International Conference on Earthquake Engineering and Disaster Mitigation 2008
PERFORMANCE OF ORDINARY STEEL MOMENT FRAMES
DESIGNED BASED ON INDONESIAN STEEL BUILDING CODE
SNI 03-1729-2002
Ima Muljati1, Hasan Santoso1
1 Civil
Engineering Department, Petra Christian University, Surabaya, Indonesia
Email: imuljati@petra.ac.id ; hasan@petra.ac.id
ABSTRACT: After Northridge- and Kobe-earthquake (1994 and 1995), Federal Emergency Management
Agency (FEMA) investigation shows that building designed as Ordinary Moment Frames (OMFs) has
performed well under moderate level of ground motion. OMFs are designed to have a large amount of
stiffness and less ductility when carrying lateral loads. Therefore, “strong column weak beam” requirement
can be neglected in its design. Unfortunately, this structural system has less attracted in the structural design
development in Indonesia, especially for steel structures. In accordance with the new published steel
structures design code for building, SNI 03-1729-2002, the objective of this study is to evaluate the
performance of OMFs at zone 2 of Indonesian seismic map. Three buildings with symmetrically plan view,
including 4-, 8-, and 12-story are evaluated. The structural performance of these buildings is analyzed using
static nonlinear pushover and dynamic nonlinear time history analysis. The results show that the 4-story
building fulfills the drift requirement but the 8- and 12-story buildings fail to fulfill the drift requirement.
However, based on the performance matrix, the damage indices of all buildings are in acceptable value.
1.
INTRODUCTION
In FEMA 450 Seismic Provision (2003), there are three types of steel moment-resisting frame
structure. One of them is Ordinary Moment Frame (OMF). The proportioning and configuration of
OMF are less restricted than Special Moment Frame (SMF) because it is designed to have limited
ductility capacity. Consequently, OMF is expected to deteriorate at lower drift levels than that of
an SMF. This is accounted for in design by prescribing a smaller response modification factor, R
and “strong column weak beam” requirement does not need to be applied. Consequently, OMF is
suitable for buildings in low seismic region.
FEMA 355F (2000) investigated three structures including 3-, 9- and 20-story buildings (12-m, 40m, and 88-m) which were designed as OMF. The results showed that the 3- and 9-story buildings
performed well under moderate earthquake. On the other hand the 20-story building showed a
considerable drift value. Therefore, OMF is only recommended for structures with the maximum
height of 30-m.
Effendi and Sie (2001) reported that the study of OMF is relatively less in Indonesia, resulting
minor application in the design practices. This study is aimed to evaluate the performance of OMF
in the low seismic area which is designed based on the latest Indonesian Steel Design Code for
Building, SNI 03-1729-2002 and Indonesian Seismic Code, SNI 03-1726-2002.
2.
BUILDING DESCRIPTION
Three office buildings which represent low- to medium-rise building (4-, 8-, and 12-story), will be
observed in this study. They are in symmetrical plan (Figure 1) and built on soft soil in the zone 2
of Indonesian seismic map (low seismic risk). The columns are placed so that the buildings have
approximately equal rigidity both in x- and y-direction. All structural elements are made of steel
grade BJ 37 with the yield strength, fy, equals to 240 MPa. The height of the first floor is 4-m,
while the others are 3.5-m. The elevation views of the structures are shown in Figure 2.
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International Conference on Earthquake Engineering and Disaster Mitigation 2008
Figure 1 Building plan
Figure 2 Elevation view
3.
DESIGN
Some assumptions are made in the design procedures, they are: (1) connection are considered to be
rigid connection; (2) secondary beams are modeled as a grid system; (3) all beams are laterally
restrained due to the rigid diaphragm contributed by the floors; (4) buildings are modeled as 3Dstructure.
Structures are designed as Ordinary Steel Frames (Struktur Rangka Penahan Momen Biasa,
SRPMB) based on Indonesian Steel Structures Design Code for Building, SNI 03-1729-2002. The
detailed calculation procedures can be found in Suwono and Juslim (2007). The required strength,
U, are calculated based on the loading combinations:
U  1.4 D
U  1.2 D  1.6 L
(1)
U  1.2 D  1LR  E
U  0.9 D  E
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International Conference on Earthquake Engineering and Disaster Mitigation 2008
where D, L, E are dead-, live-, and seismic-load, while LR is reduced live load. The seismic load is
determined in accordance to the equivalent lateral force procedure as stated in Indonesian Seismic
Design Code, SNI 03-1726-2002, using:
V
C1 IWt
R
(2)
where V, C1, I, Wt, and R are seismic base shear, seismic response coefficient, occupancy
importance factor, weight of the building, and response modification factor respectively. Then the
beams capacity is checked using moment and shear interaction:
Mu
M n
 0.625
Vu
Vn
 1.375
(3)
Finally, the columns capacity is checked using moment and axial force interaction:
M ucy 
N uc
N
8 M
 0.2; then uc   ucx 
  1.0
c N c
c N c 9  b N ncx b N ncy 
 M
M ucy 
N
N uc
If uc  0.2; then
  ucx 
  1.0
c N c
2c N c  b N ncx b N ncy 
If
(4)
M, V, and N are moment, shear, and axial force at the member; indices u, n, x and y represent
ultimate, nominal, and global axes of the building; while c, b are reduction factors for column
and bending.
