GUIDELINES FOR EARTHQUAKE RESISTANT BUILDING CONSTRUCTION: EARTHEN BUILDING (EB)

NSN E P A L N A T I O N A L B U I L D I N G C O D E
NBC 204:2015
EARTHEN BUILDING (EB)
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Government of Nepal
Ministry of Urban Planning Department of Urban Development and Building Construction
Babar Mahal, Kathmandu, NEPAL
2072
This publication represents a standard of good practice and therefore takes the form of recommendations. Compliance with it does not confer immunity from relevant legal requirements, including bylaws
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Preface
The first version of this Nepal Standard (NNBC 204: 2015 GUIDELINES FOR EARTHQUAKE
RESISTANT BUILDING CONSTRUCTION: EARTHEN BUILDING (EB)) was prepared during
1993 as part of a project to prepare a National Building Code for Nepal.
In 1988 the Ministry of Housing and Physical Planning (MHPP) (now Ministry of Urban
Development), conscious of the growing needs of Nepal's urban and shelter sectors, requested
technical assistance from the United Nations Development Programme and their executing agency,
United Nations Centre for Human Settlements(UNCHS).
A programme of Policy and Technical Support was set up within the Ministry (UNDP Project
NEP/88/054) and a number of activities was undertaken within this framework.
The 1988 earthquake in Nepal, and the resulting deaths and damage to both housing and schools
again drew attention to the need for changes and improvement in the then building construction and
design methods.
At that time, Nepal had not had any regulations or documents of its own setting out either
requirements or good practice for achieving satisfactory strength in buildings.
In late 1991 the MHPP and UNCHS requested proposals for the development of such regulations and
documents from international organizations in response to terms of reference prepared by a panel of
experts.
The first version was then prepared by the subcontractor's team working within the Department of
Building, the team including members of the Department and the MHPP. As part of the proposed
management and implementation strategy, it was prepared so as to conform with the general
presentation requirements of the Nepal Bureau of Standards and Metrology.
However for several years after the 1st version of NNBC 204 was published, the enormous
positive development in materials, technological development along with significant development
in research and scientific methods and the enormous changes in design of structures and
construction practices have been felt to be incorporated along with the positive feedback from the
professionals from the field of design and construction.
Likewise under the Earthquake Risk Reduction Recovery Preparedness (ERRRP) Program for
Nepal, Ministry of Physical Planning and Works, Government of Nepal through (UNDP/ERRRP-
Project: NEP/07/010), a set of recommendations for updating this code was received on April 10,
2009, submitted by MULTI Disciplinary Consultants (P) Ltd., K.D. Associates (P) Ltd., Khwopa
Engineering College.
Thus, recognizing the need, the Building Construction Management and Improvement Committee
(BCMIC) on January 7, 2011 decided to carry out a building code update programme for fiscal
year 2011/012 and accordingly consultants DIGICON/ RND JV were assigned through a contract
for the update of this code. A panel of in-house and external expert committee was also formed
for review and suggestions during the update process.
In this way, the revised form of “NNBC 204: 1994 Guidelines for Earthquake Resistant Building
Construction: Earthen Building (EB)” resulted into “NNBC 204: 2015 Guidelines for Earthquake
Resistant Building Construction: Earthen Building (EB) ” and as per the 12th meeting of BCMIC,
decision no. 4, it was forwarded to Ministry of Urban Development (MOUD) for approval. Then
on December 21, 2015 it received approval from the Prime Minister (also Minister of MOUD)
and was published in Nepal Gazette on November 14, 2016.
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Significant changes in this first revision include:
1. The use of this code is now limited to only ordinary residential structures and any
important structures shall be designed by competent professional engineers.
2. Figures have been updated for more clarification.
3. Field test for suitability of soil in clause 3.2 has been added for better material selection
and construction practice.
4. Clause 11.3 has been added for specification and diameter of nails.
Efforts have been made to make the code much simpler and free of confusions such that there is
no conflict with other codes. It is further expected that this revision addresses all the issues related
with the previous edition.
