Title: Cyclone and Fire
1Cyclone and Fire
- Dr. Shweta Goyal
- Assistant Professor
- Thapar University
2What are Cyclones?
- "Cyclone" is an intense whirl in the atmosphere
with very strong winds circulating around it in
anti-clockwise direction in the Northern
Hemisphere and in clockwise direction in the
Southern Hemisphere. - Word "Cyclone" is derived from the Greek, word
"Cyclos" meaning the coils of a snake. - To Henri Peddington, the tropical storms in the
Bay of Bengal and in the Arabian Sea appeared
like the coiled serpents of the sea and he named
these storms as "Cyclones". - known as Hurricane in the Atlantic and Eastem
Pacific, Typhoon in Western Pacific,
Willy-Willies in Australian sea, Baguis in the
Philippines.
3- Cyclones are intense low pressure areas - from
the centre of which pressure increases outwards-
The amount of the pressure drop in the centre and
the rate at which it increases outwards gives the
intensity of the cyclones and the strength of
winds.
4Criteria followed to classify cyclones
- As adopted by Meteorological Department of India
1 knot - 1.85 km per hour
5Mechanism of cyclones
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7Mechanism of cyclones
- A full-grown cyclone is a violent whirl in the
atmosphere 150 to 1000 km across, 10 to 15 km
high. - The central calm region of the storm is called
the "Eye". The diameter of the eye varies between
30 and 50 km and is a region free of clouds and
has light winds. - Around this calm and clear eye, there is the
"Wall Cloud Region" of the storm about 5O km in
extent, where the gale winds, thick clouds with
torrential rain, thunder and lightning prevail. - Away from the "Wall Cloud Region", the wind speed
gradually decreases. - The gales give rise to a confused sea with waves
as high as 20 metres, swells that travel a
thousand miles. Torrential rains, occasional
thunder and lightning flashes - join these - Through these churned chaotic sea and atmosphere,
the cyclone moves 300 to 500 km, in a day to hit
or skirt along a coast, bringing with it strome
surges
8Mechanism of cyclones
- Once the cyclones reach higher latitudes they
often change their direction and move north and
then north-east (south and south east
hemisphere). The process is known as
recurreature. - Before it recurves, the speed decreases and the
system remains stationary for a day or so. - When two cyclones exist near to each other, they
inter-act and move anti-clockwise with respect to
each other. - In the Atlantic, tracks often execute a parabola.
- In India, when cyclones recur they get broken up
over the Himalayas and their further eastward
movement ceases.
9Naming of cyclone
- Cyclones derive their names through a systematic
procedure laid down by the World Meteorological
Organisation (WMO) and the United Nations
Economic and Social Commission for Asia and the
Pacific (ESCAP). - naming of cyclones began in September 2004
- Eight north Indian Ocean countries - Bangladesh,
India, the Maldives, Myanmar, Oman, Pakistan, Sri
Lanka and Thailand - have prepared a list of 64
names. - Since 2004, the eight countries have faced 20
cyclones. - The countries take turns in naming the cyclones.
The last six were Nargis (Pakistan), Rashmi (Sri
Lanka), Khai-Muk (Thailand), Nisha (Bangladesh),
Bijli (India) and Aila (Maldives).
10Cyclone Map of India
11The principal dangers of a cyclone
- Gales and strong winds
- damage installations, dwellings, communication
systems, trees., etc. resulting in loss of life
and property. - Torrential rain
- may cause river floods
- Storm surges or high tidal waves
- A storm surge is an abnormal rise of sea level
near the coast caused by a severe tropical
cyclone - as a result, sea water inundates low lying areas
of coastal regions drowning human beings and
live- stock, eroding beaches and embankments,
destroying vegetation and reducing soil
fertility.
12What is Storm Surge?
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14How high will the Storm Surge be?
