5.
Safe Construction Practices
A powerful earthquake measuring 6.6 at the Richter scale struck SOUTHEASTERN IRAN on 26th
December, 2003 at 5:26:52 AM (local time) and caused enormous loss of life, and near total
destruction of physical assets, killing 30,000 people and injured another 30,000. The health and
education infrastructure was severely damaged and over 85% houses collapsed.
A super cyclone slammed the state of Orissa on October 29, 1999
with a wind speed of 270-300 kmph, accompanied by torrential rains
ranging from 400 mm to 867 mm continuously for three days. Over 7 lakh
buildings were completely damaged and 13 lakh buildings were partially
damaged.
In Class VIII and Class IX textbooks we have studied about causes, effects and mitigation strategies of
natural and manmade hazards. In this chapter we will discuss about some of the important factors to
be considered to construct a building resistant to four natural hazards: earthquake, landslide, cyclone
and flood. The cost of natural disasters to lives, property, livelihood and infrastructure have skyrocketed
in last few decades, as the world’s population has grown and people have started residing in areas that
are vulnerable to natural hazards. The most successful way to mitigate loss of life and property, is to
construct buildings that are disaster resistant. This chapter outlines some of the structural safety
measures that need to be taken up for constructing desaster resistant buildings.
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Earthquakes
On December 23, 1972, a series of earthquakes shook the
Central American nation of Nicaragua. The largest
earthquake registered 6.2 on the Richter scale. The
earthquake’s epicenter was located precisely at the capital
city of Managua. The earthquake resulted in the destruction
of the heavily populated central zone and damage to a total
area of about 27 square kilometers (10 square miles).
Subsequent fires blazed throughout the city, compounding
the damages. In the wake of the disaster, at least 8,000 of
Managua’s total population of 430,000 had died, 20,000 were
injured, over 260,000 had fled the city, 50 percent of the
employed were jobless, and 70 percent were left temporarily
homeless. At least 10 percent of the nation’s industrial
capacity, 50 percent of commercial property, and 70 percent
of government facilities were rendered inoperative. Overall,
the damage estimated in US dollars was $845 million.
GROUND MOVEMENTS
The ground movements caused by earthquakes can have
several types of damaging effects. Some of the major
effects are:
The building has tilted as a result of column
1. Ground shaking, i.e. back-and-forth motion of the failure & has partly damaged the nearby building
ground, caused by the passing vibratory waves through (Taiwan 1999). (By Bachmann H., Sesimic
the ground. Conceptual Design of Buildings)
2. Soil failures, such as liquefaction and landslides, caused by shaking;
3. Surface fault ruptures, such as cracks, vertical shifts, etc.
4. Tidal waves (tsunamis), i.e. large waves on the surface of bodies of water that can cause major
damage to shoreline areas.
EFFECT ON BUILDINGS
As the vibrations and waves continue to move through the
House
earth, buildings on the earth’s surface are set in motion.
Each building responds differently, depending on its
construction. When the waves strike, the earth begins to
move backward and forward along the same line. The
lower part of a building on the earth’s surface
immediately moves with the earth. The upper
portion, however, initially remains at rest; thus
the building is stretched out of shape.
Gradually the upper portion tries to Shaking of short and tall building due to
catch up with the bottom, but as ground acceleration
it does so, the earth moves in the other direction, causing a “whiplash”
34 effect. The vibration can cause structural failure in the building itself,
or to an adjacent building having different response characteristics.
Taller buildings also tend to shake longer than short buildings, which can make them relatively more
susceptible to damage.
PROTECTION MEASURES
The primary objective of earthquake resistant design is to prevent collapse during earthquakes thus
minimising the risk of death or injury to people in or around the buildings. There are certain features
which if taken into consideration at the stage of architectural planning and structural design of buildings,
their performance during earthquakes will be appreciably improved. Some of these are stated below :
Building configuration
★ The building should have a simple rectangular plan.
★ Long walls should be supported by Reinforced Concrete columns
as shown on the right side.
