seismic performance assessment and …girgink/conference_papers/6...c = co k s i (2) where c o is...

Institute for the Protection and Security of the Citizen European Laboratory for Structural Assessment (ELSA) I-21020 Ispra – Italy

SPEAR (Seismic Performance Assessment and Rehabilitation of Existing Buildings)

INTERNATIONAL WORKSHOP

An event to honour the memory of Prof. Jean Donea

Ispra, 4-5 April 2005

Proceedings

Editors: Michael Fardis, University of Patras

Paolo Negro, Joint Research Centre

2005 EUR 21768 EN

ii

LEGAL NOTICE

Neither the European Commission nor any person acting on behalf of the Commission is responsible for

the use which might be made of the following information.

A great deal of additional information on the European Union is available on the Internet. It can be accessed through the Europa server

(http://europa.eu.int)

Luxembourg: Office for Official Publication of the European Communities ISBN 92-894-9923-0

© European Communities, 2005 Reproduction is authorised provided the source is acknowledged

Printed in Italy

SPEAR Workshop – An event to honour the memory of Jean Donea – Ispra, 4-5 April 2005

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TABLE OF CONTENTS

Table of Contents………………………………………………………………………...….iii Acknowledgements…………………………………………………………………...……..iv INTRODUCTION M. Fardis, P. Negro………………………………………………………………………….v List of Participants………………………………………………………………………….vii PIONEERING EXPERIMENTAL ACTIVITY IN STRUCTURAL DYNAMICS – A PERSONAL ODYSSEY R. Severn………………………………………………………………………………...…...1 SEISMIC SAFETY SCREENING METHODS P. Ozdemir………………………………………………………………………………….19 REINFORCED CONCRETE BUILDING DAMAGES IN THE 2004 NIIGATA KEN CHUETSU EARTHQUAKES, JAPAN M. Inukai, M. Iiba…………………………………………………………………………..31 SEISMIC PERFORMANCE OF A BASE-ISOLATED BUILDING IN THE 2004 NIIGATA KEN CHUETSU EARTHQUAKES M. Tamari, M. Inukai……………………………………………………………………….43 SIMPLIFIED MODELLING ACCOUNTING FOR SHEAR AND TORSION J. Mazars, P. Kotronis, F. Ragueneau...………………………………………………........51 A CODE APPROACH FOR DEFORMATION-BASED SEISMIC PERFORMANCE ASSESSMENT OF REINFORCED CONCRETE BUILDINGS M. N. Aydinoglu.……………………………………………………………………………65 PRACTICAL GUIDELINES FOR PERFORMING REINFORCED CONCRETE STRUCTURE PUSHOVER ANALYSIS USING COMMERCIAL FINITE ELEMENT SOFTWARE W.T. Yeung.……………………………………………………………………………………………75 QUALITY OF CONSTRUCTION ASPECTS IN SEISMIC FRAGILITY ASSESSMENT S. Dimova, P. Negro, A. Pinto………………………………………………………………………87 SEISMIC FRAGILITY ANALYSIS OF RC STRUCTURES: USE OF RESPONSE SURFACE FOR A REALISTIC APPLICATION P. Franchin, A. Lupoi, P.E. Pinto, M. Ij. Schotanus…………………………………………….99 ULTIMATE STRENGTH AND FAILURE PROPERTIES OF FULL-SCALE WALLS OF EXISTING RC BUILDINGS H. Kato, K. Kusunoki, T. Mukai, M. Teshigawara, Y. Asano…………………………………111 SHAKE TABLE TESTS OF A 3-STOREY IRREGULAR RC STRUCTURE DESIGNED FOR GRAVITY LOADS E. Coelho, A. Campos Costa, P. Candeias, M. J. Falcao Silva, L. Mendes………………...123 FULL-SCALE PsD TESTING OF THE TORSIONALLY UNBALANCED SPEAR STRUCTURE IN THE ‘AS-BUILT’ AND RETROFIITTED CONFIGURATIONS E. Mola, P. Negro…………………………………………………………………………………..139