4.
ANALYSIS
The performance of the structures are evaluated to static non-linear pushover analysis (ATC 40,
1996) using ETABS-nonlinear (Habibullah, 1998) and non-linear time history analysis using
RUAUMOKO 3D (Carr, 2002). The properties of hinges at the beams and columns are determined
using XTRACT v3.0.5.
For the time history analysis, the study uses spectrum consistent ground acceleration modified
from N-S component of El-Centro 1940. The modification is achieved using RESMAT
(Lumantarna et al. 1997), a software program developed at Petra Christian University, Surabaya.
As stated in the basic requirement for design, the ground acceleration is based on the 500-year
earthquake return period. In order to obtain the ultimate performance of the building, the buildings
are also checked to the 1000-year earthquake return period.
The building performance evaluations are determined based on the Asian Concrete Model Code,
ACMC (2001). The drift ratio and damage index resulted from pushover and time history analysis
is plotted in the structural performance matrix shown in Figure 3.
Figure 3 Structural performance matrix based on ACMC 2001
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International Conference on Earthquake Engineering and Disaster Mitigation 2008
5.
RESULTS AND DISCUSSION
The dimension of wide flange (WF) section used as main beam and columns are shown in Table 1
and 2. The resulting displacement and drift ratio are shown in Figure 3 – 5.
Both pushover and time history analyses give relatively equal value of displacement. However, the
time history analysis detects a significant drift in the y-direction at the upper floor, especially for
8- and 12-story buildings. The large drift is caused by the use of different size of the column
section at the 4th- and 5th-floor of the 8-story building and the 9th- and 10th-floor of the 12-story
building. The maximum drift ratio resulted from both analysis are plotted in the performance
matrix shown in Table 3 and 4. Subsequently, the damage indices are shown in Table 5 and 6.
Based on the evaluation of the drift ratio, it can be drawn as follows:
1.
For the 500-years earthquake return period, the drift ratio of the 4-story building (in both
direction) is in the safety limit state. However, for the 1000-years earthquake return
period, it is in the unacceptable condition.
2.
The drift ratio of the 8- and 12-story buildings is in the safety limit state, but only in the
x-direction. While in the y-direction, they are in the unacceptable condition (detected by
the time history analysis). Thus, the arrangement of column resulting unbalanced stiffness
for the buildings. The buildings are less stiff in the y-direction than that in the x-direction.
3.
In the observed cases, the time history analysis seems to be more conservative than the
pushover analysis in predicting the drift of the structures.
Table 1 Beam dimension (WF section)
Buildings
Floor
4-story
8-story
12 Lantai
X-direction
Y-direction
Exterior
Interior
Exterior
Interior
All
300x150x5,5x8
350x175x7x11
300x150x5,5x8
350x175x7x11
1-4
300x150x5,5x8
5-7
250x125x6x9
350x175x7x11
300x150x5,5x8
8
300x150x5,5x8
All
300x150x5,5x8
400x200x7x11
350x175x7x11
350x175x7x11
350x175x6x9
400x200x7x11
Table 2 Column dimension (WF section)
Buildings
4-story
Floor
Exterior
Corner
Interior
1
350x350x14x22
350x350x13x13
400x400x13x21
2
350x350x19x19
300x300x11x17
400x400x15x15
350x350x13x13
300x300x12x12
3
4
8-story
12-story
350x350x13x13
300x300x15x15
1
400x400x13x21
350x350x16x16
400x400x18x28
2-4
400x400x15x15
300x300x10x15
400x400x13x21
5-7
300x300x10x15
250x250x11x11
350x350x12x19
8
300x300x9x14
1
400x400x18x28
350x350x12x19
400x400x20x35
2-5
400x400x21x21
350x350x10x16
400x400x18x28
6-9
350x350x16x16
300x300x12x12
400x400x18x18
10-12
250x250x9x14
250x250x8x13
350x350x13x13
4
250x250x11x11
International Conference on Earthquake Engineering and Disaster Mitigation 2008
Figure 3 Displacement and drift ratio of 4-story Building (P = Pushover, TH = Time History)
Figure 4 Displacement and drift ratio of 8-story building (P = Pushover, TH = Time History)
Figure 5 Displacement and Drift Ratio of 12-story Building (P = Pushover, TH = Time History)
Table 3 Building performance based on drift ratio (x-direction)
