Post on 14-Apr-2018
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
1/22
- 739 -
Amplification Ratio and Period of the
Earthquakes in Karaj, Iran
Ali Ghanbari
Tarbiat Moallem University, Tehran, Iran
Ghanbari@tmu.ac.ir
Amin Hassanzadeh
Research Student, Tarbiat Moallem University, Tehran, Iran
S. Sadrodin Zarangzadeh
Science and Research Campus of Islamic Azad University, Tehran, Iran
ABSTRACT
Karaj is one the largest and rapidly developing cities of Iran, located west of Tehran, the capital.
Considering its vicinity to the active faults with high seismicity and occurring strong earthquakes in
this area, the amplification ratio and period of earthquakes in different regions of Karaj have beenselected as the subject of current research. By studying more than one hundred bore holes, the required
data relating to the subsurface layers are collected and accordingly, physical and mechanical properties
of the soil in the area under study have been obtained. The study area is divided into six individual
layers. In each layer, the results of a large number of in situ and laboratory tests to determine
geotechnical properties of the soil are classified and analyzed. Using some correlation formulas, thevelocity of shear wave is calculated and assuming one-dimensional non-linear behavior being valid for
the alluvial soil, the response of site to probable quakes is determined. Finally, the response of
available structures has been classified into three groups based on their height and considering theestimated periods, the study area has also been divided into two sub domains. Ultimately, a maximum
height for the structures of each domain is suggested based on calculated amplification ratios.
KEYWORDS: Amplification ratio, Site effect, Karaj, Ground response
INTRODUCTION
Amplified response of alluvial sites can change the main characteristics of earthquake to a great
extent. Such variety is usually observed as an increase in maximum acceleration as well as duration of the
quakes. Moreover, most of cities and urban areas are constructed on alluvial soils and therefore studying
the amplification phenomenon which is usually defined as an increase in the ground motion due to the
presence of the soil deposits will be crucial.
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
2/22
Vol. 15 [2010], Bund. G 740
Many researchers have shown that the amplification ratio at soft sites is generally longer than hard
ones (Shoji et al., 2005; Kamalian et al., 2008 and Hasancebi and Ulusay, 2006). Shoji et al. (2005) also
reported lengthening the duration of the ground movements in soft sites. Shoji et al. (2005) demonstrated
that alluvial sites mainly affect seismic waves in upper 30 meters of earth, near the grounds surface.
In recent years, a number of papers on the existence of seismic hazard for the Iranian region has
appeared (Shafiee and Azadi, 2007; Amiri et al., 2006). City of Karaj is one of the important
municipalities in Iran because of its high population, large area as well as presence of many industrial
centers. This city is adjacent to some active faults like North Tehran and Mosha faults which are capable
of generating quakes with magnitudes greater than Ms=7 (Zafarani et al., 2009).
In this paper the S-waves velocity (Vs) for different layers of the soil in Karaj alluvium is acquired by
using a correlation formula between the velocity of shear wave andSPT
N . Using a computer code which
simulates the one-dimensional response of the ground considering non-linear behavior of the soil, the
effect of alluvium on seismic waves has been investigated. In order to study the amplification ratio, the
suggested method by technical committee of earthquake geotechnical engineering (TCEGE) (1999) for 2
and 3 degrees of freedom has been applied and the results obtained from two mentioned approaches have
been compared. Finally, the isovalue lines related to the variance of amplification ratio and period of
earthquake are presented for the area under study.
Introducing the study area
Karaj is a metropolitan area of Iran with a population of about 1,732,275 people based on 2006
census. Heavily congested with industrial firms and located in the neighborhood of Tehran, the capital,
Karaj city has witnessed the increase in the number of population and tall buildings constructed in it to
accommodate this large number of people. Karaj is located on an alluvial site known as Karaj alluvium.
Karaj alluvium is situated on the southern piedmont of central Alborz Mountains. General geological
conditions and tectonics of this area usually follow the pattern of central Alborz zone and mostly, all
northern peaks in the study zone can be associated to Karaj formation. Generally the age of Karaj
formation dates geologically from the Middle Eocene period to its end and in some places can lasts to the
end of Late Eocene. Green tuffs in this formation, observable everywhere, are a distinctive feature of
Karaj formation. Peaks of northern Karaj are usually made up of tuff. These tuffs play the main role in
formation of fragments and elements of Karaj alluvial plain and hence are of great importance as a source
rock in identification of Karaj alluvium.
The study area of current research is located on young alluvial sediments without any special folding.