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FULL-SCALE BIDIRECTIONAL PsD TESTING OF THE TORSIONALLY UNBALANCE SPEAR STRUCTURE: METHOD, ALGORITHM AND EXPERIMENTAL SET-UP F. J. Molina, Ph. Buchet, G.E. Magonette, O. Hubert, P. Negro…………………………….155 PRE- AND POST-TEST MATHEMATICAL MODELLING OF THE SPEAR BUILDING P. Fajfar, M. Dolšek, D. Marušic, A. Stratan ANALYTICAL ASSESSMENT OF A 3D FULL SCALE RC BUILDING TEST S.-H.Jeong, A.S. Elnashai………………………………………………………………………….189 POST-TEST NONLINEAR ANALYSIS OF THE SPEAR TEST BUILDING N. Ile, J.M. Reiynouard…………………………………………………………………………….205 CAPACITY-BASED EQUIVALENT LINEAR MODELLING OF THE SPEAR TEST FRAME M.S. Gunay, H. Sucuoglu…………………………………………………………………………..217 SEISMIC RETROFITTING TECHNIQUES FOR CONCRETE BUILDINGS M.N. Fardis, D. Biskinis, A. Kosmopoulos, S. Bousias, A-L. Spathis………………………..229 DESIGN OF THE FRP RETROFIT OF THE SPEAR STRUCTURE E. Cosenza, M. Di Ludovico, G. Manfredi, A. Prota…………………………………………..241 SEISMIC ASSESSMENT AND RETROFITTING OF A S SHAPE BUILDING WITH EXPANSION JOINTS A. Plumier, V. Denoël, L. Sanchez, C. Doneux, V. Warnotte, W. Van Alboom…………….253 RETROFITTING OF A 1960 BUILDING USING EC8 PART 3 C.Z. Chrysostomou………………………………………………………………………………….269 BUILDING VULNERABILITY REDUCTION BY EXISTING TECHNIQUES AND NEAR FAULT EFFECTS M.H. Boduroglu, E. Orakdöğen, K. Girgin……………………………………………………..281 SEISMIC RETROFIT STRATEGY FOR UNDER-DESIGNED RC FRAME SYSTEMS USING FRP COMPOSITES G.M.Calvi, S. Pampanin, A. Pavese, D. Bolognini…………………………………………….293

ACKNOWLEDGEMENTS

The SPEAR (Seismic Performance Assessment and Rehabilitation) research project

was funded by the European Commission under the Growth Programme (1998-2002), contract N. G6RD-CT2001-00525 (including Amendment No 1).

The SPEAR International Workshop was held at the JRC, with the logistical sup-port of the JRC Public Relations Services.

The ELSA Laboratory, in the person of the Unit Head, Professor Michel Geradin, hosted the event.

Ms. Elena Mola took charge of the technical organization of the SPEAR Workshop. Ms. Elena Mola took charge of assembling and sending to print the present book of

Proceedings.


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LIST OF PARTICIPANTS

Ayhan ALTINYOLLAR, ELSA Laboratory, Joint Research Centre, Ispra, Italy Gustavo AYALA, UNAM, Mexico City, Mexico M. Nuray AYDINOGLU, Bogazici University, Istanbul, Turkey Mehmet Hasan BODUROGLU, Technical University of Istanbul, Istanbul, Turkey Gianpiero BORZILLO, Regione Lazio, Protezione Civile, Roma, Italy Eric BUZAUD, Délégation Générale pour l'Armement, Centre d'Etudes de Gramat,

Gramat, France Gian Michele CALVI, Universita’di Pavia, Pavia, Italy Paulo CANDEIAS, LNEC, Lisbon, Portugal Nicola CATERINO, Universita’degli Studi di Napoli ‘Federico II’, Napoli, Italy Christis CHRYSOSTOMOU, HTI-Nicosia, Nicosia, Cyprus Ema COELHO, LNEC, Lisbon, Portugal Marco DI LUDOVICO, Universita’degli Studi di Napoli ‘Federico II’, Napoli, Italy Silvia DIMOVA, ELSA Laboratory, Joint Research Centre, Ispra, Italy Matjaž DOLŠEK, University of Ljubljana, Ljubljana, Slovenia Amr ELNASHAI, University of Illinois, Urbana-Champaign, IL, United States Peter FAJFAR, University of Ljubljana, Ljubljana, Slovenia Michael FARDIS, University of Patras, Patras, Greece Paolo FRANCHIN, Universita’ di Roma ‘La Sapienza’, Roma, Italy Michel GERADIN, ELSA Laboratory, Joint Research Centre, Ispra, Italy Konuralp GIRGIN, Technical University of Istanbul, Istanbul, Turkey Nicolas Ioan ILE, INSA-Lyon, Lyon, France Mizuo INUKAI, National Institute for Land and Construction Management, Ministry

