Proceedings of 10th IOE Graduate ConferencePeer Reviewed

ISSN: 2350-8914 (Online), 2350-8906 (Print)Year: 2021 Month: October Volume: 10

Seismic Behaviour of Buildings as per NBC 105:1994, NBC105:2020 and IS 1893:2016Rajesh Banjara a, Deepak Thapa b, Tek Bahadur Katuwal c, Sailesh Adhikari d

a, b, c, d Department of Civil Engineering, Pashchimanchal Campus, IOE, Tribhuvan University, NepalCorresponding Email:a rajesh.bie@gmai.com, b thapadeepakwrc@gmail.com, c tekkatuwal@wrc.edu.np, d sailesh.adhikari@pasc.tu.edu.np

AbstractA comparative study is performed between different RC Buildings as per Nepalese (Nepal National BuildingCode,NBC) and Indian (Indian Standard, IS) previously existing and revised standards with considerationof several design compliances. NBC 105:1994 was revised to NBC 105:2020 and also IS 1893:2002 to IS1893:2016 which are used for RC building in current study.This paper presents the analysis of low-rise RCbuilding of three storey and staircase cover. For the analysis Various response parameters are used usinglinear and non-linear static and linear dynamic approaches.The result obtained from the NBC 105:2020 wasgreater than the other codal provisions based on dynamic properties (time period, response reduction factor,overstrength, ductility) and seismic response (drift, displacement & base shear). The value of Base shearis higher by 104%, 116% and 157% in NBC 105:2020 than the other codal provisions NBC 105:2020 SLS,IS 1893:2002 and NBC 105:1994. The performance verification overestimate the value of performance limitstate due to the due to the adaptation of latest seismic index in the estimation of the seismic hazard in NBC105:2020.

KeywordsNepal National Building Code (NBC), Indian Standard (IS), Seismic Analysis, Ultimate Limit State (ULS),Serviceability Limit State (SLS)

1. Introduction

RC buildings construction practice started aroundmany decades ago as an alternative to traditionalunreinforced masonry practice which doesn’t satisfythe integrity and ductility criteria. As the nationalseismic codes are important to address the safety ofbuildings and occupants. It is noted that manybuildings codes have some relationships and thedifferentiation lines can be easily drawn among theseismic codes too. Building code comparisonespecially in terms of seismic provisions have gainedconsiderable momentum in the case of active seismicregions and help to form a most effective andeconomical building design. Nepal is a seismic pronezone and seismic activities are very frequent occurwhich is caused by the continental collision of Indianplates and Eurasian plates. The tectonic zone of Nepalis distinct and complicated with variance intopography and geology making it covered with majorseismic activities in the past as 1988 A.D. and mostrecent of 2015 A.D. After major seismic event of

1988 A.D., Nepal National Building Code (NBC) in1994 AD was formulated by Department of UrbanDevelopment and Building Construction (DUDBC).In 25th April 2015, a moment of magnitude Mw 7.8earthquake struck at 11:56 local time followed byseveral strong aftershocks hits central and eastern partof the country. This earthquake with numerousaftershocks causes about 9000 deaths and more than22,000 injured and a huge loss of lives and economy.Although, major seismic events occur within thecountry the use of the NBC 105:1994 still occurs. Thecode was still not revised since a long time althoughIndian code has been revised and question is beenarise for the use of code. As there is introduction ofNBC, there is use of IS code with no restriction onany policy level since the boundary of Nepal and Indiais along three directions with similar soil profile andtectonic environment. Considering the progressivestudy in the field of earthquake resistant design therevision of Indian Standard code IS 1893:2016 wasdeveloped. Considering the above facts, a draft of the

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new updated code has been proposed as NBC105:2019 and finally NBC 105:2020 wasimplemented. In IS 1893:2016 and NBC 105:2020major changes have been incorporated which shouldbe well understood by practicing Engineers. So, anattempt is done to study the updated compliancescodes and compare with the existing ones. Hence, thestudy is performed to compare the codal provisionswith a numerical model created in ETABS.

2. Literature Review

This research focused on the comparison of seismicdesign codes, Nepal building code (NBC) and Indianstandard (IS) both revised and existing in analysis anddesign aspect for the RC building structures withconsideration of several design compliances. Theresults of the study show that the response of buildingis greater from the revised NBC 105:2019 ascompared to other studied codal provisions.Longitudinal rebar percentage and the period ofvibration is higher than the existing ones since thereduced stiffness as it considered crack section in bothrevised IS 1893:2016 and NBC 105:2019 [9].

