NEPAL NATIONAL BUILDING CODE
NBC 105 : 1994

SEISMIC DESIGN OF BUILDINGSIN NEPAL

Government of Nepal

Ministry of Physical Planning and Works
Department of Urban Development and Building Construction
Babar Mahal, Kathmandu, NEPAL

Reprinted : 2064

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NEPAL NATIONAL BUILDING CODE
NBC 105 : 1994

SEISMIC DESIGN OF BUILDINGSIN NEPAL
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
tTsflng >L % sf] ;/sf/ -dlGqkl/ifb\_ sf] ldlt @)^).$.!@ sf] lg0f{ofg';f/ :jLs[tGovernment of Nepal

Ministry of Physical Planning and Works
Department of Urban Development and Building Construction
Babar Mahal, Kathmandu, NEPAL

Reprinted : 2064

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PrefaceThis Nepal Standard was prepared during 1993 as part of a project to prepare a draft National Building
Code for Nepal.
In 1988 the Ministry of Housing and Physical Planning (MHPP), 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 have been 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 current building construction and design
methods.
Until now, Nepal has not had any regulations or documents of its own setting out either requirements orgood practice for achieving satisfactory strength in buildings.
In late 1991 the MHPP and UNCHS requested proposals for the development of such regulations anddocuments from international organisations in response to terms of reference prepared by a panel ofexperts.
This document has been 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 proposedmanagement and implementation strategy, it has been prepared so as to conform with the general
presentation requirements of the Nepal Bureau of Standards and Metrology.
The subproject has been undertaken under the aegis of an Advisory Panel to the MHPP.
The Advisory Panel consisted of :Mr. UB Malla, Joint Secretary, MHPP
Director General, Department of Building(Mr. LR Upadhyay)
Mr. AR Pant, Under Secretary, MHPP
Director General, Department of Mines & Geology(Mr. PL Shrestha)
Director General, Nepal Bureau of Standards & Metrology(Mr. PB Manandhar)
Dean, Institute of Engineering, Tribhuvan University(Dr. SB Mathe)
Project Chief, Earthquake Areas Rehabilitation &Reconstruction Project
President, Nepal Engineers Association
Law Officer, MHPP (Mr. RB Dange)
Representative, Society of Consulting Architectural &Engineering Firms (SCAEF)
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ChairmanMemberMemberMemberMemberMemberMemberMemberMemberMember
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Representative, Society of Nepalese Architects (SONA)
Deputy Director General, Department of Building,(Mr. JP Pradhan)

MemberMember-Secretary

The Subcontractor was BECA WORLEY INTERNATIONAL CONSULTANTS LTD. of New
Zealand in conjunction with subconsultants who included :Golder Associates Ltd., Canada
SILT Consultants P. Ltd., Nepal
TAEC Consult (P.) Ltd., Nepal
Urban Regional Research, USA
Principal inputs to this standard came from :Mr. RD Jury, BECA
Dr. AS Arya, Professor Emeritus, University of Roorkee, India.
Dr. RD Sharpe, BECA (Team Leader)
Revisions and Updated to this code came from:
Mr. Purna P.Kadariya, DG, DUDBC
Mr. Kishore Thapa, DDG, DUDBC
Mr.Mani Ratna Tuladhar, Sr. Div. Engineer, DUDBC
Mr. Jyoti Prasad Pradhan, Ex. DG, DOB
Mr. Bhubaneswor Lal Shrestha, Ex. DDG, DOB
Mr. Uttam Shrestha, Architect, Architects' Module Pvt.Ltd.
Mr. Manohar Lal Rajbhandhari, Sr. Structural Engineer, MR Associates
Mr. Amrit Man Tuladhar, Civil Engineer, DUDBC

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TABLE OF CONTENTS

Preface ..................................................................................................................................................i0.

Foreword .................................................................................................................................. vi
0.1
0.2
0.3

Design Procedure ...................................................................................................................... vi
Related Codes............................................................................................................................ vi
Commentary ............................................................................................................................. vi

1

Scope..........................................................................................................................................1

2

Interpretation ............................................................................................................................2
2.1
2.2
2.3

3

General Principles of Ductile Seismic Design and Detailing .................................................6
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8

4

Structural System ...................................................................................................................... 6
Ductility...................................................................................................................................... 6
Energy Dissipation..................................................................................................................... 6
Symmetry ................................................................................................................................... 6
Uniformity of Storey Stiffness ................................................................................................... 6
Floor Diaphragms and Bracing................................................................................................. 6
Interconnection of Floors and Roof........................................................................................... 7
Interconnection of Foundations................................................................................................. 7

Design Methods & Load Combinations ...................................................................................7
4.1
4.2
4.3
4.4
4.5

5

General....................................................................................................................................... 2
Terminology............................................................................................................................... 2
Symbols ...................................................................................................................................... 4

General....................................................................................................................................... 7
Increase in Allowable Material Stresses for the Working Stress Method................................ 7
Increase in Allowable Soil Bearing Pressure............................................................................. 8
Design Load Combinations for the Working Stress Method ................................................... 8
Design Load Combinations for the Limit State Method .......................................................... 8

