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International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181http://www.ijert.org
Published by :
Vol. 9 Issue 03, March-2020
Comparative of Study the Design Spectra Defined
by Various Seismic Codes
KHadar Elmi1, Assist Prof. Dr. Erdal Coskun2 1- Institute of Graduate, Structural Engineering Program İstanbul Kültür Üniversitesi
2- Department of Civil Engineering İstanbul Kültür Üniversitesi
Abstract:- The main objective of this study is to compare
various seismic design codes, to evaluate and assess the
performance of seismic structures. The standard seismic
codes USA, European, Turkey, and Indian which mainly
considered the most seismic active regions are covering for
this study; focus on some fundamental points such as seismic
hazard specifications, soil amplification, elastic design spectra,
reduction and behavior factors, and seismic analysis
procedure. In this study Reinforced Concrete Moment
Frames are considered in the design and the structure is
applied the seismic input obtained from these contemporary
seismic codes, the seismic analysis was performed the SAP
2000 v 20. 2 Software and the result obtained from these
seismic codes, were emphasized the alteration and
resemblances among these building codes, Such as the base
shear and Inter-story drift of the structure.
Key words: Seismic Codes, Comparative Study, Drift Ratio, Base
Shear, Design Spectra, Site Classification
INTRODUCTION
Since the earthquake has become the major disaster for
structures, the seismic codes were designed to reduce the
damage of structure and to keep quality structures also to
minimize the economic loss caused by the earthquakes.
The seismic codes are updated and revised when a strong
earthquake occurs frequently, notably, Turkish is the most
seismic active regions in the world, a numerous strong
earthquake ground motions were happened for the past
decades, the Turkish seismic code is revised several times.
Two remarkable earthquake were strike Turkey in 1999
(Kocaeli and Düzce) due to these earthquakes over 18,000
are recorded for death and more than 51,000 building are
heavily damaged or collapsed. The material used for the
construction had less quality, poor design for the structures
and the range of strong ground motions are caused that
earthquake problem. (1) The Turkish seismic code 1998
were revised in 1997, however due to this strong
earthquake, another seismic code is published 2007 and
finally 2018, however during that past earthquakes are
recognized that structures are designed for lateral loads due
to the wind loads are much better than the structures are
designed for the gravity loads only, the modern seismic
codes based on the seismic design force based
methodology for elastic analysis. (2) Structures will be
expected to behave non-linear variety, producing huge
deformation and dissipating an enormous quantity of
energy, according to this the structures will be intended and
detailed imperatively to convince the essential capacity of
energy dissipation. But later is developed the displacement
based design which is importance of displacement control
for the structures particularly the damage of non-structural
elements. The perspectives of seismic codes are to control
the parameters such as base shear, drift ratio, ductile
demand and capacity demand to endorse the behavior of
structure. (3) The design base shear for structures is very
crucial to control the performance of structures given by a
ductility class. This study is covering the comparative of
major seismic building codes by studying the independent
and the multiple aspects that affects the building codes for
the design base shear.
SOIL CLASSIFICATION
The effects of soil in to the structures plays vital important
for damage structures in to contrary ways, Structures
behave differently when subject to earthquake in different
types of soil conditions for example dense soil and soft
soil. [4]. The response of structure for flexible soil and hard
soil is not same, so for that mostly seismic codes defined
soil classes or ground types based on the average shear
wave velocity at top of 30 m(Vs 30) and SPT. The seismic
codes such as Eurocode defines five different ground types
vary A to E and two soil factors which is depends on the
damping factor, the Indian seismic code defines three
different soil types, Type I, Type II and Type III, which is
represented by hard rock soil, medium and soft soil
respectively and Indian code not considered or based on the
soil average wave velocity but considered the SPT. The
Turkish soil are classify five different soil vary A to E.