- Every cyclone that affects the coast produces a
storm surge. But not all storm surges rise to
dangerous levels. The height of the surge depends
on - The intensity of the cyclone - as the winds
increase, the sea water is piled higher and the
waves on top of the surge are taller. - The forward speed of the cyclone - the faster the
cyclone crosses the coast, the more quickly the
surge builds up and the more powerfully it
strikes. - The angle at which the cyclone crosses the coast
- local zones of enhanced surge in areas such as
narrow inlets and bays. - The shape of the sea floor - the surge builds up
more strongly if the slope of the sea bed at the
coast is shallow. - Past history indicates that loss of life is
significant when surge magnitude is 3 metres or
more and catastrophic when 5 metres and above
15Surge prone coasts of India
- Vulnerability to storm surges is not uniform
along Indian coasts. - east coast of India are most vulnerable to high
surges - i) North Orissa, and West Bengal coasts.
- ii) Andhra Pradesh coast between Ongole and
Machilipatnam. - iii) Tamil Nadu coast, south of Nagapatnam.
- The West coast of India is less vulnerable to
storm surges - i) Maharashtra coast, north of Harnai and
adjoining south Gujarat coast and the coastal
belt around the Gulf of Bombay. - ii) The coastal belt around the Gulf of Kutch.
16Cyclone Accounts
- The oldest and the worst cyclone on record is
that of October 1737 hit Calcutta and took a
toll of 3,00,000 lives in the deltaic region. It
was accompanied by a 12 metre high surge. - Midnapore Cyclone of October 1942 was accompanied
by gale wind speed of 225 kmph - Rameswaram Cyclone of 17th to 24th December 1964
wiped out Dhanuskodi in Rameswaran Island from
the map. A passenger train which left Rameswaram
Road station near about the midnight of 22nd was
washed off by the storm surges sometimes later,
nearly all passengers traveling in the train
meeting water graves.
17Cyclone Accounts
- Bangla Desh Cyclone of 8-13 November 1970 which
crossed Bangla Desh coast in the night of 12th
was one of the worst in recent times, with storm
surges of 4 to 5 metres height at the time of
high tides, and with 25 cm of rain in the areas,
the inundation took toll of about 3,00,000
people. - Andhra Cyclone of 14-20 November 1977 that
crossed coast near Nizampatnam in the evening of
19th, took a toll of about 10,000 lives.
18How to avoid the catastrophe?
- Effective Cyclone Disaster Prevention and
Mitigation Plan requires - A Cyclone Forecast - and Warning Service.
- Rapid dissemination of warnings to the Government
Agencies, Marine interests like the Ports,
Fisheries and Shipping and to General Public. - Organisations to construct Cyclone Shelters in
the cyclone-prone areas and ready machinery for
evacuation of people to safer areas. - Community preparedness at all levels to meet the
exigencies.
19Cyclone warning
- "Two Stage Warning Scheme
- The first stage warning known as the "Cyclone
Alert" is issued 48 hours in advance of the
expected commencement of the adverse weather over
the coastal areas. - The second stage warning known as the "Cyclone
Warning" is issued 24 hours in advance. - Both cyclone "Alert" and "Warning" messages are
passed to the AIR stations for repeated broadcast.
20Vulnerable Communities
- vulnerability of a human settlement to a cyclone
is determined by its siting, the probability that
a cyclone will occur, and the degree to which its
structures can be damaged by it. - most vulnerable to cyclones are
- Light weight structures with wood frames,
especially older buildings where wood has
deteriorated and weakened the walls - Houses made of unreinforced or poorly-constructed
concrete block - Buildings in low- lying coastal areas or river
floodplains - Furthermore, the degree of exposure of land and
buildings will affect the velocity of the cyclone
wind at ground level, - Certain settlement patterns may create a "funnel
effect" that increases the wind speed between
buildings, leading to even greater damage.
21How High Winds Damage Buildings
- Contrary to popular belief, few houses are blown
over. Instead, they are pulled apart by winds
moving swiftly around and over the building. This
lowers the pressure on the outside and creates
suction on the walls and roof, effectively
causing the equivalent of an explosion. - Whether or not a building will be able to resist
the effects of wind is dependent not so much upon
the materials that are used but the manner in
which they are used. - common belief that heavier buildings, such as
those made of concrete block, are safer. - Truth well-built and properly-engineered masonry
house offers a better margin of safety than other
types of buildings
22Catastrophic Failures
- Foundations
- The uplift forces from cyclone winds can
sometimes pull buildings completely out of the
ground. - In contrast to designing for gravity loads, the
lighter the building the larger (or heavier) the
foundation needs to be in cyclone resistant
design.