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0.2 Objective ........................................................................................................................... 1 0.3 Background ....................................................................................................................... 1 0.4 Applicability ...................................................................................................................... 1
0.5 Interpretation ..................................................................................................................... 1 0.6 Terminology ...................................................................................................................... 2
1 Scope .............................................................................................................................................. 3 1.1 Type of Buildings Covered ............................................................................................... 3
1.2 Limitation .......................................................................................................................... 3
2 General Requirements for Earthquake-Resistance Construction.................................................. 4 2.1 Proper Site Selection ......................................................................................................... 4 2.2 Appropriate Planning ........................................................................................................ 4
2.3 Good Foundations Resting on a Firm Base ...................................................................... 4 2.4 Creating a Box Effect ........................................................................................................ 4
2.5 Better Bonding Between Masonry Units .......................................................................... 4 2.6 Controlled Size and Location of Openings ....................................................................... 4
3 Materials ........................................................................................................................................ 5 3.1 Mud ................................................................................................................................... 5 3.2 Adobe (Sun-Dried Clay Bricks/Blocks) ........................................................................... 5 3.3 Mud Mortar ....................................................................................................................... 6
3.4 Bamboo ............................................................................................................................. 6
3.5 Timber ............................................................................................................................... 6
4 Site Considerations ........................................................................................................................ 7 4.1 General .............................................................................................................................. 7 4.2 Site Selection ..................................................................................................................... 7
4.2.1 Geological Faults or Ruptured Areas ................................................................... 7 4.2.2 Areas Susceptible to Landslide ............................................................................ 7
4.2.3 Boulder Hazard ..................................................................................................... 8 4.2.4 River Banks .......................................................................................................... 8 4.2.5 Swamp/Marshy Area ............................................................................................ 8 4.2.6 Steep Slopes .......................................................................................................... 8
4.2.7 Water-Logged Areas ............................................................................................ 8 4.2.8 Filled Areas ........................................................................................................... 8
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5 Planning ......................................................................................................................................... 9 5.1 Shape ................................................................................................................................. 9 5.2 Proportions ...................................................................................................................... 10 5.3 Storey Height .................................................................................................................. 10 5.4 Number of Storeys .......................................................................................................... 10
6 Foundation ................................................................................................................................... 11 6.1 General ............................................................................................................................ 11
6.2 Strip Foundation.........................................................................................................11
7.1.1 Mud Wall Construction ...................................................................................... 13
7.1.2 Rammed Earth Wall Construction ..................................................................... 14 7.1.3 Adobe (Sun-Dried Bricks/Blocks) Wall Construction ...................................... 15
7.2 Wall Thickness ................................................................................................................ 16 7.3 Unsupported Wall Length................................................................................................16
7.4 Height of Walls ............................................................................................................... 17 7.5 Protection of Mud Walls ................................................................................................. 17
7.5.1 Foundation .......................................................................................................... 17
7.5.3 Roof Projections ................................................................................................. 18 7.5.4 Non-Erodible Mud Plaster (NEM) ..................................................................... 18
7.6 Corners and Junctions ..................................................................................................... 18
8 Openings in Walls ....................................................................................................................... 19
9 Floors and Roofs .......................................................................................................................... 20
9.1 Structure .......................................................................................................................... 20 9.1.1 Posts and Capitals ............................................................................................... 20
9.1.2 Beams and Bearings ........................................................................................... 24 9.1.3 Wall Plates .......................................................................................................... 25 9.1.4 Joists and Rafters ................................................................................................ 26
9.2 Floor Finishings and Roof Coverings ............................................................................. 27
9.2.1 Bridging Materials .............................................................................................. 27 9.2.2 Floor Finishing ................................................................................................... 29 9.2.3 Roof Covering .................................................................................................... 29
9.2.3.1 Mud.....................................................................................................29
