土耳其地震规范发展

Practice in Turkey

2.1

Introduction

This chapter describes the practice of seismic design and construction of buildings in Turkey from1940 to the present. Because reinforced concrete is the most common building material in Turkey,emphasis is placed on reinforced concrete design and construction.

Two codes influence the design and construction of reinforced concrete buildings in Turkey: TS-500, Building Code Requirements for Reinforced Concrete (Turkish 1985), termed the “buildingcode” in this report, and Specification for Structures To Be Built in Disaster Areas (Ministry ofPublic Works and Settlement 1975, 1997), termed the “seismic code.”

The building code presents requirements for the proportioning and detailing of reinforcedconcrete components, and is similar to ACI-318 (ACI 1999) except for the detailing of earthquakeeffects, which is not covered by the building code. Summary information on the building code ispresented in Section 2.3.

Since 1940, the seismic code has included procedures for calculating earthquake loads onbuildings. In 1968, restrictions on component sizes and rebar details were introduced for thedesign of ductile components. Earthquake loads for buildings are calculated using the seismiccode similar to U.S. practice in which earthquake loads are calculated using the Uniform BuildingCode (ICBO 1997). Additional information on the various editions of the code, from 1940through 1997, is presented in Section 2.4.

The following sections of this chapter present information on major earthquakes in Turkey in the20th century (Section 2.2), the requirements of the Turkish building code for reinforced concrete(Section 2.3), and Turkish seismic design codes (Section 2.4). A comparison of U.S. and Turkishcodes is presented (Section 2.5). Summary remarks are presented in Section 2.6.

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2.2Major Earthquakes in Turkey in the 20th Century

Major earthquakes in Turkey have led to substantial changes in the practice of seismic design andconstruction. Fifty-seven destructive earthquakes struck Turkey in the 20th century, mostoccurring along the 1500-km-long North Anatolian fault (see Chapter 1, Figure 1-1). The largestearthquakes on this fault occurred in 1939, 1943, 1944, 1966, 1967, 1992, and 1999 (twoearthquakes), resulting in more than 90,000 deaths, 175,000 injuries, and the destruction of650,000 residential and office buildings.

Table 2-1 lists key events in the evolution of seismic codes in Turkey. Destructive earthquakeshave usually resulted in revisions to the codes. In this table and hereafter in this report, \"ductiledetailing\" refers to the use of reinforcement details that provide ductile response in components. The M7.9 Erzincan earthquake of December 27, 1939, in northeastern Turkey, was the largestearthquake in Turkey in the 20th century. The city of Erzincan was devastated and approximately32,000 people died. Following that earthquake, the Turkish Ministry of Public Works andSettlement formed a committee to prepare a seismic zone map. The formation of this committeewas the first step toward developing regulations for the seismic design of buildings in Turkey.

Table 2-1 Key events in the evolution of seismic design codes in Turkey

Year193919401942194319441947194919531958Tosya earthquake (M7.2)Gerede earthquake (M7.2)EventErzincan earthquake (M7.9)Committee formed to develop a seis-mic zonation map for TurkeyCode developmentFirst seismic code publishedEarthquake zone map prepared; map promulgated in 1945Seismic code revisedSeismic code revisedSeismic code revisedSeismic code revisedMinistry of Reconstruction and Resettlement establishedSeismic code revisedEarthquake zone map revised196119631966Varto earthquake (M7.1)1967Adapazari earthquake (M7.1)196819751992 Erzincan earthquake (M6.9)1997Izmit earthquake (M7.4)1999Düzce earthquake (M7.2)Seismic code revisedSeismic code revised; ductile detailing introducedSeismic code revised; ductile detailing required10

2.3Building Code Requirements for Reinforced Concrete

The Building Code Requirements for Reinforced Concrete provide general proportioning anddetailing procedures for reinforced concrete components. Early versions (e.g., 1969) were basedon allowable stress design and were similar to other building codes. Major changes wereintroduced into the code in 1981 and 1985.