23Catastrophic Failures
- Steel Frames
- A common misconception the loss of cladding
relieves the loads from building frameworks. - Truth the wind loads on the structural frame
increases substantially with the loss of cladding - Usual weakness in steel frames is in the
connections. Thus economising on minor items
(bolts) has led to the overall failure of the
major items (columns, beams and rafters)
24Catastrophic Failures
- Masonry Houses
- usually regarded as being safe in cyclones.
- There are countless examples where the loss of
roofs has triggered the total destruction of
un-reinforced masonry walls.
25Catastrophic Failures
- Timber Houses
- The key to safe construction of timber houses is
the connection details. - The inherent vulnerability of light-weight timber
houses coupled with poor connections is a
dangerous combination which has often led to
disaster.
26Catastrophic Failures
- Reinforced Concrete Frames
- The design of reinforced concrete frames is
usually controlled by the seismic hazard. - If seismic design is not done, wind analysis must
be performed - ignoring this, can lead to disaster.
27Component Failures
- Roof Sheeting
- This is perhaps the commonest area of failure in
cyclones. - The causes are usually inadequate fastening
devices, inadequate sheet thickness and
insufficient frequencies of fasteners in the
known areas of greater wind suction.
28Catastrophic Failures
- Roof Tiles
- These were thought to have low vulnerability in
storms but past cyclones have exposed the problem
of unsatisfactory installation practices.
29Catastrophic Failures
- Rafters
- Of particular interest in recent cyclones was the
longitudinal splitting of rafters with the top
halves disappearing and leaving the bottom halves
in place. - The splitting would propagate from holes drilled
horizontally through the rafters to receive
holding-down straps.
30Catastrophic Failures
- Windows and Doors
- After roof sheeting, these are the components
most frequently damaged in cyclones. - Of course, glass would always be vulnerable to
flying objects. - The other area of vulnerability for windows and
doors is the hardware latches, bolts and hinges. - Walls
- Cantilevered parapets are most at risk.
- But so far walls braced by ring beams and columns
have remained safe.
31Damaging Effects of Cyclone on Houses
- Due to the high wind pressure and improper
connection of the house to the footings it can be
blown away.
32Damaging Effects of Cyclone on Houses
-
- Roofing materials not anchored can be blown away
33Damaging Effects of Cyclone on Houses
- Light weight verandah roofs are more susceptible
to damage due to high wind speed.
34Damaging Effects of Cyclone on Houses
- When cyclones are accompanied with heavy rain for
a long duration, the buildings can be damaged due
to flooding also.
35Design Wind Speed and Pressures
- The basic wind speed is reduced or enchanced for
design of buildings and structures due to
following factors - The risk level of the structure measured in terms
of adopted return period and life of structures. - Terrain roughness determined by the surrounding
buildings or trees and, height and size of the
structure. - Local topography like hills, valleys, cliffs, or
ridges, etc.
36On which elements the wind pressure effect must
be considered?
- It is considered on various elements depends on
- Aerodynamics of flow around buildings.
- The windward vertical faces being subjected to
pressure. - The leeward and lateral faces getting suction
effects and - The sloping roofs getting pressures or suction
effects depending on the slope.
37typical effects of openings in the walls
- Wind generating opening on the windward side
during a cyclone will increase the pressure on
the internal surfaces - may be sufficient to cause the roof to blow off
and the walls to explode.
38typical effects of openings in the walls
- Windward face of the building collapses under
pressure of wind force
39typical effects of openings in the walls
- During a cyclone an opening may suddenly occur on
the windward side of the house. - The internal pressure which builds up as a result
may be relieved by providing a corresponding
opening on the leeward side.
40- If the building is not securely tied to its
- foundations, and the walls cannot resist
push/pull forces, the house tends to collapse
starting from the roof with the building leaning
in the direction of the wind.
