1st International Conference on Analysis and …fportfolio.petra.ac.id/user_files/73-001/MDCMS-benjamin... · Web viewFor the performance evaluation, the drift will be obtained from

1st International Conference on Modern Design, Construction and Maintenance of Structures, 10-11 December 2007, Hanoi, Vietnam

Seismic Performance of Special Moment Resisting Frames Designed In Accordance to the Indonesian Concrete and Earthquake Codes.

B. Lumantarna, P. Pujisuryadi, M.C. Adinata, F.R. Doly (Civil Engineering Department Petra Christian University, Surabaya, Indonesia)

Abstract: The design provision for column reinforcement of a Special Moment Resisting Frames in the new Indonesian Concrete Code SNI 03-2847-2002, is adopted from ACI 318M-99. This new provision is less stringent than the previous code SNI 03-2847-1992. This study checks the seismic performance of Special Moment Resisting Frames designed in accordance to the new concrete code. Two symmetrical buildings, six and ten stories are considered and subjected to nonlinear static pushover and nonlinear time history analysis. The load pattern used in the nonlinear static pushover analysis is derived from an inverted triangular first mode, while the ground acceleration used in the nonlinear time history analysis is a spectrum consistent ground acceleration generated from El Centro 18 May 1940 North-South component in accordance to SNI 03-1726-2002. It is shown that due to 500 years return period earthquake some upper columns of the six story building develop plastic hinges although still in a very preliminary stage, with damage indices in the range of 0.02 to 0.04

Keywords: Seismic Performance; Special Moment Resisting Frames; Indonesian Concrete Code; Column design

1 IntroductionThe design provision for column reinforcement of a Special Moment Resisting Frames in the new Indonesian

Concrete Code SNI 03-2847-2002 [1] is adopted from ACI318M-99 [2], which is less stringent than the previous code SNI 03-2847-1992 [3]. In the new code, the nominal moment of the columns should satisfy the following condition:

(1)

In which:Mc = sum of moments at the center of the joint, corresponding to the nominal flexural strength of the columns

framing into that joint. Column flexural strength shall be calculated for the factored axial force, consistent with the direction of the lateral forces considered, resulting in lowest flexural strength.

Mg = Sum of moments at the center of the joint, corresponding to the nominal flexural strengths of the girders (including participating slab reinforcement) framing into that joint.

While in SNI 03-2847-1992 [3]:

(2)where:Mu,k = sum of required ultimate moment of columnsωd = dynamic magnification factor = 1.3Mkap, b = flexural moment capacity of beam The relation between the nominal strength (1) and the required ultimate moment (2) of the column is:

(3)

where k is the capacity reduction factor, while the capacity of the beam (4)

in which the overstrength factor.

__________________________

B. Lumantarna, ProfessorCorrespondence to B. Lumantarna; E-mail: [email protected]

Assuming that the capacity reduction factor, k, is 0.65 and the overstrength factor, , is 1.25, it can be shown that the column reinforcement required in accordance to the SNI 03-2847-2002 is 30 percent less than SNI 03-2847-1992 [4].

In this study the seismic performance of Special Moment Resisting Frames designed in accordance to the new concrete code is studied. Two symmetrical office buildings, six and ten stories are considered and subjected to nonlinear static pushover and nonlinear time history analysis. The load pattern used in the nonlinear static pushover analysis is derived from an inverted triangular first mode, while the ground acceleration used in the nonlinear time history analysis is a spectrum consistent artificial ground acceleration generated from El Centro 18 May 1940 North-South component in accordance to the design spectrum given in SNI 03-1726-2002 [5].

2 Performance CriteriaAsian Concrete Model Code [6] suggests three level performance criteria as shown in Figure 1. The buildings

objective are grouped into; basic objective such as offices, essential/hazardous objective such as hospitals, and safety critical objective such as nuclear power plant. In the basic objective group, the structure should satisfy the serviceability limit state if subjected to minor earthquake, the damage control limit state to moderate earthquake, and the safety limit state to severe earthquake.

An additional performance criteria related to the capacity design method is the so called strong column weak beam criteria resulting in a beam side sway mechanism as shown in Figure 2. It is expected that no plastic hinge should appear anywhere in the columns except at the base of the building.

