These pressures integrated across the area, in which overall force and
moment coefficients are calculated. These coefficients are then normalised with respect to the maximum
horizontal velocity for modelling the effect of the tornado-like vortices on the structure (Haan, Balaramudu
and Sarkar, 2010).
In comparison to normal atmospheric boundary layer conditions used in codes of practice, Haan, Balaramudu
and Sarkar, 2010 estimate lateral forces acting on the structure can equate to an increase of 50% the original
load induced from straight-lined wind over open terrain from codes. Whilst vertical uplift of 2-3 times greater
than suggested in the codes for tornadoes. Case, Sarkar and Sritharan, 2014 showed weaknesses in the
structure were heavily induced by the lack of strength from roof connections under these extreme conditions.
They concluded that due to the higher probability of lower speed tornadoes occurring, building a structure
designed for resistance against wind speeds of up to 73m/s will ensure the safety and cost-effectiveness of the
design.
5.0.
CONCLUSION
It is obvious the effects of tornadoes are of damage and destruction to the built-up environment. Whilst the
formation of tornadoes only occur in particular regions of the world. Where mixing of hot and cold air with
large temperature differences give rise to thunderstorms that indirectly form tornadoes. Their probability of
occurrence and geographical location is for the designer to consider with highest regards for stability and
safety of their structural design. Lateral loads were 1.5 times greater than those from ASCE-705 provisions,
whilst uplift forces were 2-3 times greater than values from provisions, showing the power such phenomena
have. It was seen that roof connections are crucial for structural stability of structures in presence of
tornadoes for they are the weakest part of the structure, causing structural collapse. Justification between
cost, probability of occurrence and safety is key for designing against tornadoes.
6.0.
REFERENCES
Case, J., Sarkar, P. and Sritharan, S. (2014). Effect of low-rise building geometry on tornado-induced loads.
Journal of Wind Engineering and Industrial Aerodynamics, 133, pp.124-134.
Crh.noaa.gov, (2015). National Weather Service Springfield, MO - Event Review - May 22, 2011. [Online]
Available at: http://www.crh.noaa.gov/sgf/?n=event_2011may22_survey [Accessed 22 Feb. 2015].
Eagleman, J., Muirhead, V. and Willems, N. (1975). Thunderstorms, tornadoes, and building damage.
Lexington, Mass.: Lexington Books.
Haan, F., Balaramudu, V. and Sarkar, P. (2010). Tornado-Induced Wind Loads on a Low-Rise Building. Journal of
Structural Engineering, 136(1), pp.106-116.
Joplin, Missouri hit by EF-5 Tornado on May 22, 2011. (2013). 1st ed. [eBook] Joplin: Lynn Iliff Onstot Public
Information Office. Available at: http://www.joplinmo.org/ [Accessed 22 Feb. 2015].
Joplinschools.org, (2015). Tornado Recovery / JHS/FTC. [Online] Available at:
http://www.joplinschools.org/Page/1657 [Accessed 22 Feb. 2015].
4
LiveScience.com, (2015). Tornado Alley: Where Twisters Form. [Online] Available at:
http://www.livescience.com/25675-tornado-alley.html [Accessed 20 Feb. 2015].
LiveScience.com, (2015). Tornado Facts: Causes, Formation & Staying Safe. [Online] Available at:
http://www.livescience.com/21498-tornado-facts.html [Accessed 20 Feb. 2015].
Met Office News Blog, (2013). What are tornadoes? [Online] Available at:
https://metofficenews.wordpress.com/2013/05/21/what-are-tornadoes/ [Accessed 20 Feb. 2015].
Nssl.noaa.gov, (2015). NSSL: Severe Weather 101: Tornado Detection. [Online] Available at:
https://www.nssl.noaa.gov/education/svrwx101/tornadoes/detection/ [Accessed 20 Feb. 2015].
Quickfacts.census.gov, (2015). Joplin (city) QuickFacts from the US Census Bureau. [Online] Available at:
http://quickfacts.census.gov/qfd/states/29/2937592.html [Accessed 21 Feb. 2015].
