towards a modified rapid screening procedure for medium...

13th World Conference on Earthquake Engineering Vancouver, B.C., Canada

August 1-6, 2004 Paper No. 1542

TOWARDS A MODIFIED RAPID SCREENING METHOD FOR EXISTING MEDIUM RISE RC BUILDINGS IN TURKEY

Hasan M. BODUROGLU 1, Pinar OZDEMIR 2, Alper ILKI 3, Semra SIRIN 4, Cem DEMIR 5, Fatma BAYSAN 6

SUMMARY The majority of the existing buildings in developing countries located in the earthquake prone areas do not have sufficient seismic safety that is required by the recent Earthquake Resistant Design Codes. For preventing loss of lives and economical losses after future earthquakes, these buildings should be evaluated in terms of seismic safety and necessary measures should be taken if existing seismic safety is not sufficient. However, considering the huge stock of existing buildings, it is clear that seismic evaluation of these buildings by a detailed structural analysis is practically impossible. So, it is inevitable to utilize a quick evaluation method for deciding which buildings need further detailed structural analysis, and which buildings can be used with their existing seismic safety levels. Since the characteristics of the structures, economical conditions, potential earthquake intensities are not the same everywhere in the world, a direct adaptation of the available quick inspection methods may not be appropriate. Consequently, the calibration of these available methods is necessary considering the local conditions in different aspects. For a realistic calibration, a large amount of database about the existing structures and their seismic performance is inevitable. In this study, five reinforced concrete buildings that can represent typical buildings in Turkey are examined by the Seismic Index Method. After retrofit designs of these buildings are done considering the seismic loads given by the current Earthquake Resistant Design Codes, Seismic Index Method is utilized once more for each of these retrofitted buildings. Then detailed structural analysis is carried out for all of these five buildings for their existing states and retrofitted states. Finally a comparison of the results obtained by the quick seismic safety evaluation method and detailed structural analysis is presented. Since this comparison is separately carried out for each floor and each principal direction, an important amount of data is obtained in terms of the relation between results of the detailed structural analysis and quick evaluation method.

1 Prof. Dr., Faculty of Civ. Eng., Istanbul Tech. Univ., Istanbul , Turkey, [email protected] 2 Ast. Prof. Dr., Faculty of Civ. Eng., Istanbul Tech. Univ., Istanbul , Turkey, [email protected] 3 Ast. Prof. Dr., Faculty of Civ. Eng., Istanbul Tech. Univ., Istanbul , Turkey, [email protected] 4 Post. Grad. St., Faculty of Civ. Eng., Istanbul Tech. Univ., Istanbul, Turkey 5 Post. Grad. St., Faculty of Civ. Eng., Istanbul Tech. Univ., Istanbul, Turkey, [email protected] 6 Post. Grad. St., Faculty of Civ. Eng., Istanbul Tech. Univ., Istanbul, Turkey, [email protected]

INTRODUCTION

A large number of existing buildings in Turkey and other developing countries do not have sufficient seismic safety, which is defined by the Turkish Earthquake Resistant Design Code-1998 [1] and other recent Earthquake Resistant Design Codes. Although the subject is a worldwide problem, in this paper, the problem will be analyzed considering the conditions in Turkey. The main reasons of insufficient seismic safety may be listed as; insufficient horizontal loads considered during design, improper construction resulting with low quality concrete, smaller structural member dimensions, usage of insufficient amount longitudinal and transverse reinforcing bars, poor reinforcement details, poor structural systems and degraded strength due to poor material quality and environmental effects. It should be noted that during the design of the buildings, which were constructed before the Turkish Earthquake Resistant Code-1975 [2] was published, both the level of horizontal loads are too small and reinforcing details for providing adequate ductility were not considered. Consequently, the existing buildings must be investigated and if seen necessary they must be repaired and strengthened or demolished and built again in order to reduce the risks and prevent the losses. However, since the number of existing buildings, which must be evaluated in terms of seismic safety is too high, it is not possible to carry out detailed structural analysis for all existing buildings practically and economically. Consequently, utilization of quick evaluation methods for determining the priorities is inevitable. By the help of these quick evaluation methods, valuable information can be obtained for deciding which buildings need further detailed structural analysis, and which buildings can be used with their existing seismic safety levels. There are some available methods, which are widely accepted all around the world like ATC-21-1998 [3], FEMA 310-1998 [4] and Seismic Index Method [5-10], which was basically prepared for Japan. ATC-21 method is used to for evaluating seismic safety of the buildings from outside in a very quick manner, it can also be used for having a basic idea on the possible performance of the building before detailed analysis. While this method is being used, a data collection form, which includes the photographs, usage information, type of the structural system and some basic architectural characteristics, is prepared. In FEMA 310, a three level evaluation method is given. In the first level the building is evaluated by considering the structural system, foundations, non-structural members, material quality, irregularities, transfer of the loads, soft story, weak story and similar characteristics through a check list. The decision on the seismic safety of the building is given considering the design shear forces in each story and allowable shear stresses accepted for corresponding stories. Like evaluation method given in FEMA 310, the Seismic Index Method includes three different levels [5-10], from simple to sophisticated. In this study the first level is summarized briefly. Any of these or other available quick seismic safety evaluation methods can be used in Turkey, after completing necessary adaptations considering the structural, seismic and economical conditions in Turkey. Adaptation can be done after carefully examining a data bank of existing structures, which may represent the stock of existing buildings without bias. There are two major issues, for which answers should be searched for existing structures: 1.What is the acceptable level of seismic safety? 2.What is the relationship between the results of the quick evaluation methods and detailed structural analysis? For existing buildings the acceptable seismic safety level should not be as high as the level, which is suggested by the Turkish Earthquake Resistant Design Code-1998 [1]. Otherwise almost all of the existing buildings will need to be retrofitted or demolished. Consequently, for existing structures, most of which already completed or about to complete their economic lives, another seismic safety level, which is well below than required by the Turkish Earthquake Resistant Design Code-1998 [1], which was published for the buildings to be newly constructed, should be defined. Although this issue is very important in order to decide on the seismic safety of the buildings, it is outside the scope of this study.