Fig. 1 Performance level [6]Fig. 2 Beam side sway mechanism, strong column weak beam

For the performance evaluation, the drift will be obtained from the static nonlinear pushover analysis employing ETABS nonlinear [7] and from the nonlinear time history analysis employing Ruaomoko [8]. The damage indices will be obtained from the nonlinear time history analysis using the following criteria:

(5)

where: = ductility required = ultimate ductility.

3 Structures Considered and Analysis ResultFigures 3 and 4 show respectively the plan of the six and ten story building considered in this study. Columns

and beams sizes are shown in Table 1. This structure is designed as Special Moment Resisting Frames (SMRF) in accordance to the new Indonesian Concrete Code SNI 03-2847-2002 [1] and the old SNI 03-2847-1992 [3]. The buildings are assumed to be built on soft ground located in Zone 2 of the Indonesian Earthquake Code SNI.03-1726-2002 [5]. Buildings designed in accordance to SNI 03-2847-2002 are labelled as SMRF-6-02 and SMRF-10-02 for the six and ten story building respectively, while SMRF-6-92 and SMRF-10-92 respectively stand for six and ten story building designed in accordance to SNI 03-2847-1992. Table 2 shows comparison of typical column reinforcement. It can be seen that the old SNI 03-2847-1992 [3] requires much more reinforcement that the new SNI 03-2847-2002 [1], details can be seen in reference [4].

These buildings are then subjected to a nonlinear static pushover and time history analysis due to artificial ground acceleration with various return periods. The load pattern used in the nonlinear static pushover analysis is shown in Figure 5, while the artificial ground acceleration used in the nonlinear time history analysis is shown in Figure 6. This artificial ground acceleration is a spectrum consistent ground acceleration generated from El Centro 18 May 1940 North-South component (Figure 7) using RESMAT, a program developed at Petra Christian University [9]. The response spectra of the ground accelerations and the design spectrum are shown in Figure 8. The peak ground accelerations of various return periods for Zone 2 of Indonesian seismic map are shown in Figure 9 [10].

Fig. 3 Plan of the six story building (SMRF-6)Fig. 4 Plan of the ten story building (SMRF-10)

0

1

2

3

4

5

6

0 500 1000 1500

Load (kN)

Stor

y

(a) Six story building, SMRF-6

0

1

2

3

4

5

6

7

8

9

10

0 500 1000 1500 2000 2500

Load (kN)

Stor

y

(b) Ten story building, SMRF-10Fig. 5 Load patern for nonlinear static pushover analysis

El Centro 18 May 1940 North-South Component Modified

-0,3

-0,2

-0,1

0

0,1

0,2

0,3

0,4

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Waktu (detik)

Acc

eler

atio

n (g

)

Fig. 6 Artificial ground acceleration used in nonlinear time

history analysis

El Centro 18 May 1940 North-South Component

-0,3

-0,2

-0,1

0

0,1

0,2

0,3

0,4

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Time (detik)

Acc

eler

atio

n (g

)

Fig. 7 El Centro 18 May 1940 North-South component

Response Spectra El Centro 18 May 1940 North-South Componentand

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 1 2 3

Periode(T)

Acc

eler

atio

n (g

)

Fig. 8 Response spectra of the artificial ground acceleration,

El-Centro, and design spectrum

Peak Ground Acceleration Factor

0,343

0,54379

0,71204

0,86212

1

1,275

0,21635

0,117650,00

0,20

0,40

0,60

0,80

1,00

1,20

1,40

0 100 200 300 400 500 600 700 800 900 1000

Return Period (x, year)

PGA

Fac

tor

Fig. 9 Peak ground acceleration, 500 yr return period is

scalled to 1.0 g [10]

Tab.1 Beams and columns sizesDATA SMRF-6 SMRF-10

Number of floors   6   10 Floor plan   40 x 40 m2   64 x 64 m2

Floor to floor   3.5 m   3.5 mBeam   500 x 700 mm2   500 x 700 mm2

Column ( floor 1-3) 620 x 620 mm2 ( floor 1-4) 700 x 700 mm2

  ( floor 4-6) 570 x 570 mm2 ( floor 5-7) 600 x 600 mm2

      ( floor 8-10) 550 x 550 mm2

Floor thickness   120 mm   120 mm

Concrete grade (fc’)   25 MPa   25 MPaReinforcement   400 MPa   400 MPa

Stirrups   240 MPa   240 MPa

Table 2.: Comparison of column reinforcement six story building SMRF-6. level location interior column SMRF-6-02 interior column SMRF-6-92