In this research study it deals with the NBC 105:2019Seismic Design of Buildings in Nepal which is therevised version of the original code NBC 105:1994.As there is various development in research andtechnology and new knowledge was learned fromvarious large earthquakes in last 25 years, the Nepal Anew seismic hazard map of Nepal was proposed at thebased on probabilistic approach. The PGA values forvarious locations of Nepal were updated. Theperformance requirements have been inserted in termsof collapse prevention and damage limitation andthere need to verify the performance requirementschecking in terms of ultimate limit state andserviceability limit state. In this code two differentspectra are proposed for seismic coefficient methodand modal response spectrum method. The responsereduction factors (Ductility factor and Overstrengthfactor) are introduced. The horizontal base shearcoefficient will be is determined separately forultimate limit state and serviceability limit state. Thehorizontal design spectrum for the modal responsespectrum method is different for ultimate limit stateand for serviceability limit state. This also includes tocheck the inter-story drift for both serviceability limitstate and ultimate limit state [6].

Based on static and dynamic research of two-story

and four-story RC buildings, this paper addresses theimpact of the new code on seismic load estimation forlow rise RC buildings. IS 1893:2002, IS 1893:2016,NBC 105:1994 and NBC 105:2020 were used in thestudy. The response of the buildings from theapplication of the four codes was compared based onnumerous criteria such as time period, base shear,drifts, and story forces. The structural reaction of thestructure under the new NBC 105:2020 is 60 percentto 65 percent higher than the NBC 105:1994,according to a comparison of the results based onseveral factors [7].

A history of seismic code development in Nepal,India, Japan, and the European code. NBC, IS,Japanese code BSLJ, and Euro code EC werecompared in terms of base shear and fundamentalnatural period. Ground conditions, seismicity,construction technology, and the degree of seismiccode development are all varied. EC and IS codes arerecommended for usage in Nepal. When EC isemployed in designs, it achieves the highest frequencyof the four codes. Because NBC and IS produce thesame basic period, a comparison of base shear showsthat IS code has higher base shear than NBC. Thismay lead to variation in design of lateral load resistingsystem. This study set out to provide the account andcomparison between four seismic codes. (PrajwalGiri, Anand Dev Bhatt, Dipendra Gautam andHemchandra Chaulagain)

The comparative analysis of G+21 RC building fordifferent soil category of NBC 105:1994 and IS1893:2016 is computed. The seismic coefficientmethod shows higher base shear, displacement andreinforcement demand than the model responsespectrum analysis. For soil type I and II, IS1893:2016 gives higher base shear, displacement anddrift than NBC 105:1994. For soil type III NBC105:1994 give higher base shear, displacement anddrift than IS 1893:2016. IS 1893:2016 gives higherreinforcement demand than NBC 105:1994 [4].

Structures in megacities are in great danger due tofaulty and inexperienced design and construction.Structure designers are sometimes more concernedwith constructing various load resistant memberswithout understanding their necessity or performancein the structure. Different construction configurationsmay also result in significant variations in the capacityof the same structure. Nonlinear static pushoveranalysis provides a more accurate picture of structureperformance during seismic events. This

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comprehensive study evaluates and compares theperformance of bare, different infill percentage level,different configuration of soft story and Shear wallconsisting building structures with each other, andthen, based on the findings, suggests which buildingstructures to use. Above all, the findings could beused to summarize a better understanding of theeffects of pushover analysis. According to pushoverconcerned codes, masonry walls are represented byequivalent strut. The performances of structures areevaluated for various loading conditions usingperformance point, base shear, top displacement, storydrift, and stages of number of hinges form [10].

3. Overview of Codal Provisions

For the overview of the codal provisions NBC105:1994, NBC 105:2020 and IS 1893:2016. Eachseismic code has its own set of analyzing parameters.

3.1 NBC 105:1994

NBC 105:1994 was developed on the basis of aprobabilistic seismic hazard analysis with respect toNepal’s 150 km border. As per NBC 105:1994 it isnot recommended for analyzing unusual structuressuch as power plants, bridges, dams, and structurestaller than 90 meters. Seismic analysis is based onboth the Working Stress Method (elastic method) andthe Limit State Method, but in the case of RCbuildings, the limit state design is preferred. Itsuggests using the basic seismic coefficient or modalresponse spectrum for each of the three subsoil types,Subsoil type-I, Subsoil type-II, and Subsoil type-III.The subsoil type is explained using representativeundrained shear strength for cohesive soils andrepresentative standard penetration resistance (SPT)values for cohesionless soils. The basic seismiccoefficient (C) and the basic response spectrum C (Ti)for three types of subsoils per NBC are represented inFig.1.