Spc.noaa.gov, (2015). [Online] Available at: http://www.spc.noaa.gov/climo/torn/STATIJ11.txt [Accessed 21
Feb. 2015].
Spc.noaa.gov, (2015). Annual Fatal Tornado Summaries. [Online] Available at:
http://www.spc.noaa.gov/climo/torn/fatalmap.php [Accessed 21 Feb. 2015].
Spc.noaa.gov, (2015). Storm Prediction Center Annual Report Summary - 2014. [Online] Available at:
http://www.spc.noaa.gov/climo/online/monthly/2014_annual_summary.html# [Accessed 20 Feb. 2015].
U.S. DEPARTMENT OF COMMERCE, (2011). NWS Central Region Service Assessment Joplin, Missouri, Tornado
– May 22, 2011. Kansas City, MO.
Wheatley, K. (2013). The May 22, 2011 Joplin, Missouri EF5 tornado. [Online] United States Tornadoes.
Available at: http://www.ustornadoes.com/2013/05/22/joplin-missouri-ef5-tornado-may-22-2011/ [Accessed
23 Feb. 2015].
5
ENGINEERING
Effects of Tornadoes on Urban Areas and Allowance
for in Structural Design
Mohammed Fahad Ashfaq
1243955
University of Birmingham
College of Engineering and Physical Sciences
School of Civil Engineering
Edgbaston
Birmingham
B15 2TT
United Kingdom
Submission Date: 10/03/15
CONTENTS
1.0.
Introduction ............................................................................................................................................... 1
2.0.
General Formation of Tornadoes .............................................................................................................. 1
3.0.
USA – Prime Location for Tornadoes ......................................................................................................... 2
3.1.
Tornado Effects on Urban Areas – Joplin Tornado................................................................................ 2
4.0.
Allowance for Tornadoes in Structural Design .......................................................................................... 3
5.0.
Conclusion ................................................................................................................................................. 4
6.0.
References ................................................................................................................................................. 4
Figure 1 - Tornadoes in USA, 2014 (Spc.noaa.gov, 2015) ....................................................................................... 2
Figure 2 - Track and magnitude of Joplin Tornado (U.S. DEPARTMENT OF COMMERCE, 2011) ............................ 2
1.0.
INTRODUCTION
Tornadoes are columns of air that rotate due to differences in wind velocities and temperatures, forming
below cumulonimbus clouds, which make contact with ground level (Met Office News Blog, 2013). There are
locations across the globe more prone to tornado formation due to factors such as humidity, temperature and
geographical location (LiveScience.com, 2015).
20° to 50° from both sides of the equator locate zones, around which tornadoes are concentrated. These zones
provide optimum conditions of differing air masses and high velocity air (jet stream) moving west to east; path
differs during the year, both satisfying conditions for tornado production (Eagleman, Muirhead and Willems,
1975). The devastation and magnitude of tornadoes varies significantly. Wind speeds, temperature differences
and geographical location all simultaneously affect the level of devastation that can occur. If a tornado is
formed in an area of high-speed winds, where there are large temperature differences between air masses,
whist being located in an area of high population density, the aftermath is clear to be devastation. Although
computer programs can detect tornadoes from Doppler radar data (Nssl.noaa.gov, 2015). There may also be a
need for protecting the built-environment and more importantly lives against these natural phenomena. It is
crucial for structural designs in locations known to tornado hotspots to implement methods for resistance
against such powerful wind vortices with tangential and vertical velocity components, without making designs
too costly (Haan, Balaramudu and Sarkar, 2010).
2.0.