Methods of Analysis ..................................................................................................................8
5.1
5.2

General....................................................................................................................................... 8
Selection of Method of Analysis................................................................................................. 8

6

Seismic Weight ..........................................................................................................................97

Periods of Vibration ..................................................................................................................9

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8

Seismic Design Actions...........................................................................................................10
8.1

Design Spectra and Lateral Force Coefficients....................................................................... 10
8.1.1
8.1.2
8.1.3
8.1.4
8.1.5
8.1.6
8.1.7
8.1.8

8.2

Direction of Forces and Design Eccentricity........................................................................... 17
8.2.1
8.2.2

8.3

9

Vertical Seismic Forces............................................................................................................ 18

Derivation of Design Lateral Deformations ............................................................................ 18
Building Separations................................................................................................................ 18
9.2.1
9.2.2
9.2.3

9.3

To Boundaries........................................................................................................................... 18
Within Site ................................................................................................................................ 18
Separation Space Width........................................................................................................... 18

Inter-Storey Deflections........................................................................................................... 18

Seismic Coefficient Method ....................................................................................................19
10.1
10.2

11

Direction of Forces.................................................................................................................... 17
Design Eccentricity ................................................................................................................... 17

Deformation Due to Earthquake Forces................................................................................18
9.1
9.2

10

Design Horizontal Seismic Coefficient for the Seismic Coefficient Method............................ 10
Design Spectrum for the Modal Response Spectrum Method ................................................ 10
Basic Seismic Coefficient .......................................................................................................... 10
Basic Response Spectrum......................................................................................................... 11
Site Subsoil Category................................................................................................................ 11
Seismic Zoning Factor .............................................................................................................. 12
Importance Factor.................................................................................................................... 12
Structural Performance Factor................................................................................................ 15

Horizontal Seismic Base Shear................................................................................................ 19
Horizontal Seismic Forces ....................................................................................................... 19

Modal Response Spectrum Method........................................................................................19
11.1
11.2
11.3
11.4

Design Spectrum ...................................................................................................................... 19
Number of Modes to be Considered........................................................................................ 20
Combination of Modal Effects ................................................................................................ 20
Torsion ..................................................................................................................................... 20
11.4.1
11.4.211.4.3

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General...................................................................................................................................... 20
Static Analysis for Torsional Effects ........................................................................................ 20
Three-Dimensional Analysis..................................................................................................... 21

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12

Seismic Design Requirements for Secondary Structural Elements, Architectural Finishes
and Mechanical and Electrical Equipment...........................................................................21
12.1
12.2
12.3
12.4
12.5

General..................................................................................................................................... 21
Connections.............................................................................................................................. 21
Separation from Structural System ........................................................................................ 21
Services Cut-Offs ..................................................................................................................... 21
Design Forces ........................................................................................................................... 2212.5.1
12.5.2

12.6

Separation of Elements............................................................................................................ 25
12.6.1
12.6.213

Structure Response Factor....................................................................................................... 22
Component Seismic Performance Factor ................................................................................ 22

Applicable Elements ................................................................................................................. 25
Separation Requirements......................................................................................................... 26

Structural Variations to be Approved by Designer ................................................................26

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0.

Foreword
1.

Design Procedure
This Standard provides minimum requirements for the seismic design of structures
which are within the scope of this Standard as defined in 1.

2.

Related Codes
The requirements of this section of the Nepal Building Code shall be applied inconjunction with, IS 4326 - 1976 Code of Practice for Earthquake Resistant Design andConstruction of Buildings.
Where conflict exists between any requirements of this Standard and IS 4326, therequirements of this Standard shall be taken.

3.

Commentary
A commentary, which explains the reasons for many of the clauses in this Standard,
forms an accompanying volume to this document. This Standard should always be readin association with the Commentary.

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1

Scope

This standard sets down requirements for the general structural design and seismic design loadings forstructures within any of the following categories :(a)

All buildings having a floor area greater than 20 square metres.

(b)

Any building with a height greater than five metres.

(c)

All masonry or concrete walls greater than 1.5 metres in height.

(d)Elevated tanks of up to 200 cubic metres capacity. Larger tanks than this should be the subjectof a special study.

(e)All buildings to which the general public have access.

The requirements are not intended to apply to :(a)

Unusual buildings or structures (eg, those with unusual configurations or risk - such as nuclear
power stations, etc).

(b)

Civil engineering works (eg, bridges, dams, earth structures, etc).

(c)

Buildings or structures greater than 90 m in height.

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2

Interpretation
2.1

2.2

General
2.1.1

In this Standard the word "shall" indicates a requirement that must be adopted
in order to comply with the Standard, while the word "should" indicatesrecommended practice.

2.1.2

Commentary clauses (in Part 2) are prefaced by the letter C and the number of
the appropriate clause subject to comment.

