of first level of screening for buildings in Afghanistan. ... Afghan Building Code published in 2012. ... spectrum method and time history analysis is performed.
Seismic Assessment of Recently Constructed RC Mid-rise Building in Afghanistan Afghan Structural Code Seismic assessment
Ahmad Naqi 1* Taiki Saito 2**
Mid-rise RC building Seismic Judgment Index
1. Introduction
1
Previous study [1] proposed 0.5 as a seismic safety index of first level of screening for buildings in Afghanistan. The study applied the capacity spectrum method on 15 low-rise (nine twostory building and six three-story buildings) reinforce concrete masonry structure. And, maximum inter-story drift angle relative to Afghan Structure Code (ASC) response spectra and El Centro 1940 was studied. The result was then compared with safety design limit (1/250) drift angle. The study found, low-rise building with seismic index equal or greater than 0.5 are able to satisfy the design limits. Thus, the study proposed 0.5 as Judgment Seismic Index for first level of screening. Similar methodology is practiced by this research to support the previous finding and to introduce 0.5 as judgment seismic index for reinforced concrete buildings. Mid-rise reinforced concrete frames are common in major cities in Afghanistan. Most of these buildings are constructed before the Afghan Building Code published in 2012. The seismic performance of these recently constructed buildings are mainly concerned.
2. Specimens Buildings This research examined the seismic performance of six recently constructed RC moment frame buildings. All the buildings are located in Kabul, Afghanistan. Table 1 present an outline of target buildings (such as, number of story, concrete and steel nominal compressive and yield strength). And for more detail characteristics of specimen buildings, it is refered to reference [5].
3. Methodology of Research The entire research is performed in two phases of calculation. Where in first phase the specimen seismic response is calculated basically following the actual design data of existing buildings. But in second phase of calculation, the buildings performance is increased by retrofitting the buildings with concrete shear wall. In addition, in both phase of calculation firstly the Seismic index was estimated. And then the capacity spectrum method and time history analysis is performed. At the end the results were compared and discussed.
4. Original Building’s Performance 4.1 Seismic Index (IS) Seismic Index (IS), which is defined in the Japanese Standard to evaluate the seismic performance of the low-rise and medium-rise RC buildings, is calculated by the following formula:
1
アフガニスタンのＲＣ造建物の耐震設計クライテリア
1
2
∝ ∝
∝
3 4
∑
5
∑
Where (IS) is related to the basic seismic index (E0), time index (T), and irregularity index (SD). And the basic seismic index (E0), which exhibits the seismic performance of building, is related to strength index (CC, CSC & Cw), ductility index (FC, FSC & Fw) and story-shear modification factor. The Japanese Standard defines three screening procedures for estimating the basic seismic index (E0). This study adopted the first level screening procedure to calculate the seismic index. And the result present in Table 1. Table 1: Specimens building detail and seismic-index Specimen Structure ID Bldg. 01 Bldg. 02 Bldg. 03 Bldg. 04 Bldg. 05 Bldg. 06
No. of Story
Fc (MPa)
Fy (MPa)
5.0 5.0 4.0 5.0 4.0 3.0
21.0 24.0 24.0 21.0 24.0 24.0
295.0 295.0 340.0 340.0 340.0 295.0
IS Index (Original Bldg.) Long. Trans. Dir. Dir. 0.19 0.20 0.15 0.20 0.17 0.15 0.12 0.13 0.30 0.30 0.33 0.26
IS Index (Retrofit Bldg.) Long. Trans. Dir. Dir. 0.40 0.44 0.33 0.42 0.41 0.39 0.31 0.29 0.39 0.49 0.45 0.46
4.2. Capacity Spectrum Method The non-linear static analysis method, which compare the force-displacement capacity curve of specimen structure with ASC design response spectrum, is practiced secondly. For this purpose, all the specimen building were simulated by STERA-3D software, which coded by one of author, and capacity curves are plotted. Then the capacity curves were converted to bi-linear curves. Afghanistan Structural Code (ASC) presents the mapped spectral acceleration for 1Hz and 5Hz with 5% of critical damping. These maps are available for 2%, 5% and 10% of probability of exceedance in 50 years. Using ASC maps, (the maximum considered earthquake spectral acceleration for short period SS=1.31g and one-second period S1=0.52g) the design response spectrum is generated. Then the capacity curve of the building obtained by the nonlinear push over analysis and the demand spectrum of ASC is plotted together to estimate the performance point, which describe the maximum nonlinear displacement of the building. The performance point is defined as the inter-section between capacity curve and reduced response spectrum obtained by an iterative procedure. Relative to the performance point, going back to the pushover analysis, and corresponding distribution of the maximum inter-story drift angle of the building is found, Figure 1. アーマド・ナキ 斉藤大樹
3
2
2
1
1
0 0
0.01
0.02
0.03
Longitudinal Direction (CSM)
5
Is=0.31 Is=0.4 Is=0.45 1/100 1/200 Is=0.39 Is=0.41 Is=0.33
4
3
0 0
0.01 0.02 Story Drift
Story Drift
4.3. Time History Analysis By capacity spectrum method only the maximum response calculates, whereas the structural response at a number of subsequent time instants can by estimate by time history analysis. For this reason, the THA is applied to support the conclusion and to have an intact outcome. However, the Afghanistan earthquake ground motion history data is not available but the study artificially generate ground motion following the Kobe 1995 NS earthquake phase mode by STERA-Wave program, coded by one of the author. And Figure 2 present max inter-story drift for THA of artificially earthquake adjust with Kobe 1995 NS phase mode.
