Engineering Structures 25 (2003) 103–114www.elsevier.com/locate/engstruct

Performance of reinforced concrete buildings during the August17, 1999 Kocaeli, Turkey earthquake, and seismic design and

construction practise in Turkey

H. Sezena,∗, A.S. Whittakerb, K.J. Elwooda, K.M. Mosalamc

a Graduate Student Researcher, Pacific Earthquake Engineering Research Center, University of California, Berkeley, 1301 South 46th Street,Richmond, CA 94804-9471,USA

b Associate Professor, Department of Civil, Structural, and Environmental Engineering, 230 Ketter Hall, University at Buffalo, Buffalo, NY14260, USA

c Assistant Professor, Department of Civil and Environmental Engineering, University of California, Berkeley, 733 Davis Hall, Berkeley, CA94720-1710, USA

Received 26 March 2002; received in revised form 17 July 2002; accepted 17 July 2002

Abstract

A large number of reinforced concrete buildings collapsed or were heavily damaged during the 7.4 magnitude earthquake thatstruck northwestern Turkey on August 17, 1999. Recorded peak ground accelerations were relatively low (0.3 g–0.4 g) comparedto the magnitude of the structural damage, and the elastic acceleration response spectra from the recorded motions were comparablewith the elastic design spectra specified in the current Turkish seismic code. Seismic code requirements are discussed and comparedwith observed details. Many structural deficiencies were highlighted by the earthquake damage, including: reinforced concretecolumns with insufficient confinement and transverse reinforcement, 90-degree hooks at the end of column ties, poor detailing inbeam-column joint regions, strong-beam and weak-columns, soft and weak stories, and poor quality construction. Buildings withshear wall structural elements generally performed well. 2002 Elsevier Science Ltd. All rights reserved.

Keywords: 1999 Turkey earthquake; Earthquake damage; Reinforced concrete; Seismic behavior; Codes; Design

1. Introduction

On August 17, 1999, a Mw 7.4 earthquake occurredon the 1500-km-long North Anatolian fault in northwest-ern Turkey. The epicenter of the earthquake was nearIzmit, 90 km east of Istanbul (Fig. 1). Following theearthquake, the Pacific Earthquake EngineeringResearch Center dispatched a reconnaissance team to theepicentral region to learn first hand about the perform-ance of the civil infrastructure. The geographic regionthat was impacted by the earthquake was somewhat nar-row banded and centered around the fault, and stretchedfrom Istanbul in the west to Go¨lyaka and Du¨zce in theeast. Damage to building construction was severe and

∗ Corresponding author. Tel.: (510) 231-9510; fax: (510) 231-9471.E-mail address: sezen@ce.berkeley.edu (H. Sezen).

0141-0296/03/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved.PII: S0141-0296 (02)00121-9

Fig. 1. Map of affected region showing recorded peak ground accel-erations in circles (as percentage of acceleration of gravity).

widespread (Sezen et al. [1], Aschheim [2], Scawthorn[3]). Estimates for economic losses were around 20billion US dollars. The official death toll was over17,200, with some 44,000 people injured and thousands

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left homeless. Some 77,300 homes and businesses weredestroyed, and 244,500 were damaged. The majority ofdeaths and injuries were in the cities of Kocaeli, Sakarya,and Yalova.

This paper describes briefly the state-of-practice forbuilding seismic design and construction in Turkey, andcompares the US and Turkish codes. The performanceof the reinforced concrete frame and wall buildings andtheir components during the 1999 Kocaeli earthquake ispresented, and evaluated considering the seismic designand construction practice in the epicentral region.

2. Turkish code requirements for reinforcedconcrete construction

Two codes influence the design and construction ofreinforced concrete buildings in Turkey: the “earthquakecode” (Specification for Structures to be Built in DisasterAreas, [4,5]) and the ‘building code’ (TS-500, BuildingCode Requirements for Reinforced Concrete [6]). Theearthquake code includes procedures for calculatingearthquake loads on buildings. The building codepresents requirements for the design and detailing ofreinforced concrete components but does not includeductile detailing requirements for use in seismic design.Such requirements are found in the earthquake code.