9.2.3.2 Thatch..................................................................................................30
9.2.3.3 Slates...................................................................................................31
9.2.3.5 MCR Tiles .............................................................................................. 32
9.2.3.6 CGI Sheets .............................................................................................. 32 9.3 Bamboo for Flooring and Roofing ................................................................................. 33
9.3.1 Bamboo Flooring ................................................................................................ 33 9.3.2 Bamboo Roofing ................................................................................................ 34
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10.1.1 Bamboo ................................................................................................................ 36 10.1.2 Timber .................................................................................................................. 38
10.2 Horizontal Bands ............................................................................................................. 38
10.2.1 Bamboo Bands ..................................................................................................... 39 10.2.2 Timber Bands ....................................................................................................... 40
10.3 Gable Bands .................................................................................................................... 41 10.4 Diagonal Bracing ............................................................................................................ 42 10.5 Lateral Restrainers .......................................................................................................... 43
11 Miscellaneous .............................................................................................................................. 44 11.1 Damp-Proof Courses........................................................................................................44
11.2 Drainage .......................................................................................................................... 45
11.3.1 Nails..................................................................................................................45
1.1.1 Harvesting Guidelines ........................................................................................ 47 1.1.2 Clump Cure ......................................................................................................... 47
1.2 Preservative Treatment ................................................................................................... 47
1.2.3 Brushing, Swabbing, Spraying and Dipping ...................................................... 48 1.3 Fire-Retarding Treatment ................................................................................................ 49 1.4 Storage ............................................................................................................................. 49
APPENDIX - 2 FIRE-RETARDANT TREATMENT FOR THATCH ................................................ 50
1 General ......................................................................................................................................... 50 1.1 Materials Required .......................................................................................................... 50
1.2 Method of Preparation .................................................................................................... 50 1.2.1 Preparation of Stabilised Mud Mortar ................................................................ 50 1.2.2 Preparation of Cut-Back1 Bitumen (for NEM) .................................................. 50 1.2.3 Preparation of NEM Mortar ............................................................................... 51 1.2.4 Preparation of Cut-Back2 Bitumen for Stabilised Mud Slurry .......................... 51
1.2.5 Preparation of Stabilised Mud Slurry1 for NEM ................................................ 51
1.2.6 Preparation of Stabilised Mud Slurry2 for Fire-Retardant Plaster ..................... 51
1.3 Method of Application .................................................................................................... 52 1.3.1 Dressing of Roof Surface ................................................................................... 52 1.3.2 Application of Stabilised Mud Plaster................................................................ 52 1.3.3 Application of Stabilised Mud Slurry1 ............................................................... 52
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1.3.4 Application of NEM plaster ............................................................................... 52 1.3.5 Application of Stabilised Mud Slurry2 ............................................................... 53
APPENDIX - 3 PROTECTION OF MUD WALLS .......................................................................... 54
1 Non-Erodible Mud Plaster (NEM) .............................................................................................. 54 1.1 Materials Required .......................................................................................................... 54
1.2 Method of Preparation .................................................................................................... 54 1.2.1 Preparation of Stabilised Mud Mortar ................................................................... 54 1.2.2 Preparation of Bitumen Cut-Back ......................................................................... 54
1.2.3 Preparation of NEM mortar ................................................................................... 55 1.2.4 Preparation of Stabilised Mud Slurry .................................................................... 55
1.3 Method of Application .................................................................................................... 55 1.3.1 Dressing of Wall Surface ....................................................................................... 55
1.3.2 Application of NEM plaster ................................................................................... 55 1.3.3 Application of Stabilised Mud Slurries ................................................................. 56
2 Composite Walls ......................................................................................................................... 56
APPENDIX - 5 SEASONING OF TIMBER .......................................................................................... 59
APPENDIX - 6 REFERENCE MATERIALS ........................................................................................ 67
APPENDIX - 7 GLOSSARY .................................................................................................................. 68
Figure 3.2 : Lab Testing of Strength of Soil and Adobe......................................................................6
Figure 5.1 : Recommended Forms of Buildings ...................................................................................... 9 Figure 6.1 : Details of Strip Footing Foundation for an EB ................................................................... 11 Figure 6.2 : Foundation on Sloping Land ............................................................................................... 12
Figure 7.1 : Bamboo Reinforcement Detail in Mud Wall Construction.............................................13
Figure 7.2 : Rammed Earth Wall Construction ...................................................................................... 14
Figure 7.3 : Adobe Brick/Block Wall Construction ............................................................................... 15
Figure 7.4 : Buttresses on Walls ............................................................................................................. 16 Figure 7.5 : Protection of Mud Wall Foundations .................................................................................. 17 Figure 7.6 : Reinforcing of Corners and Junctions of Mud Walls ......................................................... 18 Figure 8.1 : Openings for Earthen Buildings .......................................................................................... 19 Figure 9.1 : Details of Fixing Posts on Base Pads .................................................................................. 21