Story
3
1/100 1/200 Is=0.13 Is=0.2 Is=0.26 Is=0.3 Is=0.15 Is=0.2
4
3
2
2
1
1
0
0
3
2
1
1
0 0
0.01 0.02 Story Drift
0.03
0 0
0.01 0.02 Story Drift
0.03
Fig 3. Max inter-story drift angle by CSM (Retrofitted Building) Longitudinal Direction (THA)
5
Is=0.31 Is=0.4 Is=0.45 1/100 1/200 Is=0.39 Is=0.41 Is=0.33
4
Story
1/100 1/200 Is=0.19 Is=0.33 Is=0.3 Is=0.12 Is=0.17 Is=0.15
4
4
2
3
Transvers Direction (THA)
5
Story
Longitudinal Direction (THA)
Is=0.29 Is=0.44 Is=.46 1/100 1/200 Is=0.49 Is=0.39 Is=0.42
0.03
Fig 1. Maximum inter-story drift angle by CSM (Original Building)
5
Transvers Direction (CSM) 5
Story
Story
3
4
Similar procedure was followed for strenghted building and the reuslt presents by Figure 3 and 4, for Capasity Spectrum Method and Time History Analysis. Moreover, the siesmic index was reestimated and present in Table 1.
Story
4
1/100 1/200 Is=0.13 Is=0.2 Is=0.26 Is=0.3 Is=0.15 Is=0.2
Story
1/100 1/200 Is=0.19 Is=0.33 Is=0.3 Is=0.12 Is=0.17 Is=0.15
Transvers Direction (CSM) 5
5
Is=0.29 Is=0.44 Is=.46 1/100 1/200 Is=0.49 Is=0.39 Is=0.42
4
3
2
2
1
1
0
Transvers Direction (THA)
Story
Longitudinal Direction (CSM) 5
0 0
0.01 0.02 Story Drift
0.03
0
0.01 0.02 Story Drift
0.03
Fig 4. Max inter-story drift angle by THA (Retrofitted Building)
6. Conclusions 0
0.01
0.02
0.03
0
Story Drift
0.01 0.02 Story Drift
0.03
Fig2. Maximum inter-story drift angle by THA (Original Building)
Comparing the results obtained after target buildings retrofitted, illustrates building with seismic index larger than 0.4 are able to satisfy the serviceability design limit (1/100). Therefore, 0.5 could be a good proposal for seismic judgment index for first level of screening in Afghanistan.
5. Retrofitted Buildings Performance Because the result of seismic index (IS) for all specimen buildings are equal or less than 0.3, and none of studied building’s seismic index reaches the judgment index of 0.5, the research arbitrarily increased the seismic index by installing Shear wall. The retrofitted shear wall all have same nominal concrete comprestion and steel yield strenght as specimen building. And the shear reinfocing detail (2 layer of D13 at 150mm) and wall thickness (150mm) are considered typically for all buidlings. But the shear walls length are variouse depending the building spaces.
1* Graduate Student, Toyohashi University of Technology 2** Professor, Dr. Eng, Toyohashi University of Technology
REFERENCES 1. Proposal of Seismic Index of Low-rise Concrete Masonry Unit (CMU) Building in Afghanistan. A. Naqi, T. Saito, 2. ASC, Afghan Structural Code, ABC, ANSA, 12 April 2012. 3. Standard for Seismic Evaluation of Existing RC Building, Japan, 2001 4. Version8.9 STERA 3D. http://www.rc.ace.tut.ac.jp/saito/software-e.html 5. A Proposal for Seismic Evaluation Index of Mid-rise Existing RC Buildings in Afghanistan, Ahmad Naqi, T. Saito
1* 豊橋技術科学大学 大学院学生. 2** 豊橋技術科学大学 教授 工学博士