Alluvial sediments in Karaj are resulted from Karaj river activities coupled with rivers and seasonal
floods originating from valleys of North Mountains. Symptoms and conditions of river sediments can be
clearly observed in excavated cuts and in some parts where the sediments have remained on bed of the old
river canals, evidence of imbrications can be viewed and the dominant direction of stream might be
considered as North-North East, South-South West. It must be noted that formation of sediments has been
greatly affected by the weather conditions as well.More than 8 faults capable of producing earthquakes with magnitudes bigger than MS=7 have been
recognized within max 100 km off Karaj city. Barbarian (1976) has shown that the focal depth of faults in
this area is smaller than 15 km. Fig. 1 illustrates the seismotectonic map of the study area. Many previous
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
3/22
- 741 -
earthquakes in recent 50 years with magnitudes of greater than 6 (Ms>6) in distances up to 100 Km from
the point of study are noted in Table 1.
Figure 1: Active faults and important earthquake locations around Karaj
Table 1: Important earthquakes around Karaj in last 50 years
Event name year/mm/dd Mw Latitude(deg) Longitude(deg) Depth(km)
Rudbar 1990/06/20 7.3 36.96 49.33 12
Changureh 2002/06/22 6.4 35.63 49.20 10
Boueen Zahra 1962/09/01 7.2 35.71 49.81 ?
Classification of Karaj alluvium
Field investigations and experiments performed by authors reveals that six independent layers can bediscerned as overall representative layers in the studied alluvium. Fig. 2 shows a longitudinal section of
Karaj alluvium based on suggested classification. Points A and B have been depicted in order to facilitate
the superposition of section with plan. Characteristic features and distribution of six considered zones are
described in the following sections of this article.
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
4/22
Vol. 15 [2010], Bund. G 742
Figure 2: Sample section from Karaj alluvium extracted based on
the results of current study in 6 classified zones
It must be noted that despite dominant presence of proposed classification, sandy and sometimes
gravely lenses with thicknesses less than one meter have been observed in each of the mentioned layerswhich are usually arisen from change in conditions of sedimentation.
Clayey and silty layers (C1 & C2)
Karaj alluvium, in proposed layers, is dominantly constituted from clayey and silty soils with
considerable amount of sand. Theses layers are located in the east and central parts of the study area and
usually under fill materials of Karaj alluvium. They can be observed from surface layers to depths of
maximum 14m having interfinger connections in lateral boundaries with clayey and silty layers of C2 and
top connections with sandy layers of 1 and 2 and gravely layers of 1 and 2.
Gradation and mechanical properties for layers C1 and C2 are indexed in Table 2. According to thedata gathered in this research, gradation of soil in the mentioned layers includes fine-grained soils of CL,
ML and CL-ML. The main difference between these two layers (C1 and C2) is that C2 layer is of more
density than C1, the cause of which being the condition of sedimentation. Thus, the number of SPT and
the internal friction angle in C2 layer have been much bigger than C1.
Table 2: Geotechnical properties of Karaj alluvium for C1 and C2 layers
Soil Type S1 S2
MIN. MAX. AVE. MIN. MAX. AVE.
Clay and Silt Percentage 5 49 26.6 5 49 29
Sand Percentage 28 87 53 33 81 49
Gravel Percentage 4 41 20.4 8 44 23.4
Plasticity Index (PI) 1 16 5 1 15 7Number of SPT (N) 15 40 29 40 >60 55
Undrained Cohesion (kg/cm2) 0.2 0.7 0.29 0 1.05 0.34
Internal Friction Angle (Degrees) 23 35 30 30 41 35
Unconfined Compressive Strength (kg/cm2) 0.89 1.0 0.93 0.51 0.92 0.72
Dry Specific Weight (g/cm3) 1.58 2.0 1.75 1.8 1.9 1.85
Shear Wave Velocity (m/sec) 142 267 233 188 309 355
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
5/22
- 743 -
Sandy layers (S1 & S2):
These layers are scattered in central parts of the study area and more concentrated in west areas of
the site. They are usually spread under fill materials and sometimes under clayey and silty layers of 1 and
2, having interfinger boundary with sandy layers and top obvious connections with clayey and silty layer
1 and gravely layers of 1 and 2. The thickness of this layer in some western parts exceeds 30 meters.Mechanical properties and gradation of S1 and S2 layers are indicated in Table 3. Soil gradation of this
layer has been determined as SC, SM, SC-SM, SP-SC and SP-SM groups and from mineralogical point of
view, its been mostly made up of fractured pieces of Quartz and Feldspar.
S2 layer is of greater density than S1 with more percentage of gravel and higher specific volume.Hence, the internal friction angle and number of SPT are bigger in S2 layer than S1. Generally speaking,
moving from the center of study area to the western regions, S2 layer gradually becomes less obvious
while S1 layer gets more observable. All in all, S1 and S2 layers can be found in central and western areas
of the study area. Inside S1 and S2 layers, there are clayey and gravely lenses which are mostly thin.
Table 3: Geotechnical properties of Karaj alluvium for S1 and S2 layers
Soil Type S1 S2MIN. MAX. AVE. MIN. MAX. AVE.