The relationship between the results obtained by the rapid evaluation methods and the results of detailed structural analysis is very important for interpreting the outcomes of the rapid evaluation methods. Consequently, to evaluate and if necessary to modify the rapid seismic safety evaluation methods, a large number of buildings, which can represent the stock of existing buildings, should be investigated both by rapid evaluation methods and conventional structural analysis. In Turkey, for today, it is difficult to express that a sufficient data bank of several typical buildings is present. It is not realistic to directly use available rapid seismic safety evaluation methods, without carrying such studies and making necessary modifications in the available methods. The aim of this study is to contribute to the available data bank of the existing buildings, so that different rapid seismic safety evaluation methods can be checked or calibrated, when the number of the buildings in the data bank increases reasonably. For this purpose five typical buildings were included in this study, which were specially chosen to represent the typical medium rise buildings in Turkey. Since these buildings do not have sufficient seismic safety, retrofit designs were also carried out for these buildings. In summary, 5 original existing buildings and 5 other buildings, which were obtained by retrofitting the original existing buildings are studied in this paper. These 10 buildings are analyzed both by the first level of Seismic Index Method and conventional structural analysis. Although the second and third levels of the Seismic Index Method can give more realistic results about the seismic safety of the building, only the first level is considered, since the primary concern is on rapid seismic safety evaluation. In the paper, a brief outline of Seismic Index Method is given and then general characteristics of the investigated original and retrofitted buildings are summarized. Finally, the comparison of obtained results by Seismic Index Method and structural analysis is given with a brief explanation about the basic assumptions made during conventional structural analysis. It should be noted that the expected outcome from such an analysis should not be the exact determination about which buildings are safe, which are not.

OUTLINE OF THE SEISMIC INDEX METHOD

The method is used for rapid seismic safety evaluation of building type structures with frame, frame-shear wall and shear wall systems. Although the method consists of three different levels from simple to sophisticated, anyone of which can be applied independently, only the first stage is focused herein this study. First step of investigation involves the examination of the structural system, age and physical conditions of the building. After this examination the performance index I can be determined. Comparing this performance index I, with the adequate reference index Iso the seismic safety of the building can be estimated. This comparison should be repeated for all critical stories and for two principal directions. If for all comparisons Iso<Is then the building may be assumed to be safe against earthquakes. If for any of the comparison cases I so>Is then it is concluded that the behavior of the structure is indeterminate against earthquakes. Note that Iso<Is does not mean that the structure will not be damaged; however, it indicates that very probably the total collapse will be prevented. Reference index Iso can be calculated by Eq. (1).

UGZEI sS ∗∗∗=0 (1)

In this equation Z is zone factor, which has to be considered as 1.0 for the areas that are identified as the first or the second degree of earthquake zone by Turkish Earthquake Resistant Design Code-1998 [1] and other areas of high seismic risk. In other areas Z can be reduced according to the seismicity of the region. However, in any case Z should be considered as greater than 0.7. G ground coefficient is related with the local ground conditions. G coefficient can get values between 1.0 and 1.1, with lower values for better ground conditions. U usage coefficient is related with the importance and usage of the building. It should be decided considering the importance of the structure and the extent of possible effects of damage after earthquakes. Since the buildings, which need to be in service after earthquakes like hospitals, schools, fire

stations, etc. are out of the scope of this study, it is convenient to use U as 1.0. However if seen necessary, U can be increased up to 1.50. Es basic reference index can be considered as 0.8 for this first stage analysis. However, after accumulation of extensive data for typical existing buildings in Turkey, this coefficient may be subjected to alterations. The performance index Is of the existing building can be calculated by using Eq. (2).

TSEI Ds ∗∗= 0 (2)

In this equation Eo is the basic structural performance index. During calculation of Eo index, the vertical structural members are examined in three distinct groups as columns, short columns and shear walls. If the ratio of the clear height to the cross-sectional depth is bigger than 2 (h0/D>2), then the member is defined as column. If the ratio of the clear height to the cross-sectional depth is equal or smaller than 2 (h0/D=2), then the member is defined as short column. The calculation of Eo Index differs when contribution of short columns is neglected or not. If the contribution of short columns is neglected then Eo index is calculated by Eq. (3), othervise by Eq. (4). In these equations n is the number of stories excluding the ground floor, i is the story which is dealt with, Cw is the coefficient related with the strength of shear walls, Cc is the coefficient related with the strength of columns, Csc is the coefficient related with the strength of short columns, Fw is the coefficient related with the ductility of the shear walls, Fsc is the coefficient related with the ductility of the short columns. a1, a2 and a3 are the compatibility coefficients. a1 the displacement compatibility factor may be considered as 0.7 for buildings with shear walls, but a1 should be taken 1.0 if Cw=0. Fsc can be considered as 0.8. a2 and a3 the displacement compatibility factors for shear walls and columns should be considered as 0.70 and 0.50, respectively.

wcw FCaCinnE ∗+∗+

+= )()1( 10 (3)

sccwsc FCaCaCinnE ∗++∗+

+= )()1( 320 (4)

If the building has short column(s), the greater of the Eo values obtained by Eq. (3) and Eq. (4) should be taken into account. On the other hand, if the failure of a short column may cause a total collapse or life losses, Eo should be calculated by Eq. (4). The strength of the walls Cw can be calculated with Eq. (5). In this equation Aw1 is the sum of the cross-sectional area of walls with the boundary columns at both sides of the wall (cm2), Aw2 is the sum of the cross-sectional area for the walls with a boundary column at either side of the wall (cm2), Aw3 is the sum of the cross-sectional area of walls without boundary columns (cm2), f′c is the characteristics compressive strength of the concrete (kgf/cm2), and W is the building weight over the story under consideration (kgf). The strength of the columns can be calculated with Eq. (6). In this equation Ac1 is the sum of the cross-sectional area of the columns, for which the ratio of the clear height to the depth (h0/D) are smaller than 6 (cm2), Ac2 is the sum of the cross-sectional area of the columns, for which the ratio of the clear height to the depth (h0/D) are equal or greater than 6 (cm2). The strength of the short columns can be calculated with the Eq. (7). In this equation Asc is the sum of the cross-sectional area of short columns (cm2).

