International Conference on Earthquake Engineering and Disaster Mitigation 2008
EVALUATION OF COLUMS’ FLEXURAL STRENGTH OF SPECIAL
MOMENT RESISTING FRAME IN ACCORDANCE TO THE
INDONESIAN CONCRETE AND EARTHQUAKE CODES
Pamuda Pudjisuryadi1 and Benjamin Lumantarna1
1 Department
of Civil Engineering, PETRA Christian University, Surabaya, Indonesia
Email: pamuda@petra.ac.id and bluman@petra.ac.id
ABSTRACT: To ensure “strong column weak beam” in Special Moment Resisting Frame System (SMRFS),
SNI 03-2847-2002 requires that the nominal flexural strength of columns shall be more than 6/5 times the
nominal flexural strength of the beams. This over strength factor is much more less than what is stipulated in
the previous code. In this study the performace of two building, six and ten stories with three bays located at
zone 2 and 6 on Indonesian seismic map is evaluated. The avaluation is done using the nonlinear static
pushover analysis and dynamic nonlinear time history. The load patern used in the nonlinear static pushover
analysis is based on the first mode, while for the dynamic nonlinear time history a spectrum consistent
artificial earthquakes with a 200, 500, and 1000 years return period are used. It is shown that for buildings in
zone 6, plastic hinges appears when the structures are subjected to 200 years return period earthquake, while
in zone 2, it only appears due to 1000 years return period.
Keywords : Special Moment Resisting Frame System, flexural strength of columns
1.
INTRODUCTION
In capacity design of a Special Moment Resisting Frame (SMRF), “strong column weak beam”
concept is used to ensure no plastic hinges will be developed in columns during severe earthquake,
resulting in a safe failure mechanism called the “beam side sway mechanism”. This concept is
adopted in Indonesian new concrete code, the SNI 03-2847-2002 (Badan Standarisasi Nasional,
2002). A value of 6/5 is set as minimum requirement of the ratio of total flexural strengh of the
columns with respect to that of the beams, as follows :
∑Mc ≥ (6/5)∑Mg
(1)
∑Mc is the total nominal flexural strength of columns, while ∑Mg is the total nominal flexural
strength of beams. In the previous code, the SNI 03-2847-1992 (Departemen Pekerjaan Umum,
1992), this ratio is derived from “strain hardening” of material and “dynamic magnification
factor”, a factor represents the shifting of structure behavior when plastic hinges are developed.
The ratio from SNI 03-2847-1992 is much larger than 6/5, this raises some concerns of the seismic
performance of structures designed by using the SNI 03-2847-2002.
2.
STRUCTURES CONSIDERED
In this study, two symmetrical six and ten story buildings are designed by SNI 03-2847-1992 and
SNI 03-2847-2002. The structures are assumed to be built on soft ground in Zones 2 and 6 of
Indonesian Seismic Map according to Indonesian Earthquake Code, SNI 03-1726-2002. For
simplicity, each building will be given an identification label. Example of the typical identification
label is SRPMK-6-2, where SRPMK stands for Special Moment Resisting Frame, the following
numbers are meant for number of stories (6 stories), and Seismic Zone (Zone 2), respectively. The
building plan, and building elevation view are shown in Figures 1 and 2 respectively. Other
technical data such as properties of concrete and steel reinforcement used, element dimensions can
be seen in Tables 1, 2, and 3.
International Conference on Earthquake Engineering and Disaster Mitigation 2008
Figure 1. Typical building plan for 6 and 10 story buildings.
