1. Rules for the Provision of
Earthquake Resistance in
Small Buildings in Ghana
by
Ing. (Mrs) Carlien Bou-Chedid
Presentation at ICWES15 - Australia 2011

2. Seismic Activity in Ghana
Source: USGS National Earthquake Information Centre & International Seismological Centre
 Although earthquakes are rare in Ghana, they do occur and
can produce very damaging consequences. The largest on
record was Ms 7.1 in 1862 (Similar to Haiti). The most
recent damaging earthquake was Ms 6.5 in 1939.
Presentation at ICWES15 - Australia 2011

3. Areas at Risk
 Areas most at risk include regions where the capital city
Accra, two major port cities and two other regional capitals
are situated. These are also some of the most densely
populated areas of the country.
 Structures in Ghana must therefore be built to withstand
strong earthquakes without excessive deterioration.
 The majority of buildings in Ghana are one and two storey
buildings. Professional Engineers are often not involved in
their design or construction. Poorly trained craftsmen are
usually responsible for construction.
Presentation at ICWES15 - Australia 2011

4. Factors Affecting Building
Performance
 A study of building practice currently used in the
construction of many small buildings suggests that they will
be unable to respond favourably in event of an earthquake.
 Building performance in earthquakes is affected by
 Architectural forms
 Structural forms
 Methods of construction
 Materials used
Presentation at ICWES15 - Australia 2011

5. Architectural Forms
 Buildings are individually designed.
 They are often irregular in plan.
 Water may be stored in water tanks on the roof.
 Gable walls are common.
 Large window and door openings are used.
 Open car ports and garages can often be an integral part of
the building.
 Several decorative features such as balustrades, fin wall etc
are also used.
Presentation at ICWES15 - Australia 2011

6. Structural Forms, Materials &
Methods
 Two basic forms are common. Unreinforced masonry
usually tied at lintel level with a beam, and reinforced
concrete.
 Materials are ordinary portland cement, mild steel,
unprocessed aggregates and large masonry blocks (125mm
X 200mm X 400mm) made from cement and sand.
 Material proportions for concrete may be determined by
eye. Foundations can be shallow (750mm). Columns will
often be built to match wall thickness (125mm x 125mm).
Stirrups and links are anchored in 90o bends.
Presentation at ICWES15 - Australia 2011

7. Presentation at ICWES15 - Australia 2011

8. Vulnerability of Current
Building Stock
 Most areas in the south of Ghana lie within a seismic zone
assigned a peak ground acceleration of 0.35g. Other zones
are 0.25g, 0.15g. These correspond to VIII, VII and VI on a
Modified Mercalli Scale.
% of Buildings Reaching Each
Damage State
Damage State (Modified Mercalli Intensity)
Sandcrete Block Reinf. Concrete
VI VII VIII IX VI VII VIII IX
0 – None (No Damage) 15 0 0 0 95 90 50 20
1 – Minor( Very little non-structural damage) 55 50 15 5 5 10 25 25
2 - Moderate (Widespread non-structural damage) 25 25 25 15 - - 25 55
3 - Severe (Extensive non-structural & some structural damage) 5 25 55 55 - - - -
4 – Very Severe (Completely destroyed) - - 5 25 - - - -
Presentation at ICWES15 - Australia 2011

9. Comments
 Structural forms used in Ghana are a mixture of reinforced
concrete construction and confined masonry construction.
 Reinforced concrete construction for earthquake resistance
is complex. RC frames form the main load resisting system.
Special detailing is required and it requires special skill.
 Confined masonry construction is much simpler no special
skills are required. Masonry block walls confined by tie
beams and tie columns form the main lateral load resisting
systems. The masonry block unit must be load bearing.
Presentation at ICWES15 - Australia 2011

10. Recommended Guidelines
 Engineering rules are to be presented in two separate
guidelines.
 Guidelines for construction of single storey buildings are to
be based on confined masonry construction and may be
used by craftsmen.
 Guidelines for construction of buildings up to two stories
may be based on reinforced concrete design and must be
implemented by technologists.
 Both guidelines must give direction on good construction
practice. Especially bending of stirrups and links to 135o .
Presentation at ICWES15 - Australia 2011

11. RC buildings up to Two Stories
 These can be based on existing rules
“Guidelines for Earthquake Resistant Non-
Engineered Construction” (Arya et al, 2010)
 Cover to steel in Columns and beams
should be 30mm rather 25mm to reflect the
very aggressive atmosphere experienced in
Ghana.
 Fixing details will be required for the
prestressed precast concrete systems in
current use.
Presentation at ICWES15 - Australia 2011

12. Rules for Single Story buildings
 Minimum wall thickness 125mm
 Tie columns and tie beams to
flush with walls
 Teeth like indentation at the point
of connection with tie columns or
steel dowel bars
 Sandcrete blocks to be load
bearing.
 Minimum wall density of 5% to
reflect uncertainty associated
with sandcrete block
Presentation at ICWES15 - Australia 2011

13. Conclusion and Recommendations
 Buildings in Ghana must be constructed to
withstand earthquakes
 Guidelines for construction of buildings up to
two stories should be produced using reinforced
concrete design as a basis. Technologists can be
responsible for construction.
 Confined masonry is recommended in Ghana for
single storey construction as it is less demanding.
Craftsmen can be responsible construction.