of Land, Infrastructure Management, Tsukuba, Japan Alessio LUPOI, Universita’ di Roma ‘La Sapienza’, Roma, Italy Georges MAGONETTE, ELSA Laboratory, Joint Research Centre, Ispra, Italy Damjan MARUŠIĆ, University of Ljubljana, Ljubljana, Slovenia Jacky MAZARS, INPG-Grenoble, Grenoble, France Elena MOLA, ELSA Laboratory, Joint Research Centre, Ispra, Italy Javier MOLINA, ELSA Laboratory, Joint Research Centre, Ispra, Italy Khalid MOSALAM, University of California, Berkeley Paolo NEGRO, ELSA Laboratory, Joint Research Centre, Ispra, Italy Engin ORAKDOGEN, Technical University of Istanbul, Istanbul, Turkey


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Güney ÖZCEBE, Middle East Technical University, Ankara, Turkey Pinar OZDEMIR CAGLAYAN, Technical University of Istanbul, Istanbul, Turkey Artur PINTO, ELSA Laboratory, Joint Research Centre, Ispra, Italy Paolo PINTO, Universita’ di Roma ‘La Sapienza’, Roma, Italy André PLUMIER , Université de Liège, Liège, Belgium Jean Marie REYNOUARD, INSA-Lyon, Lyon, France Roy SEVERN, University of Bristol, Bristol, United Kingdom Haluk SUCUOGLU, Middle East Technical University, Ankara, Turkey Masatoshi TAMARI, Mitsubishi Jisho Sekkei Inc., Tokyo, Japan Fabio TAUCER, ELSA Laboratory, Joint Research Centre, Ispra, Italy

1

Building Vulnerability Reduction by Existing Techniques and Near Fault Effects

M.H.Boduroglu1, E.Orakdöğen1, K.Girgin1

1.Istanbul Technical University, Civil Engineering Department, Maslak, Istanbul, Turkey

ABSTRACT: The seismic evaluation and the retrofit design of existing buildings due to seismic loads is a very important problem of most of the earthquake prone countries. In this paper, existing four and seven story RC buildings are evaluated according to the 1998 Earthquake Code of Turkey and found to be weak and strengthened by adding shear walls and/or jacketing some columns, then results have been tested using ATC–40 guidelines and the capacity spectrum method. Moreover, in order to see the effect of near fault earthquakes, a nonlinear time history analysis has been carried out for seven story building using five ground motions of recent earthquakes in Turkey. As a conclu-sion, the buildings strengthened according to the code are over-designed and the near fault effects have to be introduced to the existing Turkish Earthquake Code.

1 INTRODUCTION

Earthquake prone countries face the problem of evaluating and strengthening of large number of existing buildings. The problem is especially important for reinforced concrete buildings which have been built during the last sixty years according to the existing codes of their times. Most of these early codes have considered the seismic loads as some percentage of the total live and dead loads of the building. A linear and approximate method of analysis has been used under this type of seismic load. Experiences from the past earthquakes have shown that large earthquakes can severely damage buildings causing inelastic behavior that dissipates energy. The last Turkish Earthquake Code has been in effect since 1998. The previous one had been in effect since 1975. Therefore most buildings designed according to 1975 and the earlier codes need to be evaluated and strengthened. The question is at what level they have to be strengthened. In this paper, the results of an investigation on two existing RC buildings are presented.