Clay and Silt Percentage 5 49 26.6 5 49 29
Sand Percentage 28 87 53 33 81 49
Gravel Percentage 4 41 20.4 8 44 23.4
Plastic Index (PI) 1 16 5 1 15 7
Number of SPT (N) 15 40 29 40 >60 55
Undrained Cohesion (kg/cm2) 0.2 0.7 0.29 0 1.05 0.34
Internal Friction Angle (Degrees) 23 35 30 30 41 35
Unconfined Compressive Strength (kg/cm2) 0.89 1.0 0.93 0.51 0.92 0.72
Dry Specific Weight (g/cm3) 1.58 2.0 1.75 1.8 1.9 1.85
Shear Wave Velocity (m/sec) 142 267 233 188 309 355
Gravely layers (G1 & G2)
The gravely layer (G1) has lower volume compared with other layers of the site and can be observed
in outcrop in most regions, especially west zones of the study area. Maximum depth of this layer is 20
meters and it has interfinger boundary with G2 layer as well as top obvious connections with other layers.
Gradation in this layer consists of GC, GP, GM, GP-GC and GP-GM groups and from mineralogical
point of view, its constituent pieces are usually from gravel stones separated from rocks of the Karaj site(Tuff, Lime Tuff, Shale, and Lime Shale and ).
The gravely layer (G2) is scattered in central and western areas and more concentrated in easternparts. This layer is the thickest layer of Karaj alluvium and its thickness exceeds 30m in some parts
having interfinger boundary with gravely layer 1 and top obvious connections with other layers.
Gradation of soil in this layer is consisted of GW-GM, GW-GC and GC-GM in addition to the mentioned
gradation for G1 layer.
From lithological point of view, this layer consists of pieces and fractures of Karaj formation and its
difference with G1 layer is in the percentage of fine-grained and coarse-grained components. The
percentage of gravel in G2 layer is much more than G1 and coarse-grained pieces have been observed
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
6/22
Vol. 15 [2010], Bund. G 744
with dimensions of 40cm in eastern parts of the study area. Generally, the shear strength, shear wave
velocity and the number of SPT have all been bigger in G2 layer compared with G1. In a small area
within the gravely layers of 1 and 2, sandy and clayey lenses with thicknesses less than 2m have been
observed. Mechanical properties and gradation of the mentioned layers are noted in Table 4. These layers
have the biggest internal friction angle and shear wave velocity in Karaj alluvium. Fine-grainedpercentage in them is less than the other layers of Karaj alluvium.
Table 4: Geotechnical properties of Karaj alluvium for G1 and G2 layers
Soil Type G1 G2
MIN. MAX. AVE. MIN. MAX. AVE.
Clay and Silt Percentage (%) 5 39 17 0 35 10.4
Sand Percentage (%) 23 41 34 0 43 19.3
Gravel Percentage (%) 28 62 49 39 100 70.5
Plastic Index (PI) 2 10 5 1 18 7
Number of SPT (N) 28 44 37.5 45 >60 56
Internal Friction Angle (Degrees) 27 33 30 31 43 38
Dry Specific Weight (g/cm3) 1.8 1.9 1.85 1.8 1.9 1.86Shear Wave Velocity (m/sec) 188 355 309 195 330 365
Based on findings of the current research and the presented discussions in previous sections of this
paper, Karaj alluvium has been evolved in a river environment and tends to a more fine-grained structure
from North-East to South-West areas. Deposition of coarse-grained sediments in North-East regions of
the river has sometimes formed pieces of rocks whereas in west and South-West areas the percentage of
fine-grained sediments increases. In central parts because of the change in river conditions clayey layers
have been deposited, as well.
Field investigations and results
In this research an area of Karaj including several important tall buildings is selected. Fig. 3 illustratesthe study area and locations of more than 100 boreholes mostly with 30 meters depth.
Field tests can play an influential role in studying the engineering geology conditions of a region.Specifically, the estimation of the shear wave velocity using the CPT-seismic cone or flat dilatometer can
be mentioned in this regard, which in addition to the geotechnical specifications determine the shear wave
velocity directly.
In the region under study about 100 boreholes and hand borings have been drilled, the overall length
of which being about 2700m. Also 1300 standard penetration tests have been carried out in all boreholes
with 1.5m distances from each other. Besides the usual tests of determining the physical properties of the
soil, 14 consolidation tests, 111 irect shear tests, 24 mono axial tests, and 32 triaxial tests have been
performed. Also among the field tests, a limitted number of the in-situ direct shear tests, field penetrationtests, and plate bearing tests have been carried out whose results have been used in the present research.
According to Shoji et al. (2005), Borcherdt et al. (1994) and Dobry et al. (2000), the alluvial layer
near the surface of the earth (about 30 meters closed to the surface) is responsible for most variations of
seismic waves. In each borehole, the standard penetration test (SPT) has been conducted in depth of 1.5
meters and samples are extracted for laboratorial tests. Fig. 4 shows an example of the variations in NSPT
with depths for two boreholes, H7 and H17.