GENERAL FORMATION OF TORNADOES
General formation occurs when humid, warm air accumulates due to solar heating of the ground. This buoyant
air rises upwards forming large cumulonimbus clouds, thus giving rise to a thunderstorm where the internal
structure develops of updrafts and circulation (Eagleman, Muirhead and Willems, 1975). Meanwhile wind
shear occurs, due to the difference in wind speeds at different altitudes. Thus causing the wind to spin in a
horizontal motion (Met Office News Blog, 2013). When this air is caught in an updraft from a thunderstorm,
enough energy is provided for the circular vortices to enhance the wind speed greatly forming a tornado; the
funnel cloud from the base of the cumulonimbus cloud moves towards the ground. Interestingly, stronger
tornadoes are formed when the base of the thunderstorm is closer to ground level, whilst it is also possible for
multiple funnels to stem from the same updraft (Eagleman, Muirhead and Willems, 1975).
1
3.0.
USA – PRIME LOCATION FOR TORNADOES
Formation can also relate specifically to geographical location. Figure 1 maps out the occurrence of tornadoes
within the USA. The Central- Eastern regions are a target to numerous tornadoes, due to the rise to conditions
suited for tornado generation. Cool, dry air moves westwards over the Rocky Mountains, simultaneously
warm, moist air heads northwards from the Gulf of Mexico. The tornado activity occurs when the cool and
warm air mix, giving rise to instable atmospheric conditions (thunderstorms) (Eagleman, Muirhead and
Willems, 1975). The tornado then forms as in the general case.
Figure 1 - Tornadoes in USA, 2014 (Spc.noaa.gov, 2015)
3.1.
TORNADO EFFECTS ON U RBAN AREAS – JOPLIN TORNADO
The average number of deaths yearly caused by tornadoes fluctuates massively, due to the unpredictability of
magnitude and whereabouts a tornado may strike. In USA, between years 2012-2014, number of deaths
occurring from tornadoes averaged only 57 yearly (Spc.noaa.gov, 2015). Whilst the year 2011 had inflicted 553
deaths to the country.
Figure 2 - Track and magnitude of Joplin Tornado (U.S. DEPARTMENT OF COMMERCE, 2011)
The major incident of that year in the USA that lead to such devastation occurred in Joplin, Missouri on May
22nd, which according to National Weather Service killed 158 directly (U.S. DEPARTMENT OF COMMERCE,
2011). The population of Joplin city at 2010 consensus equated to 50,150 people with population density of
approximately 580 people per km2 (Quickfacts.census.gov, 2015). Even though less than 0.5% of the
population were killed, over 1,000 people were injured and displaced from their homes (U.S. DEPARTMENT OF
COMMERCE, 2011). Without the ability of detecting the formation of the Joplin Tornado, it is clear that the
2
death toll would have risen. All of this damage had been caused within only 40 minutes of tornado formation
(Wheatley, 2013). Alongside such an unusually high death toll for the modern era, the costs incurred through
damages to properties (commercial and residential) equated to more than $2 billion (Joplin, Missouri hit by EF5 Tornado on May 22, 2011, 2013). The tornado had a stem of 1.6km and path length of 35.6km, rated at EF-5
on the Enhanced-Fujita Scale, with wind speeds exceeding 322km/h (U.S. DEPARTMENT OF COMMERCE,
2011).
Figure 2 shows the path Joplin Tornado had taken. A major reason for the unusual high death toll and
destruction was due to the width of the stem, allowing coverage of a larger land mass and the tornado’s ability
to reach higher speeds closer to the centre of the urban city. As the path came closer to the inner city, the
tornado levelled up further on the Enhanced-Fujita scale until it reached level 5, where it impacted city
inflicting huge damages to public facilities, such as schools, hospitals, domestic and commercial property. Eyewittness accounts confirmed steel roof trusses were rolled up like paper and extreme twisting of main
suppport beams in medium rise steel structures (Crh.noaa.gov, 2015). The impact to the extent of damage
didn’t end there, the loss of life ripped open the heart of the community. Whilst due to the destruction of
numerous workplaces, unemployment increased as a result; Work Investment Board showed an increase in
unemployment rate of 8.9% in 2011, which decreased as the recoveration process went underway to 6.9% in
2012 (Joplin, Missouri hit by EF-5 Tornado on May 22, 2011, 2013). Huge disruptions was apparent to the
general living of all, as schools were forced to close, with re-construction of some schools in Joplin taking 3
years for completion (Joplinschools.org, 2015). Whilst the impact on the transport infrastructure was further
felt due to the masses of debris that lay on roads and severe turning over of approximately 15,000 vehicles
(Crh.noaa.gov, 2015). It is evident that the simultaneous effect of high-speed tornadoes and coincidental
occurrence in urban cities is the result of such devastation.
