by Asitha Jayawardena
(BSc Eng, MPhil, AMIESL, Associate Member of
"Current popular practices in planning,
design and construction of buildings in Sri Lanka have made the
buildings we work and live today highly vulnerable to disasters
– especially earthquakes," revealed Eng (Prof) M. T. R.
Jayasinghe, Professor of Civil Engineering, University of
Moratuwa, in his presentation on "Construction of buildings to
resist natural forces including earthquakes" at the recent
seminar on "Engineering aspects to be considered when
reconstructing the tsunami devastated areas" organised by the
Institution of Engineers Sri Lanka.
Among the undesirable practices he cited are
double-storey entrance lobby of multi-storey buildings, slender
columns adopted for floor space maximisation and aesthetics, car
parks at basements, highly asymmetrical building plans, failure
to coincide the building’s shear and geometrical centres,
elongated building plans, slender (i.e., very tall) buildings,
construction of adjacent multi-storey buildings touching or very
close to each other, and inadequate tying of the building at
foundation to ensure behaviour as one unit.
Design and construction of a building
concentrating on one type of disaster can make the building
highly vulnerable to another type of disaster, he warned, citing
an example where exclusive focus on tsunami resistance severely
undermines the building’s earthquake resistance. Therefore, he
proposed an integrated approach for design and construction of
buildings against all probable types of natural disasters. This
article is based on his presentation.
Threats against buildings and their occupants
A building should be designed and constructed
to provide safe shelter for its occupants. Therefore, it should
perform satisfactorily both under normal and adverse conditions.
There are mainly two types of adverse forces
that threaten buildings and their occupants, namely, natural and
man-made. Natural forces include earthquakes, tsunami, cyclones,
floods, landslides, floods, volcanic eruptions, lightening while
man-made threats include bomb blasts, underground explosions and
vehicle accidents. This article confines itself to natural
Earthquakes are the worst of the disasters
because they are unpredictable. Earthquakes are of two types:
Inter-plate and intra-plate. Located away
from well known tectonic plate boundaries, Sri Lanka is
vulnerable only to intra-plate type earthquakes, which are due
to local effects such as active faults.
The intra-plate type is less frequent, less
severe but totally unpredictable while some level of prediction
may be successful with inter-plate type.
Although earthquakes are not frequent in Sri
Lanka, the country has experienced earthquakes. In Sri Lanka an
earthquake on 14 April 1615 killed about 2000 people while the
country experienced an earthquake measuring 4.7 on Richter scale
in 1993. Moreover, many have felt earth tremors in December
2004. Even more disturbing are the recent reports of forming a
new earthquake zone – 300 to 400km away from Sri Lanka.
Therefore, there is a possibility of inter plate type
earthquakes also being felt in Sri Lanka as tremors or minor
All buildings in Sri Lanka should be designed
and constructed with a reasonable level of earthquake resistance
because earthquakes can occur anywhere in the country. Although
severe damage is acceptable in a massive earthquake, collapse of
buildings should be avoided to prevent loss of lives.
Tsunamis are not frequent and affect only the
coastal regions. They are predictable only if an early warning
system and the people’s response to it are effective.
Cyclones are sudden but some level of prior
warning can be obtained through weather reports. Countries
located within 15 degrees of the equator are vulnerable to
cyclones. In Sri Lanka, the Northern and Eastern provinces are
the mainly vulnerable areas to cyclones. However, there is a
possibility for a cyclone to divert its path and affect any part
of the country.
Floods are not sudden and affect low-lying
areas near rivers. Landslides, too, can give prior warning.
Locations with steep slopes in wet zone are vulnerable to
landslides. Volcanic eruptions are highly unlikely to occur in
Sri Lanka. Lightning on the other hand is sudden and can hit any
An integrated strategy against natural forces
An integrated approach is essential for
design and construction of buildings against natural forces.
Suppose a building is designed and constructed to resist
tsunamis where the ground floor is kept free of walls and the
building is located in the upper floors. This will make it
highly vulnerable to earthquakes since the ground floor
supported on columns can suffer severe damage due to heavy load
concentrated on the upper floors.
An integrated strategy against natural forces
in summarised form can be presented as the following:
* Achieve a reasonable level of earthquake
resistance for all buildings irrespective of location of
* Design for other forces the building is
likely to encounter, namely, tsunami resistance for buildings
coastal regions, cyclone resistance for buildings in
cyclone-prone areas in North and East provinces, landslide
resistance for buildings in steep slopes in wet zone, and flood
resistance for buildings in low-lying areas near rivers.
* Threat of volcanic eruptions is highly
unlikely and can therefore be totally ignored since earthquake
resistant structures can have some degree of resistance against
vibrations induced by volcanic eruptions, too, if ever volcanic
* Lightning can strike anywhere. However,
resistance against lightning can be obtained by simple means
such as proper grounding, having enough number of trees around
the building and therefore requires no special design.
A cost-effective approach for earthquake
Wherever the building is located, it should
possess a reasonable level of earthquake resistance due to
several reasons. Firstly, earthquakes are unpredictable.
Moreover, they can occur anywhere and can make the building
collapse, causing loss of life.
Achieving earthquake resistance through
earthquake resistant design for any possible earthquake is
expensive. However, a dual design philosophy as can be found in
Australian code is cost-effective.