Figure 9.2 : Details of Fixing of a Series of Posts on a Base Strip......................................................... 22 Figure 9.3 : Details of Fixing Capitals on the Posts ............................................................................... 23 Figure 9.4 : Alternative Details for Fixing Struts on Posts and Beams .................................................. 23 Figure 9.5 : Details of Fixing Keys on Beams........................................................................................ 24
Figure 9.6 : Details for Fixing Wall Plates ............................................................................................. 25 Figure 9.7 : Details for Fixing Joists and Rafters ................................................................................... 26
Figure 9.8 : Details for Fixing Bridging Materials to Joists and Rafters ............................................... 28 Figure 9.9 : Details of Improved Mud Roofing ...................................................................................... 29
Figure 9.10 : Details of Improved Thatched Roofing ............................................................................ 30
Figure 9.11 : Details of Laying Slate..................................................................................................31
Figure 9.12 : Details of Fixing Clay Tiles .............................................................................................. 31
Figure 9.13 : Details for Fixing MCR Tiles ........................................................................................... 32
Figure 9.14 : Details for Fixing CGI Sheets.......................................................................................32
Figure 9.15 : Details of Bamboo Flooring .............................................................................................. 33 Figure 9.16 : Details of Simple Bamboo Roofing .................................................................................. 34
Figure 9.17 : Details of Trussed Bamboo Roofing.............................................................................35
Figure 10.1 : Bamboo as Vertical Reinforcement .................................................................................. 37
Figure 10.2 : Timber as Vertical Reinforcement .................................................................................... 38 Figure 10.3 : Bamboo for Horizontal Bands .......................................................................................... 39
Figure 10.4 : Timber for Horizontal Bands ............................................................................................ 40 Figure 10.5 : Details for Gable Bands .................................................................................................... 41 Figure 10.6 : Details for Diagonal Bracing............................................................................................. 42 Figure 10.7 : Lateral Restrainers ............................................................................................................. 43 Figure 11.1 : Damp-Proof Courses ......................................................................................................... 44
Figure 11.2 : Surface Water Drainage around a Building ...................................................................... 45 Figure A3.1 : Composite Wall ................................................................................................................ 56
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Table 3.1 : List of Hardwood and Softwood...............................................................................................7
Table 7.1 : Minimum Wall Thicknesses (mm) for Different Wall Types ............................................. 16 Table 9.1 : Size of Columns (mm) .......................................................................................................... 20 Table 9.2 : Size of Beams (mm) for Various Spans ............................................................................... 25 Table 9.3 : Minimum Size (mm) of Joists and Rafters ........................................................................... 27
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A number of documents for better seismic-resistant construction have been prepared
under the National Building Code Development Project (NEP/88/054/21.03) in
1993.Guidelines for Earthquake Resistant Building Construction: Earthen
Buildings (EB) is one of them. Originally prepared document has been revised by
DUDBC in March 2014. This document provides basic guidelines for the
earthquake resistance of earthen buildings in particular.
0.2 Objective
This guideline is prepared in order to raise the seismic safety of earthen buildings.
This is intended to be implemented by the owner/builder with some assistance from
technicians. This could also act as a basic guideline for architectural design and
construction detailing of Earthen Buildings (EB).
0.3 Background
The devastating earthquakes in the past have proved the vulnerability of most of the
vernacular buildings of Nepal. Enormous life and property were lost due to the
collapse of buildings which employed mud walls as their main load-bearing
elements. Earthquakes can neither be prevented nor predicted precisely. But the
large-scale destruction can be minimized by employing seismic-resistant measures
in buildings. This can be achieved by the use of existing building materials in
appropriate ways. This Guideline for Earthquake-Resistant Building
Construction: Earthen Buildings provides the improved techniques that can raise
the level of seismic safety of earthen buildings.
0.4 Applicability
The recommendations set forth in this standard shall be mandatory for all types of
LSM residential buildings to be built throughout Nepal.
Other occupancy types of LSM buildings shall be designed by competent
professional engineers.
0.5 Interpretation
0.5.1 In this standard the word “shall” indicates a requirement that must be
adopted in order to comply with the Guidelines, while the word “should”
indicates recommended practice.
0.5.2 Words used in either the singular or plural shall be treated as plural or
singular as deemed necessary, and vice-versa wherever the context so
requires it.
In this guidelines, unless inconsistent with the context:
EB means Earthen Buildings that employ mud walls or masonry units that are
made with unstabilized mud-like adobe blocks, sun-dried clay bricks, etc, laid in a
mud mortar.
1.1 Type of Buildings Covered
The guidelines deals with the design and construction aspects for improving
earthquake resistance of earthen houses, without the use of stabilizers, such as
cement, lime, asphalt, admixtures, etc.
1.2 Limitation
EB buildings required to conform to this Guidelines shall not exceed one storey in
height plus an additional attic floor.
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The principal seismic-resistant factors have to be properly incorporated during the
construction of a building. Some basic factors leading to enhanced seismic safety are:
2.1 Proper Site Selection
The construction site has to be stable and safe enough to withstand the total building
load, including that of its occupants and their belongings. A proper site for the
building shall be selected in accordance with section 4 of this guideline.
2.2 Appropriate Planning
The shape, size and proportions of a building are important for its seismic safety.
Buildings with asymmetric plans and elevations are more vulnerable to earthquakes
than those having symmetrical ones. The recommended form and proportion of
buildings shall be as stated in section 5.
2.3 Good Foundations Resting on a Firm Base
The quality of foundations and the base on which the foundations rest are equally
important for the safety of a building. General site investigation shall be carried out
as outlined in section 4. The dimensions and quality of masonry for the foundation
shall be as stated in section 6.