The latest version of the building code (1985) permits calculations using both allowable stressdesign and strength design. For designs in which earthquake loads are considered, stresses forcalculations are made using the two following load combinations, U,

U=G+P+EU=G+0.9E

(2-1)(2-2)

where G is the dead load effect, P is the live load effect, and E is the earthquake effect.Earthquake loads were calculated following the procedures given in the seismic code of the time.However, the building code did not contain any special seismic detailing requirements, and thedesigner was referred to the seismic code for such information.2.4

2.4.1

Evolution of Turkish Seismic Design Codes

Years 1940 to 1953

The first seismic design code for buildings was published in 1940, one year after the destructiveErzincan earthquake. The 1940 seismic code was similar to the Italian seismic code of that time(Bayülke 1992; Duyguluer 1997). The base shear, V, was calculated as the product of a lateralforce coefficient, C, and the weight of the building, W, namely

V=CW

(2-3)

The value of C was set equal to 0.10 regardless of location. The base shear force was distributedover the height of the building using a uniform load pattern.

An earthquake zonation map for Turkey was prepared in 1942 and promulgated in 1945. The maplisted all provinces in Turkey (Duyguluer 1997). Three seismic zones were identified in the map:first degree (hazardous); second degree (less hazardous); and no hazard. No earthquake analysiswas required for the no-hazard zone. The interzonal boundaries followed administrativeboundaries. According to Duyguluer, the zonation of a province or region was based on theobserved or projected intensity of earthquake shaking.

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The 1947 code utilized the 1942 maps. The values assigned to C were established on the basis ofseismic zone. In first-degree zones, C was set equal to 0.10; in second-degree zones, C was setequal to 0.05. Allowable stresses were increased by 25% for component checking usingearthquake load combinations.

In 1949, the zonation map was drawn and appended to the revised code. The coefficients werefurther reduced to between 0.02 and 0.04 in the first-degree zone, and to between 0.01 and 0.03 inthe second-degree zone. The specific value assigned to C was a function of soil and constructiontype. Duyguluer (1997) noted that the “...proper coefficient was to be established by the designengineer in charge in accordance with the soil formation at the construction site and theconstructional characteristics of the building, and approved by the supervising agency.” Theweight of the building was calculated as

W=∑wi

i

(2-4)

and

wi=gi+npi

(2-5)

where wi is the weight of the floor, gi is the dead load of the floor, n is a live load coefficient(equal to 0.33 for houses, 0.5 for commercial buildings, and 1.0 for high-occupancy buildings),and pi is the live load of the floor. Allowable stresses were increased by 50% for componentchecking using earthquake load combinations, rather than 25% per the 1947 code.

The 1953 code introduced load combinations for earthquake effects. Stresses, U, for earthquakedesign were calculated using

U=G+P+E+0.5J

(2-6)

where J is the wind-load effect. No minimum requirements were set for detailing reinforcedconcrete components.

2.4.2

Years 19 to 1967

In the 1961 revision of the seismic code, the procedure for calculating the lateral force coefficient,C, was changed to read

C=C0n1n2

(2-7)

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where C0 is a coefficient that varies with building height, and n1 and n2 are coefficients thatvary with building material, soil conditions, and earthquake zone. Figure 2-1 shows the variationof C0 with height. For heights greater than 40 m, C0 was increased by 0.01 for every 3.0 mabove 40 m. Tables 2-2 and 2-3 list values for n1 and n2. In Table 2-2, soil type 1 is “hard andmonolithic rock,” soil type II is “sand, gravel, and compact soils...,” and soil type III is “lessstrong soils other than mentioned” (IAEE 1966).