Table 1 Comparison of Site Classes of EC8, ASCE7-16 and TSC-2018 Soil Classification
Seismic Code Design
EC8 ASCE7-
16
TSC-2018 EC8 ASCE7-16 TSC-2018
A A ZA Rock or other rock-Vs>800m/s Hard Rock Vs > 1524 m/s
Rugged, hard rocks Vs > 1500 m/s
B B ZB dense sand, gravel, 360m/s < Vs
< 800m/s
Rock 762 M/S < Vs > 1524
m/s
Slightly weathered, medium solid
rocks 760m/s < Vs >1500
C C ZC Deep deposits of dense or
medium dense sand, gravel or
stiff clay 180m/s < Vs < 360m/s
Very Dense Soil 366 m/s <
Vs > 762 m/s
Very tight layers of sand, gravel and
hard clay, or weathered, cracked weak
rocks 360 m/s < Vs >760m/s
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D D ZD Deposits of loose-to-medium
cohesion less soil Vs < 180m/
Stiff Soil 183 m/s< Vs >
366 m/s
Medium tight - layers of tight sand, gravel or very solid clay 180 m/s < Vs
>360m/s
E E ZE A surface of alluvium layer with
water table a layer of Type C or D on Rock
Soft Soil Vs > 366 m/s
Loose sand, gravel or soft Vs <
180m/s
S1 F ZF A layer of at least 10 m thick
soft clays/silt
requiring site-specific
research and evaluation
Floors requiring site-specific research
and evaluation
S2 Sensitive clays, or any other soil profile
not included in types A – E or
S1
SEISMIC HAZARD SPECIFICATIONS
Ground motion intensity and return period are two
fundamental concerns related to the hazard specifications,
seismic codes mostly use the seismic hazard as the single
parameter characterized by the peak ground acceleration
(PGA). As mentioned early that building codes considered
and defined different criteria for the hazard levels,
according to these seismic codes have been used in the
study was found that Eurocode 8 consider a reference peak
ground acceleration and IS1893 describes a zone factor
defined by “Effective Peak Ground Acceleration (EPGA)”
and obtained by the 0.4 times the 5% damped for average
spectral acceleration among the period 0.1 to 0.3 sec. The
Turkish new version 2018 and ASCE7-16 does not
consider seismic zone factor but uses for design ground
motion multiple spectral ordinates such as short and long
periods respectively, despite slightly difference the
construction design spectra. In addition to seismic codes
use for seismic hazard levels for probability of return
period and the seismic codes, but commonly EC8 describes
the seismic hazard at 10% probability exceedance in 50
years for return period 475 years as the seismic actions
reference.
Four different ground motion levels are defined by the new
Turkish seismic code, DD-1: 2% probability of exceeding
in 50 years, and recurrence is 2475, DD-2: 10%,
probability of exceeding in 50 years, and recurrence is 475,
DD-3: 50% probability of exceeding in 50 years, and
recurrence is 72 and finally DD-4: 50% probability of
exceeding in 50 years, and recurrence is 43.[5] IS 1893
does not consider for return period but use for the effective
peak ground acceleration design 0.5 times the effective
peak ground acceleration and ASCE7-16 describes the
return period 2475 years, the probability of 2% seismic
inputs exceeded in 50 years, corresponding the MCE.
DESIGN RESPONSE SPECTRA
Generally most of seismic design codes adopted 5%
damped for elastic response spectra, as the design spectrum
reference. The different soil classes that building codes
adopted changes the spectral shapes and it scaled by PGA
or spectral ordinate, return period and site conditions are
modified to get design spectra. The influence of soil
conditions it is important to consider the design spectrum,
each of soil classes were provided the soil amplification
factors. The building codes often use the design based-
force.
Figure 1 Typical Elastic Design Spectra [6]
The points TB and TC describe the acceleration control
region, where the TC and TD show the constant velocity
control region and the TD is where the displacement control
regions begin. The elastic design spectra in EC8 it
recommended to adopt two horizontal spectra Type 1
which commonly used for the higher seismicity regions
and the Type 2 which is adopt if the earthquake is less than
the magnitude 5.5 or less seismicity regions as defined the
probabilistic hazard assessments. As well as EC8 described
soil factor which is depend on the damping and the ground
types. The Indian building code IS1893, the design spectra
only provides 4 sec period and not consider the constant
displacement region. The Turkish new version 2018 and
ASCE7-16 does not consider seismic zone factor but is
based on seismic hazard map, not same as the old codes
which are based on seismic zonation map. This code is not
expressed the seismic hazard in terms of PGA, but
expressed in terms of spectral acceleration, the short period
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Vol. 9 Issue 03, March-2020
and long period T=0.2 s and 1s are defined by the site-
specific acceleration maps are developed for stiff soil sites.