41- Failure of the Wall Wind forces on the walls of
the house may produce failure. Wind striking a
building produces pressure which pushes against
the building, on the windward side, and suction
which pulls the building on the leeward side and
the roof.
42- Overturning is another problem for light
structures. - This occurs when the weight of the house is
insufficient to resist the tendency the house to
be blown over.
43When choosing a site for your house, consider the
following
- 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 - 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 for 8 10 times the
height of the trees. - A tree broken close to the house may damage the
house also hence distance of tree from the house
may be kept 1.5 times the height of the tree.
44When choosing a site for your house, consider the
following
No shielding from high wind due to absence of
barriers
Shielding from high wind by permeable barriers
such as strong trees
45When choosing a site for your house, consider the
following
- In hilly regions,
- construction along ridges should be avoided since
they experience an increase of wind velocity - whereas valley experiences lower speeds in general
46When choosing a site for your house, consider the
following
- In cyclonic regions close to the coast, a site
above the likely inundation level should be
chosen. In case of non availability of high level
natural ground, construction should be done on
stilts with no masonry or cross bracings up to
maximum surge level, or on raised earthen mounds
to avoid flooding/inundation but knee bracing may
be used.
47Shape of the House
- Shape is the most important single factor in
determining the performance of buildings in
cyclones. - Simple, compact, symmetrical shapes are best.
- The square plan is better than the rectangle
since it allows high winds to go around them. - The rectangle is better than the L-shaped plan.
- This is not to say that all buildings must be
square. But it is to say that one must be aware
of the implications of design decisions and take
appropriate action to counter negative features. - The best shape to resist high winds is a square.
48Shape of the House
If other shapes are desired, efforts should be
made to strengthen the corners. If longer shapes
are used, they must be designed to withstand the
forces of the wind. Most houses are rectangular
and the best layout is when the length is not
more than three (3) times the width.
49- In case of construction of group of buildings, a
cluster arrangement can be followed in preference
to row type.
50Roofs
- Lightweight flat roofs are easily blown off in
high winds. - In order to lessen the effect of the uplifting
forces on the roof, the roof Pitch should not be
less than 22º. - Hip roofs are best
51Roofs
- General Design Considerations
- Avoid a low pitched roof, use a hip roof or a
high pitched gable roof. - Avoid overhanging roofs. If overhangs or canopies
are desired, they should be braced by ties held
to the main structures. - Avoid openings which cannot be securely closed
during a cyclone
52Overhangs, verandahs
- Avoid large overhangs as high wind force build up
under them. - Overhangs should not be more than 18 inches at
verges or eaves. - Build verandah and patio roofs as separate
structures rather than extensions of the main
building.
53Securing the Ridge
If the rafters are not secure, the ridge can fall
apart when strong wind passes over the roof.
54Securing the Ridge
- The ridge can be secured by using-
- COLLAR TIES - Timbers connecting the rafters.
Nail them to the side of the rafters
55Securing the Ridge
- GUSSETS - Usually made of steel/plywood. This is
used at the ridge.
56Securing the Ridge
- METAL STRAPS over the top of the rafters
57Securing the corrugated galvanized sheets
- The sheets are gauged by numbers. The Higher the
number the thinner the material. Example 24 gauge
galvanized sheet is superior to 28 gauge. - Failure in roofs
- If the sheeting is too thin or there are too few
fittings, the nails or screws may tear through
the sheet. - If galvanized sheets are used, 24 gauge is
recommended.
58Securing the corrugated galvanized sheets
- How to secure sheeting to the roof structure, use
- Fixings every two (2) corrugation at ridges,
eaves and overhangs. - Fixings every three (3) corrugation. Maximum
spacing at all other locations
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60Fixings for sheetings
- Screws
- Use proper drive crews for corrugated galvanized
roof sheets. - Be sure that the screws go into the purlins at
least fifty (50) mm. - use large washers under the screw heads to
prevent the roof sheets from tearing - Nails
- Nails do not hold as well as screws.
- Use nails with wide heads and long enough to bend
over below the lath. - Galvanized coated nails are better than ordinary
wire nails.