The structures having height more than 40 m height isanalyzed with model response spectrum method butup to 40 m, seismic coefficient method is applied.There is no provision of time history analysis includedin the code. The seismic weight at each level, Wi,shall be taken as the sum of the dead loads and theseismic live loads between the mid-heights ofadjacent storeys. Seismic live load is based on thedesign live load as (a) up to 3 kPa 25 percentage isused of design live load (b) above 3 kPa and vehicle

garages 50 percentage is used of design live load (c).For roofs nil. The approximate period of vibration formode of buildings for the seismic coefficient methodis based on the height of the building as shown inTable 6. For both seismic coefficient method (1) andresponse spectrum method (2), the horizontal seismicforce coefficient is obtained as:

Cd =C ZIK (1)

Cd (Ti) =C (Ti) ZIK (2)

where, Cd is the lateral seismic force coefficient; C isthe basic seismic coefficient for the translationalperiod in the direction under consideration; Z isseismic zoning factor; I is the importance factor forbuildings; K is structural performance factor; andC(Ti) is the ordinate of the basic response spectrum.The inter-story drift is limited to 0.01 when theinter-story drift to height of story ratio is consideredand the maximum value of inter-story drift is limitedto 60 mm. To calculate the horizontal seismic baseforces in the following equations:

V =Cd Wt (3)

where,Wt is total gravity load above the lateral restraint;Cd is the design horizontal seismic force coefficient

On the other hand, in the case of response spectrumanalysis, the participation of at least 90 percentage ofthe total mass is considered.

3.2 IS 1893:2016

IS 1893:2016 was designed based on deterministichazard analysis with respect to recorded time historydata. It is the sixth revision adopted by Bureau ofIndian Standard for Earthquake Resistant Design ofStructures (BIS 2016). The design response spectracurve is extended to 6s while a constant value isdepicted after 4 s. The effect of infill masonry is alsoincluded in the analysis of frame buildings in therevised version. The effect of vertical earthquakeshaking is considered when the structure is located inseismic zone IV or V, structure have plan or verticalirregularities, rested on soft soils, bridges, long spansand having horizontal overhangs of structuremembers. For the calculation of seismic force, itconsiders equivalent static and dynamic analysis

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method. It recommends the use of the basic seismiccoefficient or modal response spectrum as per threesubsoil types, Subsoil type-I, Subsoil type-II, andSubsoil type-III as Hard, Medium and Soft soils. Thedesign horizontal seismic coefficient (Ah) for threetypes of subsoils per IS are represented in Fig.2

Linear dynamic analysis is performed to obtain thedesign lateral force for all building, other than regularbuildings lower than 15m in seismic zone II. Dynamicanalysis may be performed by either the Time HistoryMethod or the Response Method. On either of themethod, design base shear estimated shall not be lessthan the design base shears calculated using afundamental period, Ta. The seismic weight at eachlevel, Wi, shall be taken as the sum of the dead loadsand the seismic live loads between the mid-heights ofadjacent storeys. Seismic live load is based on theimposed load as (a) up to 3 kPa 25 percentage is usedof imposed load (b) above 3 kPa 50 percentage is usedof imposed load. The approximate period of vibrationfor mode of buildings for the seismic coefficientmethod is based on the height of the building asshown in Table 6. The design horizontal seismiccoefficient (Ah) is calculated as:

Ah =ZISa

2Rg(4)

where, Sa/g is the average response accelerationcoefficient and is the ordinate of the basic responsespectrum; Z is seismic zoning factor; I is theimportance factor for buildings; R is responsereduction factor. The inter-story drift is limited to 0.04when the inter-story drift to height of story ratio isconsidered and the maximum value of inter-story driftis limited to 50 mm. To calculate the design seismicbase forces in the following equations:

VB = Ah W (5)

where,Ah is design horizontal seismic coefficient;W is the seismic weight of the building

Response spectrum method may be performed for anybuilding using the design acceleration spectrum usingequation of Ah or by a site-specific designacceleration spectrum. The number of modes Nm tobe used in the analysis for earthquake shaking along aconsidered direction, should be such that the sum oftotal modal masses of these modes considered is atleast 90 percent of the total seismic mass. Peakresponse quantities (member forces, displacements,

story shears, and base reactions) may be combined asper Complete Quadratic (CQC) method.

