NEWSLETTER Vol.18 No.3 JANUARY 2015 ISSN:1174-3646

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Vol.18 No.3
with adequate building codes and standards which most
technical information, but all too often there is a lack of
A Summary of Seismic retrofitting
code requirements, construction standards are low and
Virtual Site Visit No.39
countries possess. There also may be sufficient existing
implementation. Building designs may not comply with
of non-engineered masonry
there is no quality assurance at any stage of the design and
in rural Nepalp.3
construction phases. Safe buildings are not the outcome
of inadequate processes like this.
Editorial: Reducing disaster risk with safer buildings
Although there is scope for more technical information
During 14 – 18 March the UN World Conference on
at different levels in the construction industry to achieve
Disaster Risk Reduction is to be held in Sendai, Japan. As
safer buildings, the main challenge is to change the
part of the preparation for the conference a number of
cultures and practices of Governmental and local city
videos have been made to celebrate achievements during
council building departments. Here are some questions I
the Hyogo Framework for Action period, 2005 – 2015.
would like to put to the delegates of the WCDRR in order
Unfortunately none of this material includes information
to improve the situation:
on how buildings have been made safer during this
period. The draft conference programme does include a
Are there any examples of successful and unsuccessful
session “Standards for DRR including Building Codes”
government or local council initiatives to achieve safer
which shows awareness of the importance of the safety
buildings for their people? Please can they be widely
of buildings during natural hazards including earthquakes.
However we all know what a huge gap can form between
How might governments and local councils change their
codes and their correct implementation.
building departments so that the safety of buildings is
From the perspective of reducing disaster risk in urban
improved and therefore buildings represent less disaster
settings from earthquake and wind storms, the most
important action is to improve building safety. We know
that during earthquakes, buildings kill and injure people,
The time has come for talking about disaster risk reduction
and that badly damaged and collapsed buildings can no
to stop, and to do it. A vital way forward is to make
longer provide shelter and places for occupation.
whatever changes are necessary so that new construction
is safer. Governmental and local city council building
departments need to be part of this process.
The challenge is to build safely. This process begins
Earthquake Hazard Centre Newsletter, Vol. 18 No 3, January 2015
Virtual Site Visit No. 39. Seismic retrofitting by infilling RC frames, lowrise building, Wellington.
In order to bring a four storey educational building up to
the standard of the current seismic code, 11 new RC walls
are being formed at ground level. The structure above this
level has already been retrofitted by ductile steel crossbracing. The new walls will act in both plan orthogonal
directions and are spaced widely apart in plan to improve
the torsion performance of the building.
Each new wall is formed by infilling existing RC column
and beam frames with 300 mm thick RC walls. The
first step is to roughen the surfaces of the columns and
beams. This enables horizontal and vertical shear forces
to be transferred between infills and their surrounding
frame members. Then begins the drilling and grouting of
horizontal and vertical starter bars (Fig. 1). In this project
16 mm diameter Grade 500 bars are epoxy grouted 350
mm into the existing members. If no reinforcing steel is
encountered one hole takes about two minutes to drill.
Otherwise it takes longer as a new hole is drilled nearby.
Figure 1. Horizontal and vertical reinforcing starter bars
have been grouted into the existing beams and columns of the
moment frame.
Once all the starters have been grouted, horizontal and
vertical shear reinforcing is placed and tied (Fig. 2). The
bar spacing is determined by the amount of shear force
the new wall will resist. Note that the bending moments
on the walls are resisted by compression and tension axial
forces in the existing columns. Their ability to resist these
forces was confirmed during the design process. The
columns can be considered as flanges to the infills which
themselves can be thought of as webs of the structural
Figure 2. A completed reinforcing cage ready to be enclosed by
formwork prior to casting the concrete.
Door openings are necessary in some infills. In these areas
additional reinforcing steel is required to ensure adequate
force paths (Fig. 3). Horizontal drag bars ensure similar
levels of shear stress on each side of the opening, and
vertical steel trimming the opening resists secondary
bending moments generated by the presence of the
Once all the reinforcing has been placed and checked,
formwork shutters are placed on each side of the infill. In
this project self-compacting concrete is pumped into the
top of the wall though several openings. It is essential that
the new concrete thoroughly bonds with all vertical and
horizontal surfaces, especially the surfaces of the upper
beam soffits.
Earthquake Hazard Centre Newsletter, Vol. 18 No 3, January 2015
Figure 3. Additional reinforcing steel is required to trim
openings and to ensure adequate force paths within the infill.
A Summary of “Seismic retrofitting
of non-engineered masonry in
rural Nepal,” by Joshua Macabuag, Ramesh
therefore, high-lights some of the key stages of developing
a seismic retrofit for non-engineered dwellings, from early
development to community implementation.