The Turkish seismic code is also considered for the spectral
ordinates such as short and long periods. The Eurocode is
considered for two different spectra, but, for this case Type
1 is considered for the design and applied for strong ground
motion which produced a magnitude greater than 5.5, the
soil classes are considered the design is rock soil, soft soil,
and medium soil. The modal response spectrum in modes
should not be less than 90% the mass of the structure (EC8-
2004) while American code considers 85% the modal
analysis in base shear force [7].
REDUCTION FACTOR IN SEISMIC CODES
The seismic design codes specify the inelastic dissipation
energy effects to design to decrease the design force [8].
Despite Seismic codes are use different for the design, but
commonly seismic codes use force based methodology,
however, the classification according to the structural type
is different such as detailing. Detailing significantly effects
the structural strength, the elastic response spectrum shape
as well are different however seismic codes considers
reduction factor which structures hold the capacity to resist
earthquake beyond the elastic limit, structures will be
expected to behave non-linear variety, producing huge
deformation and dissipating an enormous quantity of
energy, according to this the structures will be intended and
detailed imperatively to convince the essential capacity of
energy dissipation. The supply of ductility in structural
system tolerates the reduction of elastic response spectrum,
ductility reduction factor generally rely upon the period of
structure. Seismic codes describes reduction factors
changing in to elastic spectra in design spectra in a purpose
of structural systems, mostly the reduction factors defines
the purpose of ductility classes. In addition to seismic
codes use for different ductility classes ASCE7 defines
three ductility classes, Ordinary Moment Resistance
Frame, Intermediate Moment Resistance Frame and
Special Moment Resistance Frame and IS 1893 only
considered two ductility class Ordinary Moment Resistance
Frame and Special Moment Resistance Frame and each one
is corresponding to different reduction factor.
NUMERICAL EXAMPLE
The layout of the building basically bisymmetric in plan,
which assumed by regular form, the number of bays is four
that have a same width of 5 m in both directions. The
storey height is used for 3 m which is normally the height
of residential buildings and the bottom of the structure was
assumed for fixed. 12 story building for moment frame is
used for the design and three different soil conditions is
considered the design to understand the impact of soil
condition for design spectra, while four contrary seismic
codes is considered to perform the structure. The structural
concrete element of structure also is assumed as correctly
to keep the failure structure, the compressive strength of
concrete is considered grade C30 for design spectrum to
design a new structure. Hence the building is reinforced
concrete the constant properties such as modulus of
elasticity will be assumed poisons ration is 0.2. The density
of concrete used by 24 KN/m3 the damping ratio is taken
by 5%, the design for gravity loads includes the dead loads
and self-weight, the live load is considered 2.5kN/m2, for
another side the overall mass of the building including the
self-weight and floor cover plus 25% of live load will be
considered in the seismic design. The medium soil is
considered for the design and the ductility classes are
considered as the each seismic code defines. The spectral
acceleration for long period and short period for
considerations Turkish and American code were used
SS=0.927 and S1=0.259, SS=1.573 and S1=0.701,
respectively, [9] [10]. Where Eurocode was use the shape
of spectrum Type 1 and Ag = 0.25g and the Indian code is
consider the design zone IV [11] [12]. Table 2 describes
the required section elements for reinforced concrete
elements such as beam, column and slab.
Table 2 the section of RC elements
Element
Dimension(mm)
Column 500 X 500
Beam 350x 500
Slab 150
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Figure 2 Floor Plan
Figure: 3 3D Model
ANALYSIS AND RESULT
The analysis of the structure has been carried out by
SAP2000 v20.2 using four different seismic codes, the
results obtained the design response spectrum and
equivalent lateral force for the standard seismic codes has
been compared them, to make the possible comparison
such as base shear and displacement elastic spectra have
been performing the analysis and the reduction factors and
behavior factor are consider for the inelastic design spectra.