2 COMPARISON OF 1975 AND 1998 TURKISH EARTHQUAKE CODES

In the 1975 Turkish Earthquake Code (TEC-1975), the equivalent seismic load is evaluated using the following formula


2

F=CW (1)

in which W is the total weight and C is the seismic coefficient obtained from

C = Co K S I (2)

where Co is seismic coefficient of the region, K is the structural type coefficient, S is the spectral coefficient evaluated by S = 1 / (0.8 + T – To ), and I is the importance coefficient taken as 1.0 for the usual buildings. In the 1998 Turkish Earthquake Code (TEC-1998) however, the equivalent seismic load or the base shear is calculated using the following formula,

Vt = W Ao I S ( T ) / Ra ( T1 ) ≥ 0.10 Ao I W (3)

where Ao is the effective ground acceleration for the seismic zone, S ( T ) is the spectral coefficient given by

S( T ) = 1+1.5 T/TA ( 0 ≤ T ≤ TA ) (4)

S( T ) = 2.5 ( TA< T ≤ TB ) (5)

S( T ) = 2.5 (TB/T)0.8

(T > TB ) (6)

in which TA and TB are corner periods of the spectrum related to local soil conditions chosen as 0.15 sec and 0.60 sec respectively, Ra ( T1 ) is the load reduction factor defined by

Ra(T) = 1.5 + ( R-1.5)T/TA ( 0 ≤ T ≤ TA ) (7)

Ra(T) = R (T > TA ) (8)

in which R is the structural behavior constant showing the ductility property of the structure and is usually taken as 4 for the existing structure. 3 EVALUATION OF FOUR STORY EXISTING RC BUILDING

In this chapter, firstly, push-over analysis of a four-story existing RC building, Kesim (2004), designed according to the 1975 Turkish Earthquake Code ( TEC-1975), is per-formed for obtaining the push-over or capacity curve and performance point according


3

to ATC-40 (1996). The push-over analyze is performed by SAP2000 (2004) computer program. Typical ground and normal story plans are given in Figure 1, total story weights considered in the equivalent lateral load calculations, are given in Table 1, equivalent lateral loads of the existing building according to the 1975 Turkish Earth-quake Code are given in Table 2 and the parameters considered in the analysis are given as in the following.

The building has a ground story in 3.1 m height and three normal stories in 2.85 m heights each one and plan dimensions of the building are 12.20 m x 11.20 m. The coef-ficients for the equivalent lateral load calculations are taken as effective ground accel-eration, (Ao) = 0.40, intensity factor of design earthquake, E = 1.0, building importance factor, (I) = 1.0, Soil class = Z4, characteristic spectral periods, TA = 0.20 sec, TB = 0.90 sec, fundamental periods of the building, Tx= 0.602 and Ty= 0.531 sec and struc-tural behavior constant, (R) = 4 for existing and the strengthened buildings.

Figure 1. Typical story plan of the existing building

Table 1. Total story weights

Story #

Weight due to the dead loads

(kN)

Live load reduction factor (n)

Weight due to the live loads (Wq)

(kN)

Total story weight (Wi = Wg+ nWq)

(kN) 3 1146.55 0.3 240.91 1218.83 2 1418.24 0.3 293.62 1506.33

1 1465.75 0.3 293.62 1553.83

G 1537.67 0.3 293.62 1625.76 Total weight of the building (W3+ W2 +W1 +WG) 5904.75


4

Table 2. Equivalent Lateral Loads for existing building

Story # Equivalent Lateral Loads Both Directions (TEC-1975) (kN)

3 200.87 2 187.52

1 130.79

Ground 71.30

The push-over analysis for the equivalent lateral loads according to the TEC-1975 could not be completed due to the insufficient longitudinal reinforcements of the col-umns. It is concluded that the building is under-designed according to the TEC-1975 and it needs to be strengthened. 3.1. Strengthening of the existing building

The existing building is strengthened with five RC shear walls. Three of them are placed in the direction “X” and two of them are placed in the direction “Y”. The RC shear wall locations are chosen as to be the torsional effects are minimal. Shear walls are placed also between the two existing neighboring columns and the columns are jacketed. Moreover, new footings are designed for the shear walls. The typical story plan of the strengthened building and the shear wall locations are shown in Figure 2. Fundamental periods of the strengthened building in the directions of “X” and “Y” are 0.3035 sec and 0.2542 sec, respectively and the structural behavior constant is taken as R=4 for both directions. Equivalent Lateral Loads considered in analysis and design, are taken from the TEC-1998. The total storey weights and the Equivalent Lateral Loads calculated according to the TEC-1998 are given in Table 3 and Table 4.