Table 2-2 Values of n1

Soil ClassificationIIIIIIBuilding TypeSteel0.60.81.0Reinforced Concrete0.80.91.0Table 2-3 Values of n2

Earthquake zoneFirst degreeSecond degreeThird degreen21.00.600.60In 1963 the earthquake zonation map was substantially revised and the number of zones wasincreased to four: Zone 1 (first degree), Zone 2 (second degree), Zone 3 (third degree), and Zone4 (no hazard). The four zones were defined on the basis of the maximum expected shaking usingthe Modified Mercalli Intensity (MMI) scale. In Zone 1, shaking greater than or equal to MMIVIII was expected; in Zone 2, shaking equal to MMI VII was expected; in Zone 3, shaking equalto MMI VI was expected; and in Zone 4, shaking less than or equal to MMI V was expected.Figure 2-2 is the 1963 earthquake zonation map for Turkey. Because the interzonal boundariesshown in this figure continued to follow administrative boundaries, it was possible to movedirectly from a first-degree zone (maximum shaking) to a no-hazard or out-of-danger zone (minorshaking).

2.4.3

Years 1968 through 1971

The 1968 seismic code was substantially different from earlier codes. The 1968 code changed theprocedures for calculating earthquake demands on building components, introduced requirementsfor detailing reinforced concrete components, and introduced modern concepts relating to spectralshape and dynamic response. The design base shear of Equation 2-3 was calculated using theweight estimate of Equation 2-5 and a lateral force coefficient, C, that was defined as

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C=Coαβγ

(2-8)

where C0 is a seismic zone coefficient and equal to 0.06, 0.04, and 0.02 for Zones 1, 2, and 3,respectively; α is a soil coefficient equal to 0.80 for rock, 1.00 for sand, gravel, and hard clay, and1.20 for “...loose soil containing water and poorer soils...”; β is an importance factor equal to 1.50for critical, high-occupancy, or historically important buildings, and 1.00 otherwise; and γ was adynamic coefficient, which is calculated as 0.5/T for fundamental period, T, greater than 0.5 secbut not less than 0.3, and 1.00 for T less than or equal to 0.5 sec. A coefficient, γ, introducedspectral shape into the Turkish seismic code for the first time. The code wrote that thefundamental period could be calculated as

H

T=0.09-------D(2-9)

where H is the height of the building in meters above the foundation, and D is the width of thebuilding in the direction under consideration.

The base shear was distributed over the height of the building using the following equation

wihi

Fi=V--------------∑wihi

i

(2-10)

where hi is the height of the floor above the foundation. Equation 2-10 served to replace theuniform load profile of earlier codes with a load profile similar in shape to the typical first modeshape in a building.

Geometry and detailing requirements for reinforced concrete components were also introduced inthe 1968 code. Minimum dimensions were specified for beams (150 mm x 300 mm [width timesdepth]), columns (the smaller of 0.05 times the story height and 240 mm), and shear walls (0.04times the story height and 200 mm).

The code did not specify minimum spacing for beam stirrups and column ties, but required that“...sufficient transverse reinforcement shall be provided...” and “...where beams frame intocolumns, the spacing of stirrups and column ties shall be half the spacing at the mid-regions ofthese members, within a distance not less than the effective depth of the deepest member framinginto the joint. Column ties shall be continued within the story beams. ...”

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The addendum to the 1968 code included requirements for the use of shear walls. Specifically, thecode wrote that if the height of a building exceeded a threshold value (12 m in a first-degree zone,15 m in a second-degree zone, and 18 m in a third-degree zone), shear walls “...extending alongthe height of the building shall be provided to transfer lateral earthquake loads to the foundation.”

2.4.4

Years 1972 through 1996

The earthquake zonation map was updated in 1972 and the seismic code was revised in 1975. Keychanges to the zonation map included an increase in the number of zones from 4 to 5. Importantadditions to the seismic code included new methods for calculating earthquake loads on buildingsand ductile detailing requirements for reinforced concrete. Information on earthquake effects andanalysis, design, and detailing are presented below.

In 1968 the Ministry of Reconstruction and Resettlement embarked on a project to update theearthquake zonation maps based on new information on geologic structure, plate tectonics,historical seismicity, and earthquake occurrence (Duyguluer 1997). Zones were defined on thebasis of maximum observed earthquake shaking in the period 1900 through 1970, measured interms of the Modified Mercalli Intensity, namely, Zone 1 for MMI greater than or equal to IX;Zone 2 for MMI equal to VIII; Zone 3 for MMI equal to VII; Zone 4 for MMI equal to VI, andZone 5 for MMI less than or equal to V.