The fundamental period is obtained for the structure is
1.572 for longitudinal direction of the building and the
model analysis obtained the total mass of the building in
98% in horizontal direction and transversal direction.
STORY-DRIFT
The structures deform when subjected to the seismic
actions and that deform causes structure to move its actual
position to another potion except only the bottom of the
structure that is fixed. However, the story drift ratio of the
structure can be found to the percentage of displacement
between the two floors divided by the height of the
structure. The most codes give the drift ratio a limit, the
story drift indicates the damage of the building in both
structural and non-structural damages. According to the
ASCE7, the limit of story drift should not be less than for
the moment frames building 0.025 times the height of the
structure for the category III and 0.002 for the design
category I and II. If the drift ratio should be greater than the
allowable drift ratio should not be acceptable. The lower
floors are greater drift when compared to the top floors.
The IS 1893 limits the interstorey drift 0.4% for design
load. And it is depends on the ductility class.
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Figure: 4 Story Drift for Medium Soil
BASE SHEAR
The Base shear is defined by the approximation of the
maximum contemplated lateral force which happens
according to the ground motion at bottom of the building.
however, the base shear rely upon some significance
factors such as the ground motion, natural period, and the
main factor which is reduced the base shear is reduction
factor. However, the result of base shear obtained from the
spectral analysis and the equivalent lateral force method
describes that spectral analysis is more conservative than
the equivalent lateral force method. However, as the figure
5 describes that base shear obtained from the TSC code is
more than the other codes and this significance difference
is due to the reduction and behavior factors are considered
for the design and as well as the difference peak ground
acceleration is considered when performing the design for
this contrary seismic design codes.
Figure: 5 Base Shear- X-Directio.
CONCLUSION
The main objective of this study is to compare various seismic design codes, to evaluate and assess the performance of seismic
structures. These contemporary seismic codes are fundamental for earthquake resistance design, the seismic codes provide level
ductility due to the energy dissipation range, however, seismic codes, are considered reduction factors and behavior factor to
reduce even the design force.
Seismic codes use for seismic hazard levels for probability of return period and the EC8 describes the seismic hazard at 10%
probability exceedance in 50 years for return period 475 years as the seismic actions reference. Four different ground motion
levels are defined by the new Turkish seismic code, DD-1: 2% probability of exceeding in 50 years, and recurrence is 2475,
DD-2: 10%, probability of exceeding in 50 years, and recurrence is 475, DD-3: 50% probability of exceeding in 50 years, and
recurrence is 72 and finally DD-4: 50% probability of exceeding in 50 years, and recurrence is 43. IS 1893 does not consider for
return period but use for the effective peak ground acceleration design 0.5 times the effective peak ground acceleration and
0
1
2
3
4
5
6
7
0 0.5 1 1.5 2 2.5 3 3.5
Sto
ry
Inter storey-drift ratio %
Story drift-medium soil
EC8-2004
IS 1893
TSC-2018
ASCE7-16
0 500 1000 1500 2000 2500 3000 3500
IS
ASC
TSC
EC8
Base Shear X Direction
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ASCE7-16 describes the return period 2475 years, the probability of 2% seismic inputs exceeded in 50 years, corresponding the
MCE
The base shear obtained the spectral analysis for Indian seismic code is underestimated and non-conservative when compared to
the other seismic codes because of the lack of soil amplification for the short period range, it only considered the longer period
range.
The main difference among these seismic codes is the design spectra, for the designing ground motion parameters ASCE7, and
TSC-2018 are used to spectral ordinates rather than seismic zone factor, the Indian seismic code is considered for the design
spectra 4 sec only, also ignores the soil amplification for the short period range.
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Design Codes
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[10] ASCE/SEI 7-16. “Minimum Design Loads and Associated Criteria for Buildings and Other Structures” [11] EN 1998-1: 2004 “Eurocode 8, Design of Structures for Earthquake Resistance– Part 1: General Rules, Seismic Actions and Rules for Buildings.
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