)102030(200 321 www

cw AAA

W

fC ++∗

′= (5)

)710(200 21 cc

cc AA

W

fC +∗

′= (6)

scc

sc AW

fC 15

200∗

′= (7)

SD is an index to evaluate the physical properties and the geometry of the structure, like the irregularity in plan, length-width ratio of the plan, clearance of the expansion-joints, atriums, eccentricities in plan, irregularity of story heights, existence of piloti, etc. This index can be determined from elsewhere [5] according to the properties that are explained above. For example if the building has a symmetric plan, SD can be considered as 1.0. However, if the building has an asymmetric plan such as L, T or U, SD should be considered as 0.9.

T is an index, which is determined according to the existing damage of the building due to environmental effects, aging effects, fire etc. Details of index T can also be found elsewhere [5] according to the deformations, cracks and other damages in the building. The values index T can take are between 0.8 and 1.

GENERAL CHARACTERISTICS OF THE BUILDINGS

Avcilar Building The building is in Avcilar Town of Istanbul, where a significant number of buildings were severely damaged during 1999 Kocaeli Earthquake. The maximum horizontal base acceleration in this area was around 0.25g. It is a residential with one basement, one ground story and three normal stories. The building is designed in 1993. From one side, the building is adjacent to another building. The story height of the building is 2.70 m in the basement and 2.75 m in the other stories. The building is a frame system with slabs with beams and slab thickness of 100 mm. The dimensions of the beams are generally 200/500 mm/mm. Some of the 200/500 mm/mm beams in the ground and 1st story are removed in the 2nd and 3rd stories. As a result of this, the frame system of the building is quite irregular along x direction. The circumference of the basement is surrounded by the concrete shear walls. The characteristic compression strength of the concrete is 10 MPa. The stirrups and longitudinal reinforcements are round bars with the characteristic yield strength of 220 MPa. In the columns and beams, the lateral reinforcement is 8 mm bars with 200 mm spacing. No confinement zone is formed in the vicinity of joints. The local soil type is Z4 according to Turkish Earthquake Resistant Design Code-1998 [1], which is the worst type. After the 1999 Kocaeli Earthquake evident cracks were seen in the columns and beams. In the exterior walls and interior partitioning walls, shear cracks were also seen. The age of the building is less than 20 years and the building did not experience fire. The structural analysis of the building showed that the building does not have sufficient seismic safety. Consequently, the building is strengthened with 2 shear walls along each principal direction. These shear walls continue through all height of the building. The existing columns that form the edges of the newly added shear walls are also jacketed from four sides with 150 mm thick concrete. The characteristic concrete compressive strength for the newly added shear walls and column jackets is 20 MPa and the reinforcement of these members is deformed bars with the characteristic yield strength of 420 MPa. DSI Building This is a 5 story building, with one basement, one ground floor and three normal stories. The circumference of the basement is surrounded by the concrete shear walls. The height of all of the stories is 2.80 m. The thickness of the slabs is 10 mm in all stories. The dimensions of the beams are 200/600 mm/mm in all stories. The dimensions of the columns are same in all stories. No soft or weak story is

present. The characteristic concrete compression strength is 11 MPa. Plain bars of 220 MPa characteristic yield strength are used for both longitudinal and transverse reinforcement. The 8 mm diameter transverse bars are placed with 200 mm spacing and there is no confinement zone in beams and columns. The age of the building is less than 20 years and the building never experienced a fire. No evident deformation or crack is visible either due to past earthquakes or environmental conditions, aging, etc. The local soil type is Z1, which is the strongest according to the Turkish Earthquake Resistant Design Code-1998 [1]. After the structural analysis, it is seen that the building does not have sufficient seismic safety. Consequently, the building is strengthened with 2 shear walls in each direction, along the height of the building, P1, P2, P3 and P4. The columns that form the edges of newly added shear walls are also retrofitted with the 150 mm thick concrete jackets on four sides. The columns that form the edge part of P4 shear wall is not jacketed due to architectural necessities, however, anchorage reinforcement between the newly added shear wall and existing columns can provide the members working together. The characteristic concrete compression strength of the newly added members and column jackets is 20 MPa and the reinforcement of these members is deformed bars with the characteristic yield strength of 420 MPa. Building at Kucukbakkalkoy This three-story office building is located in Kucukbakkalkoy, Istanbul. Story height is 3.8 m for first story and 3.2 m for other stories. The building has a typical structural system in Turkey, which consists of reinforced concrete rigid frames with masonry infill walls of hollow clay brick units. The thickness of the floor slab is approximately 150 mm at each story. The dimension of the beams is 300 mm by 600 mm. The average concrete compressive strength is 13 MPa. The yield strength of the reinforcing steel is 220 MPa. Plain round bars of 8 mm diameter are used as transverse reinforcement with the spacing of 200 mm. The building is built on Z2 type soil and there is no damage due to 1999 Kocaeli Earthquake. 3 shear walls with dimensions 250 by 6000 mm and a shear wall with dimensions 300 by 2100 mm through Y axis and 4 shear walls with dimensions 4600 by 250 mm through X axis are added to the structural system for strengthening the building. The concrete compressive strength is 20 MPa for strengthened system members and the yield strength of the reinforcing bars used for retrofitting is 420 MPa. Building in Izmit This is an office building in Izmit and has a cellar, a ground floor and 4 stories. Story height is 3.00 m for each story. Beam dimensions are 500 by 400 mm, 600 by 400 mm, 200 by 400 mm. In some parts of the ground floor I100 steel profiles are used as beams. The floor system is ribbed slab with 100 mm plate thickness. Type of soil is Z4, which is the weakest defined in Turkish Earthquake Resistant Design Code-1998 [1]. The concrete compressive strength is 20 MPA and the characteristic yield strength of the steel reinforcing bars is 420 MPa. After Kocaeli Earthquake, the building did not experience any damage. On the other hand, after the earthquake the building is strengthened by the shear walls. The width of shear walls is 250 mm. The columns at the end points of the shear walls are also jacketed with 250 mm concrete. The concrete and steel strengths for retrofitting members are same as the original members. Building in Esenyurt This is a three-story school building in Esenyurt, in Istanbul. The story heights are 3.20 m for each story. First floor was constructed as ground floor. In this story, eight rigid concrete walls, four in X direction and four in Y direction. Only two shear walls in Y direction continue in the upper floors. The average concrete compressive strength is 15 MPa. The characteristic strength of the steel is 220 MPa. There is no damage in the structural system, either due to past earthquakes or other reasons. For strengthening, 4 shear walls with dimensions 6550 by 350 mm are added through X axis. 2 shear walls with dimensions 300 by 3680 mm are added through Y axis. The adjacent columns to these new retrofit shear walls are also jacketed for a providing better integration of retrofit system and existing building. Three other columns are also jacketed to improve their axial load capacity. The concrete compressive strength is 25 MPa and