Terminology
In this standard, unless inconsistent with the context :ANALYSIS METHODS :SEISMIC COEFFICIENT METHOD means a method of analysis using
static loads to simulate the effects of earthquake ground motion.
MODAL RESPONSE SPECTRUM METHOD means a method of dynamic
analysis in which a given earthquake design spectrum is applied to amathematical model of the structure and the response of several modes are
determined, and combined.
DEAD LOAD means the weight of all permanent components of a building including
walls, partitions, columns, floors, roofs, finishes and fixed plant and fittings that are an
integral part of the structure.
DESIGN means the use of rational computational or experimental methods inaccordance with the established principles of structural mechanics.
DIAPHRAGM means a member composed of a web (such as a floor or roof slab), ora truss which distributes forces to the horizontal load resisting system.
DUCTILITY means the ability of the building or member to undergo repeated andreversing inelastic deflection beyond the point of first yield while maintaining asubstantial proportion of its initial maximum load carrying capacity.
ELEMENTS includes primary and secondary elements :PRIMARY ELEMENTS means elements forming part of the basic load
resisting structure, such as beams, columns, diaphragms, or shear walls
necessary for the building's survival when subjected to the specified loadings.
SECONDARY ELEMENTS means elements such as intermediate orsecondary beams, partition walls, panels, or veneers not necessary for the

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survival of the building as a whole but which may be subject to stresses due toload applied directly to them or to stresses induced by the deformations of the
primary elements.
FRAME means a system composed of interconnected members functioning as acomplete self-contained unit with or without the aid of horizontal diaphragms or floor
bracing systems.
MOMENT RESISTING FRAME means a load carrying frame in which themembers and joints are capable of resisting horizontal loads through bending
moments.
HORIZONTAL LOAD RESISTING SYSTEM means that part of the structural
system to which the horizontal loads prescribed by this Standard are assigned.
LEVEL OF LATERAL RESTRAINT is the level at which the ground motion of theearthquake is transmitted to the structure by interaction between the foundationmaterials and the foundation elements by friction and bearing.
LIVE LOAD means the load assumed or known to result from the occupancy or useof a building and includes the loads on floors, loads on roofs other than wind, loads on
balustrades and loads from movable goods, machinery, and plant that are not an
integral part of the building.
SET BACK means any offset horizontally in from the plane of an exterior wall of astructure.
SHEAR WALL means a wall of any material required to resist horizontal loads
through the transfer of shear forces.
STOREY means the space between two adjacent floors or platform levels.

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2.3

Symbols

Symbols used in the Standard shall have the following meanings :bmaximum horizontal dimension of the building at the particular level measured
perpendicular to the direction of loadingC

basic seismic coefficient for the seismic coefficient methodC(Ti)ordinate of the basic response spectrum for translational period Ti

Cddesign horizontal seismic force coefficientCd(Ti)

ordinate of the design spectrum for translational period Ti

DLdesign dead loadD'overall length of the building at the base in the direction under consideration(m)dihorizontal displacement of the centre of mass at level i under the horizontal
seismic loading specified by this Standard (ie Fi)

E

design earthquake loaded

design eccentricity of the seismic load at a particular leveleccomputed eccentricity of the centre of mass from the centre of rigidity

Fihorizontal seismic force applied at a level designated as i

Fp

design seismic force for elements and components designed in accordance with
8g

acceleration due to gravity. To be taken as 9.81 m/s2

Hheight to the top of the main portion of the building or the eaves of the building(m)hiheight to the level designated as i from the level of lateral restraintI

importance factor for the building

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K

structural performance factor appropriate for the particular structural type

Kp

component seismic performance coefficient

LL

design live loadP

structural response factor

S

modal combination factor

SL

design snow, or ice load

T1

natural period of vibration of the first mode of the structureTitranslational period of vibration for mode iVtotal horizontal seismic base shear

Wi

proportion of Wt contributed by level iWpweight of the element, component or item of equipment

Wt

total of the gravity loads Wi above the level of lateral restraint

Z

seismic zoning factor

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3

General Principles of Ductile Seismic Design and Detailing
3.1

Structural System
Buildings shall be designed with a clearly defined (identifiable) load path, or paths, totransfer the inertial forces generated in an earthquake to the supporting soils.

3.2

Ductility
Buildings and all their seismic load resisting elements should be designed and detailed
to perform in a ductile manner.
Satisfactory ductility can be assumed if the structure will withstand, without significant
loss of vertical and/or lateral load carrying capacity, the lateral deflections specified in
9.1 applied through several reversals (cycles).
For the purposes of this Standard the above general requirement may be assumed to beadequately met if the specific requirements of Table 8.2 are complied with.

3.3

Energy Dissipation
In addition to the provision of adequate ductility, structures should also be designed toprevent the concentration of the demand for ductility in a few members, except where
special provisions are made to increase the ductility available in those members.
The demand for ductility should be spread throughout the structure so that theearthquake induced energy is dissipated uniformly.
For the purpose of this Standard the above general requirements may be assumed to beadequately met if the specific requirements of Table 8.2 are complied with.

3.4

Symmetry
The seismic load resisting elements of a structure should be located, as nearly aspracticable, symmetrically about the centre of mass of the structure.
Re-entrant angles in the plan shape of a structure should be avoided.