★ Large buildings having plans with shapes like T, L, U and X should
preferably be separated into rectangular blocks by providing gaps
in between.
Foundation
Buildings which are structurally strong to withstand earthquakes
sometimes fail due to inadequate foundation
design. Tilting, cracking and failure of structure
may result from soil liquefaction. Soil liquefaction
refers to transformation of soil from a solid state
to a liquid state as a consequence of increased
pressure.
Use of seperation gaps
Tilting of building due to liquefaction (Adapazari, Turkey 1999)
By Bachmann H., Sesimic Conceptual Design of Buildings
Depending on the type of soil conditions the depth of the foundation has to be decided.
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Control on openings in walls
Door and window openings in walls should preferably be small and more
centrally located. Too many or large openings will make the wall vulnerable
to collapse during earthquakes. The location of openings should not be
too close to the edge of the wall.
RIGHT: Damage to columns due
to long openings & windows
located at the edge of the
column (Northridge, California
1994)
LEFT: Long window opening
caused additional shear stress
& column failure (Izmit, Turkey
1999) By Bachmann H., Sesimic
Conceptual Design of Buildings
Reinforced concrete bands in masonry Legend
1 Lintel band
buildings 2 Eave level
(Roof) band
For integrating the walls of an enclosure to 3 Gable band
4 Floor band
perform together like a rigid box reinforced 5 Plinth band
concrete bands are provided which run 6 Vertical band
7 Rafter
continuously on all external and internal walls 8 Holding Down bolt
9 Door
including fixed partition walls. One or more of 10 window
the following bands may be necessary in a
building. Plinth band, lintel band, roof band, and
gable band are names used for the band
depending on the level of the building where the Overall arrangement of reinforcing
in masonry double storey building
band is provided. having pitched roof
Vertical reinforcement
Vertical reinforcement should be provided at corners and junction of
walls. It shall be passing through the lintel bands and floor slabs or
floor level bands in all storeys.
Earthquake doesn’t kill people. It is the badly designed buildings
that kill the people. So to prevent an earthquake hazard from
becoming a disaster our buildings should be properly designed
incorporating the earthquake resistant design features
into it.
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Landslides
Landslides are among the major natural disasters or calamities in the world. In hilly terrains of India,
including Himalayan mountains landslides have been a major and widely spread natural disasters that
strike life and property almost perennially and occupy a position of major concern. These landslides,
year after year, bring about untold misery to human settlements apart from causing devastating damages
to transportation and communication network.
Landslides, debris fall, debris slide, debris flow, rock toppling etc. cause destruction of slope and ground
surface, initiating the change of uncontrolled erosion in the mountain terrains.
On 21st August, 2002, heavy monsoon in eastern Nepal triggered landslides and flashfloods which killed
419 people and injuring 105 people. More than 53,152 families were affected and about 19,485 houses
were destroyed. A total of 47 districts were affected.
FACTORS THAT CAUSE LANDSLIDES
Landslides occur because of the interplay of
several factors.
Natural factors
★ Intensity of rainfall
★ Steep slopes
★ Stiffness of slopes
★ Highly weathered rock layers
★ Soil layers formed under gravity
★ Seismic activity
★ Poor drainage
Man made factors Normal life disrupted in the hilly terrains of
Uttaranchal
★ Deforestation leading to soil erosion
★ Non-engineered excavation
★ Mining and quarrying
★ Non-engineered construction
★ Land use pattern
MOST VULNERABLE HOMES
Vulnerable houses are those which are situated on:
★ Existing landslides area.
★ Steep natural slopes.
★ Areas in or at the mouths of drainages (such
as canyons).
★ Houses constructed near foothills.
Large volume of sediments, rudiments of
buildings and other debris were transported
by debris flows and high flood water 37
PROTECTION MEASURES FROM DAMAGE TO BUILDINGS
Site Selection
Landslides generally happen where they have occurred in
the past, and in identifiable hazard locations. Areas that are
typically considered safe from landslides include areas that
have not moved in the past; relatively flat areas away from
sudden changes in slope; and areas at the top of or along
ridges. Houses built at the toe of steep slopes are often
vulnerable to slides and debri flows.