The lateral force coefficient of the 1975 code was defined as

C=CoKIS

(2-11)

where Co is a seismic zone coefficient and equal to 0.10, 0.08, 0.06, and 0.03, for Zones 1, 2, 3,and 4, respectively; K is a coefficient related to the type of framing system, I is an importancefactor (identical to β in the 1968 code), and S is a spectral coefficient. Values of K for differentframing systems are presented in Table 2-4. The spectral coefficient was calculated as

1

S=-------------------------------0.8+T–To

(2-12)

where T and To are the fundamental periods of the building and soil column, respectively. Figure2-3 presents spectral shapes for soil types I through IV, respectively. Soil types were classified onthe basis of blow counts or shear wave velocity, and values for To were set for each type. Shearwave velocities for soil types I through IV were set at greater than 700 m/sec for I, 400 to 700 m/sec for II, 200 to 400 m/sec for III, and less than 200 m/sec for IV. The fundamental period wastaken as the smaller of the value calculated using Equation 2-9 and

0.07N≤T≤0.10N

(2-13)

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where N is the number of stories in the building above the foundation and “... the value of thecoefficient ... shall be determined by interpolation between the values of 0.07 and 0.10 accordingto the degree of general structural flexibility.”

Table 2-4 Structural type coefficient, K, from 1975 code

Structure TypeAll building framing systems except as hereafter classifiedBuildings with box systems with shear wallsa. ductile moment-resisting frameBuildings with frame systems where the frame resists the total lateral forceb. nonductile moment-resisting frameFiller wall type1--abcabcaShear wall systems with ductile frames capable of resisting at least 25% of the total lateral forcebcpartition walls; c = light partition walls or prefabricated concrete partition walls

K1.001.330.600.801.001.201.501.500.801.001.201. Filler wall types: a = reinforced concrete or reinforced masonry walls; b = unreinforced masonry block

Geometry and detailing requirements for reinforced concrete components were modified in the1975 code. Minimum dimensions were specified for beams (200 mm x 300 mm [width timesdepth, = B x D]), columns (the smaller of 0.05 times the story height and 250 mm), and shearwalls (0.05 times the story height and 150 mm). Minimum reinforcement ratios and sizes were setfor beams (minimum stirrup diameter of 8 mm and minimum stirrup spacing of B or 0.5D) andshear walls (ρ = 0.0025, 0.0020 for horizontal and vertical reinforcement, respectively;maximum rebar spacing of 300 mm or 1.5 times the wall thickness). Figure 2-4 shows sampledetailing requirements for beams and shear walls. Minimum floor slab thicknesses were set at 100mm. Infilled joist slab construction (termed \"asmolen\" construction) was permitted only inbuildings taller than 12 m if shear walls were used as the lateral force-resisting system.

The 1975 code provided much information on minimum details for columns. The minimumrectangular column dimension was limited to 250 mm or 0.05 times the story height; themaximum column width-to-depth ratio was 3.0. The minimum and maximum longitudinal rebarratios were 0.01 and 0.035, respectively. Columns were divided into three regions as shown in

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Figure 2-5: confinement regions at each end of the column clear height, a middle region, andbeam-column joint regions. The confinement region was defined as the distance not smaller than0.167 times the column clear height or 450 mm, measured from the slab soffit or beam topsurface. The volumetric ratio of transverse reinforcement, ρ, in this region was set at

f'-ρ=0.12---c

fy

(2-14)

where f'c and fy are the concrete compressive strength and rebar yield strength, respectively.Hooks of 135° were required on ties in confinement regions; the minimum tie diameter was 8mm, and the minimum and maximum tie spacings were 50 mm and 100 mm, respectively. In themiddle region, tie sizes were based on gravity and earthquake forces (calculated using Equation 2-11). The maximum tie spacing, s1 in Figure 2-5, was the smaller of 200 mm and 12 times thediameter of the longitudinal rebar.

