This document discusses design considerations for buildings in cyclone-prone areas. It begins with an introduction to cyclones, noting they cause strong winds and rains. It then discusses various cyclone characteristics like formation, structure with an eye, and coastal impacts. Several key aspects for building design are covered, including roofing, wall-roof junctions, doors/windows, foundations, and walls. Reinforcing these vulnerable areas is recommended through techniques like additional bracing, straps, and reinforced connections. Site selection factors are also outlined, such as using natural shields from hills or trees and avoiding ridges. The overall document provides guidance on strengthening building construction against high winds and flooding from cyclones.

1. ACROPOLIS INSTITUTE OF
TECHNOLOGY AND RESEARCH, INDORE
DEPARTMENT OF CIVIL ENGINEERING
DESIGN OF BUILDINGS IN
CYCLONE PRONE AREAS
ANKIT SHAH
ASST. PROF

2. INTRODUCTION
A CYCLONE is an atmospheric
phenomenon which causes
extremely strong winds and
torrential rains. This
phenomenon occurs at the end
of summer when the waters
from the tropical oceans are
hotter.
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3. • Large hot air masses which absorb vapour becoming lighter are created on the oceanic
waters. So, an accelerated spiral ascension of these large vapour masses is produced,
reaching high speeds and forming enormous clouds that may reach up to 16 km of
height!. This phenomenon is called Tropical Cyclone, Hurricane, Typhoon an other
denominations, depending on the different locations where it occurs. Every year about
80 cyclones are formed in the world. Their radius of action may have between 100 and
1000 Km.
• The cyclones show a sensational aspect: a large spiral of clouds that circulates around its
centre. It forms a round hole which has between 20 and 60 km of diameter, known as
EYE which moves in a speed that may reach 40-50 km/h.
• The strong winds around the Eye cause the movement in the sea of enormous
quantities of water which elevates themselves in giant waves. Usually these will collide
with all their force in the coastal region that constitutes the biggest danger of deaths in
the event of a cyclone. This atmospheric phenomenon may last for various days and
even weeks.
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CED-AITR, INDORE 3

4. Cyclonic storms draw most of their energy
from the latent heat released by the
condensation of water vapor.
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5. SPEED OF
CYCLONES
A cyclone reaches a maximum speed over the ocean and loses
part of its strength when it enters into the continent, where
it is stopped by the morphology of the terrain. When this
occurs, large quantities of water fall down in the form of
heavy rains, which usually fill the rivers causing FLOODS in
the lower areas.
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6. ATMOSPHERIC IMPORTANCE OF CYCLONES
• Despite their devastating effects, cyclones are very
important since they cause large air masses and clouds
to circulate, contributing for an atmospheric
equilibrium that allows us to live in this planet...
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CED-AITR, INDORE 6

7. ACTION OF WIND
ON CONSTRUCTION
The most important
recommendations to reduce
the impact of the wind on
constructions are as follows:
• The action of wind-breaks
and of vegetation
• The form of construction
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CED-AITR, INDORE 7

8. The Action of Wind
Breaks and of Vegetation
Planting low height vegetation and
applying wind-breaks serves to
deviate the wind upwards and filter
it in such a way that enables you to
protect your own house.
Therefore, the function of wind-
breaks is to reduce the strength of
the wind and not to face it.
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9. Vegetation considerably reduces strength
of wind
Trees release the wind from the majority
of dust and sand that it transports
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10. The form of
construction
• The form of constructions that better
faces the wind is compact and
symmetrical. (fig 3)
• When constructions are open the wind
passes through them!
• When constructions are closed, the wind
produces an effect of sucking upwards on
the roof which may lift up the roof
completely..................... (fig 1 & 2)
Fig 1 Fig 2
Fig 3

11. It is important to create ventilations on the top parts!
• When the wind enters into the house through a door
or a window, it increases the pressure on the roof.
• In this case it is very important to open the other
window or the door from the other side of the house
in order to allow the wind to pass through.
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CED-AITR, INDORE 11