3.3 NBC 105:2020

The principal objective of revising national buildingcode NBC 105:1994 Seismic Design of Buildings inNepal to update it by endorse earthquake resistantdesign knowledge and technology acquired throughout worldwide by the different countries. This codalprovision covers the required parameters for seismicanalysis and design of various building structures to beconstructed in the territory of the Federal Republic ofNepal. This code is applicable to all type of buildingstructures, low to high rise buildings, in general. Thiscode is applicable to buildings made of reinforcedconcrete, structural steel, steel concrete composite,timber and masonry. A new seismic hazard map ofNepal is introduced based on probabilistic approach.The PGA values for selected cities/municipalities ofNepal were revised.

The performance requirement is introduced in termsof collapse prevention and damage limitation and alsoused to verify the performance requirements checkingin terms of ultimate limit state and serviceability limitstate. Hence, the main aim is to check life safety anddamage limitation performance requirements. Fourtypes of site sub soil category are used. Very soft soilcategory is added in addition to previous NBC105:1994. This new soil category represents a verydeep soft soil found in Kathmandu valley. This codeintroduces the non-linear methods of analysis. Theempirical formulae for determination of fundamentaltranslation period is revised and Rayleigh method isintroduced. The calculated period of vibration ismultiplied by amplification factor 1.25 and tabulatedin Table 6. The structural performance factor iscalculated by interpolation. The importance factors,load combinations for both the parallel andnon-parallel and load factors are revised. Theresponse reduction factors (Ductility factorandOverstrength factor) are introduced. Two differentspectra are used for seismic coefficient method andmodal response spectrum method. The horizontalbase shear coefficient will be determined separatelyfor ultimate limit state and serviceability limit stateand shown in Figure 3.

Cd(T 1) = (C(T 1))/((R)(Wu)) (6)

Cd(T 1) = (Cs(1))/Ws (7)

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Where,Cd(T1) = Elastic Site Spectra for Ultimate Limit StateCs (T1) ) = Elastic Site Spectra for Serviceability LimitStateR= Ductility FactorΩu = Over strength Factor for Ultimate Limit StateΩs = Over strength Factor for Serviceability LimitStateThe horizontal seismic base shear at the base of thestructure in the direction is calculated as:

V =Cd(T 1)W (8)

Where,Cd(T1) = Horizontal base shear coefficientW = Seismic Weight of the structure

The Vertical Distribution of Seismic Forces induced ateach level ‘i’ shall be calculated as:

??? (9)

Where,Wi = seismic weight of the structure assigned to level‘i’;hi= height (m) from the base to level ‘i’;n= total number of floors/levelsV= horizontal seismic base shear

The horizontal design spectrum for the modalresponse spectrum method is also different forultimate limit state and for serviceability limit state. Aseparate section on structural irregularity has beenadded. This code includes checking the inter-storydrift for both ultimate limit state and serviceabilitylimit state as 0.025 and 0.006.

Response spectrum method is performed as thecombination of modal effects (such as story shear,moment, drift, displacements) shall be carried outusing an established method such as Square Root ofthe Sum of the Squares (SRSS) or the CompleteQuadratic Combination (CQC) method or any othergenerally accepted combination methods. Modes shallbe considered to be closely spaced if their frequenciesare within 15 percentage. For such modes, if theSRSS combination method is used, the modal actioneffects from any modes shall be first combined bydirect summation ignoring any signs.

4. Aims and Scope

The aim of this research work is to observe andevaluate the response of the buildings and analyzed as

per NBC 105:2020, NBC 105:1994 and IS 1893:2016.The primary objectives are as follows:

1. To evaluate the performance of buildings with allsignificance structural parameters based on the effectof variation on shape and size in response toearthquake.

2. To evaluate the performance of buildings usinglinear and nonlinear static analysis procedures.

5. Methodology

Five different shape and size RC residential buildingswere taken in consideration for the modeling. Thesedifferent buildings were analyzed and a comparison ismade between different shape and size of buildingsagainst the effect of lateral loads due to theearthquake. This research mainly deals with anumerical study of the effect of different shape andsize RC building on the response to the earthquake.These structures are widely used throughout the Nepalfor the residential purposes. This section includes thematerial property and section property used for theanalysis of the structure. Building features used forthe study are listed on Table 1 and building model areshown in Figure 4, 5, 6, 7 and 8.