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International Conference on Earthquake Engineering and Disaster Mitigation 2008
Earthquake
return
period
500-years
Building
Serviceability
PO
TH
Performance Level (%)
Damage
Safety
Control
PO
TH
PO
TH
4-story
1,61
1,60
8-story
1,60
1,54
12-story
1,41
1,71
4-story
1000-years
1,95
8-story
Unacceptable
PO
TH
2,03
2,09
12-story
2,04
1,87
Maximum drift (%)
0,5
1,0
2,04
2,0
>2,0
Table 4 Building performance based on drift ratio (y-direction)
Earthquake
return
period
Building
Serviceability
PO
TH
4-story
8-story
12-story
4-story
1000-years
8-story
12-story
Maximum drift (%)
Performance Level (%)
Damage
Safety
POControlTH
PO
TH
1,75
1,73
1,36
500-years
Unacceptable
PO
TH
1,70
2,11
2,39
2,20
2,73
2,40
2,20
2,21
1,74
0,5
1,0
2,0
>2,0
Table 5 Building performance based on damage index (x-direction)
Earthquake
return
period
Building
Serviceability
PO
TH
4-story
8-story
12-story
4-story
1000-years
8-story
12-story
Damage index
500-years
0,1-0,25
Performance Level (%)
Damage
Safety
POControlTH
PO
TH
*
0.614
*
0.573
*
0.667
*
0.739
*
0.824
*
0.787
0,25-0,4
0,4-1,0
Unacceptable
PO
TH
>1,0
Table 6 Building performance based on damage index (y-direction)
Earthquake
return
period
Building
4-story
8-story
12-story
4-story
1000-years
8-story
12-story
Damage index
Serviceability
PO
TH
Performance Level (%)
Damage
Safety
POControlTH
PO
TH
*
500-years
*
*
0,1-0,25
*
0,25-0,4
0.642
0.787
0.726
*
0.751
*
0.978
0.784
0,4-1,0
Unacceptable
PO
TH
>1,0
Based on the damage index criteria, all buildings are in the safety limit state both for the 500- and
1000-years earthquake return periods. However, for the 1000-years earthquake return period, the
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International Conference on Earthquake Engineering and Disaster Mitigation 2008
buildings are in considerable damage. Similar to the drift consideration, the time history analysis is
more conservative in predicting the damage indices of the buildings.
6.
CONCLUSION
Based on the analysis of the observed buildings, it can be concluded:
7.
1.
The design of ordinary moment frame on soft soil in low seismic area based on the
Indonesian Steel Design Code for Building, SNI 03-1729-2002, is conservative and
suitable for low rise buildings (up to 20-m). For medium-rise building (20- to 40-m),
some caution should be taken especially in the less-stiff-axes of the buildings due to the
drift requirement.
2.
In the case of analysis, the use of pushover analysis is applied only for low-rise buildings.
For better accuracy, time history analysis is recommended due to its wide range
applicability.
ACKNOWLEDGEMENT
This paper is dedicated to our students Kenneth Ivan Suwono and Hans Yulius Rukma Juslim with
gratitude for contributing the work and collaboration, and for patiently enduring the six months of
preparation with us.
8.
REFERENCES
FEMA-450. (2003). “NEHRP Recommended Provisions for Seismic Regualations for New
Buildings and Other Structures”, Federal Emergency Management Agency.
FEMA-355F. (2000). “State of the Art Report on Performance Prediction and Evaluation of Steel
Moment-Frame Buildings”, Federal Emergency Management Agency.
ACMC (2001). “Asian Concrete Model Code, Level 1 & 2 Documents”, International Comittee on
Concrete Model Code.
Effendi, C. and Sie, W.A. (2001). “Analisa Performance Based Design untuk Sistem Rangka
Penahan Momen (SRPM) yang direncanakan sesuai SNI”, Undergraduate Thesis No. 1161 S,
Petra Christian University.
SNI 03-1729-2002. (2002). “Tata Cara Perencanaan Struktur Baja untuk Bangunan Gedung”,
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Gedung”, Departemen Pemukiman dan Prasarana Wilayah.
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ATC 40. (1996). “Seismic Evaluation and Retrofit of Concrete Buildings”, Volume I. Applied
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Habibulah, A. (1998). “ETABS, Three Dimensional Analysis and Design of Building Systems”,
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Carr, A. (2002). ”Ruaumoko Computer Program Library”, University of Canterbury - New
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Lumantarna, B. and Lukito, M. (1997). “Resmat, Sebuah Program Interaktif untuk Menghasilkan
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Indonesia, pp. 128-135.
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