4.0.
ALLOWANCE FOR TORNADOES IN STRUCTURAL DESIGN
It is of utmost importance for the designer to consider designing a structure to withstand load effects from
tornadoes in tornado prone areas in a cost-effective manner. Whilst also noting probability of occurrence of
tornadoes within the region and having an appreciation of the duration of these extreme events, as they only
last for a few hours at most (Wheatley, 2013).
ASCE 7-05 provisions provides designers in USA with methods for resisting loadings induced by tornadoes in
employing a 3-s gust velocity e.g. 40m/s in “Tornado Alley” region (Haan, Balaramudu and Sarkar, 2010).
However, these provisions assume flow in 1-D of straight-lined winds in conventional atmospheric boundary
layer (ABL) conditions, the reality of tornadoes is much more complex, as they are devised from horizontal
wind forces, tangential velocity components and uplift forces, all acting simultaneously with each other.
Thus, methods for allowance have stemmed from wind tunnel modelling to simulate the extreme case of the
three components that make up a tornado. Haan, Balaramudu and Sarkar, 2010 have modelled the impact of
changing tornado stem diameters, alongside different orientations of building faces whilst increasing velocity
speeds on a one-storey building with a gable roof. Case, Sarkar and Sritharan, 2014 went further to assess
required changes in structural design that need further strengthening, by wind tunnel modelling; replicating a
real tornado to model scale and utilising various different structural models with slight variations in geometry.
The use of wind tunnel testing has allowed for investigations into the tornado skeleton and structure-tornado
interaction. Bluestein and Golden, 1993 cited by Haan, Balaramudu and Sarkar, 2010 showed 90% of all
tornadoes had maximum wind speeds of smaller than 72m/s. Results from Haan, Balaramudu and Sarkar, 2010
displayed slower moving tornadoes with smaller stem diameters caused greater damage to structures then
faster moving tornadoes with larger stem diameters. It was apparent that a greater time for interaction
between structure and tornado was available, whilst a greater uplift force was generated by the slower and
smaller stemmed tornadoes. Largest generation of lateral loading occurred from the edges of the tornado-like
3
vortices. These results were obtained from wind tunnel testing, hence up-sizing the outcomes for such results
doesn’t necessarily reflect actual results from tornadoes in reality, due to effects e.g. debris impact on
structures that can accumulate with time.
For application in design, from wind tunnel modelling, sensors initiated to detect the surface pressures acting
on the walls and roof of the building. These pressures integrated across the area, in which overall force and
moment coefficients are calculated. These coefficients are then normalised with respect to the maximum
horizontal velocity for modelling the effect of the tornado-like vortices on the structure (Haan, Balaramudu
and Sarkar, 2010).
In comparison to normal atmospheric boundary layer conditions used in codes of practice, Haan, Balaramudu
and Sarkar, 2010 estimate lateral forces acting on the structure can equate to an increase of 50% the original
load induced from straight-lined wind over open terrain from codes. Whilst vertical uplift of 2-3 times greater
than suggested in the codes for tornadoes. Case, Sarkar and Sritharan, 2014 showed weaknesses in the
structure were heavily induced by the lack of strength from roof connections under these extreme conditions.
They concluded that due to the higher probability of lower speed tornadoes occurring, building a structure
designed for resistance against wind speeds of up to 73m/s will ensure the safety and cost-effectiveness of the
design.
5.0.