3.5

Uniformity of Storey Stiffness
Significant changes in the stiffness over the height of the building should be avoided.

3.6

Floor Diaphragms and Bracing
The horizontal bracing system or diaphragm at each floor shall be designed to distributeforces to the individual elements of the horizontal load resisting system in proportion totheir rigidities.

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3.7

Interconnection of Floors and RoofConcrete and masonry walls shall be anchored to all floors or roofs that are required toprovide them with horizontal support or stability. Such anchorage shall be designed forthe loads determined from 12, or a minimum load of 3 kN per metre of wall, whicheveris greater. Spacing of such anchors shall not exceed one metre unless the wall isdesigned to span between them.
Such connections to walls shall also comply with the requirements of 12.2.

3.8

Interconnection of Foundations
Individual foundations of a building shall be interconnected in two directions, generally
at right angles, by members designed for an axial tension and compression equal to 10% of the maximum vertical load on either foundation under seismic conditions.
If the axial load on one of the interconnected foundations is less than 20 % of that on
the other, the design axial load in the interconnecting elements shall be taken as 10 % of
the average vertical load on the two foundations under seismic conditions.

4

Design Methods & Load Combinations
4.1

GeneralDesign for earthquake actions shall be in accordance with either :(a)

The Working Stress Method (elastic method), or(b)

The Limit State Method

provided that reinforced concrete design shall be in accordance with the Limit State
Method unless specifically noted otherwise.
4.2

Increase in Allowable Material Stresses for the Working Stress Method
Whenever earthquake forces are considered along with other design forces, theallowable material stresses may be increased by one third but shall not exceed thefollowing limits :NBC105V2.RV5(a)Steels with a definite yield stress; the yield stress(b)

Steels without a definite yield stress; 80 percent of the ultimate strength or the
0.2 percent proof stress whichever is smaller.

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4.3

Increase in Allowable Soil Bearing Pressure
Whenever earthquake forces are considered along with other design forces, theallowable soil bearing pressures may be increased by up to 50 percent.

4.4

Design Load Combinations for the Working Stress Method
The design loads including earthquake for the Working Stress Method shall be not lessthan whichever of the following load combinations gives the greatest effect :DL + LL + E
0.7 DL + E
DL +SL + E

4.5

Design Load Combinations for the Limit State Method
The design loads including earthquake for the Limit State Method shall be not less thanwhichever of the following load combination gives the greatest effect :DL + 1.3 LL + 1.25 E
0.9 DL + 1.25 E
DL + 1.3 SL + 1.25 E

5

Methods of Analysis
5.1

GeneralAnalysis for the design earthquake actions shall be in accordance with one of thefollowing methods :(a)

The Seismic Coefficient Method as outlined in 10, or,(b)

The Modal Response Spectrum method as outlined in 11.

Note : Analysis using numerical integration time history procedures is not covered bythis Standard.
5.2

Selection of Method of Analysis
For structures of up to 40 m in height the Seismic Coefficient Method may be used. For
all other structures the Modal Response Spectrum Method shall be used.

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The Modal Spectrum Method should be used for :6a)Buildings with irregular configurations(b)

Buildings with abrupt changes in lateral resistance(c)

Buildings with abrupt changes in lateral stiffness with height(d)

Buildings with unusual shape, size or importance.

Seismic WeightThe seismic weight at each level, Wi, shall be taken as the sum of the dead loads and the seismic
live loads between the mid-heights of adjacent storeys.
The seismic live load shall be taken as a percentage of the design live load as given in Table
6.1.
Design Live Load

Percentage of Design Live Load

Up to 3 kPa
Above 3 kPa and for vehicle garages
For Roofs

25
50
NIL
Table 6.1

The seismic weight for roofs shall include allowance for ice if appropriate.

7

Periods of Vibration
7.1

The periods of vibration, Ti, shall be established from properly substantiated data, orcomputation, or both.

7.2

Where the Seismic Coefficient Method is used, the fundamental translation period in
the direction under consideration, Ti, shall be determined from :_____________
7.1
Ti = 2 π √ Σ Wi di2 /g Σ Fi diwhere di may be calculated ignoring the effects of torsion.

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7.3

For the purposes of initial member sizing, the following approximate formulae for Ti
may be used :
(a)

(b)

For framed structures with no rigid elements limiting the deflection :T1 = 0.085 H ¾ for steel frames

7.2

T1 = 0.06 H ¾ for concrete frames

7.3

For other structures :T1 =0.09 H-----√D'

7.4

If T1 calculated using these equations is greater than 120 percent of that finallycalculated using Equation 7.1, the seismic forces shall be re-assessed.