Guragain and Subhamoy Bhattacharya. From
Currently available retrofitting techniques for nonStructures and Buildings Vol. 165, Issue SB6, 2012.
engineered masonry
Structural collapse under seismic loading displays many
possible failure mechanisms often related to the interaction
between structural components (e.g. separation of walls
or floor–wall connections). When considering individual
walls, earthquake loading can have components both
within the plane of the wall (in-plane) and orthogonal to
the plane of the wall (out- of-plane).
Motivation for this study
Nearly 75% of all earthquake fatalities in the last century
have resulted from building failures with a growing
disparity be- tween vulnerability of those in developing and
developed countries. The greatest risk is by far presented
to inhabitants of non-engineered masonry structures (Fig.
4) as demonstrated in the 2003 Bam (Iran) earthquake,
where many of the thousands of deaths were attributable
to vulnerable adobe (mud brick) structures. Similarly
vulnerable, non-engineered masonry is widespread
throughout the developing world and replacement of all
such dwellings is both infeasible and undesirable, given
that they are often the embodiment of local culture and
Methods required to meet the needs of the large
populations in danger of non-engineered masonry
collapse must be simple and inexpensive to match the
available resources and skills. There are several examples
of low-cost retrofitting techniques suitable for nonengineered, non-reinforced masonry dwellings.
This paper focuses on the technique of polypropylene
(PP) meshing.
Procedure and previous uses
PP meshing uses common PP packaging straps (PP
bands) to form a mesh, which is then used to encase
masonry walls (i.e. fixing to both faces of each wall). The
mesh prevents the separation of structural elements and
the escape of debris, maintaining sufficient structural
integrity to prevent collapse. The mesh is formed by
arranging the individual bands into a grid and electrically
‘welding’ at intersecting points (using a plastic welder such
as that shown later in Fig. 7(c)). Each wall to be retrofitted
is stripped of existing render or covering, holes are drilled
through the wall at regular spacing, anchor beams are
installed at ground level (Fig. 7(a), see later) and a ring
beam at top of wall level if lacking. The mesh is connected
to both faces of the wall, fixing to the anchor beams and
ring beam and passing through openings and around
corners with sufficient overlap. Meshes are connected
together through the wall by wires passing through the
previously drilled holes. Finally the mesh is rendered over
Figure 4. Non-engineered adobe house in Peru showing
vertical crack and separation of orthogonal walls owing to
out-of plane forces
tradition. Therefore, it is often more feasible to consider
low-cost retrofitting of such buildings. Almost 50% of
the population in the developing world live in earthen
dwellings yet technical research into this housing type
is limited. Consider, for example, the limited volume of
design guidance and supporting research in the adobe
building codes of, say, Peru and New Zealand, compared
with established masonry design codes such as Eurocode
6. Research is often not realised because of the difficulty
of communicating developments to communities that
conduct self- build without professional input. This paper,
Earthquake Hazard Centre Newsletter, Vol. 18 No 3, January 2015
Retrofit subsidisation programmes for low-income
PP band retrofitting is specifically aimed at the lowestincome communities, costing
about$30 – $70/
house for
materials. However, such lowest-income
communities may struggle to meet basic needs and so
retrofitting for earthquake safety still cannot be afforded
without additional subsidy.
protecting the mesh from sunlight, improving fixity to the
wall and making the retrofit invisible (Fig. 5).
PP bands are used as packaging the world over (e.g. tying
furniture flat-packs in the UK) and are, therefore, cheap
Considering this economical issue is, therefore, crucial to
be able to disseminate the technology to the low-income
communities that most need it.
Meguro Lab, Tokyo University has proposed several
systems for subsidising seismic retrofits including the
‘two-step incentive system’ and ‘new earthquake microinsurance system’. In the proposed two-step incentive
system, house owners are encouraged to retrofit their
homes by receiving the necessary materials and a subsidy
upon satisfactorily carrying out the work. If the retrofitted
houses are damaged in an earthquake, the owners then
receive twice the compensation than the house owners
who did not retrofit. Table 1 shows predictions for the
number of lives saved for several earthquakes, using data
from dynamic experiments to calculate the percentage of
building collapses that could have been prevented.
Considering the percentage of buildings potentially
saved (Table 1) the reduction in expenditure of both the
government and homeowners if this two-step incentive
system had been in place was also estimated.
Figure 5. Retrofitted house in Pakistan before and after
application of covering mortar layer. Note that the mesh is
also applied to the inner face of the walls, with inner and outer
meshes connected with through-wall ties.
and readily available, while the retrofitting technique is
simple and suitable for local builders. PP meshing has
had application in Nepal, Pakistan and Kathmandu. Fig. 5
shows a retrofitted house in Pakistan following the 2005
To investigate the practical issues of implementation a
pilot scheme was conducted in a seismically active region
of the Kathmandu Valley, Nepal.