2.4 Creating a Box Effect
A building has to act as a single unit for it to have good earthquake resistance. This
can be achieved by incorporating certain elements in its construction. The following
elements shall be introduced as recommended in section 10.
Vertical reinforcement
in masonry
Lateral restraints
2.5 Better Bonding between Masonry Units
The type and quality of the bond within the walling units is the main contributor to
the integrity and strength of the walls. All the masonry units have to be properly laid
to provide the integrity.
2.6 Controlled Size and Location of Openings
Large un-stiffened openings create a soft-storey effect which leads to a greater
deformation of a building during an earthquake. To prevent such effects, the opening
size and location have to be controlled. The recommended proportions and locations
of openings are given in section 8.
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3 Materials
3.1 Mud
The mud used for walls shall be free from organic materials. It should be neither too
sandy nor too clayey. The sand content shall not be more than 40 % by volume.
3.2 Adobe (Sun-Dried Clay Bricks/Blocks)
The mud used for making sun-dried bricks/blocks shall be free from organic
materials. These bricks shall preferably be dried in a shed to prevent large shrinkage
cracks. They shall be free from major defects and obvious cracks.
3.2.1 Suitability of soil
The quality of materials, particularly clay content of the soil may vary somewhat for
the type of construction. But in general the following qualitative tests are sufficient
for determining the suitability of a soil for earthen construction:
3.2.1.1 Field Test
a. Dry strength test
Five or Six small balls of soil of approximately 2 cm in diameter are made. Once they
are dry (after 48 hours), each ball is crushed between the forefinger and the thumb. If
they are strong enough that none of them breaks, the soil has enough clay to be used
in the adobe construction, provided that some control over the mortar micro-fissures
caused by the drying process is exercised, Fig 3.1
If some of the balls break, the soil is not considered to be adequate, because it does
not have enough clay and should be discarded.
Fig 3.1 Field Testing of Strength of Soil
b. Fissuring control test
At least eight sandwich units are manufactured with mortars made with mixtures in
different proportions of soil and coarse sand. It is recommended that the proportion of
soil to coarse sand vary between 1:0and 1:3 in volume. The sandwich having the least
content of coarse sand which, when opened after 48 hours, does not show visible
fissures in the mortar, will indicate the most adequate proportion of soil/sand for
adobe constructions, giving the highest strength.
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Strength test of adobe
The strength of adobe can be qualitatively ascertained as follows: After 4 weeks of
sun drying the adobe should be strong enough to support in bending the weight of a
man, Fig 3.2. If it breaks, more clay and fibrous material is to be added.
Quantitatively, the compressive strength may be determined by testing 10 cm cubes
of clay after completely drying them. A minimum value of 1.2 N/mm2 will be
desirable.
Fig 3.2 Qualitative testing of strength of soil and adobe
3.3 Mud Mortar
Mud for mortar shall be free from organic materials. It shall also be free from
pebbles and other hard materials which would upset the mortar thickness. The sand
content in the mud shall not be more than 30 % in order that a satisfactory
cohesiveness is attained. Dry mud shall be thoroughly kneaded with water to achieve
a dense paste.
3.4 Bamboo
Only matured bamboo that is a minimum of three years old and free from damage
shall be used. It is preferable that treated bamboo be used. The treatment may be
carried out in a traditional manner. One of the simplest ways is to soak the bamboo in
running water two- three weeks continuously. (Details are presented in Appendix 1.)
3.5 Timber
Well seasoned locally available timber can be used. Seasoning should be done in a
traditional manner. Preferably Sal wood, or any other locally available hardwood
timber, shall be used instead of softwood timber for the main structural elements such
as beams, columns, bands, etc. (According to indigenous experience, deciduous trees
are much less susceptible to bacterial and insect rot if felled during August to
December.)List of the hardwood and softwood timber available are as follows:
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HARD WOOD SOFT WOOD
4.1 General
The building site shall be the safest available with respect to natural hazards. Any
existing buildings shall be studied for any evidence of inherent natural hazards in the
locality. These hazards include susceptibility to landslides, erosion and land
subsidence. The local practice used to manage such hazards, if any, shall be judged
against the required level of acceptable risk. Areas with a high potential of
liquefaction during earthquakes should also be avoided.
4.2 Site Selection
Site selection shall be done so as to minimize the risk against natural hazards. No
buildings shall be constructed in hazardous areas, including the areas stated here
under:
4.2.1 Geological Faults or Ruptured Areas
Geological fault lines or rupture lines that are usually visible to the naked eye
and are permanent,…