8

Seismic Design Actions
8.1

Design Spectra and Lateral Force Coefficients
8.1.1

Design Horizontal Seismic Coefficient for the Seismic Coefficient Method
The design horizontal seismic force coefficient, Cd shall be taken as :Cd = CZIK

8.1

Where C is the basic seismic coefficient for the fundamental translational period
in the direction under consideration.
8.1.2

Design Spectrum for the Modal Response Spectrum Method
The design spectrum, Cd (Ti), shall be taken as :Cd (Ti) = C (Ti) ZIK

8.2

Where C (Ti) is the ordinate of the basic response spectrum for translational
period, Ti.
8.1.3

Basic Seismic Coefficient
The basic seismic coefficient, C, shall be determined from Figure 8.1 for theappropriate site subsoil category using the fundamental structural period
determined in accordance with 7.2 for the direction under consideration.

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8.1.4

Basic Response Spectrum
The basic spectrum, C(Ti), shall be determined from Figure 8.1 for theappropriate site subsoil category, and period, Ti.

8.1.5

Site Subsoil Category
The site shall be classified into one of the following site subsoil categories :Type I

Rock or Stiff Soil Sites.
Sites with bedrock, including weathered rock with an
unconfined compression strength greater than 500 kPa, overlain
by less than 20 m of :(a)very stiff cohesive material with an unconfinedcompression strength greater than 100 kPa, or(b)very dense cohesionless material with N > 30, where N is
the standard penetration (SPT) value.

Such sites will typically have a low amplitude natural period ofless than 0.2 s.
Type II

Medium Soil Sites
Sites not described as either Type I or Type III

Type IIISoft Soil Sites
Sites where the depth of soil of a particular type exceeds thefollowing values :a)Cohesive Soils
Cohesive Soil
Classification

Representative
undrained shear
strength (kPa)

Minimum
Depth of Soil
(m)

Soft

12.5 - 25

20

Firm

25 - 5025

Stiff

50 - 10040

100 - 200

60

Very Stiff
contd.../

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Cohesionless Soils
Cohesionless
Soils
Classification

Representative
SPT values(N)

Minimum
Depth of Soil
(m)

Loose

4 - 1040

Medium Dense

10 - 3045

Dense

30 - 50

55

Very Dense

> 50

60

Gravels> 30

100

Such sites will typically have a low amplitude natural period
greater than 0.6 s.
8.1.6Seismic Zoning Factor
The seismic zoning factor, Z, shall be obtained from Figure 8.2 for theappropriate location.

8.1.7

Importance Factor
The importance factor, I, for the structure shall be obtained from Table 8.1.

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Figure 8.1 : BASIC SEISMIC COEFFICIENT, C
BASIC RESPONSE SPECTRUM, C(TI)

13

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ZONE FACTORS FOR SELECTED MUNICIPALITIESMANICIPALITY
Shadrapur
Bharatpur
Bidur
Birendra Nagar
Biratnagar
Birganj
ButwalByas

FACTOR.Z
0.93
0.99
1.00
1.02
0.93
0.85
0.90
1.00

Damak
Dhanagadi
Dhanakuta

MUNICIPALITY
DharanDipayalGaur
IlamJanakpur
Kathmandu
Valley Towns
Mahendra
Nagar
Nepalganj
PokharaTulsipur

0.96
0.90
1.00

FACTCR.Z
1.00
1.10
0.82
0.97
0.89
1.00
0.91
0.91
1.00
1.00

0.8
0.9
1.0
1.1
1.1
1.0

0.8

Z = 1.1

0.8
1.1

0.9

0.8

0.8
1.0
0.8

Z = 1.0
1.0
Kathmandu
0.8
0.9

1.0

0.8

Outside of the shaded areas. the Seismic
Zoning Factor shall be determined byinterpolation between the contours.
Outside of the hatched areas, the Seismic
Zoning Factor shall be determined byinterpolation between the contours.

Figure 8.2 : SEISMIC ZONING FACTOR, Z

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Type of Building

Importance Factor I(a)Monumental Buildings

1.5

(b)

Essential facilities that should remain functional after anearthquake

1.5

Examples of these facilities would be :Hospitals and other medical facilities
Fire and Police stations
Emergency vehicle shelters/garages
Food storage structures
Emergency relief stores
Power stations (including standby power-generating
equipment for essential facilities)
Water works and water towers
Radio and television facilities
Telephone exchanges and transmission facilities
Offices and residential quarters for senior personnel requiredfor central and district-level rescue and relief operations(ministers, secretaries, police and army chiefs; CDO, LDO
and DDC chairmen, district-level army and police chiefs
Places of assembly (schools, colleges, cinemas, convention
halls, temples, dharmsalas).
(c)
(d)
(e)

Distribution facilities for gas or petroleum products in urban
areas.

2.0

Structures for the support or containment of dangerous
substances (such as acids, toxic substances, etc.).

2.0

Other structures
1.0
Table 0.1 : Importance Factor I
8.1.8

Structural Performance Factor
The minimum permissible value of the structural performance factor, K, andassociated detailing requirements shall be as given in Table 8.2.
In order to qualify for the K factors given in Table 8.2, the chosen structural
type shall meet the minimum detailing requirements shown.
The structural type may be different in each of two directions in a building andin that case the appropriate value for K shall be selected for each direction.

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When more than one structural type is used in the structure, for the direction
under consideration, the structural performance factor for the element providing
the majority of the seismic load resistance shall be applied provided that theelements of the other structural types have the ability to accept the resulting
deformations.