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
7/22
- 745 -
Figure 3: Study area and location of boreholes
Figure 4: Two typical engineering logs illustrating the subsurface ground conditions
and Nspt in study area
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
8/22
Vol. 15 [2010], Bund. G 746
Estimation of amplification ratio from the velocity of shear wave
There are four basic waveforms generated within a semi-infinite elastic halfspace: compression (or P-
waves), shear (or S-waves), surface or Rayleigh (R-waves), and Love waves (L-waves). The P- and S-waves are termed as body waves and they are the most commonly-utilized terms in geotechnical site
characterization. The other two types are special types of hybrid compression/shear waves that occur at
the free boundary of the ground surface (R) and soil layer interfaces (L).
S-wave velocity is one of the key parameters in construction engineering. For example, Imai and
Tonouchi (1982) studied P- and S-wave velocities in an embankment and also in alluvial, diluvial, and
Tertiary layers, showing that S-wave velocities in such deposits correspond to the N-value (Craig, 1992),
an index value of the formation hardness used in soil mechanics and foundation engineering (Xia et al.,
1999).
In this research, S-wave velocities are calculated by correlation formulas between the number of SPT,
NSPT, and the velocity of shear wave. Using empirical relations and with the aid of computationalmodeling, explained in next the sections of this paper, the amplification ratio of the site has been
estimated.
Calculating the velocity of shear wave fromSPT
N
Several researches have been conducted to find a relation between VS and NSPT. Considering 192
samples, Imai and Yoshimura (1975) presented an empirical correlation between the velocity of shear
wave and some properties of the soil. Iyisan (1996) reported the similarity in values of VS obtained from
the number of SPT by the available correlations for soils, except gravels. As an alternative solution,
instead of using average interpolated relations and after studying 327 data set related to different regions
of Turkey, Ulugergerli and Uyanik (2007) proposed two equations for upper and lower bound values ofVS with respect to NSPT.
Many other correlations have been proposed between VS and NSPT, some of which are indicated in
Table 5. (Ohba and Toriuma, 1970; Ohta and Goto, 1978; Seed and Idriss, 1981; Okamoto et al., 1989;
Lee, 1990; Kanai, 1996; Pitilakis et al., 1999; Kiku et al., 2001; Tamura and Yamazaki, 2002; Hasancebiand Ulusay, 2006 and Dikmen, 2009)
In this research two relationships suggested by Ohta and Goto (1978) and Tamura and Yamazaki
(2002) in which the effect of depth has been taken into account are chosen for calculation of VS in order
to study the Karaj alluvium. Although the investigation of results show a small overestimation by the
relationships proposed by Tamura and Yamazaki (2002), no significant difference can be inferred
between the two equations and the variance has not been more than 10m/s.
Fig. 5 depicts the small difference between the results of these two relationships in depth of 30
meters. Finally, both groups of the results have been employed to estimate the velocity of shear wave in
Karaj alluvium. If the Karaj formation is to be classified based on IS-2800 (2002), as the V S varies
between 175 m/s to 375 m/s, it must be categorized as a formation of degree 3 . However, according to
NEHRP (2003), since the VS in study area differs from 180 m/s to 360 m/s therefore the site will be of
Class D.
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
9/22
- 747 -
Table 5: Some correlations had been demonstrated
Researchers Equation
Imai and Yoshimura (1975)33.076NV
s=
Ohba and Toriumi (1970)31.084NV
s=
Ohta and Goto (1978)* 212.017.0
69 FFDNVs =
Okamoto et al. (1989)3.0125NV
s=
Tamura and Yamazaki (2002)179.0187.08.105 DNV
s=
Hasancebi and Ulusay (2006)309.090NV
s=
Dikmen (2009)39.0
58NVs=
*:1
F and2
F depend to soil type and D is depth in meters
Figure 5: Shear wave velocity estimated at depth 30 meter
Estimation of amplification ratio by empirical equations
Based on the previous researches, the velocity of shear wave in surface layer is an appropriate
parameter for calculating the amplification ratio of the site. Shima (1987) showed that estimated
amplification ratio has a linear relationship with the ratio of VS for surface layer to the VS of bedrock.
After investigation of many earthquakes, some researchers have demonstrated an agreeable consistency
for a certain depth between the average VS in surface layer and amplification ratio (Brocherdt et al., 1991;Midorikawa 1987).
In this research, two empirical relationships between VS and the amplification ratio, presented by
Brocherdt et al. (1991) and Midorikawa (1987) and recommended by TCEGE (1999) are employed
(Equations (1-1) and (1-2) are proposed by Brocherdt et al., 1991 while equations (2-1) and (2-2) have
been presented by Midorikawa, 1987).