2.1. Building code requirements for reinforcedconcrete

The building code is similar to ACI 318-95 [7] butdoes not address design and detailing for earthquakeloads. The engineer is referred to the earthquake code[4,5] for such information. Early editions (e.g., 1969) ofthe building code were based on allowable stress design.Major changes were introduced into the code in 1981and 1985. The latest version of the code [6] permits bothallowable stress and ultimate strength design. For thelatter, earthquake effects are considered using two loadcombinations,

U � G � P � E and U � 0.9G � E (1)

where U is the required strength, G, P and E are thedead, live, and earthquake load effects, respectively.Earthquake loads are calculated following the pro-cedures defined in the seismic code of the time.

2.2. Earthquake codes

Major earthquakes in Turkey have led to substantialchanges in the practice of seismic design and construc-tion. Fifty-seven destructive earthquakes struck Turkeyin the 20th century, most occurring along the 1500-km-long North Anatolian fault. The M 7.9 Erzincan earth-quake of December 27, 1939, in northeastern Turkey,

was the largest of these earthquakes. Following the Erz-incan earthquake, the first seismic design code for build-ings was published in 1940. The base shear, V, was cal-culated as the product of a lateral force coefficient, C,and the weight of the building, W, namely:

V � C W (2)

The value of C was set equal to 0.10 regardless of thelocation of the designed structure in Turkey. The baseshear force was distributed over the height of the build-ing using a uniform load pattern.

In 1968, the earthquake code was substantiallychanged. In addition to introduction of limitations on thecross-sectional dimensions of reinforced concretecomponents, modern concepts relating to spectral shapeand dynamic response were included. The uniform loadprofile of earlier codes was replaced with a first mode(inverted triangle) profile similar to that used in currentUS codes such as the 1997 Uniform Building Code [8].

In 1975, important provisions were added to the seis-mic code, including new methods for calculating earth-quake loads on buildings and ductile detailing require-ments for reinforced concrete structures. The lateralforce coefficient of the 1975 code was defined as

C � CoKIS (3)

where Co was a seismic zone coefficient and variedbetween 0.10 and 0.03, K was a coefficient related tothe type of framing system, I was an importance factor,and S a spectral coefficient.

Geometry and detailing requirements for reinforcedconcrete components were modified in the 1975 code.With respect to transverse reinforcement spacing anddetailing requirements, columns were divided into threeregions as shown in Fig. 2a: confinement regions at eachend of the column clear height, middle region, and beam-column joint regions. A maximum tie spacing (s1 in Fig.2a) of 200 mm or 12 times the longitudinal bar diameter,and 135-degree hooks were required on ties in confine-ment regions. In the middle region, the amount of trans-verse reinforcement was based on satisfying gravity andearthquake forces that were calculated using Eq. (3).

Response-spectrum and linear and nonlinear dynamicanalysis procedures were introduced in the 1998 editionof the seismic code. The lateral force coefficient C ofthe 1975 code was replaced by

C �A(T)Ra(T)

�AoIS(T)Ra(T)

(4)

where A is the spectral acceleration coefficient; T is thefundamental period; and Ao is the effective ground accel-eration coefficient. The importance factor varies between1 and 1.5, and is equal to 1.0 for ordinary structures.The spectrum coefficient, S, which defines the designacceleration spectrum, is given by three equations in theshort-period, constant acceleration, and constant velocity

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Fig. 2. Column details from (a) 1975 and (b) 1998 Turkish seismic codes.

ranges. These ranges are delineated by spectrum charac-teristic periods, which vary as a function of soil type.The maximum spectral amplification is 2.5, which isidentical to that of US codes [8] for 5% damping. Theseismic load reduction factor, Ra, is similar to theresponse modification factor in US codes, except that theseismic load reduction factor reduces linearly from themaximum value of structural behavior factor, R, whichis tabulated in the code, to 1.5 at zero period. Themaximum value of R depends on the assumed ductility(high or nominal) of the system and varies between 3and 8.