2.4.5

Years after 1997

The earthquake zonation map was updated (Figure 2-6) and the seismic code revised in 1997. Inaddition to the equivalent static load method (Equation 2-3), the mode superposition method andlinear and nonlinear dynamic analyses were introduced for the seismic design of buildings. Thelateral force coefficient was replaced by A(T)⁄Ra(T) , where A is the spectral accelerationcoefficient calculated as

A(T)=AoIS(T)

(2-15)

The effective ground acceleration coefficient, A0 , is 0.4, 0.3, 0.2, and 0.1 for the first fourseismic zones, respectively. Note that the fifth seismic zone was specified to have no earthquakehazard. The importance factor, I, is 1.0 for ordinary structures and varies between 1.0 and 1.5. Thespectrum coefficient, S, which defines the design acceleration spectrum, is given by threeequations in the short-period, constant-acceleration, and constant-velocity ranges, respectively.These ranges are delineated by spectrum characteristic periods, TA and TB, which vary as afunction of soil type. The maximum spectral amplification is 2.5. The seismic load reductionfactor in this code is similar to the response modification factor in U.S. codes, except that theseismic load reduction factor reduces linearly from the maximum value of R, which is tabulated inthe code, to 1.5 at zero period. The value of R depends on the assumed ductility (high or normal)of the system and varies between 3 and 8.

Reinforced concrete buildings are classified as systems of either high or nominal ductility basedon the detailing of the components. Detailing requirements are more stringent for systems withhigh ductility. Transverse reinforcement requirements for beams are presented in Figure 2-7.These requirements apply for frames of both high and nominal ductility.

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The detailing requirements for columns of high and nominal ductility levels are most similar. Theminimum cross-section dimensions are 250 mm by 300 mm. Information on the transversereinforcement requirements along the height of a column are shown in Figure 2-8. All hoopsmust have 135° seismic hooks at both ends. Cross ties may have 90° hooks at one end. The sum ofthe column strengths at a beam-column joint must exceed 120% of the sum of the beam strengthsat that joint. The shear strength of a column must exceed the shear force associated with theplastic moments in the column. The only major provision that is not applicable for columns ofnominal ductility level is the spacing of transverse reinforcement along the confinement zones(Figure 2-8), which is required to be half the spacing in the column middle region. Lap splices ofcolumn longitudinal rebar should be made in the middle third of the column. If column rebar arespliced at the bottom of a column, the splice length is increased to 125% or 150% of thedevelopment length of the bar in tension, depending on the number of bars being spliced. Forcolumns in frames of nominal ductility, the maximum spacing of the transverse reinforcementbetween the confinement zones is increased by a factor of 2 over the spacing shown in Figure 2-8.For shear walls, the minimum wall thickness is the smaller of 0.067 times the story height and 200 mm. 2.5

Comparison of United States and Turkish Codes of Practice

Figure 2-9 presents 5% damped linear elastic acceleration response spectra for rock and soft soilsites calculated using the provisions of the 1997 Uniform Building Code (ICBO 1997) and the1997 Turkish Specification for Structures To Be Built in Disaster Areas (Ministry 1997) for theregions of highest seismicity in each country. The Uniform Building Code (UBC) spectra shownin this figure do not include near-field amplification factors, Na and Nv , that must be applied ifthe site of the building is within 15 km of a major active fault. Putting these factors aside, thespectral demands of the two current codes are very similar.

Figure 2-10 presents the lateral force coefficient spectra (C in Equation 2-3) for the 1975 and1997 Turkish codes and the 1997 UBC for reinforced concrete moment-resisting frames on rockand soft soil sites. Such frames were chosen for the purpose of comparison because reinforcedconcrete moment-resisting frames are the most common seismic framing system in Turkey forbuilding construction. To construct the \"allowable-stress-design\" spectra for the 1975 Turkishcode, K was taken as 0.80 and 1.50 for ductile and nonductile reinforced concrete moment frames,respectively; C0 was set equal to 0.10. The ordinates were then increased by 40% to construct\"strength-design\" spectra to facilitate comparison with the 1997 Turkish seismic code and the1997 UBC. To construct the spectra for the 1997 Turkish code, A0 and the importance factorswere set equal to 0.40 and 1.0, respectively, and R was set equal to 4 and 8 for reinforced concretemoment-resisting frames of nominal and high ductility, respectively. To construct the spectra forthe 1997 UBC, soil types SB and SE were assumed for the rock and soft soil sites, respectively;near-field factors were not considered; the importance factor was set equal to 1.0, and R was setequal to 3.5 and 8.5 for ordinary moment-resisting frames (OMRF) and special moment-resistingframes (SMRF), respectively. (The OMRF and SMRF of the UBC correspond approximately toframes of nominal and high ductility in the Turkish code, respectively.)