330
340
350
360
370
380
390
400
410
0 10 20 30 40 50SPT-N
Shearwavevelosity(m/s)
Ohta and Goto (1978)
Tamura and Yamazaki (2002)
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
10/22
Vol. 15 [2010], Bund. G 748
sVAHSA 701=
Low strain data 1-1
sVAHSA 598= Loma Prieta strong-motion 1-2
6.0
68
=s
VA
smVs
1100 2-2
In the above equations, VS is the average velocity of shear wave (m/s) 30 meters closed to the surface,
A is the amplification ratio for maximum velocity of ground and AHSA is the average horizontal
spectrum amplification in periods between 0.4 and 2.0 seconds. The average velocity of shear wave, V s,
has been calculated in depth of 30m by equation (3) proposed by NEHRP (2003).
=
== n
isii
n
ii
s
Vd
dV
1
1
(3)
where Vs is the velocity of shear wave, id is the thickness of ith layer of soil and Vsi is the velocity of
shear wave in related layer.
Taking notice of the fact that the calculated V s by equation (3) is smaller than 1100 m/s in all parts of
the study area, the equation (2-1) has been employed for determination of the amplification ratio. Also
since the probable earthquakes in this research are assumed to be strong shakes (M>7), equation (1-2) has
been designated. After fulfilment of the calculations, the amplification ratio obtained by the equations (1-
2) and (2-1) are found to be within the ranges of 2.19 to 2.72 and 1.95 to 2.82, respectively. In most cases,
the calculated results from the two equations have been close to each other.
Estimation of amplification ratio based on one-dimensionalanalysis of the ground response
Analytical method employed in this research is based on one-dimensional equivalent-linear modeling
of the soil layers. Numerical simulation has been implemented by a computer code developed for this
purpose.
Main assumptions in one-dimensional analysis of the ground response are as follows:
1. Movement of shear waves is considered vertical to the soil layers.
2. Boundaries of layers are all assumed to be horizontal.
3. Surface of the soil and bedrock are assumed to be laterally infinite.
Based on this method, the amplification frequency is mainly dependant upon the geometry (thickness)
and material properties (Vs). Description of applied method is presented in Fig. 6 for one-dimensional
analysis of site response. One advantage of this algorithm is namely its ability to determine the
transformation function in a desired frequency for amplification or damping of passing waves through the
soil (Kramer, 1996). Accepted assumptions of this function in current research are associated with the
stratus of the soil damping on elastic bedrock. The situation of the considered structure with one degree of
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
11/22
- 749 -
freedom and layering of the soil are demonstrated in Figs. 7 and 8. In these figures G is the shear
modulus, D is damping ratio, is the shear strain and is the rate of shear strain.
Although G and D vary during the earthquake (Ishihara, 1996) and thus the response of the soil will
be non-linear, in this method the shearing modulus (G) and damping of soil (D) are considered to be
constant, yet to overcome this weakness, equivalent linear method has been applied in order to determinethe properties of the soil in one-dimensional analysis of the ground response. The whole procedure is
illustrated in an algorithm shown in Fig. 9. To perform calculations of the equivalent linear method
(Estimation of new G and D with respect to the shear strain), charts of 0G G versus proposed by Sun
et al. (1988) for clays and those presented by Seed and Idriss (1970) for sand and gravel as well as curves
ofD against suggested by Idriss (1990) for clays, gravel and the sand have been applied, one of which
is shown in Fig. 10 as an example.
Dynamic properties of the soil are determined by above-mentioned charts ( 0
GG D ).
Specific gravity of the soil is calculated based on the experimental data and velocity of shear wave is
obtained using mentioned equations in previous sections of this article. These data constitute the input of
the employed computer code. Applying seismic loads to the bedrock and performing calculations, output
of computer code has been recorded for further study.
Figure 6: Employed algorithm for one dimensional analysis of ground response
Specifying soils reduction function based on
response reduction function of systems with
ingle degree of freedom
Changing the displacement history of bedrock to
Fourier series by FFT
Multiplying each part of Fourier series of bedrockdisplacement by reduction function. Result is
displacement Fourier series of ground surface.
Changing the displacement Fourier series into
displacement history by IFFT
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
12/22
Vol. 15 [2010], Bund. G 750
Figure 7: One degree of freedom model used for simulating of soil behavior
Layer Properties Thickness
1111
,,DG 1
h
2222
,,DG
. . .
. . .
. . .
NNNN
DG ,, N
h
Figure 8: Schematic soil stratification employed for one dimensional analysis of gound response
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
13/22
- 751 -
Figure 9: Employed algorithm for modeling of equivalent linear behaviour of soil
Figure 10: Dynamic properties of soil used for equivalent linear modeling of soil behaviour
0
0.2
0.4
0.6
0.8
1
0.0001 0.001 0.01 0.1 1 10
Shear Strain (%)
G/Gmax
0
5
10
15
20
25
30
DampingRatio(%)
Shear Modulus (sun et al., 1988)
Damping Ratio (Idriss, 1990)
Estimating first G andD for each soillayer ( for low strains)
Calculating ground response (shear strain history) based on estimated
G andD
Specifying effective shear strain for each layer ( details are available
in Kramer (1996) )
Estimating new values for
Gand
Dbased on effective shear
strain specified in last stage
Difference between new
G andD , and last G andD is less than a
desired value
Finish
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
14/22
Vol. 15 [2010], Bund. G 752
Seismic load used in the current research has been the real earthquake occurred in Manjil and Rudbar
at 21:00 on June 20, 1990 with the magnitude of 7.3 and maximum horizontal acceleration of 0.6g,
recorded in Qazvin accelerograph station. The reason for selecting this earthquake has been the similarity
between functionality of its originating fault with the chief faults near Karaj as well as Qazvin
accelerograph station situated at quiet neighbourhood of the study area. Fig. 11 shows the accelerogramof the mentioned earthquake. This technique is accepted by the TCEGE (1999) as a Grade-3 method for
investigation of the site effects. Grade-3 method considers the effect of the site through using
geotechnical data gathered from the site and available analytical and numerical techniques.