In the 1998 edition of the earthquake code, reinforcedconcrete buildings are classified as systems of either highor nominal ductility, based on the detailing of thecomponents. Detailing requirements are more stringentfor systems with high ductility. The detailing require-ments for columns being designed for high or nominalductility levels are very similar. Information on thetransverse reinforcement requirements along the heightof a column is shown in Fig. 2b. All hoops must have135-degree seismic hooks at both ends. The shearstrength of a column must exceed the shear force asso-ciated with the plastic moment in the column. The onlymajor provision that is not applicable for columnsdesigned for a nominal ductility level is the spacing oftransverse reinforcement in the confinement zones,which is required to be half the spacing used in the col-umn middle region. For columns in frames of nominalductility, the maximum spacing of the transversereinforcement between the confinement zones wasincreased by a factor of 2 over the spacing shown inFig. 2b.

3. Design and construction practice prior to the1999 Kocaeli earthquake

From discussions with local engineers in Turkey andinspection of buildings, it is clear that the Turkish earth-quake code provisions were rarely enforced for theengineering of commercial and residential constructionin the epicentral region prior to the August 17, 1999earthquake [9]. The ductile reinforcement detailsdescribed in the 1975 earthquake code were rarelyobserved in buildings inspected by the authors after theAugust 17, 1999, earthquake. Details of the seismicdesign and construction practice prior to the 1999 Koca-eli earthquake are provided in [1].

4. Response spectra

Fig. 3 presents 5% damped linear elastic accelerationresponse spectra for rock and soft soil sites calculatedusing the provisions of the 1997 Uniform Building Code[8] and the 1998 Turkish earthquake code [5] for theregions of highest seismicity in each country. The Uni-form Building Code (UBC) spectra shown in the figureinclude near-field amplification factor of 1.0. The elasticspectral demands of the two current codes are very simi-lar.

The peak ground accelerations (PGA) recorded in theregion affected by the earthquake are shown in Fig. 1.Recorded peak ground accelerations were relatively low(0.3 g–0.4 g) compared to the extent of the structuraldamage. Fig. 3 includes the elastic response spectra at5% damping from one horizontal component of the

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Fig. 3. Elastic response spectra for 5% damping.

ground motion recorded at the following sites: YPTstation in Yarimca near Golcuk (PGA 0.23 g, soft soil),SKR station in Adapazari (PGA 0.41 g, stiff soil), andthe DZC station to the east of Golyaka (PGA 0.32 g,soft soil). The elastic acceleration response spectra fromthe recorded motions are not substantially different fromthe elastic design spectra specified in the current US andTurkish seismic codes.

Fig. 4 presents lateral-force-coefficient spectra (C inEq. (1)) for the 1975 and 1998 Turkish codes and the1997 UBC for reinforced concrete moment-resistingframes on soft soil sites. Such frames were chosen forthe purpose of comparison because reinforced concretemoment-resisting frames are the most common seismicframing system in Turkey for building construction. Toconstruct the spectra for the 1975 Turkish code, K wastaken as 0.80 and 1.50 for ductile and nonductile

Fig. 4. Lateral-force-coefficient spectra for the 1975 and 1998 Turk-ish seismic codes and the 1997 Uniform Building Code.

reinforced concrete moment frames, respectively; Co wasset equal to 0.10. These allowable stress design spectrawere scaled to the strength level by multiplying the spec-tral ordinates by 1.4. To construct the spectra for the1998 Turkish code, Ao and the importance factor, I, wereset equal to 0.40 and 1.0, respectively; and R was setequal to 4 and 8 for reinforced concrete moment-resisting frames of nominal and high ductility, respect-ively. To construct the spectra for the 1997 UBC, soiltype SE was assumed; near-field factors were not con-sidered; the importance factor was set equal to 1.0, andR was set equal to 3.5 and 8.5 for ordinary moment-resisting frames (OMRF) and special moment-resistingframes (SMRF), respectively. (The OMRF and SMRFof the UBC correspond approximately to frames of nom-inal and high ductility in the Turkish earthquake code,respectively.)