(a) 6 Story Building
(b) 10 Story Building
Figure 2. Typical elevation view of the buildings
Table 1. General data used for design
Floor to floor height
3.5 m
Slab thickness
120 mm
Compressive strength of concrete
30 MPa
Yield strength of longitudinal bars
400 MPa
Yield strength of transversal bars
240 MPa
International Conference on Earthquake Engineering and Disaster Mitigation 2008
Table 2. Element Dimensions (in mm) used in 6 Story Building
Seismic Zone
Story
Beams
Interior
Columns
Exterior
Columns
Corner
Columns
1
400 x 700
560 x 560
500 x 500
475 x 475
2
400 x 700
560 x 560
500 x 500
475 x 475
3
400 x 700
530 x 530
475 x 475
450 x 450
4
400 x 700
530 x 530
475 x 475
450 x 450
5
400 x 700
500 x 500
450 x 450
425 x 425
6
400 x 700
500 x 500
450 x450
425 x 425
1
400 x 650
600 x 600
600 x 600
600 x 600
2
400 x 650
600 x 600
600 x 600
600 x 600
3
400 x 650
550 x 550
550 x 550
550 x 550
4
400 x 650
550 x 550
550 x 550
550 x 550
5
400 x 650
500 x 500
500 x 500
500 x 500
6
300 x 550
420 x 420
420 x 420
420 x 420
2
6
Table 3. Element Dimensions (in mm) used in 10 Story Building
Seismic Zone
Story
Beams
Interior
Columns
Exterior
Columns
Corner
Columns
1
400 x 700
650 x 650
550 x 550
525 x 525
2
400 x 700
650 x 650
550 x 550
525 x 525
3
400 x 700
625 x 625
525 x 525
500 x 500
4
400 x 700
625 x 625
525 x 525
500 x 500
5
400 x 700
575 x 575
500 x 500
475 x 475
6
400 x 700
575 x 575
500 x 500
475 x 475
7
400 x 700
525 x 525
475 x 475
450 x 450
8
400 x 700
525 x 525
475 x 475
450 x 450
9
400 x 700
500 x 500
450 x 450
425 x 425
10
400 x 700
500 x 500
450 x 450
425 x 425
1
400 x 700
700 x 700
700 x 700
700 x 700
2
400 x 700
700 x 700
700 x 700
700 x 700
3
400 x 700
650 x 650
650 x 650
650 x 650
4
400 x 700
600 x 600
600 x 600
600 x 600
5
400 x 700
600 x 600
600 x 600
600 x 600
6
400 x 700
600 x 600
600 x 600
600 x 600
7
400 x 700
550 x 550
550 x 550
550 x 550
8
350 x 600
550 x 550
550 x 550
550 x 550
9
350 x 600
550 x 550
550 x 550
550 x 550
10
300 x 550
360 x 360
360 x 360
360 x 360
2
6
International Conference on Earthquake Engineering and Disaster Mitigation 2008
3.
RESULTS AND DISCUSSION
Nonlinear static pushover analysis using ETABS software v.9.07 (Computer and Structures, Inc.,
2003) and dynamic nonlinear time history analysis using RUAUMOKO 3D software (Carr, Athol
J., 2001) are performed to evaluate the seismic performances of the buildings. The MomentCurvature of beam and column sections are analyzed by ESDAP (Pono et. al., 2003), a software
developed by Petra Christian University. The first mode is used for load pattern of nonlinear static
pushover analysis, while modified spectrum consistent ground motion is used for nonlinear
dynamic time history analysis. Modification of El Centro 15th May 1940, N-S component ground
motion is done by RESMAT (Lumantarna et.al., 1997), to develop an artificial ground motion that
produce response spectrum in accordance to SNI 03-1726-2002. Three levels of earthquake are
used for evaluation the seismic performances, which are earthquakes with 200, 500, and 1000
years return period.
Figures 3 to 8 show the seismic performance of the buildings from nonlinear static pushover
analysis as well as nonlinear dynamic time history analysis in terms of plastic hinges’ location,
displacement, and inter-story drift ratio.
Return
Period
Nonlinear Static Pushover
Exterior Frame
Interior Frame
Nonlinear Time History
Exterior Frame
200
years
500
years.
1000
years
Figure 3. Plastic hinges’ location in SMRF-6-2.
Interior Frame
International Conference on Earthquake Engineering and Disaster Mitigation 2008
Return
Period
Nonlinear Static Pushover
Exterior Frame
Interior Frame
Nonlinear Time History
Exterior Frame
Interior Frame
200
years
500
years
1000
years
Figure 4. Plastic hinges’ location in SMRF-6-6.
Return
Period
Nonlinear Static Pushover
Exterior Frame
Interior Frame
Nonlinear Time History
Exterior Frame
200
years
500
years
1000
years
Figure 5. Plastic hinges’ location in SMRF-10-2.
Interior Frame
International Conference on Earthquake Engineering and Disaster Mitigation 2008
Return
Period
Nonlinear Static Pushover
Exterior Frame
Interior Frame
Nonlinear Time History
Exterior Frame
Interior Frame
200
years
500
years
1000
years
Figure 6. Plastic hinges’ location in SMRF-10-6.
The symbols
show failure of plastic hinges (damage index > 1.0).
