ACCORDING TO SNI 03-2847-1992 AND SNI 03-2847-2002 ... A 10-storey
building in Zone 2 of Indonesian seismic map (SNI 03-1726-. 2002) is chosen.
International Civil Engineering Conference "Towards Sustainable Civil Engineering Practice" Surabaya, August 25-26, 2006
PERFORMANCE OF SPECIAL MOMENT RESISTING FRAME DESIGNED ACCORDING TO SNI 03-2847-1992 AND SNI 03-2847-2002
Ima MULJATI1, Pamuda PUDJISURYADI1
ABSTRACT: The Indonesian Reinforced Concrete Code has changed from SNI 03-2847-1992 to SNI 03-2847-2002. In this study, performance of Special Moment Resisting Frame System designed using both codes are compared. A 10-storey building in Zone 2 of Indonesian seismic map (SNI 03-17262002) is chosen. The structural performances are analyzed by static non-linear pushover and dynamic non-linear time history analysis. The results show that both structures have similar seismic performace, even though the amount of column reinforcement differs significantly. KEYWORDS: Special Moment Resisting Frame System, Static Non-Linear Analysis (Pushover), Dynamic Non-Linear Time History Analysis. 1. INTRODUCTION Moment resisting frame system consists of beams and columns in which bending of these members provides the resistance to lateral forces. There are two primary types of moment frame, ordinary and special. Special moment resisting frames are detailed to ensure ductile behavior of the beam-tocolumn joints and normally used in zones of higher seismicity [1]. Indonesian Reinforced Concrete Code which has been changed from SNI 1992 [2] to SNI 2002 [3], is applicable for moment resisting frame system. Both standards adopt the concept of capacity design. Both standards show that the design of beams is similar, but significant changes are found in the design of columns [4]. Although both standards adopt same concept known as strong-column-weakbeam, they present it in different formulas as shown in Equation (1) and (2) for SNI 2002 and SNI 1992 respectivley.
6 Mg 5 ≥ 0.7ωd ∑ M kap ,b
ΣM e ≥
∑M
u ,k
(1) (2)
Me and Mg in Equation 1 are the total of nominal moments in columns and beams connecting to a joint. Mu,k dan Mkap,b are the total of design/ultimate moments in column and total of nominal moments in beams multiplied by an overstrength factor, φo, as large as 1.25 (for steel with yield strength 400 MPa), while the value of dynamic magnification factor, ωd, is 1.3. In SNI 2002, the design axial forces of columns are determined by combination of factored axial forces due to load cases, but in SNI 1992 they are determined by the shear capacity of beams as well 1
Lecturer, Dept. of Civil Engineering, Petra Christian University, Indonesia.
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as the combined factored axial forces of the columns. No significant changes are found for shear design, only maximum spacing of transverse reinforcement in SNI 2002 seems to be relatively strict. 2. ANALYZED STRUCTURE A 10-storey building in the zone 2 of Indonesian Seismic Map is designed as Special Moment Resisting Frame (full ductility capacity design). Plan and elevation view of the building can be seen in Figure 1, where other technical data is presented in Table 1.
8.00 m
5
10 @ 3.50 m
8.00 m
4
8.00 m
3
8.00 m
2
1 8.00 m
8.00 m
8.00 m
8.00 m
8.00 m
8.00 m A
B
C
D
8.00 m
8.00 m
E
Figure 1. Plan and elevation view Table 1. Technical data
Number of stories Typical Storey Height Beam Dimension Column Dimension Slab Thickness Compressive Strength of Concrete (fc’) Longitudinal reinforcement yield stress (fy) Transverse reinforcement yield stress (fy)
10 stories 3.50 m 400 x 700 mm2 600 x 600 mm2 120 mm 30 MPa 400 MPa 240 MPa
3. DESIGN RESULTS The amount of flexural reinforcement of beams shows unsignificant difference between two standards. On the other side, the number of transverse reinforcement of beams is different where SNI 2002 produces more reinforcement. The difference is caused by the formulation applied for shear design in both standards. In this study, it was found that the shear design forces differ as much as 25% in average [4]. Unlike beam reinforcement, SNI 1992 requires more longitudinal reinforcement in columns compared to SNI 2002 (about 41%). However, the transverse reinforcement of columns of SNI 1992 is 45% less than SNI 2002 [4]. The use of Equation 1 results a minimum longitudinal reinforcement for most columns in this study.