Signs and Warnings
If your house is on a hill, you can detect possible slope
failure if you watch for these signs:
★ Doors or windows stick or jam for the first time.
★ New Cracks appear on plaster, tile, brick or foundations.
★ Outside walls, walks or stairs begin pulling away from the building.
★ Slowly developing, widening cracks appear on the ground or on paved areas such as streets or
driveways.
★ Underground utility lines break.
★ Fences, retaining walls, utility poles or trees tilt or move.
★ Water or bulging ground appears at the base of a slope.
Take Preventive Action
The potential for landslides and destructive erosion can be greatly reduced or prevented with proper
development, sound construction techniques, seasonal inspections and regular maintenance of drainage
facilities.
Protect Vulnerable Areas
Keep surface drainage water away from vulnerable areas,
such as steep slopes, loose soils and non-vegetated surfaces.
Collect Runoff
Collect and direct water from patios, driveways, non-vegetated
surfaces, into catch basins; and confine water flow in drainpipe
such as a drainage ditch, drywell, gutter, natural drainage or
holding pond. Roof water may go directly to the drainpipe.
Intercept Surface Water
When surface water flows onto your property, and where a discharge point is available, dig a
shallow, gently sloping ditch to intercept the water and direct it into a natural water course,
vegetated drainage area, street pavement, or road drainage ditch. Your intercepting
ditch should be nearly horizontal, with a minimum slope, sufficient to allow water
to flow slowly. Smoothen the sides of the ditch and grow vegetation ; keep all
38 ditches free of debris.
Stabilize Slopes
★ Improve your soil’s ability to resist erosion by stabilizing slopes by increasing vegetation and trees.
★ Straw, woodchips, or bark applied to a depth of at least one inch are effective in holding soil in place
on slopes.
BARRIERS
Property owners at the toe of steep slopes may be
able, in some situations, to create barriers or
catchments that trap smaller landslides. Such
structures must be designed to withstand the volumes
and velocities of material in any potential slide. In
addition, designs must allow removal of trapped
material. Barriers may consist of reinforced walls on
the side of a building facing the slope.
Floods
Bangladesh is a riverine country where recurrent flooding is both common and necessary. Every year
large areas are submerged during the monsoon season and fertilized by deposits of fresh alluvium, i.e.,
the soil deposited by moving water. However, if the waters remain stagnant for too long, these beneficial
floods become major disasters. Such was the case in the summer and fall of 1974 when flooding extended
over nearly one-half of the country and stagnated for more than a month. At least 1,200 people died in
the floods and another 27,500 died from subsequent disease and starvation. Approximately 425,000
houses were destroyed or severely damaged. A total of 36 million people suffered severe hardship and
losses due to the disaster.
Water is a source for all life forms. Without water no life is sustainable. How tragic it is, when water in the
form of floods takes away thousand of human and cattle lives. More than one million huts and poor houses
are lost every year in floods in India. Can we prevent this loss?
MOST VULNERABLE HOMES
1. Buildings, which are constructed with earth-based materials or using stone and brick in mud mortar
are highly vulnerable to damage in heavy rains and/or floods.
2. The huts made from biomass materials like bamboo, leaves, thatch or light construction
using metal sheets are easily destroyed in floods and washed away.
3. The occupation of areas within the flood plain of rivers has increased the
vulnerability, especially in areas of high population concentration. Flood plains
attract poor people because of inexpensive land values.
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EFFECT ON BUILDINGS
The damage to buildings due to floods are as follows:
1) Houses are washed away due to the impact of the water
under high stream velocity. The houses are commonly
destroyed or dislocated so severely that their reconstruction
is not feasible.
2) Houses constructed out of light weight materials like wood
float when they are not anchored properly.
3) Damage caused by inundation of house. The house may
remain intact on its foundation, but damage to materials
Flood disrupting normal life
may be severe. Repair is often feasible but may require
special procedures to dry out properly.
4) Undercutting of houses. The velocity of the water may scour and erode the foundation of the
house or the earth under the foundation. This may result in the collapse of the house or require
substantial repair.