For modern reinforced concrete moment-resistingframes of high ductility (equivalent of SMRF in the US),the ordinates of the 1998 Turkish lateral-force-coef-ficient spectra exceed those of the 1997 UBC. Recogniz-ing that the prescriptive details of the 1997 UBC and the1998 Turkish code for frames of high ductility are verysimilar, the performance of buildings designed to eithercode should be similar if the construction standards aresimilar and the fundamental period exceeds 0.2 sec. Forshort-period buildings and identical construction stan-dards, buildings designed and detailed according to the1998 Turkish earthquake code will be stronger thanbuildings designed and detailed using the 1997 UBC [8].

5. Typical moment-resisting frame construction

The construction quality for residential and commer-cial buildings in the epicentral region varied widely.Although the general construction quality for residentialbuilding was poor according to US standards, many ofthe engineered reinforced concrete commercial buildings(e.g., office buildings) were observed to have satisfactoryconstruction quality. Many of the failures and collapsesof engineered commercial construction observed by thereconnaissance team, and reported in Sezen et al. [1],can be attributed to the use of nonductile details and notpoor quality construction.

Residential buildings in the epicentral region typicallyrange in height from two to seven storeys. Fig. 5a showsa photograph of a three-storey moment resisting framebuilding that was under construction at the time of theearthquake. A plan of the second floor is shown in Fig.5b. Note that ten of the columns are stronger in the x-direction (parallel to the street), whereas five columnsare stronger in the y-direction. The column orientationsand locations are such that all of the moment-resistingframes include one or more columns with their weakaxis perpendicular to the frame direction. These obser-

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Fig. 5. 3-storey building near Golcuk; (a) elevation, (b) floor plan.

vations, which were typical of most buildings in theepicentral region, would suggest that the framing systemis much stiffer and stronger in the direction perpendicu-lar to the street assuming that similar rebar are used inall beams and all columns. Such framing likely possesseslimited strength and stiffness, which if coupled with non-ductile reinforcement details, results in a vulnerablebuilding in the event of earthquake shaking.

6. Behavior of moment-resisting frame construction

Reinforced concrete moment-resisting frame buildingsbehaved poorly during the Kocaeli earthquake. Accord-ing to official estimates, more than 20,000 moment-frame buildings collapsed, and many more sufferedmoderate to severe damage. Three- to seven-storeyapartment buildings were hard hit, although many hadbeen constructed in the past 20 years. These apartmentbuildings were likely designed and detailed to complywith the requirements of the building code [6] and 1975earthquake code [4] for construction in a first-degreeseismic zone. Many of the collapses are attributed to theformation of soft first storeys that formed as a result ofdifferences in framing and infill wall geometry betweenthe first and upper stories, the use of nonductile details,and poor quality construction in some cases.

Fig. 6 shows two six-storey nonductile moment-frame

Fig. 6. Variability of building response.

buildings in Golcuk. One of the buildings collapsedcompletely, whereas the adjacent building exhibitedshear cracks in the first storey. Careful inspection of thefirst storeys in both buildings showed that the buildingshad a similar plan footprint and construction details. Itis likely that the two buildings were nominally identicaland that both buildings were constructed by the samecontractor. Both buildings were likely subjected to simi-lar levels of earthquake shaking, yet one building perfor-med well, while the other collapsed. This raises manyquestions regarding the limit state for nonductilemoment frames. Small differences in the strength ofthese nonductile buildings possibly caused by the vari-ation in material strength, construction practice, andworkmanship could account for the drastic differencein performance.