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International Civil Engineering Conference "Towards Sustainable Civil Engineering Practice"
4. SEISMIC PERFORMANCE Based on available reinforcement, moment-curvature relation of every beams and columns’ sections are analyzed by ESDAP [5], a program developed at Petra Christian University. The static non-linear pushover analysis [6] was conducted to examine the performance of designed structures when subjected to lateral forces. A load pattern based on the static equivalent forces according to SNI-031726-2002 [7] is used to push the structures. The capacity curve produced is plotted against the Demand Response Spectrums. Four demand spectrums equivalent to earthquakes with 100, 200, 500 and 1000 years return period are used to determine the performance points [1]. In order to check the structural performance produced by the static non-linear pushover analysis, a non-linear time history analysis (using RUAUMOKO 3D [8]) was performed in this study. The earthquake acceleration used is the El Centro 1940 N-S component. This record is modified so that it will give response spectrum consistent to earthquake with 500 years return period in zone 2 of Indonesian seismic map (using RESMAT [9], a program developed at Petra Christian University). The acceleration of original and modified El Centro N-S Component can be seen in Figure 2, while the consistent response spectrum is shown in Figure 3. For earthquakes other than 500 years return period, the response spectrums are scaled from 500 years return period response spectrum by using peak ground acceleration (PGA) ratio factors [10]. -
Original Ground Acceleration
Modified Ground Acceleration
0.40
0.3 0.2
0.30
0.2
a ( g)
0.20
a (g)
0.1 0.1
0.10
0.0 0.0
0.00
-0.0
-0.10
-0.1 -0.1
-0.20
-0.2 -0.2
-0.30 0
1
2
3
4
5
6
7
8
9
0
10 11 12 13 14 15 16 17 18 19 20
1
2
3
4
5
6
7
8
t (second)
9
10
11
t (second)
12
13
14
15
16
17
18
19
2
Figure 2. Ground acceleration of El Centro 1940 N-S component Response Spectrum of El Centro 18th May 1940 (N-S) 1 0.9
Original Respons Spectrum Modified Respons Spectrum SNI-Respons Spectrum (500-years)
0.8 0.7
a (g)
0.6 0.5 0.4 0.3 0.2 0.1 0 0.0
0.5
1.0
Tn (s)
1.5
2.0
2.5
3.0
Figure 3. Response spectrum of El Centro 1940 N-S component
The total base shear and the corresponding roof displacements from the pushover analysis can be seen in Table 2. The interstory drift and plastic hinges locations are presented in Figures 4, and 5.
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Table 2. Total base shear (V) and roof displacements (D) Return Period (years) 100 200 500 1000
Return Period (years)
SNI 03-2847-1992 V (kN) D (m) 3847.456 0.093 4111.905 0.130 4328.581 0.206 4492.534 0.293
Pushover
Time History
10
10
9
9
8
8
7
7
6
6
Story Tingkat
Story Tingkat
100
SNI 03-2847-2002 V (kN) D (m) 5405.435 0.089 5623.382 0.115 5837.155 0.167 6004.745 0.235
5 4
5 4
3
3
2
2
1 0 0.00
1
0.50
1.00
1.50
0 0.00
2.00
0.50
10
10
9
9
8
8
7
7
6
6
5 4
3 2
1.00
1.50
0 0.00
2.00
0.50
10
9
9
8
8
7
7
6
6
Tingkat Story
Tingkat Story
10
5 4
4 3
2
2
1
1 1.00
1.50
0 0.00
2.00
0.50
9
8
8
7
7
6
6
Tingkat Story
Story Tingkat
10
9
5 4
2.00
1.50
2.00
4 3
2
2
1
1 1.00
1.50
5
3
0.50
1.00
Drift (%) (m) Simpangan
10
0 0.00
2.00
5
3
0.50
1.00
Simpangan (m) lantai (%) Simpangan Drift (%) antar
Simpangan Drift (%) (m)
1000
1.50
1
0.50
Simpangan (m) lantai (%) Drift (%) antar Simpangan
0 0.00
2.00
4
2 1
500
1.50
5
3
0 0.00
1.00 Simpangan Drift (%) (m)
Tingkat Story
200
Story Tingkat
Simpangan Drift (%) (m)
1.50
2.00
0 0.00
Drift (%) Simpangan (m)
0.50
1.00
Drift (%) (m) Simpangan
Remark : SNI 03-2847-2002 SNI 03-2847-1992 Figure 4. Interstory drift
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International Civil Engineering Conference "Towards Sustainable Civil Engineering Practice"
Return Period (years)
Time History Exterior Frame SNI 03-2847-2002 SNI 03-2847-1992
Interior Frame SNI 03-2847-2002 SNI 03-2847-1992
100
200
500
1000
Figure 5. Plastic hinges locations
4. STRUCTURAL PERFORMANCE LEVEL It can be seen that the result from pushover analysis is in accordance to that of time history analysis. In general, from the pushover analysis, the displacements of structure designed by SNI 2002 are smaller than SNI 1992. Besides, the time history analysis produces the same condition, except the results for 500-, and 1000-years return period due to plastic response of the structure. Furthermore, the plastic hinges formations from both structures are relatively the same. Performance of both structures is shown in matrix form (ACMC [11]) in Table 3 and 4 using interstory drift and damage index as parameters. One percent interstory drift (upper limit for damage control limit state) is observed at both structures when subjected to target earthquake (with 500 years return period). While maximum damage indices of both structures are only as much as 0.568,
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indicating no failures occurred due to target earthquake. Pushover analysis, being simpler method to analyse structure performance, gives similar result to time history analysis for lower earthquake intensities (100, 200, and 500 years), while conservative result is shown for severe earthquake (100 years). Table 3. Performance matrix based on interstory drift Return Period
Standard
Serviceability Limit State 0.46 (0.40) 0.49 (0.47)
Performance Level Damage Control Limit State
Safety Limit State SNI 100 2002 years SNI 1992 SNI 0.66 200 2002 (0.66) years SNI 0.73 1992 (0.73) SNI 0.95 2002 (0.99) 500 years SNI (0.90) 1.14 1992 SNI (1.15) 1.32 1000 2002 years SNI (1.06) 1.65 1992 Maximum