61Roof cladding
- As the corners and the roof edges are zones of
higher local wind suctions and the connections of
cladding/sheeting to the truss need to be
designed for the increased forces. - following precautions are recommended-
- Sheeted roofs- A reduced spacing of bolts, ¾ of
that admissible as per IS800, recommended. - For normal connections, J bolts may be used but
for cyclone resistant connections U bolts are
recommended.
62- Alternatively, strap may be used at least along
edges to fix cladding with the purlins to avoid
punching through the sheet.
63- Clay tile roofs- Because of lower dead weight,
these may be unable to resist the uplifting force
and thus experience heavy damage, particularly
during cyclones. - Anchoring of roof tiles in R.C. strap beams is
recommended for improved cyclone resistance. - As alternative to the bands, a cement mortar
screed, reinforced with galvanized chicken mesh,
may be laid over the high suction areas of the
tiled roof.
64Foundations
- The foundation is the part of the house which
transfers the weight of the building to the
ground. It is essential to construct a suitable
foundation for a house as the stability of a
building depends primarily on its foundation. - It is desirable that information about soil type
be obtained and estimates of safe bearing
capacity
65Parameters need to be properly accounted in the
design of foundation
- Effect of surge or flooding-
- Invariably a cyclonic storm is accompanied by
torrential rain and tidal surge (in coastal
areas) resulting into flooding of the low lying
areas. - Flooding causes saturation of soil and thus
significantly affects the safe bearing capacity
of the soil. - In flood prone areas, the safe bearing capacity
should be taken as half of that for the dry
ground. - Also the likelihood of any scour due to receding
tidal surge needs to be taken into account while
deciding on the depth of foundation - Buildings on stilts-
- Where a building is constructed on stilts it is
necessary that stilts are properly braced in both
the principal directions. - Knee bracings will be preferable to full diagonal
bracing so as not to obstruct the passage of
floating debris during storm surge.
66main types of foundation
- Slab or Raft Foundation
- Used on soft soils.
- Spread the weight over a wider area
67main types of foundation
- Strip Foundation
- Used for areas where the soil varies.
- Most common.
- Supports a wall.
68main types of foundation
- Stepped Foundation
- Used on sloping ground.
- Is a form of strip foundation.
69main types of foundation
- Pile Foundation
- deep foundations for small or large buildings.
- Under reamed piles often used in expansive clay
or alluvial soils.
70Masonry walls
71Masonry walls
- Strengthening of walls against high
wind/cyclones. - Reinforce the walls by means of reinforced
concrete bands and vertical reinforcing bars as
for earthquake resistance.
72Wall Openings
- general areas of weakness and stress
concentration, but needed essentially for light
and ventilation. - The following are recommended in respect of
openings. - Openings in load bearing walls should not be
within a distance of h/6 from inner corner for
the purpose of providing lateral support to cross
walls, where h is the storey height upto eave
level. - Openings just below roof level be avoided
- Since the failure of any door or window on the
wind-ward side may lead to adverse uplift
pressures under roof, the openings should have
strong holdfasts as well as closing/locking
arrangement.
73Wall Openings
74Glass Panes
- Glass windows and doors are, of course, very
vulnerable to flying objects - Use thicker glass panes.
- reduce the panel size to smaller dimensions.
- Also glass panes can be strengthened by pasting
thin film or paper strips
75CYCLONES - Do's Dont's
- Before the Cyclone season
- Check the house secure loose tiles, carry out
repair works for doors and windows - Remove dead woods or dying trees close to the
house anchor removable objects like lumber
piles, loose tin sheds, loose bricks, garbage
cans, sign-boards etc. which can fly in strong
winds - Keep some wooden boards ready so that glass
windows can be boarded if needed - Demolish condemned buildings
- Keep some dry non-perishable food always ready
for emergency use
76CYCLONES - Do's Dont's
- When the Cyclone starts
- Listen to the radio about weather warnings
- Pass on the information to others. Believe in the
official information - Remember that a cyclone alert means that the
danger is within 24 hours. Stay alert. - If your house is securely built on high ground
take shelter in the safer part of the house.