Figure 1: Building-1 Structure used for analysis

Figure 2: Building-2 Structure used for analysis

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Figure 3: Building-3 Structure used for analysis

Figure 4: Building-4 Structure used for analysis

Table 1: General features of the building use in studyType of building Residential BuildingStructure system RCC frame structure; SMRF

Plinth area

Building-1: 77.458 m2

Building-2: 210.613 m2

Building-3: 58.058 m2

Building-4: 67.980 m2

Building-5:135.340 m2

No. of story 3 (Three) story+ Stair coverFloor to floor height 3 mTypes of Slab 125 mm thick; Two-way Slab, 150 mm thick staircase slabTypes of Beam Rectangular main beam (230mm×450mm)Types of Column Rectangular column(300mmx300mm)Materials Cement, Brick, Sand, Rebar etc.Unit weight of brick 19.2KN/m3

Grade of Concrete M20Grade of Steel Fe500Method of analysis Static and dynamic

The seismic loads for selected RC buildings modelswere calculated by following the respective codalprovision NBC 105:2020, NBC 105:1994 and IS1893:2016. The selected building models are not inregular in geometry, mass, and stiffness. The initiallateral stiffness of a building is essential to its overallresponse. The amount of lateral load resisted by

individual building members is determined by theirlateral stiffness; stiffer elements attract more forcethan flexible ones. Furthermore, adequate overallstiffness in a building is required to control overalllateral displacement during earthquake shaking. As aresult, uniform distribution of stiffness in a building isessential to ensuring uniform distribution of lateraldeformation and lateral forces across the plan andelevation of a building. As, the buildings used for theanalysis are different in shape and size. Thus, themass of the buildings is different from each other’s.So, both the equivalent static method and responsespectrum method are used for computation of baseshear coefficient. The step by step procedure for thecalculation of seismic load and its distribution amongdifferent floors as provided in NBC 105:2020, NBC105:1994 and IS 1893:2016 are explained in theoverview section and calculation is done in resultsection.

The research deals with the numerical modeling. Forlinear analysis NBC 105:2020 stipulates the use of theelastic flexural and shear stiffness properties of thecracked concrete elements through rational analysis.However, in absence of such analysis, the effectivestiffness of the cracked section shall be used and theall other respective properties code is given in Table 2.

In this study, no rational analysis was made to evaluatethe elastic flexural and shear stiffness properties ofthe cracked concrete section so effective stiffness ofcracked section was used in the analysis.

The dead loads used in the calculation is used fromIndian standard for computation of dead load (IS 875(Part 1):1987) and live loads were used using Indianstandard for computation of Imposed load (IS 875(Part 2):1987). The seismic loads were calculatedfollowing as per their respective codal provisions. Thedetailed procedure for the calculation of seismic loadsis explained in detail in overview section. The seismicload was combined with gravity load using the loadcombination given in NBC 105:2020 and all the loadcombination of respective codes is shown in Table 3.

The estimation of base shear for both the regular andirregular buildings is obtained by response spectrumanalysis using the response spectra curve. The curvehaving the values of acceleration and times as per therespective codes. The Modal Response SpectrumMethod may be used for all types of structures and thestructures where Equivalent Static Method is notapplicable. A three-dimensional analysis shall be

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performed for torsional sensitive structures. Theprocedure for the calculation of the base shear andother parameters using respective codes are providedin the literature review section. The design of theprototype building is performed according to IS456:2000 for all the models. The loads considered inthe analysis is as per IS 875 Part(II). The generalloading parameters used in the study and theirstandard value are listed on the Table 4.

The structural performance of the building during anearthquake can be verified in different ways. Thestructural performance can be evaluated from a locallevel or global level structural response. The locallevel structural response includes componentstress-strain, component rotation or curvature, storydrift, and so on. Similarly, the global structuralresponse includes the drift limit of the roof or otherreference points, structural stability indices, and so on.The respective codes having different inter-story driftlimit for performance verification which is shown inTable 5. The earthquake-resistance design philosophyincludes that the structure should have sufficientstrength and stiffness to resist moderate earthquake,damage limitation objective and structure must bedetailed to ensure that the probability of collapse in asevere earthquake. Life safety objective are verifiedby the SLS and ULS respectively as per NBC105:2020. The SLS for ordinary buildings is based onearthquake ground motion with a return period of 20years. Similarly, the ULS for ordinary buildings isbased on earthquake ground motions with a returnperiod of 475 years.