Item

Structural Type

Minimum Detailing
Requirements

Structural
Performance
Factor K

1.(a)Ductile moment-resistingframe

Must comply with the detailing for ductility
requirements.

(b)

Frame as in 1(a) withreinforced concrete shearwalls

For frames : as for 1(a).
Reinforced concrete shear walls must comply
with appropriate3 detailing for ductility
requirements.

2.(a)Frame as in 1(a) witheither steel bracing
members detailed for
ductility or reinforced
concrete infill panels

For frames : as for 1(a).
Steel bracing members must comply with thedetailing for ductility requirements NBC 11194.
Reinforced concrete infill panels must comply
with the detailing requirements of NBC 10994.

(b)

Frame as in 1(a) withmasonry infills

Must comply with the detailing for ductility
requirements.

3.

Diagonally-braced steel
frame with ductile bracing
acting in tension only

Must comply with the detailing for ductility
requirements of Nepal Steel Construction
Standard

2.0

4.

Cable-stayed chimneys

Appropriate materials Standard

3.0

5.

Structures of minimal
ductility including
reinforced concrete
frames not covered by 1
or 2 above, and masonry
bearing wall structures.

Appropriate materials Standard

4.0

1.0
1.01

1.51,2

2.01,2

cont..../

Table 0.2 :Structural Performance Factor K and other Design
Requirements for Horizontal Load-Resisting Systems of
Buildings and other Structures

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Table 8.2 continued
NOTES :

8.2

1

These factors shall apply only if the steel bracing members, the shear
walls and/or the infill panels are taken into consideration in both thestiffness and lateral strength calculations.

2.

These factors shall apply only if the frame acting alone is capable ofresisting at least 25 percent of the design seismic forces.

Direction of Forces and Design Eccentricity
8.2.1

Direction of Forces
For structures with seismic resisting systems located along two perpendicular
directions, the specified forces may be assumed to act separately along eachof these two horizontal directions. For other buildings, different directions ofapplication of the specified forces shall be considered so as to produce themost unfavourable effect in any structural element.

8.2.2

Design Eccentricity
The design eccentricity, ed , shall be determined as follows :(a)

If ec is less than 0.1 b and the building is 4 storeys or less in height :ed may be taken as equal to 0(b)

If ec is less than 0.3 b and 8.2.2(a) does not apply;
ed = ec + 0.1 b or ed = ec - 0.1 b

8.3

whichever is the most severe for the element under consideration.
(c)

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If ec is greater than 0.3 b, the structure should be analyzed using athree-dimensional modal response spectrum analysis with the mass ateach level displaced by ± 0.1 b, whichever is the most severe for theelement under consideration.

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8.3

Vertical Seismic Forces
The effect of the vertical components of seismic motion need not be considered indesign of a structure except as specified in 12. Where consideration of verticalseismic forces is required, the design vertical seismic coefficient shall be taken as
one half of the horizontal seismic coefficient given in 8.1.1.

9Deformation Due to Earthquake Forces
9.1

Derivation of Design Lateral Deformations
The design lateral deformations shall be taken as the deformations resulting from theapplication of the forces or design spectrum as specified in 10 or 11 respectively,
multiplied by the factor 5/K.

9.2

Building Separations
9.2.1

To Boundaries
Above ground level, each building of greater than three storeys shall have aseparation from the boundary, except adjacent to a designed street or publicway, of not less than the design lateral deflection determined in accordancewith 9.1 or 0.002 hi or 25 mm which ever is the greater.

9.2.2

Within Site
Parts of buildings or buildings on the same site which are not designed to act
as an integral unit shall be separated from each other by a distance of not lessthan the sum of the design lateral deflections determined in accordance with
9.1 or 0.004 hi or 50 mm which ever is the greater.

9.2.3

Separation Space Width
Separation spaces shall be detailed and constructed to remain clear of debris
and other obstructions. The width of such spaces shall allow for all
constructional tolerances.

9.3

Inter-Storey Deflections
The ratio of the inter-storey deflection to the corresponding storey height shall not
exceed 0.010 nor shall the inter-storey deflection exceed 60 mm (refer also to
12.6.2).

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10

Seismic Coefficient Method
10.1

Horizontal Seismic Base Shear
10.1.1 The horizontal seismic shear force acting at the base of the structure, in the
direction being considered, shall be :V = Cd Wt

10.1

where Cd is as defined in 8.1.1.

10.2

Horizontal Seismic Forces
10.2.1 The horizontal seismic force at each level i shall be taken as :Fi = V Wi hi / Σ Wi hi

10.2

Provided that :(a)Where the height to width ratio of the horizontal load resisting system
is equal to or greater than 3, then 0.1 V shall be considered asconcentrated at the top storey and the remaining 0.9 V shall be
distributed in accordance with the equation above.

(b)

For chimneys and smoke-stacks resting on the ground, 0.2 V shall beconsidered as concentrated at the top and the remaining 0.8 V shall be
distributed in accordance with the equation above.