12. CONSTRUCTION OF HOUSES
IN CYCLONE PRONE AREAS
Minimum standards for the design, construction
and performance of buildings to “withstand
extreme climate related natural hazard events”
depending upon their locations should be set.
The Most Vulnerable Parts of Construction:
The wind attacks constructions mainly in the
following points:
1. Roofing
2. Junction of roofing with walls
3. Doors and Windows
4. Foundations and junction of wall with the
soil
5. Walls
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13. 1. ROOFS
Probably the most common area of failure during cyclones is roofs.
The reasons are inadequate sheet thickness, less number of fasteners,
inadequate fastening devices.
The ways of protecting roofs are:
• Installing hip roofs with the pitch in the range of 25 degree to 40
degree.
• Avoiding overhangs of more than 18 inches at eaves or verges
• Patio roofs and verandas to be built as separate structure from the
roof
• Securing the main ridge using gussets, collar ties and metal straps
• Use of proper drive screws which go at least 50 mm in the purlin
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14. The capacity wind speed with a partial safety factor of unity and less
than 20% porosity for different types of roof is as shown in Table
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CED-AITR, INDORE 14

15. The Junction of roofing
with its structure
In order to reduce the risk of seeing the
roofing of the house removed
by the cyclone, it is fundamental to
properly fix the roofing with its
structure.
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CED-AITR, INDORE 15
Contd…

16. • The correct spacing between the
wooden joists to fix the zinc sheet
roofing is 60 cm.
• Nails are fixed according to this
spacing and in every 2 waves towards
the joists.
• Should the nails go beyond the
thickness of the joist, these should be
bended in the lower part.
• Nails to fix zinc roof sheets are
striated, with washer heads and a
rubber joint.
Note: Nails should always be applied on the upper
part of the wave so as to avoid rainwater leakage, as
the water flows along the lower part of the wave.
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CED-AITR, INDORE 16

17. Reinforce the
roofing structure
Usually the roofing structure is
made of triangular roof truss and
wooden joists placed on the upper
part of the walls. This structure
may be reinforced in various
forms. The figures only show
some options.
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CED-AITR, INDORE 17
Contd…

18. • The use of wood slabs or other
material on the roofing structure gives
more weight to the roofing and serves
as defence against the wind and the
rain if zinc roof sheets are lifted up.
• In this perspective, a thermal isolation
of the roofing may be obtained by
installing vegetal material such as mats
or reeds under the roofing (false
roofing).
• By placing a mixture of sand and straw
between the joists on a wood slab
covered by a plastic sheet, there is an
increase of weight on the roofing and
the inner part of the house is isolated
even further from the external
temperature and the water.
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AITR, INDORE 18
Contd…

19. The traditional roofing
structures may be
reinforced by applying
metal straps or pieces
of wood. Taking into
account that the
buildings are light, the
idea is to stabilize the
structure without
losing the elasticity.
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CED-AITR, INDORE 19

20. 2. JUNCTION OF
ROOFINS WITH WALLS
Junction of roofing with walls is the
most important junction in design of
houses in cyclone prone areas.
A. Junctions in Masonry Houses
In brick or cement blocks houses, a
wooden piece fixed with spindles in
the form of J or irons leaded in the
upper part of the wall allows using
metallic joints to strongly secure the
roofing structure with the stone-
walling wall.
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CED-AITR, INDORE 20
Contd…

21. When the roofing structure adjusts
directly on the upper beam of the slab,
metal straps that are bended on the
structural element of the roofing can be
placed and are nailed on both sides.
Spindles, pieces of iron or other
metallic elements with similar functions
may also be used.
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CED-AITR, INDORE 21
Contd…

22. • It is not recommendable that on
the edges of the roof and the
upper part of the walls, zinc roof
sheets are exposed to the wind.
(figure 1)
• The (figure 2) shows that a form
of mitigating this situation is to
firmly fix the zinc roof sheets to
the roofing structure using
metallic elements, and close the
space between the wall and the
roofing with blocks and pieces of
wood.
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AITR, INDORE 22
Fig 1
Fig 2
Contd…