Figure 11: Accelerogram of earthquake used in this research
Amplification ratios obtained in this research vary between 1.83 to 3.4 values. Amplification ratios
against fluctuations and the response spectrum for three damping ratios of 0, 0.5 and 10 percent in BH122
borehole are depicted in Fig. 12. Contours shown in Fig. 13 illustrate the variation of amplification ratios
in study zone. The obtained results from empirical equations and computational modelling are
demonstrated in Fig. 14 for some boreholes which reveal the relative harmony between the two methods.
Figure 12: Amplification ratio and response spectra for BH122
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0 10 20 30 40
Time (sec)
Acceleration(g)
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
0.00 5.00 10.00 15.00 20.00 25.00
Frequensy (Hz)
Amplificationratio
0.00
0.50
1.00
1.50
2.00
2.50
3.00
0.01 0.10 1.00 10.00
Period(s)
Spectralacceleration(g)
0% damping
5% damping
10% damping
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
15/22
- 753 -
Figure 13: Amplification ratio values Estimated with computer code in study area
Figure 14: Comparison of amplification ratios in study area
Period of the site
To determine the main period of the site, as previously applied by Hasancebi and Ulusay (2006) in
their own research, the frequency of amplification or the frequency in which maximum amplification
ratio occurs is gained and then the period of considered soil column has been calculated by the following
equation:
1=T (4)
where T is the period of the site in seconds, s, and is the frequency in Hz. Since the frequency of
amplification in most parts of the study zone lies in the range of 1.2 to 1.4 Hz, the period calculated by
equation (4) will naturally be limited to 0.71 and 0.83 s which does not differ a lot with suggested period
for the sites of degree 3 as recommended in second edition of IS-2800 (2002). Fig. 15 shows variations of
the period as contours for the study area.
0
0.5
1
1.5
2
2.5
3
3.5
4
3 14 21 34 48 57 65 72 81 93 100 108 117 126
Borehole number
Amplificationratio
Software
Empirical (Brocherdt et al.,1991)
Empirical (Midorikawa et al., 1987)
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
16/22
Vol. 15 [2010], Bund. G 754
Figure 15: Period values at study area
In order to determine which types of building would be better to avoid in each district, firstly an
attempt has been made to divide the study area into four zones based on their period. But because of
observing the small variations in the period (0.71-0.83) the study area has been divided into two zones,
both of which are shown in Fig. 16. The periods of the first zone vary somewhere between 0.71 to 0.77
seconds and the periods relating to the second zone vary between 0.77 to 0.83 s.
Figure 16: Classified zones based on site period
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
17/22
- 755 -
Using the suggested methods by IS-2800 (2002) and NEHRP (2003), the type and height of the
buildings which to be avoided in these two districts are determined. The indicated formulas in the
mentioned codes and limitations for height of the buildings relating to each zone are noted in Table 6.
Table 6: Equations for determination of buildings period by IS-2800 (2002) and NEHRP (2003) andheight limitations in study area
Standard Building type Period EquationZone 1
(height (m))
Zone 2
(height (m))
NEHRP (2003)
Steel frame 8.00724.0 hT= 17-19.5 19-21
Concrete frame 9.00466.0 hT= 20.5-22.5 22-24.5
Braced 75.00731.0 hT= 20.5-23 23-25.5
Other 75.00488.0 hT= 35.5-39.5 39-44
IS-2800
(2002)
Steel frame 75.008.0 hT= 18-20.5 20-23
Concrete frame 75.007.0 hT= 22-24.5 24-27
Other75.0
05.0 hT= 34-38.5 38-42.5
Generally if the buildings are classified into three groups of 1-5, 5-10 and 10-15 story buildings, as
schematically shown in Fig. 17, it will be inevitable to accept a limited period in each zone for
constructing safe buildings. Table 7 shows the available regulations for the buildings based on two codes
of IS-2800 (2002) and NEHRP (2003). If the buildings period does not lie between 0.69 and 0.79 seconds
in zone 1 and between 0.75-0.85 seconds in zone 2, there would be no limitation for such buildings,
hence, they are presented as OK in Table 7.