(c)

For elevated tanks, the force Fi is equal to V and acts through thecentre of gravity of the total weight of the structure and contents.

10.2.2 The set of equivalent static forces specified in this clause shall be assumed toact simultaneously at each level in the direction being considered and shallbe applied through points eccentric to the centre of rigidity as specified in
8.2.2.

11

Modal Response Spectrum Method
11.1

Design Spectrum
The design spectrum used for the Modal Response Spectrum Method shall as given
in 8.1.2.
The relative response of each contributing mode i shall be determined by

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multiplying the mode response by the value of C(Ti) from 8.1.2.

11.2

Number of Modes to be Considered
A sufficient number of modes shall be considered to ensure that at least 90 % of themass is participating in the direction under consideration.

11.3

Combination of Modal Effects
11.3.1 An established method shall be used for the combination of modal effects.
11.3.2 The combination method shall take into account the effect of closely spacedmodes. Modes shall be considered to be closely spaced if their frequencies
are within 15 %.
11.3.3 The combined modal effects shall be scaled by the modal combination factor,
S, where :0.9 Cd Wt

S=

11.1

Σ combined modal base shears in the direction under consideration

provided that S shall not be taken as less than 1.0.

11.4

Torsion
11.4.1 General
An analysis for torsional effects may be conducted by the static method in
11.4.2.
For structures where ec is greater than 0.3 b, torsional effects should
evaluated using three-dimensional analysis and the provisions of 11.4.3.
11.4.2 Static Analysis for Torsional Effects
For a static analysis for torsional effects, the applied torsion at each level
shall use either the forces calculated by the Seismic Coefficient Method or
the combined storey inertial forces found in a translational two-dimensional
modal response spectrum analysis, and a design eccentricity, ed calculated inaccordance with 8.2.2.
Torsional effects shall be combined with the translational effects by direct
summation, with signs chosen to produce the most adverse combined effects
in the element under consideration.

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11.4.3 Three-Dimensional Analysis
For each direction of loading the position and distribution of the mass at eachlevel shall be adjusted to account for an eccentricity about the centre of massof ± 0.1 b. The sign of the eccentricity shall be that producing the largest
design actions in the element under consideration.

12

Seismic Design Requirements for Secondary Structural Elements,
Architectural Finishes and Mechanical and Electrical Equipment
12.1

GeneralAll architectural elements and mechanical and electrical systems shall meet therequirements of 12 as these may be a safety hazard in the event of an earthquake or
may be required to be functional immediately following such an event.
Contents of museums and similar items of historical or artistic value that are nonfunctional items should be restrained against seismic loads. Specialist advice should
be obtained for detailing such restraints.

12.2

Connections
All elements, components or equipment shall be positively connected to the structure
to resist the specified seismic loads. Friction due to gravity shall not be used toprovide the required resistance to horizontal loads.
Connections to ornamentations, veneers, appendages and exterior panels including
anchor bolts, shall be corrosion-resisting and ductile, with adequate anchorages. In
the case of precast concrete panels, anchorages shall be attached to, or hooked
around, panel reinforcing.

12.3

Separation from Structural System
Interaction with the structural system shall be avoided where specified in 12.6.1 byproviding adequate separations as defined in 12.6.2.

12.4

Services Cut-Offs
If continued operation of a facility during strong seismic motions presents anexcessive risk, an automatic shut-off system, which will operate at a pre-determinedground acceleration, not exceeding 0.2 g, shall be provided. In such cases, allequipment required for safe shut-down shall be capable of resisting the shut-off levelirrespective of other requirements of this Section.

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12.5

Design Forces
All elements and components shall be designed for a seismic force Fp, in any
direction given by :Fp = Cp P Kp Wp

12.1

For elements supported by the structure, Cp is equal to Cd for the structure
determined in accordance with 8.1.1 or 8.3 as appropriate.
For elements supported on the ground and independent of the structure, Cp is equal
to Cd determined in accordance 8.1.1 using the element fundamental period.
12.5.1 Structure Response Factor
The structural response factor, P, reflects the distribution and amplificationof the ground motion by the structure supporting the particular component
and shall be taken as :P = 1.0 + hi / H

12.2

P shall be taken as 1.0 for structures supported directly on the ground.
The P factor for more important elements of the structure should be
calculated from a more detailed analysis using the Modal Response Spectrum
Method.
12.5.2 Component Seismic Performance Factor
The component seismic performance factor, Kp is an allowance for both theestimated performance of the element or component and the importance of its
performance during and immediately following an earthquake. The value ofKp shall be obtained from Table 12.1.
If the period of vibration of an element is close to that of the structure,
considerable amplification may occur. If the ratio of the period of thestructure to that of the element is between 0.6 and 1.4, the value of Kp shallbe multiplied by 2 unless a special analysis is carried out.

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Kp

ELEMENT OR COMPONENTGROUP A
Secondary Elements or Components :1.

Walls and Partitions(a)Adjacent to an exit way, street or public placeor required to have a fire resistance rating.

4(b)Cantilevered walls and parapets.