The drift value for the ULS is obtained by multiplyingthe horizontal deflection found from the Equivalentstatic method or Modal response spectrum method bythe Ductility factor. Similarly, the drift value for theserviceability limit state is obtained by taking equalto the deflection obtained from the Equivalent staticmethod or Modal response method.

Table 2: Performance requirement as per respectivecodes

Performance limit state Inter-story drift limitationNBC 105:2020 (ULS) 0.025NBC 105:2020 (SLS) 0.006

NBC 105:1994 0.0012IS 1893:2016 0.004

Pushover analysis is a static, nonlinear procedure inwhich the magnitude of the lateral force is

incrementally increased, maintaining the predefineddistribution pattern along the height of the building.With the increase in the magnitude of the loads, weaklinks and failure modes of the building are found.Pushover analysis can determine the behavior of abuilding, including the ultimate load and themaximum inelastic deflection. Local Nonlineareffects are modeled and the structure is pushed until acollapse mechanism gets developed. At each step, thebase shear and the roof displacement can be plotted togenerate the pushover curve. It gives an idea of themaximum base shear that the structure was capable ofresisting at the time of the earthquake. For regularbuildings, it can also give a rough idea about theglobal stiffness of the building.The material model used in the static Nonlinearpushover analysis is based on the proceduresproposed by the documents, defining force –deformation criteria for the hinges used in thepushover analysis. Figure 2 describes the typicalforce-deformation relation proposed by thosedocuments. Five points labeled A, B, C, D and E areused to define the force deflection behavior of thehinge and these points labeled A to B – Elastic state,B to IO- below immediate occupancy, IO to LS –between immediate occupancy and life safety, LS toCP- between life safety to collapse prevention, CP toC – between collapse prevention and ultimatecapacity, C to D- between C and residual strength, Dto E- between D and collapse ¿E – collapse.

Table 3: Force-Displacement Curve in Push overAnalysis, Image Source: http://research gate

6. Results and Discussion

The response of the building is analyzed by usinglinear static and linear dynamic approaches for thedifferent codal provisions. The response parametersunder comparison were response spectrum curve, baseshear, time period of vibration, maximumdisplacement, inter story drift, eccentricity.Response-spectrum analysis (RSA) helps tounderstand the dynamic behavior by measuringspectral acceleration as a function of structural periodas per the height of the building and level of damping.

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The prediction of displacements and member forces instructural systems is one of the computational benefitsof using the response spectrum method of seismicanalysis. Using smooth design spectra that are theaverage of several earthquake motions, the methodcalculates only the maximum values of displacementsand member forces in each mode. The responsespectrum curve of pre-defined three different code ofpractice is presented graphically in Figure 10. NBC105:2020 and IS 1893:2016 building code gives thesame value for the acceleration followed by NBC105:1994 in the decreasing order. As, the designacceleration coefficient for the different types of soildepends upon the peak ground accelerationcorresponding to time period of structures in IS1893:2016 and in case of NBC 105:2020 lower andupper time period, peak ground acceleration andcoefficient that controls the descending branch.

Figure 5: Comparison based on Response SpectrumCurvee

Time period of the structure depends on stiffness andon the mass of the structure. With increase in heightof structure the time period is higher showing theflexibility of the structure. Usually several codalprovisions provides the fundamental period ofvibration (approximate) which depends upon theheight of the structure. The estimated time perioddoesn’t depend upon the shape and size of thestructure. For the analysis for torsional effects, theapplied torsion at each level is based on theeccentricity allowed for providing the severe effect onlateral force resisting elements.

The design horizontal base shear coefficient parametermainly dependent on the time period of the structureas the time period of the structure depends on theheight of building to be analysis. Here we considersame height of the structure for all five model hencetime period is also same for all structure as per theirrespective code. So, design horizontal seismic forcecoefficient is same for different structure in their

respective code. From the Comparison of Base ShearCoefficient, it is found that Base Shear coefficientvaries from 0.08 to 0.125. Hence, the designhorizontal seismic coefficient is maximum as perNBC 105:2020 ULS because of consideration of latesthazard index followed by NBC 105:2020 SLS, IS1893:2106 and NBC 105:1994 minimum value amongfour codes since the response reduction factor forNBC 105:20220 ULS is only 6 and NBC 105:20220ULS is 1.25 while the response reduction (2R)considered in IS 1893:2016 is 10 which is presentedin Table 6.