    longitudinal stirrups longitudinal stirrups6 top 8 D 25 4 Ø 12 12 D 25 4 Ø 10  bottom 12 D 25 4 Ø 12 20 D 25 4 Ø 105 top/bottom 12 D 25 4 Ø 12 20 D 25 4 Ø 104 top/bottom 12 D 25 4 Ø 12 20 D 25 4 Ø 103 top/bottom 16 D 25 4 Ø 12 24 D 25 4 Ø 102 top 16 D 25 4 Ø 12 24 D 25 4 Ø 10  bottom 28 D 25 4 Ø 12 40 D 25 4 Ø 101 top 28 D 25 4 Ø 12 40 D 25 4 Ø 10  bottom 20 D 25 4 Ø 12 16 D 25 4 Ø 10

level location exterior column SMRF-6-02 exterior column SMRF-6-92    longitudinal stirrups longitudinal stirrups6 top 8 D 25 4 Ø 12 16 D 25 4 Ø 10  bottom 12 D 25 4 Ø 12 20 D 25 4 Ø 105 top/bottom 12 D 25 4 Ø 12 20 D 25 4 Ø 104 top/bottom 12 D 25 4 Ø 12 16 D 25 4 Ø 103 top/bottom 12 D 25 4 Ø 12 20 D 25 4 Ø 10 2 top/bottom 12 D 25 4 Ø 12 24 D 25 4 Ø 101 top 12 D 25 4 Ø 12 24 D 25 4 Ø 10  bottom 8 D 25 4 Ø 12 8 D 25 4 Ø 10

.

The pushover analysis on SMRF-6-02 shows plastic hinges appearing in some upper columns in the exterior frames due to 500 years return period earthquake (Figure 10), which is not the case with SMRF-6-92 (Figure 11),

El CentroArtificial

Design spectrum

SMRF-10-02, and SMRF10-92. The same phenomena are also detected in the nonlinear time history analysis as damage indices bigger than zero (Figure 12 and 13) although the locations are not the same with the plastic hinges shown in the pushover analysis. In Figure 12 and 13; numbers above beam lines are the damage indices, numbers below the beam lines are beam numbers, numbers on the right of column lines are damage indices, and numbers on the left are column numbers.

Fig. 10 Plastic hinges on columns in the exterior frame, SMRF-6-02, 500 yrs return period Fig. 11 Plastic hinges in exterior frame, SMRF-6-92, 500 yrs

return period

Fig. 12 Damage indices in the exterior frame, SMRF-6-02, 500 yrs return period

Fig. 13 Damage indices in exterior frame, SMRF-6-92, 500 yrs return period

Figures 14 and 15 show respectively typical results of the lateral displacement and drift of structures designed in accordance to SNI 03-2847-2002 compared to the one designed in accordance to SNI 03-2847-1992. Figure 15 shows that the lateral displacement and drift of SMRF-10-02 and SMRF-10-92 are practically the same, there is no plastic hinge appearing in the columns of both buildings. The performance matrices are shown in Figures 16 to 19. Figure 16 shows the performance matrix of SMRF-6, while Figure 17 is the performance matrix of SMRF-10 both using drift as the performance criteria. Figure 18 and 19 show respectively the performance matrices of SMRF-6 and SMRF-10 using individual member damage index as the performance criteria.

0

1

2

3

4

5

6

0 0,05 0,1 0,15 0,2

Displacement (m)

Stor

y

SMRF-6-02

SMRF-6-92

(a) Displacement of SMRF-6

0

1

2

3

4

5

6

0 0,005 0,01 0,015

Drift

Stor

y

SMRF-6-02

SMRF-6-92

(b) Drift of SMRF-6

Fig. 14 Displacement and Drift of SMRF-6, 500 yrs Retirn Period

(a) Displacement of SMRF-10 (b) Drift of SMRF-10

Fig. 15 Displacement and drift of SMRF-10, 500 yrs retirn period

Return period (yrs) 

Earthquake Performance Level

  Serviceability Damage Control Safety Limit State20 SMRF-6-02   0.153              

  SMRF-6-92   0.153              100 SMRF-6-02     0.473            

  SMRF--92     0.473            200 SMRF-6-02         0.652        

  SMRF-6-92         0.640        500 SMRF-6-02           0.950      

  SMRF-6-92           0.942      1000 SMRF-6-02             1.292    

  SMRF-6-92             1.270    Drift 0.5 1.0 2.0

Fig. 16 Performance matrix of SMRF-6, using drift as performance criteria

Return period (yrs)