7. Role of infill walls in response of moment-framebuildings

Hollow clay tile and gas–concrete masonry infill wallsare widely used in the epicentral region. Many of thebuildings were constructed with hollow clay tile infillwalls in the frames perpendicular to the sidewalk.Frames parallel to the sidewalk were often infilled withhollow clay tile only above the first storey to allow forcommercial space on the ground level. Such an arrange-

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ment of tile infill walls created stiffness discontinuitiesin these buildings, which may have contributed to theircollapse by concentrating the drift demands in the firststorey. These walls are almost always unreinforced andabut the frame columns without being tied to framemembers. The high in-plane stiffness of the masonryinfill walls, which is developed by diagonal strut action,can dictate the response of the more flexible moment-resisting frame. Damage to masonry infill walls was con-centrated in the lower stories of buildings because ofhigher story shear demands on the strength of themoment frame-infill wall system.

Fig. 7 shows views of a collapsed apartment buildingin Golcuk. The first two storeys of this building failedcompletely, but damage in the upper four storeys withunbroken glass windows was limited. The long infillwalls in the upper four storeys have significant elasticstrength and stiffness—probably much greater stiffnessand strength than the moment-resisting frame. If theinfill walls in the upper four storeys of the building areindicative of the infill in the failed storeys, the first- andsecond-storey infill walls likely played an important rolein the collapse of the building. The brittle fracture ofthe first- and second-storey masonry infill walls prior toflexural yielding of the columns would have overloadedthe nonductile first- and second-storey columns in shear,likely resulting in the observed gravity load failure.

The first two storeys of the building in Fig. 8 col-lapsed. The masonry infill walls and moment-frame con-struction in the third and fourth storeys (first and secondstoreys in the photograph of the collapsed building) suf-fered major damage. Damage in this building reducedwith increased height above the ground. Failure of themasonry infill in the first and second storeys of the build-ing likely precipitated the collapse of the building.

Irregular placement of masonry infill walls can pro-duce discontinuities of stiffness in moment- frame build-ings. Consider the building in Fig. 9 in which themoment frame is both flexible and weak in the first sto-rey by comparison with the upper storeys. In the firststorey of this building, masonry infill walls are present

Fig. 7. Views from a collapsed apartment building in Golcuk.

Fig. 8. Failure of two stories of a moment-frame building with infillmasonry walls.

in the back face of the building and in the two facesperpendicular to the sidewalk. The front of the buildingwas open in the first storey. The lateral stiffness of thebuilding was considerably larger in the direction perpen-dicular to the sidewalk compared with parallel to thesidewalk. Deformations are concentrated in the first sto-rey of this building parallel to the sidewalk, due to theweakness and flexibility of the moment frame becauseof lack of masonry infill walls in the front of the build-ing. The first-storey columns in this building were sever-ely damaged and likely close to failure due to gravityload instability.

8. Detailing and response of components ofmoment-frames

Previous sections of this paper on moment-frame con-struction have focused on the response of moment-framesystems. This section addresses the response of thecomponents of moment frames, namely beams, columns,and beam-column joints. Based on the authors’ obser-vations, typical details for an existing column and beamreinforcing bar details are shown in Fig. 10. Bent-up bars

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Fig. 9. Formation of a soft and weak storey.

Fig. 10. Typical beam and column rebar details observed by thereconnaissance team.

are shown in the typical beam section. Corner columnbar are spliced above the floor slab with lap lengths of40–70 bar diameters. Side-face column rebar are eitherspliced per corner rebar or terminated above and belowthe joint with 180-degree hooks as shown Fig. 10. Noadditional transverse reinforcement for the purpose ofconfinement is provided in the hinge, joint, or spliceregions. In general, typical 80-mm–120-mm thickreinforced concrete floor slabs performed well. Vulner-abilities and description of the damage to the commonlyused joisted floor slab framing system are provided inSezen et al. [1].

8.1. Beams

Typical beam spans ranged between 3 and 5 m. Beamwidths and depths ranged between 200–250 mm and500–600 mm, respectively. Transverse ties are smoothreinforcing bars of 6–10 mm diameter with 90-degreehooks. Bent-up longitudinal reinforcing bars, often usedfor reasons of economy to provide shear resistance togravity loads and to increase negative moment-resistance

Fig. 11. Damage to nonductile reinforced concrete beam.