5) Damage caused by debris. Massive floating objects like
trees, electric poles, etc. may damage the standing houses.
PROTECTION MEASURES FROM DAMAGE TO BUILDINGS
The most effective measures for prevention against inundation
are:
1. to avoid residing on river banks and slopes on river sides and
the sides of gorges.
2. to build at least 250 meters away from the sea coast/river
Roof tops being used as shelter
banks places during floods
3. to build proper drainage system in all flood prone areas, so
that the water can be drained off quickly to prevent accumulation.
4. to construct the building with a plinth level higher
than the known high flood level.
5. to construct the whole village or settlement on
a raised platform higher than the high flood level.
6. to construct buildings on stilts or columns with
wall-free space at ground level permitting free
flow of water (inundation or flowing), provided
that columns are circular and strong. In
dry weather condition the ground area could be fenced and used for cattle, sheep poultry
farming, or storage etc.
40
Not only do we contribute to the causes of floods, but
reckless building in vulnerable areas, poor watershed
management, and failure to control the flooding also help
create the disaster condition. Therefore there is an urgent
need to mitigate the flood hazard by proper habitat
management, watershed management and incorporating
flood resistant features in our buildings.
Use of stilts for raised floor above flood level
Cyclones
Cyclones pose a major threat to life and property in many parts of the
world. Every year these sudden, violent cyclones bring widespread
devastation to coastlines and islands lying in their erratic paths. A
windstorm’s destructive work is done by the high wind; flood producing
rains and associated storm surges.
On November 19, 1977, a cyclone, which had been expected to hit
Tamil Nadu, instead struck the central coast of Andhra Pradesh State
in the Krishna Godavari Delta. Many people perished because
advance warning was either too slowly or too narrowly disseminated.
Damage in Andhra Pradesh was caused primarily by a storm surge
that devastated some 65 villages, about 21 of which were completely
washed away. The storm surge was reported to have been 5.7 meters
(19 feet) high, 80 kilometers (50 miles) long, 16 kilometers (10 miles)
wide, with a speed of 190 kilometers per hour (120 miles per hour).
Many of the victims of the Andhra Pradesh cyclone were migrant
laborers. This made identification of the dead difficult.
MOST VULNERABLE HOMES
The vulnerability of a human settlement to a cyclone is determined by
its location, the probability that a cyclone will occur, and the degree
to which its structures can be damaged by it. Buildings are considered
vulnerable if they cannot withstand the forces of high winds and storm
surge. Generally those most vulnerable to cyclones are lightweight
structures with wooden frames, especially older buildings where wood Pictures showing the effect of
has deteriorated and weakened the walls. Houses made of poorly cyclone on structures
constructed concrete blocks are also vulnerable.
Urban and rural communities on low islands or in unprotected low-lying coastal areas or
river floodplains are considered vulnerable to cyclones. Furthermore, the degree of
exposure of land and buildings will be affected by the velocity of the cyclone
wind at ground level.
41
EFFECTS ON BUILDINGS
As a consequence of the storm surge and high wind speed following types of damage are commonly
seen :
★ Uprooting of trees which disrupt transportation and relief supply missions.
★ Damage to signposts, electric poles and transmission line towers.
★ Damage to improperly attached windows or window frames.
★ Damage to roof/lintel projections.
★ Failure of improperly attached or constructed parapets.
★ Overturning failures of compound walls of various types.
★ Failure of roofing elements and walls along the gable ends particularly due to high internal pressures.
★ Failure of large industrial buildings with lightweight roof coverings and long/tall walls due to combination
of internal & external pressures.
★ Brittle failure of asbestos.
★ Punching and blowing off of corrugated iron roofing sheets attached to steel trusses
PROTECTION MEASURES FOR DAMAGE TO BUILDINGS
1. Site selection
Cyclonic windstorms commonly generate storm tides leading to coastal inundation. In cyclonic regions,
close to the coast, a site above the likely inundation level should be
given preference. In case of non availability of high elevation natural
ground, construction should be done on stilts with no masonry or
bracings upto maximum surge level, or raised earthen
mounds as shown to avoid flooding/inundation.