characteristic yield strength of the longitudinal bars for the strengthened members is 420 MPa. The building is on Z2 type soil in the second level seismic area. The dimensions of the vertical structural members of the investigated buildings are presented in Table 1-4, and the floor plans are given in Fig. 1-5.

Table 1. Member dimensions for (a) Avcilar Building, (b) DSI Building (m) (a) (b)

Table 2. Member dimensions for Kucukbakkalkoy Building (m)

No X

Y

No X

Y

No X

Y

No X

Y

No X

Y

S 01 0.30 0.50 S10 0.30 0.50 S19 0.30 0.50 S28 0.30 0.50 S37 0.30 0.50 S 02 0.30 0.60 S11 0.30 0.50 S20 0.30 0.50 S29 0.30 0.50 S38 0.30 0.50 S 03 0.30 0.50 S12 0.30 0.50 S21 0.30 0.50 S30 0.30 0.50 S39 0.30 0.50 S 04 0.30 0.50 S13 0.30 0.60 S22 0.30 0.50 S31 0.30 0.50 S 05 0.30 0.50 S14 0.30 0.50 S23 0.30 0.50 S32 0.30 0.50 S 06 0.30 0.50 S15 0.30 0.50 S24 0.30 0.50 S33 0.30 0.50 S 07 0.30 0.50 S16 0.30 0.50 S25 0.30 0.50 S34 0.30 0.50 S 08 0.30 0.50 S17 0.30 0.50 S26 0.30 0.50 S35 0.30 0.50 S 09 0.30 0.50 S18 0.30 0.50 S27 0.30 0.50 S36 0.30 0.50 P2 4.60 0.25 P24 0.25 6.60 P30 4.60 0.25 P35 4.60 0.25 P8 4.60 0.25 P29 0.25 6.60 P33 0.30 2.10 P39 0.25 6.60