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for gravity loads at supports, however do not properlyresist cyclic shear forces induced by earthquake shaking.

Little damage to interior moment-frame beams wasobserved by the reconnaissance team because columnswere generally weaker than beams. One type of beamdamage is shown in Fig. 11. The building in this figuresuffered a partial storey collapse because the fault rup-tured beneath the building. The beams shown were for-ced to accommodate the partial collapse and were badlydamaged at the beam-column connection due to slip ofthe smooth longitudinal beam reinforcing bars. In manycases, beam bottom reinforcing bars were inadequatelyanchored through the beam-column joint.

8.2. Columns

Column plan dimensions range between 150 mm×500mm–250 mm×800 mm. Most columns in residential con-struction are blade columns with a depth-to-width ratioof approximately three. The longitudinal rebar ratioranges between 1% and 2%; 12–16 mm diameter smoothrebar are generally used. Transverse ties are smoothrebar of 6–10 mm diameter with 90-degree hooks. Thespacing of transverse ties is typically 200–250 mm uni-form along the clear height of the column. Table 1 shows

Table 1Observed and code specified column detailing and dimensions

ACI 318–95 Turkish 1975 Turkish 1998 Observed

Ductile NonductileTurkish 1975 TS500-1985

Min width (W) �300 mm �250 mm �250 mm �250 mm typical:�0.4∗D �H/20 250 mm

�D/3 common:200 mm

Min depth (D) �300 mm �250 mm �250 mm �300 mm typical:400–600 mm

ρ (longitudinal) 0.01�ρ�0.06 0.01�ρ�0.04 0.008�ρ�0.04 0.01�ρ�0.04 typical:0.01 to 0.02

Column middle �150 mm s2�200 mm �200 mm su�200 mm typical:zone: �6∗(db) long. s2�12∗(db) long. �12∗(db) long. su�W/2 150–250 mmTie spacing s2�D/2Hooks 135° 90° or 135° 135° all 90°

Column end �100 mm s1�100 mm sc�100 mm typical:zones: �W/4 s1�50 mm sc�50 mm 150–250 mmTie spacing sc�W/3 100 mm or less

not observedHooks 135° 135° 135° 135° all 90° hooks

no 135° hooks

W: Minimum member dimension (width), D: longer member dimension (depth), H: column height, ρ: longitudinal reinforcement ratio, (db) long.:longitudinal bar diameter, s1, s2, sc, su : shown in Fig. 2.

the column dimensions and details observed by thereconnaissance team for a typical building, and compareswith those dimensions and details given in Chapter 21of ACI 318-95 [7], the Turkish building code [6], andrecent Turkish seismic codes, [4,5]. The data of Table1 coupled with field observations clearly show that theTurkish earthquake code provisions were not followedin detailing reinforced concrete columns, especially inpotential plastic hinge zones at the end of the columns.In damaged columns, the authors did not observe a tiespacing of less than 100 mm or 135-degree hooks at theend of column ties as required by all codes except forthe Turkish building code, TS-500 [6], which in generaldoes not include ductile detailing requirements for col-umns.

The majority of moment-frame component failureswas in columns and was due to (a) the use of nonductiledetails and unconfined lap splices, (b) excessive beamstrength, and (c) interaction between the columns andthe masonry infill walls. Lap splices in moment-framecolumns were typically made immediately above thefloor framing or the foundation. The exposed lap spliceof Fig. 12a is from a moment-frame building in Adapaz-ari. The lap splices in this column were approximately35 bar diameters in length and were located in a plastic

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Fig. 12. Column failures.

hinge zone. Transverse reinforcement was widely spacedwith 90-degree hooks, and no cross ties were present.The 90-degree hooks on the ties opened during the earth-quake and the limited strength and confinement affordedby the ties were lost.