The effect of these base shear coefficients on thedesign result, however, cannot be judged solely on thevalue of the base shear coefficient values. Because theload combination used in NBC 105:2020 differssignificantly from that used in NBC 105:1994 and IS1893:2016. When the seismic load is combined withthe gravity load, NBC 105:2020 considers only onefactor, whereas the other two codes assume a factor ofup to 1.5. The base shear coefficient has a direct effecton the lateral deformation caused by lateral loading inthe direction of the earthquake attack, which is usedas a performance verification method in the respectivecodes. So, due to the differences in load combinationsused, the base shear coefficient alone may not affectthe design output results. However, the designprocedure such as capacity design may affect theresult; however, the base shear coefficient directlyaffects the amount of lateral deformation induced bythe design level of earthquake loading.

Design base shear has a vital role in the seismicanalysis as it influences all the analysis parameter ofthe structure. The comparison of the design base shareis also the major objective of this study. In thissection, the base shear force obtained from static anddynamic methods are compared along with thecomparison between manually calculated andsoftware derived base shear. In the analysis as shownin figure 11, maximum static base shear is obtainedfrom NBC 105:2020 ULS followed by NBC 105:2020SLS and IS 1893:2016 and minimum from NBC105:1994.

In dynamic analysis with scale factor greater than one,as shown in figure 12, maximum base shear is given byNBC 105:2020 ULS followed by NBC 105:2020 SLSand IS 1893:2016 and minimum from NBC 105:1994.Here scale factor is to increase dynamic load is greaterthan one for all respective code. Thus, for the structureused in my study it is compulsory for dynamic analysis

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for all respective codes. In dynamic analysis the valueof the base shear is make equal to the value of staticbase shear by increasing scale factor from the EQ andRS value.

Figure 6: Graphical representation of static baseShear from ETABS

Table 4: Graphical representation of dynamic baseShear from ETABS

Figure 7: Representation of Pushover Analysis ofBuilding-3 model

Also, here from figure 13 graphical representation ofthe base shear which is calculated manually and figure11 graphical representation of base shear usingETABS, normally the value of base shear calculatedmanually is more than calculated from ETABS sincethe pattern of difference between the manually andETABS calculated base shear is nearly same.

The result of performance assessment using nonlinearstatic procedures shows that all the building modelssatisfies the performance limit state. This result showsthat the building-3 model have sufficient capacity toresist the given hazard and achieve the earthquakeresistance design objective of damage limitation andlife safety.

7. Conclusions

A study is performed between different RC BuildingNepalese (Nepal National Building Code, NBC) andIndian (Indian Standard Code, ISC) previouslyexisting and revised standards with consideration ofseveral design compliances. NBC 105:1994 wasrevised to NBC 105:2020 and also IS 1893:2002 to IS1893:2016 which are used for RC building in currentstudy. After the interpretation and throughobservation of the results, some conclusions are foundout. However, the conclusion made here does notrepresent in a broad sense because only limitedbuilding was used in this study. The building selectedhere was a low-rise RC building of three stories plusstaircase cover that lie on soil type ’B’. The designbasis of Indian Standard Codes for seismic hazardanalysis is deterministic approach whereas NepalBuilding Code is based on probabilistic and impactare studied. Seismic Demand (MCE, DBE and PGA),Dynamic properties (time period, response reduction

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factor, overstrength, torsional irregularity) andSeismic response (drift, displacement and base shear)from the four codes were compared in this study usinglinear static, linear dynamic and non-linear analysisapproaches.

The conclusions of this study are listed below:

1. From the response analysis different parameterswere observed to be estimated greater from the NBC105:2020 as compared to other studied codalprovisions. The major reason behind this is theadoption of the latest seismic index in estimation ofthe seismic hazard.

2. Based on the different shape and size of residentialbuildings from static and dynamic base shear, differentpattern was observed. Hence, it can be concluded thatshape and size have effects on the base shear of thestructure.