Table 7: Classification of buildings based on their height in study area
Standard Building type Zone 1-5Stories
5-10Stories
10-15Stories
NEHRP
(2003)
Steel Frame1 OK - OK
2 OK - OK
ConcreteFrame
1 OK - OK
2 OK - OK
Braced1 OK - OK
2 OK - OK
Other1 OK OK -
2 OK OK -
IS-2800(2002)
Steel Frame1 OK - OK
2 OK - OK
ConcreteFrame 1 OK - OK2 OK - OK
Other1 OK OK -
2 OK OK -
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
18/22
Vol. 15 [2010], Bund. G 756
Karaj (Alvand)Karaj (Danesh Amouz)
Karaj (Leylestan)
A: 1 5 Story Buildings B: 5 -10 Story Buildings C: 10 15 Story Buildings
Figure 17: Schematic presentation of building height classification (a) 1-5 stories, (b) 5-10 stories and (c)
10-15 stories
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
19/22
- 757 -
CONCLUSION
In the present study, the available formulas betweens
V andSPT
N proposed by previous researchers
were firstly reviewed and consequently the relationships suggested by Ohta and Goto (1978) and Tamura
and Yamazaki (2002) were chosen for further investigations. The study site was then classified based on
the values ofsV obtained by these equations, resulting in the site to be classified as degree 3, based on
IS-2800 (2002) and D class according to NEHRP (2003).
The amplification ratio of the study site has been investigated by the empirical equations as well as
numerical modelling with the aid of computer code for one-dimensional analysis of the ground response,
assuming equivalent linear behaviour for the considered soil. The results of calculations proved that the
range of amplification ratio for the site varies from 1.83 to 3.40. Period of the site has been determined
based on the frequency of amplification and was shown to be in the range of 0.71 to 0.83s. Finally
according to achieved periods for the study site and periods of different buildings mentioned in Is-2800
(2002) as well as NEHRP (2003), the study area has been classified with respect to the type and height of
the structures. Overall procedure followed throughout the current research is demonstrated as an
algorithm in Fig. 18.
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
20/22
Vol. 15 [2010], Bund. G 758
Figure 18: General algorithm used for this research
Perform in situ and laboratory tests,
specially SPT
Specify the relation between shear wave
velocity and SPT-N, and specifys
V inresearch area
Classifying the investigated site based on the values ofs
V andintervals of each site grade suggested by Iranian 2800 standard
andNEHRP(2003)
Selecting the relationships between amplification ratio and shear
wave velocity for 30(m) layer, and estimating the amplification
ratio in researched site
Estimating amplification ratio by use of 1-D analysis of site
response and based on equivalent linear behaviour of soil, with
software, and showing the results on a map
Estimating site period based on resonance frequency
Grading structures based on their
height, and specifying the
limitations ofeach grade in site
based on buildings and site period
Site grading based on site
period, and specifying the best
buildingsin each site grade based
on their period
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
21/22
- 759 -
REFERENCES1. Amiri G. G., Motamed, R., Hashemi, R., Nouri H. R. 2006. Evaluating the seismicity parameters
of Tehran, Iran. Proceeding of ICE, Geotechnical Engineering. 159, 275-283.
2. Building and Housing Research Center (BHRC), official web site. http:// www.bhrc.gov.ir.3. Building Seismic Safety Council (BSSC). 2001. NEHRP recommended provision for seismic
regulations for new buildings and other structure. Report FEMA 450. Washington, DC.
4. Brocherdt, R.D., Wentworth, C. M., Janssen, A., Fumal, T., Gibbs, J. 1991. Methodology forpredictive GIS mapping of special study zones for strong ground shaking in the San Francisco
Bay Region. Proc. 4th International Conference on Seismic Zonation. Vol. 3, pp.545-552.
5. Craig, R. F. 1992, Soil mechanics: Chapman and Hall.
6. Dikmen, U. 2009. Statistical correlations of shear wave velocity and penetration resistance forsoils. Journal of Geophysics and Engineering 6, 61-72.
7. Hasancebi, N. Ulusay, R. 2006. Evaluation of site amplification and site period using different
methods for an earthquake-prone settlement in Western Turkey. Engineering Geology 87, 85-104.
8. Idriss, I.M. 1990. Response of soft soil sites during earthquakes. Proc. Memo. Symp. to honorProf. Harry Bolton Seed, Berkeley, California. Vol. II.
9. Imai, T., Yoshimura, Y. 1975. The relation of mechanical properties of soil to P and S-wavevelocities for ground in Japan. Technical Note OYO Corporation.
10. Imai, T., Tonouchi, K. 1982, Correlation of N-value with S-wave velocity: 2nd Euro. Symp. onPenetration Testing, Proceedings, 67 72.
11. IS-2800 2002.. Iranian Code of Practice for Seismic Resistant Design of Buildings. Building andHousing Research Center. 3rd edition. Tehran, Iran.