The Himalayan region is an example of one area of
constant seismic activity, high population density, and
wide-spread use of non-reinforced masonry built outside
of current building standards. Given the high potential
for future loss of life several PP band implementation
programmes have been run in this region.
PP meshing was first formally proposed in 2000, and
published in 2001.
Earthquake Hazard Centre Newsletter, Vol. 18 No 3, January 2015
Bam earthquake (2003)
Totally collapsed houses
Kashmir earthquake (2005)
49 000
(83% reduction)
203 579
(97% reduction)
67 561
(66% reduction)
(97% reduction)
(66% reduction)
154 098
13 080
(92% reduction)
78 550
(61% reduction)
(92% reduction)
(61% reduction)
Part ially collapsed houses
Fatalities due to total
Fatalities owing to partial
Java earthquake (2006)
196 573
43 200
(83% reduction)
58 668
16 367
Table 1. Reduction in casualties had the ‘two-step incentive
system’ been adopted
aspects of earth- quake construction: appropriate site
selection, building layout and construction techniques
(in masonry, timber and reinforced concrete (RC)),
strengthening and repairing of existing structures and
retrofitting using the PP mesh.
Given that the dwellings most at risk are built outside of
building regulations it is clear that a sustainable solution
can only be achieved by raising local awareness of available
methods and allowing the building owners and tradesman
to themselves become the disseminators of the proposed
Many of the masons were very experienced in their trades
but had never received training, or a formal education (a
high level of illiteracy is another reason why a training
course is required over simply producing training manuals).
The aim was, therefore, to introduce small changes to
current practice that can be implemented through simple
rules of thumb but which significantly improve building
earthquake safety. Some example features are shown in
Fig. 6.
In 2006 a public, low-tech shake-table demonstration was
held in Kashmir (following the 2005 earthquake) followed
by the retrofit of a full-scale building by local masons
under supervision (Fig. 4). Material costs for the retrofit
were around US$30 and the total installation cost was less
than 5% of the total construction cost.
This section describes an implementation programme
conducted in November 2008, funded by the Mondialogo
Engineering Award. The programme was conducted as a
partnership between Oxford University; the Institute of
Industrial Science, Tokyo University; the Indian Institute
of Technology, Bombay; Nepal Engineering College;
Khwopa Engineering College, Nepal and the National
Society of Earthquake Technology (NSET). The
implementation project involved a six-day training course
for local, rural masons, focusing on both earthquake
construction and the pp-retrofitting technique. At the
end of the course was a public low-tech shake-table
demonstration of the PP band technology, inviting the
community, press and key individuals and institutions.
Figure 6(a) shows a load bearing masonry wall with
buttressing and vertical reinforcement and with the
masons preparing to add horizontal reinforcement at
corners and orthogonal walls. Fig. 6(b) shows oftenomitted details for local RC frames such as a double-cage
for the column with a link within the beam/column joint
and the beam rebar being completely contained within the
column rebar and continuous through the joint.
Fig. 6(c) shows a simplified introduction to applying
the PP mesh to a masonry wall. Note that the PP mesh
would not usually be applied in conjunction with internal
reinforcement but was applied to the reinforced masonry
model purely as a simple tool for demonstrating the
basics of applying the mesh. During the course it was
stressed that PP retrofitting is intended for use with
Training programme for rural masons
The training course was coordinated by Khwopa
Engineering College and engaged rural masons in several
Earthquake Hazard Centre Newsletter, Vol. 18 No 3, January 2015
Figure 6. Six-day training programme for rural masons,
Bhaktapur, Nepal 2008
adobe where holes can be drilled through bricks as well as
mortar, allowing more accurate spacing of through-wall
connectors, giving a tighter mesh. The real retrofit is also
continued and overlapped around corners and through
openings and connected to the foundations and ringbeam (Fig. 7, see below).
Outcomes of training course and demonstration
Following the training course, feedback from the masons
was that they were motivated on the need for earthquake
safety, very positive to be armed with simple rules-ofthumb that can be implemented easily but have an impact
and keen to learn more about the PP retrofit.
Public low-tech shake table demonstration
The public demonstration was coordinated by NSET,
involved two 1:6 scale masonry models (one with the PP
mesh and one without) and utilised a simple spring-loaded
shake-table. The demonstration was designed to allow the
masons to apply what they had learnt, for the public to
graphically witness the necessity to safeguard their homes
and to encourage municipalities and other potential
funders to adopt a retrofitting programme. The event
received radio and television coverage in Nepal. Note that
the simple table used is not intended to simulate accurate
earthquake motion, but simply to demonstrate the effect
that general ground motion can have on structures.
The main feedback from the community after the
demonstration was that community members were
also motivated on the need for earthquake safety, keen
to retrofit their homes but concerned over the cost of
retrofitting. Municipalities and officials were keen to
retrofit homes but concerned over costs.