No X

Y

S1 0.25 0.60

S2 0.60 0.25

S3 0.60 0.25

S4 0.25 0.70

S5 0.25 0.70

S6 0.60 0.25

S7 0.25 0.70

S8 0.50 0.25

S9 0.40 0.25

S10 0.25 0.60

S11 0.50 0.25

S12 0.25 0.60

S13 0.25 0.60

S14 0.25 0.60

S15 0.25 0.90

P1 0.35 4.10

P2 0.35 4.10

P3 3.60 0.35

P4 3.30 0.35

No X

Y

No X

Y

No X

Y

No X

Y

S101 0.30 0.40 S201 0.30 0.40 S301 0.30 0.40 S401 0.30 0.40

S102 0.30 0.40 S202 0.30 0.40 S302 0.30 0.40 S402 0.30 0.40

S103 0.30 0.40 S203 0.30 0.40 S303 0.30 0.40 S403 0.30 0.40

S104 0.30 0.40 S204 0.30 0.40 S304 0.30 0.40 S404 0.30 0.40

S105 0.30 0.40 S205 0.30 0.40 S305 0.30 0.40 S405 0.30 0.40

S106 0.30 0.40 S206 0.30 0.40 S306 0.30 0.40 S406 0.30 0.40

S107 0.30 0.40 S207 0.30 0.40 S307 0.30 0.40 S407 0.30 0.40

S108 0.40 0.30 S208 0.40 0.30 S308 0.40 0.30 S408 0.40 0.30

S109 0.40 0.30 S209 0.40 0.30 S309 0.40 0.30 S409 0.40 0.30

S110 0.50 0.30 S210 0.40 0.30 S310 0.40 0.30 S410 0.40 0.30

S111 0.50 0.30 S211 0.40 0.30 S311 0.40 0.30 S411 0.40 0.30

S112 0.40 0.30 S212 0.40 0.30 S312 0.40 0.30 S412 0.40 0.30

S113 0.30 0.40 S213 0.30 0.40 S313 0.30 0.40 S413 0.30 0.40

S114 0.30 0.40 S214 0.30 0.40 S314 0.30 0.40 S414 0.30 0.40

S115 0.30 0.40 S215 0.30 0.40 S315 0.30 0.40 S415 0.30 0.40

S116 0.30 0.50 S216 0.30 0.50 S316 0.30 0.50 S416 0.30 0.50

S117 0.30 0.40 S217 0.30 0.40 S317 0.30 0.40 S417 0.30 0.40

S1P1 0.20 0.80 S2P1 0.20 0.80 S3P1 0.20 0.80 S4P1 0.20 0.80

PY1 0.20 5.70 PY1 0.20 5.70 PY1 0.20 5.70 PY1 0.20 5.70

PY2 0.20 5.70 PY2 0.20 5.70 PY2 0.20 5.70 PY2 0.20 5.70

P4X 3.00 0.20 P4X 3.00 0.20 P4X 3.00 0.20 P4X 3.00 0.20

P5X 5.75 0.20 P5X 5.75 0.20 P5X 5.75 0.20 P5X 5.75 0.20

Table 3. Member dimensions for Izmit Building (m) N

o X

Y

No X

Y

No X

Y

No X

Y

No X

Y

S201 0.20 0.40 S301 0.20 0.40 S401 0.20 0.40 S501 0.20 0.40 S601 0.20 0.40 S202 0.25 0.50 S302 0.25 0.50 S402 0.25 0.50 S502 0.25 0.50 S602 0.25 0.50 S203 0.25 0.50 S303 0.25 0.50 S403 0.25 0.50 S503 0.25 0.50 S603 0.25 0.50 S204 0.20 0.60 S304 0.20 0.60 S404 0.20 0.60 S504 0.20 0.60 S604 0.20 0.60 S205 0.20 0.40 S305 0.20 0.40 S405 0.20 0.40 S505 0.20 0.40 S605 0.20 0.40 S206 0.60 0.30 S306 0.60 0.30 S406 0.60 0.30 S506 0.60 0.30 S606 0.60 0.30 S207 0.25 0.25 S308 0.30 0.60 S408 0.30 0.60 S508 0.30 0.60 S608 0.30 0.60 S208 0.30 0.60 S309 0.20 0.40 S409 0.20 0.40 S509 0.20 0.40 S609 0.20 0.40 S209 0.20 0.40 S310 0.60 0.30 S410 0.60 0.30 S510 0.60 0.30 S610 0.60 0.30 S210 0.60 0.30 S312 0.30 0.60 S412 0.30 0.60 S512 0.30 0.60 S612 0.30 0.60 S212 0.30 0.60 S313 0.20 0.40 S413 0.20 0.40 S513 0.20 0.40 S613 0.20 0.40 S213 0.20 0.40 S314 0.60 0.30 S414 0.60 0.30 S514 0.60 0.30 S614 0.60 0.30 S214 0.60 0.30 S316 0.30 0.60 S416 0.30 0.60 S516 0.30 0.60 S616 0.30 0.60 S215 0.25 0.25 S317 0.20 0.40 S417 0.20 0.40 S517 0.20 0.40 S617 0.20 0.40 S216 0.30 0.60 S318 0.60 0.30 S418 0.60 0.30 S518 0.60 0.30 S618 0.60 0.30 S217 0.20 0.40 S320 0.25 0.60 S420 0.25 0.60 S520 0.25 0.60 S620 0.25 0.60 S218 0.60 0.30 EPX1 5.30 0.25 EPX1 5.30 0.25 EPX1 5.30 0.25 EPX1 5.30 0.25 S219 0.25 0.25 EPX2 3.80 0.25 EPX2 3.80 0.25 EPX2 3.80 0.25 EPX2 3.80 0.25 S220 0.25 0.60 EPY1 3.30 0.25 EPY1 3.30 0.25 EPY1 3.30 0.25 EPY1 3.30 0.25 EPX1 5.30 0.25 EPY2 3.30 0.25 EPY2 3.30 0.25 EPY2 3.30 0.25 EPY2 3.30 0.25 EPX2 3.80 0.25 EPY3 3.20 0.25 EPY3 3.20 0.25 EPY3 3.20 0.25 EPY3 3.20 0.25 EPY1 3.30 0.25 EPY4 3.20 0.25 EPY4 3.20 0.25 EPY4 3.20 0.25 EPY4 3.20 0.25 EPY2 3.30 0.25 EPY3 3.20 0.25 EPY4 3.20 0.25

Table 4. Member dimensions for Esenyurt Building (m)

No X

Y

No X

Y

No X

Y

No X

Y

No X

Y

S101 0.80 0.60 S127 0.80 0.60 S208 0.60 0.80 S232 0.60 0.80 S319 0.50 0.40 S102 0.60 0.80 S128 0.80 0.60 S209 0.80 0.60 S233 0.30 0.50 S320 0.50 0.40 S103 0.30 0.50 S129 0.30 0.50 S210 0.30 0.50 S234 0.80 0.60 S321 0.30 0.50 S105 0.40 0.50 S130 0.60 0.80 S211 0.30 0.50 S235 0.80 0.60 S323 0.60 0.80 S107 0.30 0.50 S131 0.40 0.50 S212 0.30 0.50 P204 0.30 5.00 S324 0.60 0.80 S108 0.60 0.80 S132 0.60 0.80 S213 0.30 0.50 P206 0.30 5.00 S326 0.30 0.50 S109 0.80 0.60 S133 0.30 0.50 S214 0.50 0.40 P201 6.55 0.30 S327 0.80 0.60 S110 0.30 0.50 S134 0.80 0.60 S215 0.50 0.40 P208 6.55 0.30 S328 0.80 0.60 S111 0.30 0.50 S135 0.80 0.60 S216 0.50 0.40 P221 6.35 0.30 S330 0.60 0.80 S112 0.30 0.50 P104 0.30 5.00 S217 0.80 0.70 P228 6.35 0.30 S331 0.40 0.50 S113 0.30 0.50 P106 0.30 5.00 S218 0.50 0.40 P237 0.30 3.68 S332 0.60 0.80 S114 0.80 0.70 P153 6.55 0.35 S219 0.50 0.40 P242 0.30 3.68 S334 0.80 0.60 S115 0.50 0.40 P154 6.55 0.35 S220 0.50 0.40 S301 0.80 0.60 S335 0.80 0.60 S116 0.50 0.40 P155 6.35 0.35 S221 0.30 0.50 S302 0.60 0.80 P304 0.30 5.00 S117 0.80 0.70 P156 6.35 0.35 S222 0.30 0.50 S305 0.40 0.50 P306 0.30 5.00 S118 0.50 0.40 P157 0.20 4.15 S223 0.60 0.80 S308 0.60 0.80 P301 6.55 0.30 S119 0.50 0.40 P158 0.20 4.15 S224 0.60 0.80 S309 0.80 0.60 P308 6.55 0.30 S120 0.80 0.70 P136 0.30 3.68 S225 0.30 0.50 S310 0.30 0.50 P315 6.35 0.30 S121 0.30 0.50 P142 0.30 3.68 S226 0.30 0.50 S313 0.30 0.50 P320 6.35 0.30 S122 0.30 0.50 S201 0.80 0.60 S227 0.80 0.60 S314 0.50 0.40 P327 0.30 3.68 S123 0.60 0.80 S202 0.60 0.80 S228 0.80 0.60 S315 0.50 0.40 P332 0.30 3.68 S124 0.60 0.80 S203 0.30 0.50 S229 0.30 0.50 S316 0.50 0.40 S125 0.30 0.50 S205 0.40 0.50 S230 0.60 0.80 S317 0.80 0.70 S126 0.30 0.50 S207 0.30 0.50 S231 0.40 0.50 S318 0.50 0.40