Figure 2. Typical story plan of the strengthened building and shear wall locations


5

Table 3. Total story weights

Story # Total dead load g (kN)

Total Live Load q (kN)

Total story weight (kN)

3 1187.13 240.91 1259.4 2 1548.6 293.62 1636.69 1 1585.05 293.62 1673.13

Ground 1661.03 293.62 1749.12

Table 4. Equivalent lateral loads according to the TEC-1998

Story # Story lateral forces ( Directions “X” and “Y”) (kN)

3 521.6 2 511.9 1 353.5

Ground 192.8 Total Base Shear 1579.8

3.2. Base shear capacities of the strengthened building

Push-over analyses of the strengthened building are performed by SAP2000 and capac-ity curves for the directions “X” and “Y”, are obtained. Base shear capacities and the corresponding top story displacements in the directions “X” and “Y” are Vx=3372.26 kN, dx=0.0335 m and Vy=2938 kN, dy=0.0423 m. It is seen from the pushover results that base shear capacities of the strengthened build-ing are greater than the base shears taken from the TEC-1998 in both directions.

3.3. Determination of performance points of the strengthened building

In this paper, capacity spectrum method given in ATC-40, is utilized for obtaining the performance points. Thus, capacity curves are transformed into capacity spectrum curves in spectral acceleration-spectral displacement format and then reduced response spectrum curves are drawn by using the formulas given in ATC-40. Effective damping ratios are found as 8.3 % for direction “X” and 11.6 % for direction “Y”. The corre-sponding reduction coefficients are calculated as SRA=0.8369, SRV=0.8754 and SRA=0.7279, SRV=0.7909 for the directions “X” and “Y”, respectively. Finally, per-formance point coordinates are obtained by intersecting the capacity spectrum curves and reduced response spectrum curves as Sap=0.565, Sdp=0.0143 for direction “X” and Sap=0.559, Sdp=0.0120 for direction “Y”.

Capacity spectrum curves, response spectrum curves with 5 % damping and re-duced response spectrum curves in directions “X” and “Y” are shown in Figure 3 and Figure 4, respectively.


6

Figure 3. Performance point in direction “X”

Figure 4. Performance point in direction “Y” According to the obtained spectral displacements, strengthened building is found to

be in collapse prevention range for the design earthquake in both directions. 4 EVALUATION OF SEVEN STORY EXISTING RC BUILDING In the analysis of the seven story building, Ayan (2003), the base shear is calculated as 14% and 17 % of the weight in the “X” and “Y” directions, respectively. For different load combinations, the story drifts calculated according to the TEC-1998 are given in Tables 5 and 6. Most of these values exceed the code limited value of 0.0035 in the di-rection “X” and also the ultimate strengths of some columns are being exceeded.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0.00

00

0.00

35

0.00

74

0.01

14

0.01

54

0.01

93

0.02

33

0.02

72

0.03

10

0.03

45

0.03

81

0.04

17

0.04

53

0.04

88

0.05

24

0.05

60

SPECTRAL DISPLACEMENT (Sd)

(Sa)

PERFORMANCE POINT

5% DAMPING

11.6% DAMPING

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0.00

00

0.00

35

0.00

74

0.01

14

0.01

54

0.01

93

0.02

33

0.02

72

0.03

10

0.03

45

0.03

81

0.04

17

0.04

53

0.04

88

0.05

24

0.05

60


(Sa)

PERFORMANCE POINT

5% DAMPING

11.6% DAMPING

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0.00

00

0.00

31

0.00

63

0.00

94

0.01

25

0.01

56

0.01

88

0.02

19

0.02

53

0.02

92

0.03

31

0.03

70

0.04

09

0.04

49

0.04

88

0.05

27


(Sa)

PERFORMANCE POINT

5% DAMPING

8.3% DAMPING

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0.00

00

0.00

31

0.00

63

0.00

94

0.01

25

0.01

56

0.01

88

0.02

19

0.02

53

0.02

92

0.03

31

0.03

70

0.04

09

0.04

49

0.04

88

0.05

27


(Sa)

PERFORMANCE POINT

5% DAMPING

8.3% DAMPING

PERFORMANCE POINT

5% DAMPING

8.3% DAMPING


7

Therefore the building needs to be strengthened. Typical story plan and RC shear wall locations is shown in Figure 5.