4(c)

All walls not specified in 1(a), 1(b) or 2.

2.5

2.

Stairs and their enclosing shaft walls, and shaft
walls for lifts.

43.

Veneers, exterior prefabricated panels and ornamental
appendages, and their connections.

8

4.

Ceilings with tiles exceeding 2 kg in weight (Refer Note 5).
(a)
In an exit way or a ceiling required to have a fire rating.

3

(b)

2

5.

Other ceilings not included in 4(a).

Furniture
In an exit way or furniture that would pose a safety
hazard when subject to earthquake loads.

2

6.

Towers, chimneys or smoke stacks not exceeding 10 % of
the mass of the building (Refer Note 3).

2.5

7.

Penthouse or plant room structures on the top of astructure.

2.5

8.

Horizontally cantilevered floors, beams, sunshades, etc.
Note : The force acts vertically upward or downward.

5(continued on next page)

Table 12.1 : Component Seismic Performance Coefficient

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Kp

ELEMENT OR COMPONENTGROUP B
Mechanical and Electrical Components :9.

Boilers, furnaces, incinerators, water heaters or otherequipment using combustible or high temperature energy
sources. Pressure vessels. (Refer Note 1).

10.

Containers and their supporting structures for (Refer Note 1) :(a)
Toxic liquids and gases, spirits, acids, alkalis, molten metals or
uch dangerous materials.

6(b)Fire sprinkler systems including wet and dry risers

6

(c)

Other

4

11.

Switchgear, transformers, substations, electrical motor
control devices.

12.

Lighting fixtures :

13.

6

6

(a)

Rigidly mounted

2.5

(b)

Hanging or swinging type fixtures. (Refer Note 2)

3.5

Duct and piping distribution systems (Refer Note 1) :
(a)

(b)

Rigidly mounted -Flexible supports -(i)for toxic or dangerous substances

6

(ii)

other

3

(i)

for toxic or dangerous substances

8

(ii)

other

5

14.

Shelving for batteries and dangerous goods (Refer Note 4).

415.

Lift machinery, guides, etc.

3

16.

Emergency standby equipment required to function immediately after an
6earthquake.
(continued on next page)
Table 12.1 continued

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Table 12.1 continued
NOTES :
1.

The seismic weight of containers and the like shall include the weight of the contents.

2.

Hanging or swinging lights shall have a safety cable attached to the structure and the
fixture, capable of supporting a lateral load equal to four times the weight.

3.

Where towers, chimneys or smoke stacks exceed 10 % of the weight of the structure, thestructure shall be analyzed considering these elements.

4.

Shelving in Item 14 shall provide positive restraint to horizontal movement of the contents.

5.

Suspended Ceilings :Suspended ceilings with tiles weighing more than 2 kg shall satisfy the following
requirements :(a)

The support systems for suspended ceilings shall be designed and constructed so as
the avoid sudden or incremental failure or excessive deformations that would
release ceiling components.

(b)

Ceiling elements and lighting fixtures or other heavy fittings built into the ceiling,
shall be positively anchored to their supports against a net upward force equal to
one-third their weight.

(c)

The ceiling shall be designed for the horizontal loads in Item 4 with the support
members positively connected to each other and to the building or other horizontal
restraint.

Ceilings in important areas (such as hospital operating rooms) where loss of ceiling units
cannot be tolerated, should be fixed rigidly and directly to the structure.
Ceilings with tiles weighing less than 2 kg need not be designed to these requirements.

12.6

Separation of Elements
12.6.1 Applicable Elements
The requirements of 12.6.2 for the separation of elements shall apply to thefollowing :(a)NBC105V2.RV5

Elements such as stairways, rigid partitions, and non-structural
masonry walls of part or full height.

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(b)

Flexible partitions not capable of altering the intended structural
behaviour but required to have a fire resistance rating, provided that
this need not apply when it can be shown that the partition retains its
fire resistance after being subjected to the specified deformation.

(c)Precast concrete cladding and other cladding of similar mass.

(d)

Glass windows and other rigid, brittle, exterior cladding.

Elements which can accept inter-storey deflections of four times those
calculated in accordance with 9 without being damaged and without affecting
the structure need not comply with the separation requirements of 12.6.2.
12.6.2 Separation Requirements
Requirements for the separation from the structure of elements listed in
12.6.2 shall be as follows :

13

(a)

Ratio of inter-storey deflection to storey height not exceeding 0.0012: No requirements for separation.

(b)

Ratios of inter-storey deflection to storey height exceeding 0.0012 but
not greater than 0.015 or 60 mm : Elements shall be positively
separated from the structure so as to allow the structure to deform as
calculated in accordance with 9 without the elements coming into
contact with the structure or with adjacent elements. A minimum
separation of 10 mm shall be maintained between the structure andthe vertical surfaces of the element. Construction tolerances shall not
reduce the required separations.

Structural Variations to be Approved by Designer
The structural designer shall make the builder or contractor aware of the dangers that canarise when structural elements or details are changed or varied without the specific approvalof the structural engineer. Any variations approved by the designer shall comply with therequirements of this Standard.

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