The design philosophy we can adopt is as
follows. Design for an earthquake that may occur during the life
span of the building. For Sri Lanka, a magnitude of 5 to 6
Richter scale is sufficient. Then, ensure that the possibility
of collapsing the building is very low in the event of a severe
earthquake, which is a very rare occurrence.
For this, the building should be made robust
and ductile and the strong elements (e.g. lift core, stair well)
and columns should be prevented from collapse. In other words,
in the event of a severe earthquake, severe damage is acceptable
but not collapse, which will cause loss of life.
This approach is an integration of desirable
structural forms, reinforcement detailing and planning practices
together, and comprises the following:
* Tie the different parts of the building
together so that the building does not fall apart when
confronted by the horizontal forces of an earthquake acting on
the building’s base.
* Enhance ductility of the building so that
the building can effectively dissipate the energy transferred
from the earthquake forces.
* Ensure that beams of the building develop
plastic hinges before its columns. Make the chances of the
columns failing as much remote as possible in order to prevent
total collapse of the building. Do not optimise the columns as
much as possible, but use columns of generous cross sections.
* Prevent adjacent buildings hitting each
Several measures for earthquake resistance
for reinforced concrete buildings are:
* For plan of the building, adopt simple
shapes (e.g. square, rectangle without much difference in width
and length, circle) and avoid shapes like T, I or U.
* Arrange shear centre of the building to
coincide with the geometric centre of the building’s plan (e.g.,
in a multi-storey building, arrange the lift core/ staircase as
closest to the building plan’s geometric centre as possible)
* Avoid a building with elongated plan (e.g.,
avoid a rectangular plan with length "too long" and width "too
* Avoid slender and very tall buildings
* Avoid soft storeys (e.g., double height
mezzanine floor for entrance lobby, car park at basement). If
these are unavoidable, make columns of these soft storeys as
bulkier and stronger as practically possible.
* Tie the building at the base itself
* Provide shear links for columns within beam
depth as well
* Use full length reinforcement bars at
bases, avoiding starter bars
* Do not construct multi-storey buildings
touching or very close to each other
In brickwork buildings one-brick thick walls
(220 to 230 mm thick) are sufficient for achieving a significant
level of earthquake resistance. Several desirable measures for
brickwork buildings are:
* Avoid many openings (i.e., doors and
windows) on one particular wall
* Use tie beams of reinforced concrete round
the entire building at the base of the building, plinth level,
window sill level and lintel level.
* Support gable walls with return walls up to
roof level (i.e., above ceiling level)
* Adopt reinforced concrete columns where
large open spaces such as living room are required.
In both cases, the foundation should be
properly designed taking the soil conditions of the site into
consideration. Failure of the foundation during an earthquake
will cause the building to collapse no matter how ever much the
building possesses earthquake resistance.
An integrated solution against natural disasters
Earthquake resistance should be integrated
with the other relevant resistances. For example, consider a
three-storey brickwork building to be built in a coastal area.
Besides earthquake resistance, the building should possess
For tsunami resistance, the building can be
designed on stilts (i.e., columns only without much support from
walls). However, this creates a soft storey at the ground floor
level, undermining the building’s resistance to earthquakes.
Therefore, an integrated solution should be
developed for this building:
* Arrange the building on stilts to achieve
* To strengthen the consequent "soft storey",
make the stilts (i.e., columns of the open-plan ground floor)
bulkier and stronger than necessary.
* Use the staircase as the strong element by
arranging a brickwork wall round it. To coincide the geometric
and shear centers, locate the staircase in the centre of the
* To tie the building together, use
reinforced concrete tie beams at plinth level and the window
sill levels and lintel levels of the first and second storeys.
The building with both earthquake resistance
and tsunami resistance is given in Figure.
Suppose the building will be located in
coastal area in a cyclone-prone region. For cyclone resistance,
a roof slab is more appropriate than a roof, which will "fly
away" when confronted by a cyclone. However, the roof slab will
adversely affect the indoor thermal comfort. For enhancement of
indoor thermal comfort, roof insulation can be adopted. The
building will thus possess earthquake-, tsunami-, cyclone
In summary, therefore, an integrated solution
should be developed in design and construction of buildings in
Sri Lanka. All buildings should possess a substantial level of
earthquake resistance to prevent the building from collapsing in
the event of a severe earthquake – severe damage is acceptable,
but not collapse, which will kill people. Then the earthquake
resistance should be blended with other relevant resistances,
for example, tsunami resistance for coastal buildings.
At this seminar, Eng Dr (Ms) Premala
Sivaprakasapillai spoke on "Design and construction of buildings
to resist foreseeable wind forces", Eng Tudor Munasinghe on
"Sewerage infrastructure associated with reconstruction", Eng
Ananda Ranasinghe on "Appropriate contract documents to expedite
construction", and Eng (Gp Capt) Mervyn Gunasekera on "Post
disaster project management. Another article highlighting the
important aspects of these presentations will be published
Veteran musician Shelton Premaratne and his
pupils performing at a musical workshop conducted for the
benefit of the children in the tsunami affected areas in the
Mount Lavinia area. The event was held recently at the
Subodharama Vihara with the participation of Attorney Keerthi
Udawatta, Provincial Council Member and Attorney Wasantha
(Pic by Bernard Chandrasekera, Dehiwala)