Table 5. Storey dirfts in the “X” direction for the existing building

Relative story displacements (x10-3)

Stories Loading 1 2 3 4 5 6 7

1.4DL+1.6LL+EX 3.42 5.44 4.31 3.61 3.89 3.47 2.42 1.4DL+1.6LL-EX 3.42 5.44 4.31 3.61 3.89 3.47 2.42

0.9DL + EX 3.42 5.44 4.31 3.61 3.89 3.47 2.42 0.9DL – EX 3.42 5.44 4.31 3.61 3.89 3.47 2.42

Table 6. Storey dirfts in the “Y” direction for the existing building

Relative story displacements (x10-3)

Stories Loading 1 2 3 4 5 6 7

1.4DL+1.6LL+EY 1.95 3.02 2.81 2.56 2.49 1.96 1.30 1.4DL+1.6LL-EY 1.95 3.02 2.81 2.56 2.49 1.96 1.30

0.9DL + EY 1.95 3.02 2.81 2.56 2.49 1.96 1.30 0.9DL – EY 1.95 3.02 2.81 2.56 2.49 1.96 1.30

Figure 5. Typical story plan and shear wall locations of the 7 story strengthened building

4.1. Nonlinear analyses of the existing and strengthened buildings 4.1.1. Existing building Using the basic procedure of ATC-40, a static pushover analysis is performed on the existing structure utilizing the SAP 2000 software different load patterns are applied. These are the loading distributions with respect to the first mode, unit load, triangular


8

load, and unit acceleration load. Capacity spectrum method yields no performance point for the existing structure as expected.

4.1.2. Strengthened building For the strengthened building shown in Figure 5, pushover analysis is performed with similar load distributions. Modified capacity curves are shown in Figure 6 in direction “X” for different loadings. Since the structure is being strengthened using the TEC-1998, it might be seen as if it were over-designed. The building has a factor of safety between 2.70 and 3.36 for the base shear. For testing the validity of the 2D model, another pushover analysis is carried out using 3D model. The results are shown in Figure 7 and Figure 8 for a unit load and triangular load distributions. It is shown from the analyses that approximations are acceptable. Comparison of capacity curves using 2D and 3D models is shown in Figure 9 Performance study revealed that the building as a whole has an immediate occupancy level but having two columns with life safety level.

Figure 6. Modified pushover curves for the strengthened building in direction “X”

Figure 7. Modified pushover curves for the strengthened 2-D model


9

Figure 8. Comparison of capacity curves using 2D and 3D models

4.2. Nonlinear time history analysis of the strengthened building A nonlinear time history analysis is carried out to determine the effectiveness of the traditional code basis and the static pushover analysis results and to study the effect of near field earthquakes. For the nonlinear analysis, SAP 2000 is utilized with the Wilson -θ numerical integration method. Five recent earthquake records are used given in Table 7. For the soil classes B and C the average shear wave velocities are about 360 - 750 m/sec and 180 – 360 m/sec, respectively.

Table 7. Properties of the earthquake records

Earthquake Date Record

S.C. M.A. D.F. T.S. A.D.

Erzincan 1992 Erzincan (EW) C 486 2 0.005 0 – 20

Kocaeli 1999 Duzce (EW) C 353 12.7 0.01 0 – 25

Kocaeli 1999 Sakarya (EW) B 369 3.1 0.01 30 –

55

Duzce 1999 Duzce (EW) C 525 8.2 0.005 0 – 25

S.C : Soil Class, M.A. : Maximum Acceleration (cm/sec2), D.F. : Distance to Fault (km), T.S. : Time Step (sec), A.D. : Applied Duration (sec)


10

4.3. Nonlinear analysis of the strengthened 7 story building In the first analysis these record have been scaled down to give a maximum ground acceleration of 0.30g. For the strengthened building three scaled down acceleration records are used. The results obtained are shown in Table 8.