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For modern reinforced concrete moment-resisting frames of high ductility (the SMRF in theU.S.), the ordinates of the 1997 Turkish lateral-force-coefficient spectra exceed those of the 1997UBC for both rock and firm soil sites. Recognizing that the prescriptive details of the 1997 UBCand the 1997 Turkish code for frames of high ductility are similar, the performance of buildingsdesigned to either code should be similar if the standards of construction are comparable.Table 2-5 presents values of R in the 1997 UBC and the 1997 Turkish codes for different framingsystems. These values are similar for each type of framing system. Further review of the twocodes indicates similarities in most other regards. Because the linear-elastic acceleration responsespectra (Figure 2-9) are similar in both codes for the regions of highest seismicity, buildingsdesigned and constructed in accordance with these two codes should perform equally if theconstruction quality is similar.

Table 2-5 Response modification factors in current seismic codes

Lateral force-resisting systemReinforced concrete shear wallReinforced concrete moment-resisting frameSteel eccentrically braced frameSteel moment-resisting frame1. Framing systems of high ductility2. 1997 codes in Turkey and USA

Country1997 Turkey1,268781997 USA25.58.578.52.6Summary Remarks

Revisions to the practice of earthquake engineering in Turkey have generally followed major,damaging earthquakes. This trend is not unique to Turkey because changes in design practice inJapan, Mexico, and the United States have followed major earthquakes in those countries.Provisions for special detailing of reinforced concrete moment-resisting frames for ductileresponse were introduced in Turkey in 1975. Such requirements were similar to those introducedin the United States in the early 1970s. However, the construction of buildings with ductile detailswas not mandated as it was in California in the 1970s. Rather, buildings could be constructedwithout special details for ductile response (frames of nominal ductility) or ductile details (framesof high ductility). Because it was cheaper to construct stronger buildings without special detailsfor ductile response (nonductile detailing) than weaker buildings with ductile detailing,nonductile moment-resisting frame construction was most prevalent in Turkey up to the time ofthe Izmit earthquake.

The current codes of practice in Turkey and the United States are similar in terms of strength anddetailing requirements. However, two key changes to the Turkish Specification for Structures ToBe Built in Disaster Areas are recommended:

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1.A factor that accounts for the close proximity of a structure to a fault (i.e., a near-field factor) should be included in the design force equation.2.Special details for ductile component response and the use of rules for ductile system response should be mandatory in moderate and severe seismic zones, regardless of the lateral forces used for design.

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Co0.100.090.0840 m

0.070.066 m6 m6 m6 m16 mFigure 2-1 Distribution of coefficient C0 with height above grade in 1961 seismic code

Figure 2-2 1963 earthquake zonation map (IAEE 1966)

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Figure 2-3 Spectral coefficients, S, from 1975 seismic code

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Figure 2-4 Detailing requirements for beams and shear walls from 1975 seismic code

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Figure 2-5 Detailing requirements for columns from 1975 seismic code

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Figure 2-6 Earthquake zonation map of Turkey in the 1997 seismic code

Figure 2-7 Transverse reinforcement requirements for beams in the 1997 seismic code

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Figure 2-8 Column confinement zones and detailing requirements in the1997 seismic code

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Figure 2-9 Comparison of elastic response spectra from the 1997 UBC and the Turkish seismic

codes

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a. soft soil sites

b. rock sites

Figure 2-10 Comparison of lateral force coefficient, C, in the 1997 UBC, and 1975 and 1997

Turkish seismic codes

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