In Figures 3 to 6, it can be seen that location of plastic hinges obtained from nonlinear static
pushover and nonlinear time history are quite similar. But in some location, results from nonlinear
time history analysis show more severe damages, especially in exterior frames. An unstabe “soft
story mechanism” is observed in exterior frame SMRF-10-6, when the building is subjected to
earthquakes with 500 and 1000 years return period (see Figure 6).
International Conference on Earthquake Engineering and Disaster Mitigation 2008
SMRF-6-2
6
6
5
5
4
4
Story
Story
SMRF-6-2
3
3
2
2
1
1
0
0
0
0.1
0.2
0.3
0
0.005
Displacem ent (m )
0.01
0.015
0.02
Drift Ratio
PO200
TH200
PO500
PO200
TH200
PO500
TH500
PO1000
TH1000
TH500
PO1000
TH1000
Figure 7. Displacements and inter-story drift ratios in SMRF 6-2.
SMRF-6-6
6
6
5
5
4
4
Story
Story
SMRF-6-6
3
3
2
2
1
1
0
0
0
0.2
0.4
0.6
0
0.01
Displacem ent (m )
0.02
0.03
Drift Ratio
PO200
TH200
PO500
PO200
TH200
PO500
TH500
PO1000
TH1000
TH500
PO1000
TH1000
Figure 8. Displacements and inter-story drift ratios in SMRF 6-6.
0.04
International Conference on Earthquake Engineering and Disaster Mitigation 2008
SMRF-10-2
10
10
9
9
8
8
7
7
6
6
Story
Story
SMRF-10-2
5
5
4
4
3
3
2
2
1
1
0
0
0
0.1
0.2
0.3
0.4
0
0.005
Displacem ent (m )
0.01
0.015
0.02
Drift Ratio
PO200
TH200
PO500
PO200
TH200
PO500
TH500
PO1000
TH1000
TH500
PO1000
TH1000
Figure 9. Displacements and inter-story drift ratios in SMRF 10-2.
SMRF-10-6
10
10
9
9
8
8
7
7
6
6
Story
Story
SMRF-10-6
5
5
4
4
3
3
2
2
1
1
0
0
0
0.2
0.4
0.6
0.8
0
0.01
Displacem ent (m )
0.02
0.03
0.04
Drift Ratio
PO200
TH200
PO500
PO200
TH200
PO500
TH500
PO1000
TH1000
TH500
PO1000
TH1000
Figure 10. Displacements and inter-story drift ratios in SMRF 10-6.
According to SNI 03-1726-2002, the maximum inter-story drift in ultimate limit state should not
exceed 2 %. Form Figures 7 and 10, it can be seen that for both buildings (6 and 10 story
buildings), the requirement is met for Zone 2, but not for Zone 6.
International Conference on Earthquake Engineering and Disaster Mitigation 2008
4.
CONCLUSION
From the results, it can be concluded that the ratio of total flexural strength of the columns with
respect to that of the beams (=6/5) according to SNI 03-2847-2002 does not ensure “strong column
weak beam” criteria, especially in high risk seismic Zone (Zone 6 in this study). Unstable “soft
story mechanism” begin to show in building subjected to Earthquake with 500 years return period,
which is not acceptable. According to maximum inter-story drift criteria set by the code, the same
conclusion can be made.
5.
REFERENCES
Badan Standarisasi Nasional. (2002). “Standar Tata Cara Perhitungan Struktur Beton Untuk
Bangunan Gedung”, SNI 03-2847-2002. Jakarta, Indonesia
Departemen Pekerjaan Umum. (1992). “Standar Tata Cara Perhitungan Struktur Beton Untuk
Bangunan Gedung” , SNI 03-2847-2002, Jakarta, Indonesia.
Badan Standarisasi Nasional. (2002). “Tata Cara Perencanaan Ketahanan Gempa Untuk
Bangunan Gedung”, SNI 03-1726-2002, Jakarta, Indonesia.
Computer and Structures, Inc. (2003). ETABS Non Linear v. 9.07. “Extended Three Dimensional
Analysis Of Building System”, Berkeley, California, USA, 2003.
Carr, Athol J.(2001). RUAUMOKO, Inelastic Dynamic Analysis, 3-Dimensional Version,
University of Canterbury, New Zealand.
Pono, Bill R. dan Lidyawati. (2003), ESDAP, “Educational Section Design And Analysis Program”,
PETRA Christian University, Surabaya, Indonesia.
Lumantarna, B., Lukito, M. (1997), “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