Fig. 1. Avcilar Building Ground and Normal Story Plans (original and retrofitted)

Fig. 2. DSI Building floor plans for all stories (original and retrofitted)

Fig. 3. Kucukbakkalkoy Building floor plans ground story (original and retrofitted)

COMPARISON OF THE STRUCTURAL ANALYSIS AND THE SEISMIC INDEX METHOD

For all the buildings given above, three dimensional mechanical models are prepared and linear structural analysis is carried out by SAP2000 [11]. The analysis is carried out for vertical and horizontal loads determined considering the Turkish Earthquake Resistant Design Code-1998 [1]. At the end of the structural analysis design moments (Md) and shear forces (Vd) are recorded for all vertical structural members in two directions for each story. Then the moment capacities (Mr) and shear strengths (Vr) are determined for these members according to the rules and calculation principles of TS500 [1]. The design forces and corresponding section capacities of vertical structural members are added to determine the total design forces and corresponding capacities in each story level for two principal directions. Then ΣMr/ΣMd and ΣVr/ΣVd ratios are determined and these ratios are given in the Table 5. If these ratios are greater than 1, it can be concluded that the considered story is safe for considered direction. Otherwise, the considered story is not safe with increasing insufficiency, with lower values of these ratios. Then for each story in two principle directions, Is and Iso values are calculated by using Seismic Index Method and Is/Iso ratios are determined. Similar to ΣMr/ΣMd and ΣVr/ΣVd ratios, if Is/Iso ratios are greater than 1, it can be concluded the considered story is safe for considered direction. Otherwise, the considered story is not safe with increasing insufficiency, with lower values of this ratio. It is expected that changes of ΣMr/ΣMd and ΣVr/ΣVd ratios should be parallel to changes of Is/Iso ratios. The relationships between ΣMr/ΣMd and Is/Iso and between ΣVr/ΣVd and Is/Iso are presented in Fig. 6 for existing original buildings.

S1 S2 S3 S4 S5 S6

S7 S8 S9 S1 S1 S1 S1 S1 S1 S1 S1

S1 S1 S2 S2 S2 S2 S2 S2 S2 S2 S2

S2 S30 S3 S3S33

S3 S3 S3 S3 S3 S3

Fig. 4. Izmit Building floor plans for ground and normal stories (original and retrofitted)

S305 S306

S301S302

S320

S316

S312

S303

S308

S304

S217

S213

S209

S205

S201 S202

S206

S210

S214

S218 S219

S215

S207

S203S204

S208

S212

S216

S220

S309

S317S318

S313 S314

S310

S21

S21

S20

S20

S20 S20

S20

S21

S21

S21

S21

S21

S20

S20S20

S20

S21

S21

S22

S30

EPX

EPX

EPY

EPY EPY

EPY EPY

EPY

EPX

EPY

EPY

EPX

S31 S31

S31 S31

S31

S30 S30

S30 S30

S32

S31

S31

S30

S30

S30

S101

S112

S119

S103 P104 S105 P106 S107 S108 S109

S110

S111

S113

S114

S115 S116 S117 S118

S120

S121 S122

S123 S124

S125 S126

S127 S128 S129 S130 S131 S133

S102

S134 S135

P153 P154

P155 P156

P157 P158

S132

S201

S212

S219

S203 P204

S205 P206

S207 S208 S209

S210

S211

S213

S214

S215 S216 S217 S218

S220

S221 S222

S223 S224

S225 S226

S227 S228 S229 S230 S231 S233

S202

S234 S235

S232

S101

S112

S119

S103 P104 S105 P106 S107

S108 S109

S110

S111

S113

S114

S115 S116 S117 S118 S120

S121 S122

S123 S124

S125 S126

S127 S128 S129 S130 S131 S133

S102

S134 S135

P153 P154

P155 P156

P157 P158

S132

P136 P142

S201

S212

S219

S203 P204

S205 P206 S207 S208 S209

S210

S211

S213

S214

S215 S216 S217 S218 S220

S221 S222

S223 S224

S225 S226

S227 S228 S229 S230 S231 S233

S202

S234 S235

S232

P201 P208

P221 P228

P237 P242

Fig. 5. Esenyurt Building floor plans (original and retrofitted)