2. Platforms and Orientation
(a) For individual buildings, a circular or polygonal
plan shape is preferred over rectangular or square Fig 1. If natural elevation is not
plans. available construction on stilts or on
artificially raised earth mounds
(b) A symmetrical building with a compact plan-form
is more stable than an asymmetrical building with
a zig-zag plan, having empty pockets as the latter
is more prone to wind/cyclone related damage.
3. Foundations
The following parameters need to be properly accounted
for in the design of foundation.
(a) Effect of Surge or Flooding: Invariably a cyclonic
storm is accompanied by torrential rain and tidal Fig. 2 Desirable orientation & plan form for
reducing wind damage.
surge (in coastal areas) resulting into flooding
of the low-lying areas. The flurry of tidal surge diminishes as it travels on shore, which can
extend even upto 10 to 15 km.
(b) Building on Stilts: Where building is constructed on stilts, it is
necessary that stilts are properly braced on both the directions.
42
4. Wall Openings
(a) Openings just below roof level are avoided except that two small vents without shutters are
provided in opposite walls to prevent suffocation in case room gets filled with water if people try
to climb up on lofts.
(b) Doors and windows should have strong closing/ locking arrangements and glass/wooden panels
be securely fixed.
5. Glass Panelling
(a) One of the most damaging effects is the extensive breakage of glass panes caused by high wind
pressure or impact of flying objects in air. The large size door or window glass panes may shatter
because they are too thin to resist the wind pressures.
(b) Reduce the panel size to smaller dimensions. Pasting thin plastic film or paper strips can
strengthen Glass panes.
(c) Provide a metallic fabric/mesh outside the panels.
(d) Provide proper locking arrangement of shutters. Securely fix the frames to walls.
6. Roof Architecture
(a) The overall effect of wind
on a pitched roof building
and the critical locations
are shown in figures.
Therefore, the roof
projections should be
kept minimum, say not
exceeding 500 mm, or Fig. 4 LEFT: Large overhangs get Fig. 5 RIGHT: Avoid large
lifted and broken overhangs and use ties
else, are tied down
adequately.
(b) For the purpose of reducing wind forces on the roof, a hipped or pyramidal roof is preferable to
the gable type roof as shown in figure 6.
Fig. 6 Effects of roof architecture on uplift force
43
The damage due to cyclones can be minimised by adopting
the technologies and procedures mentioned above. It is
advisable to have shelterbelts plantation across the wind
direction, in coastal areas and in all large establishments to
check the wind speed and reduce damage.
A shelter with special feature to withstand
Reference for further reading:
cyclones and floods. Traditional homes can
● http://www.bte.gov.au/docs/r103/chapter1.htm be improved by building in disaster resistant
features. Such homes could withstand
● http://gujarat-earthquake.gov.in/ cyclones with moderate speeds.
● h t t p : / / w w w. b e n f i e l d h r c . o r g / S i t e R o o t / a c t i v i t i e s /
misc_papers/DEVRISK/BENSON.HTM
● http://www.adrc.or.jp/countryreport/IND/INDeng02/India07.htm
● http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/earthquake_effects.html
● Guidelines For Improving Earthquake Resistance Of Housing – BMTPC
● Guidelines For Improving Flood Resistance Of Housing – BMTPC
● Guidelines For Improving Wind/Cyclone Resistance Of Housing – BMTPC
● http://quake.ualr.edu/HazardMitigation/claymitg-plan/Landslides.htm
1. What should be the configuration of an earthquake resistant building?
2. How should the foundation be constructed in soft and firm soil?
3. Which are the most vulnerable homes due to flood?
4. What are the general protection measures for buildings against flood damage?
5. What are the considerations for selecting the site in area prone to landslides?
6. Write about the slope stabilization methods by drainage?
7. What are the desirable plan forms and orientations for cyclone resistant buildings?
8. What kind of roof designs should be used in cyclone prone areas and why?
44