However, if asked to evacuate do not hesitate to
leave the place. - Provide strong suitable support for outside
doors. - Keep torches handy
- Be sure that a window and door can be opened only
on the side opposite to the one facing the wind. - If the centre of the cyclone is passing directly
over your house there will be a lull in the wind
and rain lasting for half and hour or so. During
this time do not go out because immediately
after that very strong winds will blow from the
opposite direction. - Switch off electrical mains in your house.
- Remain calm
77CYCLONES - Do's Dont's
- When Evacuation is instructed
- Pack essentials for yourself and your family to
last you a few days, including medicines, special
foods for babies and children or elders. - Head for the proper shelter or evacuation points
indicated for your area. - Do not worry about your property
- At the shelter follow instructions of the person
in charge. - Remain in the shelter until you have been
informed to leave
78CYCLONES - Do's Dont's
- Post-cyclone measures
- You should remain in the shelter until informed
that you can return to your home. - Strictly avoid any loose and dangling wires from
the lamp posts. - Clear debris from your premises immediately.
- Report the correct loss to appropriate authorities
79Fire
80Elements of fire protection
- Include
- use of non-combustible building materials,
- use of fire-resistive building assemblies,
- installation of automatic detection devices and
sprinklers, - development of improved fire fighting techniques
81Fire-resistive construction
- A building construction in which the structural
members (including walls, partitions, columns,
floors, and roof) are of noncombustible materials
having fire-endurance ratings at least equal to
those specified by the appropriate authorities
82fire-resistive ratings
- "fire resistance rating" is a legal term utilized
by model codes to regulate building construction. - The fire-resistive ratings of various materials
and constructions are established by laboratory
tests - Specified in terms of hours a material or
assembly can be expected to withstand exposure to
fire. - For exterior walls, floors, and roof of masonry
or fire-resistive material with a fire-resistance
rating of at least 2 hours.
83Fire-Resistive Assemblies
- An assembly is a combination of materials put
together in a specific way that achieves the fire
resistance rating required in the building code. - For example, gypsum wallboard applied to a steel
stud. - Fire-resistance ratings apply only to assemblies
in their entirety.
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85Fireproofing of Construction Materials
- In construction, heavy wood timbers have a
relatively high fire resistance, because fire
tends to burn very slowly inward from the
surface, leaving enough sound timber in the
center to prevent collapse. - Wood framing can also be impregnated with
ammonium phosphate solution or covered with
special mastics. - To be classed as fire resistive, buildings must
be made of reinforced concrete or protected steel
that will stand considerable fire with minor
damage - While steel retains its strength up to a very
high temperature, it fails rapidly at
temperatures over 1,000F (540C).
86Fireproofing of Construction Materials
- Structural steel may be protected in a number of
ways. It can be faced with brick, concrete, or
tile however, construction with these materials
usually adds too much weight to a building. - A protective layer of concrete over all surfaces
of a beam or over the steel bars in reinforced
concrete has to be at least 2.5 in. (6.4 cm)
thick to be effective - hollow clay tile used to cover beams and girders
has to be at least 4 in. (10 cm) thick. - most buildings use lightweight fireproofing such
as gypsum, perlite, and vermiculite mixed in
plaster one inch (2.5 cm) of such materials will
absorb an equivalent amount of heat as 2.5 in.
(6.4 cm) of concrete. - Some recent buildings circulate water inside each
column, protecting the structure against
meltdown. - In urban areas, buildings must also provide
protection against fire in neighboring buildings
through fireproof exterior walls-preferably
windowless, since windows are fire openings.
87How to Build a Fire Resistant House
- Frame your home with metal studs. Metal studs
cannot combust in the same way that wood studs
can. - Install GFI (ground fault circuit interrupters)
outlets and circuit breakers.. It can, in just
1/30 of a second, trip the internal circuit,
effectively cutting off the flow of electricity
in the event of a possible short. - Use as much concrete as possible in the structure
of your home. - Use hard materials for flooring, doors and
roofing. Carpet is highly combustible. - Install safety features. Fire alarms
88Thank You