Earthquake Performance Level

Serviceability Damage Control Safety Limit State20 SMRF-10-02   0,190              

  SMRF-10-92   0,187              100 SMRF-10-02     0,490            

  SMRF-10-92     0,470            200 SMRF-10-02         0,720        

  SMRF-10-92         0,716        500 SMRF-10-02           1,041    

  SMRF-10-92             1,021    1000 SMRF-10-02               1.446  

  SMRF-10-92               1.399  Drift 0.5 1.0 2.0

Fig. 17 Performance matrix of SMRF-10, using drift as performance criteria

Return period (yrs) 

Earthquake Performance Level

Serviceability Damage Control Safety Limit State500 SMRF-6-02           0.515    

  SMRF-6-92             0.553    1000 SMRF-6-02               0.685  

  SMRF-6-92               0.694  Maximum DI 0.1-0.25 0.25-0.4 0.4-1.0

Fig. 18 Performance matrix of SMRF-6, using maximum damage index as performance criteria

Return period (yrs) 

Earthquake Performance Level

Serviceability Damage Control Safety Limit State500 SMRF-10-02         0.308  

  SMRF-10-92         0.306    1000 SMRF-10-02           0.415  

  SMRF-10-92           0.400  Maximum DI 0.1-0.25 0.25-0.4 0.4-1.0

Fig. 19 Performance matrix of SMRF-10, using maximum damage index as performance criteria

4 Discussions and ConclusionsThe design provision for column reinforcement of a Special Moment Resisting Frames in the new Indonesian

Concrete Code SNI 03-2847-2002 is less stringent than the previous code SNI 03-2847-1992. A study of the seismic performance of Special Moment Resisting Frames designed in accordance to the new concrete code (SMRF-6-02 and SMRF-10-02) and the old code (SMRF-6-92 and SMRF-10-92) shows that both passed the performance evaluation as shown in the performance matrices (Figures 16 to 19). However a very important finding needs to be noted in this study. It is shown that due to 500 years return period earthquake some upper columns of the six story building designed in accordance to SNI 03-2847-2002 (Figures 10 and 12), while the ones designed in accordance to SNI 03-2847-1992 (Figures 11 and 13) do not show the same phenomena. The formation of these plastic hinges although still in a very preliminary stage, with damage indices in the range of 0.02 to 0.04, raise some concern that an unsafe failure mechanism could developed in special moment resisting frames designed in accordance to the new code SNI 03-2847-2002.

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Nasional, Jakarta, 2002 [2]. Building Code Requirements for Structural Concrete (ACI 318M-99) and Commentary(ACI 318RM-99) [M],

ACI Committee 318, 1999.[3]. Tata Cara Perhitungan Struktur Beton untuk Bangunan Gedung SNI 03-2847-1992[M], Badan Standarisasi

Nasional, Jakarta, 1992. [4]. Adinata, M.K., Dolly, F.R., Perbandingan kinerja struktur sistem rangka pemikul momen khusus sesuai SNI 03-

2847-2002 dan struktur daktail penuh sesuai SNI 03-2847-1992 pada wilayah gempa 2 SNI 03-1726-2002 [M], undergraduate theses, Petra Christian University, Surabaya, 2006.

[5]. Tata Cara Perencanaan Ketahanan Gempa untuk bangunan Gedung, SNI 03-1726-2002 [M], Badan Standarisasi Nasional, Jakarta, 2002.

[6]. Asian Concrete Model Code, Level 1 & 2 Documents, Second Draft [M], International Comittee on Concrete Model Code, Japan, 1999

[7]. Habibullah, A., ETABS, Three Dimensional Analysis and Design of Building Systems [M], Computer and Structures, Inc., Berkeley, California, USA, 1998

[8]. Carr, Anthol J. Ruaumoko, 3-Dimensional Version. University of Canterbury [M], April 6, 2001. [9]. Lumantarna, B., Lukito, M., Resmat, Sebuah Program Interaktif untuk Menghasilkan Riwayat Waktu Gempa

dengan Spektrum Tertentu [C], Proc. HAKI Conference 1997, Jakarta, Indonesia, 13-14 August 1997: 128-135[10]. Susila, I.G.M., Seismic Microzonation and Site Spesific Respons Analysis for Denpasar [M], Geotechnical

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