12. Ishihara, K. 1996. Soil Behaviour in Earthquake Geotechnics. Oxford Engineering Science
Series, 46. Clarendon Press.
13. Iyisan, R., 1996. Correlation between shear wave velocity and in-situ penetration test results.Chamber of Civil Engineers of Turkey. Teknik Dergi 7 (2), 1187-1199 (in Turkish).
14.Kamalian, M., Jafari, M.K., Ghayamghamian, M.R., Shafiee, A., Hamzehloo, H., Haghshenas,E., Sohrabi-bidar, A. 2008. Site effect microzonation of Qom, Iran. Enginrg. Geology 97, 63-79.
15.Kanai, K. 1966. Conference on Cone Penetrometer. The Ministry of Public Works andSettlement (Ankara, Turkey).
16.Kiku, H., Yoshida, N., Yasuda, S., Irisawa, T., Nakazawa, H., Shimizu, Y., Ansal, A., Erkan, A.,2001. In-situ penetration tests and soil profiling in Adapazari, Turkey. Proc. ICSMGE/TC4
Satellite Conference on Lessons Learned from Recent Strong Earthquakes, pp. 259-265.
17.Kramer, S.L. 1996. Geotechnical Earthquake Engineering. Prentice-Hall International Series inCivil Engineering and Engineering Mechanics. Pearson Education.
18.Lee, S.H. 1990. Regression models for shear wave velocities Journalof theChinese InstituteofEngineers13, 519-532.
19.Midorikawa, S. 1987. Prediction of isoseismal map in the Kanto plain due to hypotheticalearthquake. Journal of Structural Engineering 33, 43-48.
7/30/2019 Amplification Ratio and Period of the Earthquakes in Karaj,Iran
22/22
Vol. 15 [2010], Bund. G 760
20.Ohba, S., Toriuma, I. 1970. Dynamic response characteristics of Osaka plain. Proc. Ann.Meeting AIJ (in Japanese).
21.Ohta, Y., Goto, N. 1978. Empirical shear wave velocity equation in terms of characteristic soil
indexes. Earthquke Engineering and Structural Dynamics 6, 167-187.22.Okamoto, T., Kokusho, T.,Yoshida, Y., Kusuonoki, K. 1989. Comparison of surface versus
subsurface wave source for PS logging in sand layer. In: Proc. 44th. Annual Conf. JSCE, Vol. 3,
pp. 996997 In Japanese .
23.Pitilakis, K., Raptakis, D., Lontzetidis, K. T., Vassilikou, T., Jongmans D. 1999. Geotechnicaland geophysical description of Euro-Seistests, using field and laboratory tests, and moderate
strong ground motions. Journal of Earthquake Engineering 3, 381-409.
24.Seed, H.B. Idriss, I.M. 1970. Soil Moduli and Damping Factors for Dynamic Response Analysis.Earthquake Engineering. Research centre, University of California, Berkeley. Report No.
UCB/EERC-70/10.
25.Seed, H.B. Idriss, I.M. 1981. Evaluation of liquefaction potential sand deposits based onobservation of performance in previous earthquakes. ASCE National Convention. pp. 81-544.
26.Shafiee A., Azadi A. 2007. Shear-wave velocity characteristics of geological units throughoutTehran City, Iran. Journal of Asian Earth Sciences 29, 105115.
27.Shima, E. 1978. Seismic microzonation map of Tokyo. Proc. of the 2nd International Conferenceon Microzonation. Vol. 1, pp. 433-443.
28.Shoji, Y., Tanii, K., Kamiyama, M. 2005. A study on the duration and amplitude characteristicsof earthquake ground motions. Soil Dynamics and Earthquake Engineering. 25, 505-512.
29.Sun, J. I., Golsorkhi, R., Seed, H.B. 1988. Dynamic Moduli and Damping Ratios for CohesiveSoils. Earthq. Eng. Research center, University of California, Berkeley. Report No. UCB/EERC-
88/15, 42p.
30.Tamura, I., Yamazaki, F. 2002. Estimation of S-wave velocity based on geological survey datafor K-NET and Yokohama seismometer network. Proceedings of JSCE (Japan Society of Civil
Engineers), Vol. 696, pp237-248.
31.TCEGE 1999. Manual for zonation on seismic geotechnical hazards. Publication of the JapaneseGeotechnical Society. Revised Version. 209 pp.
32.Ulugergerli, U. E., Uyanik , O. 2007. Statistical correlations between seismic wave velocities andSPT blow counts and the relative density of soils. Journal of Testing and Evaluation 35, 1-5.
33.Xia, J., Miller, R. D., Park, B. 1999. Estimation of near-surface shear-wave velocity by inversionof Rayleigh waves. Geophysics 64, 691-700.
34.Zafarani, H., Noorzad, A., Ansari A., Bargi K. 2009. Stochastic modeling of Iranian earthquakesand estimation of ground motion for future earthquakes in Greater Tehran. Soil Dynamics and
Earthquake Engineering 29, 722-741.
2010 ejge