3. The time period of vibration estimated by the NBC105:2020 is higher than IS 1893:2016 and NBC105:1994 since it includes effective stiffness ofcracked sections (flexural and shear) and amplificationfactor. 4. The distribution of base shear at differentfloor levels is linear in NBC 105:1994 but distributedis in parabolic pattern in IS 1893:2016 and linearinterpolation in NBC 105:2020. As per given codalprovision IS 1893:2016, NBC 105:2020 shows toscaled up the base shear in dynamic analysis result ifit is less than the static base shear. However, NBC105:1994 does not provide any provision on this scalefactor. In this study, scale factor is greater than 1 asper all codes used. So, dynamic base shear is requiredto scale up according to all the codes used.

5. The value of Base shear is higher by 104%, 116%and 157% using compared codes NBC 105:2020 ULSto NBC 105:2020 SLS, IS 1893:2016 and NBC105:1994. Similarly, the value of inter story drift ishigher by 4%, 4% and 150% using compared NBC105:2020 ULS to NBC 105:2020 SLS, IS 1893:2016and NBC 105:1994.

6. In some of the buildings as per respective codalprovision the process for performance verification ofthe buildings using linear analysis proceduresoverestimate the value of performance limit state.

8. Recommendations

1. This study is based on the different shape and sizeof residential building. As per the conclusion in most

building structure the value of performance verificationis beyond the limit in all codes so the size of the beamand column need to be increased.

2. By increasing the size of the beam and columnthe percentage of the reinforcement is also increased.The cost of the construction of the residential buildingincreased from the economical point of view.

3. Hence, the base shear coefficient should be reducedto a certain portion by using performance factorwithout compromising the performance requirements,so that economy in the building construction can beachieved at the same time the performance objectivesof damage limitation and life safety can be achieved.

References

[1] NBC 105:1994. National Building Code of Nepal,Seismic Design of Buildings in Nepal

[2] NBC 105:2020. National Building Code of Nepal,Seismic Design of Buildings in Nepal

[3] Standards, B. of I. (2016). IS 1893:2016 - IndianStandard Criteria for Earthquake Resistant Design ofStructures, Part 1 - General Provisions and Buildings.Bureau of Indian Standards (Vol. 1893).

[4] Pandit, P., and Vasudev, M., (2019) ”ComparativeAnalysis of NBC 105:1994 And Is 1893:2016 SeismicCodes With G+21 Rc Building”, InternationalResearch Journal of Engineering and Technology(IRJET), Vol. 6, No. 11, PP. 1995-2000

[5] Aryal, A., and Dhungana, S., (2020) ”ComparativeAnalysis of NBC With Is Code for Rc Structures”International Research Journal of Engineering andTechnology (IRJET), Vol. 6, No. 24, PP. 2113-2117

[6] Maskey, P., Dhakal, R., Tamrakar, M., Bista, M., Ojha,S., Gautam, B., Acharya, I., and Chamlagain, D., (2020)”NBC 105:2019 Seismic Design of Buildings in Nepal:New Provisions in the Code” 17th World Conferenceon Earthquake Engineering, 17WCEE, 2b-0036

[7] Shrestha, J., Paudel, N., Koirala, B., Giri, B., andLamichhane, A., (2021) ”Impact of Revised CodeNBC 105 on Assessment and Design of Low RiseReinforced Concrete Buildings in Nepal” Journal ofInstitute of Engineering, Vol. 16, No. 1, PP. 1-5

[8] Lamichhane, K., Lamichhane, G., Ghimire andAdhikari, K.,(2021) ”Analysis of Irregular Structurewith Addition of Shear Walls as Per Nepal BuildingCode (NBC 105:2020)” International Journal ofEngineering Research and Technology (IJERT), Vol.10, No. 03, PP. 608-612

[9] Bhusal, B., and Paudel, S., (2021) ”Comparative studyof existing and revised codal provisions adopted inNepal for analysis and design of Reinforced concrete

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structure” International Journal of AdvancedEngineering and Management. Vol 6, No. 1 PP. 16-24

[10] Yousuf Dinar, Y., Hossain, M., Biswas, R. and Rana,M., (2014) ”Descriptive Study of Pushover Analysisin RCC Structures of Rigid Joint” IOSR Journal ofMechanical and Civil Engineering . Vol 11, No. 1 PP.

60-68

[11] Garlock, M., Richard Sause, R. and Ricles, J., (2004) ”Design and Behavior of Post-tensioned Steel MomentFrames” 13th World Conference on EarthquakeEngineering., No. 2560

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