Earthquake Hazard Centre Newsletter, Vol. 18 No 3, January 2015
This shows that once awareness has been raised, people
are keen to safeguard their homes but subsidisation will
be necessary if retrofitting is to be an option for lowincome communities. It can also be seen that studies are
necessary to quantitatively show municipalities and other
funders the benefits of pre-emptively retrofitting rather
than rebuilding post-disaster.
Real retrofit of adobe home in Nepal
The final stage of the pilot implementation programme
involved retrofitting an adobe residential building in
Nangkhel Village of Bhaktapur District, Nepal. The
masons involved had taken part in the training course. The
objectives of the real scale implementation work were:
The retrofitting procedure differed from that used
previously in that rather than preparing the mesh off-site
and fixing to the wall, the mesh was formed directly onto
the wall (Figs. 7(b) and (c)). This change was proposed
by the masons themselves to improve buildability and
it was suggested that in this way, it might no longer be
necessary to connect the bands using the plastic welder
for future projects (previously the most expensive part of
the retrofit technique). This suggestion requires further
(a) to retrofit a pilot building using the PP band
retrofitting technique
(b) to observe practically the technical, economical and
cultural appropriateness of the retrofitting technique
under the local site conditions
(c) to give hands-on training to the local masons on
the retrofitting technique and receive feedback and
practical suggestions to improve the retrofitting
The general process of the retrofit can be seen in Fig. 7.
An anchor beam was first fixed to the base of the wall
inside and out; vertical PP bands were fixed between the
internal and external base anchor beams; horizontal bands
were then woven between and welded to the vertical
bands; meshes on opposite faces of each wall were
Figure 7. Retrofit of a real adobe dwelling, Nangkhel, Nepal
Earthquake Hazard Centre Newsletter, Vol. 18 No 3, January 2015
connected to each other through the wall by steel wires
passing through drilled holes; finally a render was applied
to cover the mesh. Note that this house also required
additional refurbishment work in replacing rotten floor
and roof beams and infilling unnecessary openings.
(c) PP band technology is cheap, readily available and
easy to install, so is suitable as a retrofit for lowincome communities
The main objective of the implementation work was
to help disseminate safer seismic construction and
retrofitting techniques to rural communities with a high
proportion of non-engineered dwellings.
The work was carried out by one NSET technician, two
masons and two unskilled labourers over 4 weeks. The
material costs associated with the PP retrofit came to $250.
Details on full-scale retrofitting and the process described
here are given in the final report of the implementation
(a) The pilot implementation programme in Kathmandu,
Nepal (training course for rural masons and public
shake-table demonstration) showed that
(i) directly engaging masons is an effective way
of transferring knowledge of earthquake-safe construction directly to those responsible for
the construction
(ii) communities and officials are keen to retrofit
homes but despite the low-cost, were still
concerned over expense for low-income
communities where supply of basic needs was
more urgent.
(b) Subsidisation schemes are required to make retrofitting
an attractive option for low-income households. The
increased number of retrofits would in-turn lead to a
substantial reduction in loss of life and cost following
the next strong earthquake, for both governments
and homeowners.
The outcomes of the live retrofit were as follows:
(a) the retrofit was successfully implemented and showed
that it is technically feasible to retrofit residential
adobe houses using the PP band retrofitting technique
(b) by training through hands-on implementation the
masons are now able to do this type of retrofitting
(c) the modification to the retrofitting process proposed
by the masons of forming the mesh directly onto the
wall proved an effective time saver; this highlights
the potential benefits of developing the technique
alongside those who will implement it.
This paper has introduced the technique of polypropylene
meshing for preventing or prolonging the collapse
of adobe buildings under strong earthquakes. Both
development and implementation of this technique was
considered. The main findings during the development of
PP meshing are as follows:
(a) the complete PP mesh prevents loss of material
and maintains wall integrity for large deformations,
allowing redistribution of the load throughout the
mesh and masonry
(b) PP retrofitting was shown to enhance the safety
of existing single-storey masonry buildings even in
worst-case earthquake scenarios such as intensity
Earthquake Hazard Centre
Promoting Earthquake-Resistant Construction
in Developing Countries
The Centre is a non-profit organisation based at the School of
Architecture, Victoria University of Wellington, New Zealand.
Director (honorary) and Editor: Andrew Charleson,
ME.(Civil)(Dist), MIPENZ
Research Assistant: Nick Denton, BSc, BAS
Mail: Earthquake Hazard Centre, School of Architecture,
PO Box 600, Wellington, New Zealand.
Location: 139 Vivian Street, Wellington.
Phone +64-4-463 6200
Fax +64-4-463-6024
Email: [email protected]
The Earthquake Hazard Centre Webpage is at:
Earthquake Hazard Centre Newsletter, Vol. 18 No 3, January 2015

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