23. B. In houses built with local materials:
• In this case the junction between the
roofing and the walls may be
reinforced by using wire, ropes of
metal straps. (fig 1)
• Apart from collecting rain water, it was
observed that gutter pipes effectively
protect the extremes of the roofing
from the action of the wind. (fig 2)
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AITR, INDORE 23
Fig 1
Fig 2
Contd…

24. C. Attached roofing
In traditional and modern constructions, additional roofing to the main structure of the
house is often attached.
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CED-AITR, INDORE 24

25. 3. DOORS AND WINDOWS
Any kind of opening whether needed for light or
ventilation acts as an area of stress concentration. The
reasons are non-uniform distribution of winds, across
wind vibrations.
Doors and windows represent the most probable entry
points of the wind inside the house.
The ways of protecting doors and windows are:
• Installation of wind locks and braces in doors;
• Every opening in the windward side to be supported
by the opening on the leeward side;
• Sum of length of openings should be less than half
the width of the structure;
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CED-AITR, INDORE 25

26. • Distance of the opening from the inner
corner should be greater than one sixth
length of the height of the structure;
• There should be a centrally located shutter
catch for every window;
• Every door frame should have at least 6
holdfasts; each holdfast being at least 9 inches
long;
• Every window frame should have at least 4
holdfasts; each holdfast being at least 9 inches
long.
• It is suggested that windows are properly
protected with wooden lids. These may be
fixed to the wall in such a way that they are
always available if needed.
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27. • The doors apart from being
strong and hard, they should be
closed with reinforced systems
using pieces of wood or made of
metal in order to resist to the
pressure and the effect of suction
generated by the cyclone.
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28. 4. Foundations
Foundation of any structure needs to be strong enough so
that it can prevent the structure from blowing away.
Moreover, the foundation helps the structure in
withstanding the surge or flooding which follow the
cyclone.
In particular, the foundations or linkage of walls with the
soil should be strong so as to avoid that the building is
completely lifted up by the wind.
The ways of protecting foundations are:
• Know-how of the type of soil so that the foundation is
laid at a proper depth;
• Knee bracing to be adopted over full diagonal bracing as it
allows the flow of debris;
• Proper bracing to be done in both the principal directions
of the stilts
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29. • Reinforced connection between reinforced concrete
foundation and wooden column;
• Posts having cross members which are connected at
the lower end should be embedded in the ground with
a depth at least 750 mm;
• Walls should be raised from a well compacted ground
or well compacted lean concrete bed from depth at
least 450 mm from the ground level
• The lighter the construction is, the bigger (or heavy)
the foundation should be.
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CED-AITR, INDORE 29

30. 5. Walls
Walls bears the ultimate load both from the windward
and leeward side. The whole structure collapses if they
fail, therefore proper care should be taken while
constructing them.
The ways of protecting walls are:
• Reinforcing the walls with the help of concrete bands
and vertical reinforcing bars and lateral ties;
• For improving the lateral load resistance of long
walls, buttresses should be provided;
• Using Ferro-cement plating around the exterior
perimeter if horizontal bands could not be provided;
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31. • Undesirable openings near the corner to be closed so as to improve the
strength of the cross walls;
• The individual structures like roof and foundation should be properly
braced and anchored with the walls.
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CED-AITR, INDORE 31

32. SITE
SELECTION
• Though cyclonic storms always approach from the
direction of the sea towards the coast, the wind
velocity and direction relative to a building remain
random due to the rotating motion of the high
velocity winds. In non-cyclonic region where the
predominant strong wind direction is well established,
the area behind a mound or a hillock should be
preferred to provide for natural shielding.
• Similarly a row of trees planted upwind will act as a
shield. The influence of such a shield will be over a
limited distance, only from 8 to 10 times the height of
the trees. A broken tree close to the house may
damage the house also hence distance of tree from the
house may be kept about 1.5 times the height of the
tree.
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INDORE 32

33. In hilly regions, construction
along ridges should be avoided
since they experience an
accentuation of wind velocity
whereas valleys experience
lower speeds in general.
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CED-AITR, INDORE 33

34. 34
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