As it can be seen from these representations, there is an approximately linear relationship between ΣMr/ΣMd and Is/Iso and between ΣVr/ΣVd and Is/Iso. Note that for Esenyurt building building importance factor in Turkish Earthquake Resistant Design Code-1998 [1] and usage factor in seismic index method are taken into account as 1.4 and 1.25, relatively, since this is a school building. For this building Ao in Turkish Earthquake Resistant Design Code-1998 [1] and Z in seismic index method are taken into account as 0.3 and 0.8, respectively, considering that the building is in the second level seismic area. Considering the material safety and load increment factors in TS500 [12], and the remaining economical lives of the existing buildings, it may be rational to consider the limiting (capacity/design force) ratio as 0.7 instead of 1.0, for severe damage risk of the existing buildings. Examining Fig. 6 with this basic assumption, it can be concluded that the Is/Iso ratio of 0.4 or smaller indicates that further analysis is needed for seismic evaluation of the building, while Is/Iso ratio greater than 0.4 indicates that the building can be used with its existing seismic safety. Surely, this investigation should be carried out in the most critical story of the building. It should be noted that these results are for the five typical buildings investigated in this study. For more general conclusions, the number of investigated buildings needs to be increased. Since all the investigated buildings have insufficient seismic safety to different extents, retrofit designs are carried for all five buildings considering the Turkish Earthquake Resistant Design Code-1998 [1]. The floor plans and dimensions of retrofitted members are given in figures and tables above. Since, number of shear walls and their heights are greater than demanded by the structural analysis for preventing irregularities in plan and elevation, there is a significant overstrength factor for the retrofitted buildings, particularly in the upper floors. The relationship between the ratios of Mr/Md and Is/Iso and between Vr/Vd and Is/Iso are given in Fig. 7. As seen in Fig. 7, although scattering is much, the relationships between Is/Iso and Mr/Md , and between Is/Iso and Vr/Vd are close to linear. Fig. 7 also indicates that retrofitting considering the Turkish Earthquake Resistant Design Code-1998 [1] may result with significant overstrength. Like in the case of existing buildings, for more general conclusions about retrofitted buildings, number of investigated buildings should be increased.

Table 5. Is/Iso , Mr/Md and Vr/Vd ratios for original and retrofitted buildings Avcilar STOREY E0 SD IS IS/IS0 Mr/Md Vr/Vd Avcilar E0 SD IS IS/IS0 Mr/Md Vr/Vd

Original GROUND 0.21 1.00 0.19 0.22 0.32 0.90 Retrofit 1.04 1.00 1.04 1.18 3.40 4.30

X 1. ST. 0.23 1.00 0.21 0.24 0.40 0.96 X 1.16 1.00 1.16 1.32 4.90 4.64

2.ST. 0.27 1.00 0.24 0.27 0.54 1.08 1.47 1.00 1.47 1.67 7.83 5.55

3.ST 0.47 1.00 0.42 0.48 0.71 1.49 2.58 1.00 2.58 2.93 16.55 7.72

Avcilar STOREY E0 SD IS IS/IS0 Mr/Md Vr/Vd Avcilar E0 SD IS IS/IS0 Mr/Md Vr/Vd


Y 1. ST. 0.26 1.00 0.24 0.27 0.65 1.05 Y 1.55 1.00 1.55 1.76 6.43 5.68

2.ST. 0.33 1.00 0.29 0.33 0.78 1.25 1.99 1.00 1.99 2.26 10.47 6.72

3.ST 0.57 1.00 0.52 0.59 0.92 1.69 3.48 1.00 3.48 3.95 21.36 8.84

DSI STOREY E0 SD IS IS/IS0 Mr/Md Vr/Vd DSI E0 SD IS IS/IS0 Mr/Md Vr/Vd


X 1. ST. 0.24 1.00 0.24 0.30 1.07 1.96 X 1.01 1.00 1.01 1.26 3.29 4.72

2.ST. 0.33 1.00 0.33 0.41 1.22 2.64 1.39 1.00 1.39 1.74 7.14 6.28

3.ST 0.74 1.00 0.74 0.92 1.96 5.57 3.09 1.00 3.09 3.87 12.77 12.51

DSI STOREY E0 SD IS IS/IS0 Mr/Md Vr/Vd DSI E0 SD IS IS/IS0 Mr/Md Vr/Vd


X 1. ST. 0.27 1.00 0.27 0.33 1.41 2.08 Y 1.04 1.00 1.04 1.30 3.46 6.23

2.ST. 0.37 1.00 0.37 0.46 1.53 2.80 1.43 1.00 1.43 1.79 6.77 8.37

3.ST 0.83 1.00 0.83 1.03 2.03 5.55 3.18 1.00 3.18 3.98 15.63 16.01

Kucuk STOREY E0 SD IS IS/IS0 Mr/Md Vr/Vd Kucuk E0 SD IS IS/IS0 Mr/Md Vr/Vd

Bakkalkoy GROUND 0.18 1.00 0.18 0.23 0.50 1.05 Bakkalkoy 1.06 1.00 1.06 1.33 1.61 4.14

Original 1. ST. 0.23 1.00 0.23 0.29 0.62 1.32 Retrofit 1.35 1.00 1.35 1.69 1.51 4.68

X 2. ST. 0.45 1.00 0.45 0.56 0.72 1.89 X 2.53 1.00 2.53 3.16 1.80 7.37

Kucuk STOREY E0 SD IS IS/IS0 Mr/Md Vr/Vd Kucuk E0 SD IS IS/IS0 Mr/Md Vr/Vd

Bakkalkoy GROUND 0.24 1.00 0.24 0.30 0.53 0.22 Bakkalkoy 1.13 1.00 1.13 1.41 1.71 4.25