The transverse tie details of Fig. 12b were common,namely smooth rebar, widely and often unequally spacedties (200–250 mm), and 90-degree hooks. The widespacing of the ties resulted in shear failures (Figs. 12band 12d), buckling of longitudinal rebar (Fig. 12c), andpoor confinement of the core concrete.

8.3. Beam-column joints

Damage to beam-column joints is shown in Fig. 13.Much of the framing (Fig. 13a) is essentially intact butmany of the beam-column joints are heavily damaged.A view of one of the damaged joints is shown in Fig.13b. Beam reinforcing bars anchorage in the joint isinadequate and no transverse ties are present in thejoint region.

The photograph of a building (Fig. 14) that was underconstruction in Adapazari at the time of the earthquakeshows severe damage in the beam-column joints, but thehorizontal transverse ties maintained the integrity ofthe joints.

9. Behavior of shear-wall construction

Buildings constructed using shear walls as the primarylateral load-resisting system performed quite well in the1999 Kocaeli earthquake. Some buildings with a dualwall-frame lateral load-resisting system were damagedbecause the shear walls were not sufficiently stiff to keepthe displacements of the nonductile framing system inthe elastic range. Storey collapses were not observed inbuildings containing shear walls, but it should be notedthat shear walls were not widely used in the epicentralregion. The reconnaissance team toured a number ofbuildings that would be classified as dual wall-frame sys-tems in the United States. The most significant damage

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Fig. 13. Building collapse due to failure of beam-column joints.

Fig. 14. Damage to new moment-frame beam-column joint.

observed by the team in a dual wall-frame building isshown in Fig. 15. The wall and first-storey exterior col-

Fig. 15. Collapsed dual wall-frame building in Adapazari, (a) view of collapsed 5-storey building, (b) failure of the shear wall and perimeter col-umns.

umns shown (Fig. 15b) failed and shortened. Thesecomponents displaced out of the plane of the facade asseen in Fig. 15b. Another example of damage to beamsand columns in a dual wall-frame building is shown inFig. 16. No cracks were observed in the shear wall, butthe right end settled approximately 500 mm due to bear-ing failure of the supporting soils. Although the shear wallwas likely sufficiently stiff to protect the nonductileframe, the rotation at the base of the shear wall and thesettlement of the footings beneath the moment-frame col-umns contributed to the failure of the first-story columns.

Blade columns or narrow shear walls were often con-structed near stairwells (Fig. 17). These walls or bladecolumns were detailed similarly to regular moment-frame columns with light transverse reinforcement with90-degree hooks and no cross ties. The damage shownin Fig. 17 is similar to that observed in moment-framecolumns.

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Fig. 16. Damaged wall frame building due to ground failure andwall rotation.

Fig. 17. Shear failure of wall/blade column.

10. Conclusions

Much has been written in the aftermath of the August17, 1999, earthquake about the poor quality of residentialand commercial construction in the epicentral region.The detailing and quality of the residential construction,perhaps most of it not rigorously engineered, was poorby modern US and Turkish standards. The reconnais-sance team also documented many collapses of commer-cial reinforced concrete moment frame buildings thatwere likely carefully engineered. Both poor constructionpractices and the continued use of nonductile seismicdetailing were the primary reasons for most of the build-ing collapses. Shear reinforcement was lacking in mostdamaged columns observed by the authors. In contrastwith the code design provisions, common use of 90-degree hooks for transverse reinforcement reduced thelateral strength and confinement of columns. Short col-umns, poor detailing in beam-column joints, strong-beam weak-columns, and use of inconsistent unre-inforced masonry infill walls were among other reasonsfor the widespread destruction in the region affected bythe earthquake. For the most part, buildings with shearwalls survived with limited or no damage.

Acknowledgements

The work described in this paper made use of thePacific Earthquake Engineering Research Center sharedfacilities supported by the Earthquake Engineering Cen-ters Program of the National Science Foundation underAward Number EEC-9701568. This support is grate-fully acknowledged.

References

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