Table 8. Nonlinear analysis with scaled down acceleration records Kocaeli –

Duzce Duzce – Duzce Duzce - Bolu

Max. Base Shear ( 10 kN) 1563 1177 1325 Max. Roof Displacement(cm) 4.265 3.210 3.785

Max. Interstory Drift 0,00268 0.00207 0.00227 The three earthquakes give different base shears but all within the capacity curves.

The maximum total drift for immediate occupancy requires a value of 0.01. The interstory drift values are less than this value of 0.01. Therefore the building performance is at immediate occupancy level for all three earthquakes.

4.4. Nonlinear analysis for near fault effects on strengthened building Five earthquake acceleration records are used to study the near fault effects for the nonlinear analysis of the strengthened building. The results obtained are summarized in Table 9. The maximum base shear and the maximum roof displacement occur for the acceleration record of Bolu Earthquake with the maximum acceleration value among the five records. The maximum story displacements due to five records are given in Table 9 and the plastic hinge developments due to these earthquakes are summarized in Table 10.

Table 9. The maximum base shear and the maximum roof displacements Earthquake Record

Max. Base Shear (10KN)

Max. Roof Displacement (cm)

Max. Interstory Drift

Erzincan 2105 5.695 0.00359 Kocaeli – Duzce 1834 5.129 0.00320 Kocaeli – Sakarya 1339 3.153 0.00190 Duzce – Duzce 1937 5.858 0.00366 Duzce – Bolu 2789 11.050 0.00774

The interstory drifts due to both the scaled down and normal records of four

earthquakes are given in Figure 9. The Bolu record of Duzce Earthquake (Duzce –


11

Bolu) gives the maximum interstory drifts. This is mainly due to the impulsive character of the earthquake.

Figure 9. Story displacements from the nonlinear analysis for near fault effects

Table 10. Plastic Hinge Developments due to Near Field Earthquakes

Earthquake Explanation

Erzincan One shear wall up to second floor and two shear walls in the first floor

Kocaeli – Duzce All three shear walls in the first floor

Kocaeli – Sakarya

No plastic deformation

Duzce – Duzce Same as the first case above

Duzce -Bolu One shear wall up to third floor, one shear wall up to second floor and one shear wall in the first floor

5 CONCLUSIONS

Evaluation and strengthening of existing RC buildings present a challenging work because TEC-1998 states that this work has to be carried out according to this code. In order to find the deficiencies and difficulties arises from the code requirements, a study is performed on four and seven storey existing RC buildings making use of the ATC-40 approach. The results show that the 1998 Earthquake Code gives a conservative results when it is checked against the static pushover study. A nonlinear time domain analysis is also carried out for the strengthened seven story building for five local earthquakes. The results show that for the scaled down records the performance of the


12

scaled down buildings are at immediate occupancy. When the original records of the earthquakes are used to see the near fault effects, the interstory drifts for one earthquake of impulsive character are found to be causing more plastic hinge developments in the strengthened building. It would be very necessary to add a section to the current code about the near fault effects, since very many towns are along the Northern and Eastern Anatolian Faults and also in the western part of Turkey.

6 ACKNOWLEDGEMENT

The authors gratefully thank to Prof. Melike Altan and Prof. Metin Aydoğan of Istanbul Technical University for providing some of the numerical data.

7 REFERENCES

ATC-40, (1996), Seismic Evaluation and Retrofit of Concrete Buildings, ATC, California, USA.

Ayan, A.K., (2003), Performance Assessment of a Reinforced Concrete Building with Nonlinear Static and Dynamic Analysis, M.S. Thesis, Istanbul Technical University, Istanbul, Turkey, (in Turkish).

Kesim, B., (2004), Performance Assessment of a Reinforced Concrete Building with Static Pushover Analysis, M.S. Thesis, Istanbul Technical university, Istanbul, Turkey, (in Turkish).

Turkey Earthquake Code, TEC-1998 (1998), Ministry of Construction, Ankara, (in Turkish).

SAP2000 (2004), Structural Analysis Software, Computers and Structures Inc., Berkeley, CA, USA.

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