CONCLUSION
It is obvious the effects of tornadoes are of damage and destruction to the built-up environment. Whilst the
formation of tornadoes only occur in particular regions of the world. Where mixing of hot and cold air with
large temperature differences give rise to thunderstorms that indirectly form tornadoes. Their probability of
occurrence and geographical location is for the designer to consider with highest regards for stability and
safety of their structural design. Lateral loads were 1.5 times greater than those from ASCE-705 provisions,
whilst uplift forces were 2-3 times greater than values from provisions, showing the power such phenomena
have. It was seen that roof connections are crucial for structural stability of structures in presence of
tornadoes for they are the weakest part of the structure, causing structural collapse. Justification between
cost, probability of occurrence and safety is key for designing against tornadoes.
6.0.
REFERENCES
Case, J., Sarkar, P. and Sritharan, S. (2014). Effect of low-rise building geometry on tornado-induced loads.
Journal of Wind Engineering and Industrial Aerodynamics, 133, pp.124-134.
Crh.noaa.gov, (2015). National Weather Service Springfield, MO - Event Review - May 22, 2011. [Online]
Available at: http://www.crh.noaa.gov/sgf/?n=event_2011may22_survey [Accessed 22 Feb. 2015].
Eagleman, J., Muirhead, V. and Willems, N. (1975). Thunderstorms, tornadoes, and building damage.
Lexington, Mass.: Lexington Books.
Haan, F., Balaramudu, V. and Sarkar, P. (2010). Tornado-Induced Wind Loads on a Low-Rise Building. Journal of
Structural Engineering, 136(1), pp.106-116.
Joplin, Missouri hit by EF-5 Tornado on May 22, 2011. (2013). 1st ed. [eBook] Joplin: Lynn Iliff Onstot Public
Information Office. Available at: http://www.joplinmo.org/ [Accessed 22 Feb. 2015].
Joplinschools.org, (2015). Tornado Recovery / JHS/FTC. [Online] Available at:
http://www.joplinschools.org/Page/1657 [Accessed 22 Feb. 2015].
4
LiveScience.com, (2015). Tornado Alley: Where Twisters Form. [Online] Available at:
http://www.livescience.com/25675-tornado-alley.html [Accessed 20 Feb. 2015].
LiveScience.com, (2015). Tornado Facts: Causes, Formation & Staying Safe. [Online] Available at:
http://www.livescience.com/21498-tornado-facts.html [Accessed 20 Feb. 2015].
Met Office News Blog, (2013). What are tornadoes? [Online] Available at:
https://metofficenews.wordpress.com/2013/05/21/what-are-tornadoes/ [Accessed 20 Feb. 2015].
Nssl.noaa.gov, (2015). NSSL: Severe Weather 101: Tornado Detection. [Online] Available at:
https://www.nssl.noaa.gov/education/svrwx101/tornadoes/detection/ [Accessed 20 Feb. 2015].
Quickfacts.census.gov, (2015). Joplin (city) QuickFacts from the US Census Bureau. [Online] Available at:
http://quickfacts.census.gov/qfd/states/29/2937592.html [Accessed 21 Feb. 2015].
Spc.noaa.gov, (2015). [Online] Available at: http://www.spc.noaa.gov/climo/torn/STATIJ11.txt [Accessed 21
Feb. 2015].
Spc.noaa.gov, (2015). Annual Fatal Tornado Summaries. [Online] Available at:
http://www.spc.noaa.gov/climo/torn/fatalmap.php [Accessed 21 Feb. 2015].
Spc.noaa.gov, (2015). Storm Prediction Center Annual Report Summary - 2014. [Online] Available at:
http://www.spc.noaa.gov/climo/online/monthly/2014_annual_summary.html# [Accessed 20 Feb. 2015].
U.S. DEPARTMENT OF COMMERCE, (2011). NWS Central Region Service Assessment Joplin, Missouri, Tornado
– May 22, 2011. Kansas City, MO.
Wheatley, K. (2013). The May 22, 2011 Joplin, Missouri EF5 tornado. [Online] United States Tornadoes.
Available at: http://www.ustornadoes.com/2013/05/22/joplin-missouri-ef5-tornado-may-22-2011/ [Accessed
23 Feb. 2015].
5