Y 2. ST. 0.51 1.00 0.51 0.64 0.62 1.21 Y 2.73 1.00 2.73 3.41 2.55 7.15

Izmit STOREY E0 SD IS IS/IS0 Mr/Md Vr/Vd Izmit E0 SD IS IS/IS0 Mr/Md Vr/Vd


X 2. ST. 0.29 1.00 0.29 0.33 0.48 0.70 X 0.85 1.00 0.85 0.97 2.58 5.32

3. ST 0.32 1.00 0.32 0.36 0.55 0.85 1.10 1.00 1.10 1.25 3.06 8.65

4. ST. 0.36 1.00 0.36 0.41 0.77 1.19 1.39 1.00 1.39 1.58 2.97 9.34

5. ST. 0.46 1.00 0.46 0.52 1.15 2.11 1.94 1.00 1.94 2.20 6.55 18.94

Izmit STOREY E0 SD IS IS/IS0 Mr/Md Vr/Vd Izmit E0 SD IS IS/IS0 Mr/Md Vr/Vd


Y 2. ST. 0.32 1.00 0.32 0.36 0.51 0.64 Y 0.97 1.00 0.97 1.10 2.28 4.85

3. ST 0.37 1.00 0.37 0.42 0.60 0.77 1.19 1.00 1.19 1.35 2.70 5.81

4. ST. 0.46 1.00 0.46 0.52 0.79 1.08 1.80 1.00 1.80 2.05 4.21 8.93

5. ST. 0.67 1.00 0.67 0.76 1.15 1.93 2.56 1.00 2.56 2.91 5.87 13.28

Esenyurt STOREY E0 SD IS IS/IS0 Mr/Md Vr/Vd Esenyurt E0 SD IS IS/IS0 Mr/Md Vr/Vd

Original 1 0.64 1.00 0.64 0.80 0.89 1.18 Retrofit 1.25 1.00 1.25 1.56 1.06 2.67 X 2 0.25 1.00 0.25 0.31 0.33 0.86 X 1.67 1.00 1.67 2.09 1.08 2.74 3 0.42 1.00 0.42 0.53 0.37 1.12 2.99 1.00 2.99 3.74 1.07 3.79

Esenyurt STOREY E0 SD IS IS/IS0 Mr/Md Vr/Vd Esenyurt E0 SD IS IS/IS0 Mr/Md Vr/Vd

Original 1 0.42 1.00 0.42 0.53 0.97 1.25 Retrofit 0.85 1.00 0.85 1.06 1.19 2.50 Y 2 0.24 1.00 0.24 0.30 0.46 0.74 Y 0.88 1.00 0.88 1.10 1.22 2.70 3 0.40 1.00 0.40 0.50 0.75 1.00 1.54 1.00 1.54 1.93 1.61 3.82

Fig. 6. Mr/Md - Is/Iso and Vr/Vd - Is/Iso relationships for existing original buildings

Fig. 7. Mr/Md - Is/Iso and Vr/Vd - Is/Iso relationships for retrofitted buildings

CONCLUSIONS As a result of the comparison of the results of the three dimensional linear structural analysis and Seismic Index Method for 10 buildings (5 original and 5 retrofitted), the following conclusions were derived. There is an approximately linear relationship between ΣMr/ΣMd and IS/IS0 and between ΣVr/ΣVd and IS/IS0

(between capacity/design force ratios and structure index/judgment index ratios). The Is/Iso ratios of 0.4 or smaller indicate that further analysis is needed for seismic evaluation of the building, while Is/Iso ratios greater than 0.4 indicate that the building can be used with its existing seismic safety. Retrofitting, considering the Turkish Earthquake Resistant Design Code may result with significant overstrength. It should be noted that these results are for the five typical buildings investigated in this study. For more general conclusions, the number of investigated buildings needs to be increased.

REFERENCES

1. “Turkish Earthquake Resistant Design Code”, Ministry of Construction, Ankara, 1998 (in Turkish). 2. “Turkish Earthquake Resistant Design Code”, Ministry of Construction, Ankara, 1975 (in Turkish).

0.0

0.5

1.0

1.5

2.0

2.5

0 0.4 0.8 1.2

Is/Iso

Mr/M

d

Mr/Md : 0.70

Is/Iso : 0.4

0

1

2

3

4

5

6

0 0.4 0.8 1.2

Is / Iso

Vr

/ Vd

Vr / Vd : 0.70

Is / Iso : 0.40

0

5

10

15

20

25

0 1 2 3 4 5

Is/Iso

Mr/M

d

0

5

10

15

20

0 1 2 3 4 5

Is/Iso

Vr/V

d

3. “ATC-21. Rapid Visual Screening of Buildings for Potential Seismic Hazards: A Handbook, Applied Technology Council”, USA, 1988. 4. “FEMA 310. Handbook for the Seismic Evaluation of Buildings-A Prestandard, Federal Emergency Management Agency”, USA, 1998. 5. “Standard for Evaluation of Seismic Capacity of Existing Reinforced Concrete Buildings”, Japan Building Disaster Prevention Association, Tokyo, 1990. 6. Kaminosono, T., “Evaluation Method for Seismic Capacity of Existing Reinforced Concrete Buildings in Japan”, Proceedings of Int. Conf. on Earthquake Loss Estimation and Risk Reduction, Bucharest, Romania, 2002. 7. Ohkubo, M., “The Method for Evaluating Seismic Performance of Existing Reinforced Concrete Buildings”, Seminar in Structural Engineering, Dept. of AMES, University of California, San Diego, 1990. 8. Ilki, A., Boduroglu, H., Ozdemir, P., Baysan, F., Demir, C and Sirin, S., “Comparison of the results obtained by sismic index method and structural analysis for existing and retrofitted buildings”, Proceedings of 5th National Earthquake Engineering Conference, Istanbul, Turkey, (in Turkish), 2003. 9. Baysan, F.F., “Evaluation of the Seismic Safety of a Building with the Structural Analysis and Japan Seismic Index Method”, Graduation Project supervised by A. Ilki, Istanbul Technical University, Istanbul, Turkey, (in Turkish), 2002. 10. Hirosava, M., Sugano S., Kaminosono T., “Essentials of Current Evaluation and Retro Fitting for Existing Buildings in Japan”, IISEE, Building Research Institute, Tsukuba, Japan, TBIC JR 94-21, 1995. 11. SAP2000, Structural Analysis Software, Computer and Structures Inc., Berkeley, CA. 12. TS500, “Requirements for Design and Construction of Reinforced Concrete Structures”, Turkish Standard Institute, Ankara, (in Turkish), 2000.

towards a modified rapid screening procedure for medium...

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