AN ANALYTICAL STUDY OF A BASE-ISOLATED BUILDING BASED ON SEISMIC CODES OF JAPAN, CHINA AND TAIWAN
Demin FENG*, Chief Researcher, Technology Development Division, Fujita Corp. 2025-1 Ono, Atsugi City, Kanagawa 243-0125, JAPAN Email: [email protected] Keiji MASUDA, Chief Researcher, Technology Development Division, Fujita Corp. 2025-1 Ono, Atsugi City, Kanagawa 243-0125, JAPAN Email: [email protected] Wenguang LIU, Professor, Earthquake Engineering Research Test Centre, Guangzhou Univ. 248 Guangyuan Zhong Road, Guangzhou 510405, CHINA Email: [email protected] Tzusheng HSU, TPCE, 9F, No.28 Tung-Hsing RD., Taipei, TAIWAN Email: [email protected]
Keywords: Building code, Equivalent linear analysis, Time history analysis, Isolated structure Summary Seismic codes of buildings with isolation devices in Japan, China and Taiwan are introduced first. Spectral accelerations at the surface layer of Tokyo, Beijing and Taipei are compared then. An analytical study on a typical 14F RC building model base-isolated by lead rubber bearings (LRB) is carried out. Both equivalent linear analysis and time history analysis methods are used. Base share coefficient and the maximum displacement of base-isolation floor by these two methods are compared.
1. Introduction After the 1994 Northridge earthquake in USA, the 1995 Hyogo-ken Nanbu earthquake in Japan and the 1999 Chi-Chi earthquake in Taiwan, buildings with seismic isolation devices have increased rapidly. At the same time, building codes are revised to include the design of buildings with seismic isolation devices [1-5]. In this paper, seismic codes Japan, China and Taiwan are introduced. The building codes took effective in Japan in 2000 and in China and Taiwan in 2002. Okamoto has reported situation in Japan [6]. Zhou had a summary on the development of China [7]. ChangExample reported the status of applications in Taiwan [8]. A typical 14F RC building model base-isolated by lead rubber bearings (LRB) is analyzed based on those three building codes. The building’s characteristics such as weight, height, hysteresis properties and soil condition are fixed in all cases. The isolation devices are also fixed to LRBs whose total yield load is 4% of the total weight, so that the discussion will restrict to the hysteresis type dampers. To consider the seismic region coefficients, the construction sites are assumed at Tokyo, Beijing and Taipei, respectively. A fixed soil profile classified as “Class II” in Chinese code is assumed. The deformation of the isolation floor and shear force coefficient along the building are compared. While a dynamic response analysis method is recommended in all three building codes. A simplified design procedure based on the equivalent linear analysis is also introduced at limited conditions. Since several safety factors have to be considered beyond the result due to the equivalent linear analysis, the dynamic response analysis method usually gives more economic design. To compare the results by these two analytical methods, parameters defined in the codes may not be applied exactly. Base share coefficient and the maximum displacement of base-isolation floor by these two methods are compared.
2. Building Codes 2.1 Design Spectra A-Two-Stage-Design-Philosophy is introduced in Japan and China’s building codes. The two stages are usually divided into damage limitation and life safety. In the damage limitation stage, the structural safety performance should be preserved in the considered earthquake. In the life safety stage (Level 1), the building should not collapse to assure the safety of human life. In this paper, response analyses in the life safety stage (Level 2) will be discussed. Corresponding with totally different earthquake background, the return periods of considered seismic criteria are summarized in Table 1. It should be noticed that allowable story drift is also different. In a building with seismic isolation devices, the story drift angle is nearly restricted to half or less than half of the above value. A design spectrum is usually related with zoning factor, soil condition and damping factor as shown in Eq.(1). The bedrock design spectrum consists of roughly two parts, i.e., a uniform acceleration portion in shorter periods, and a uniform velocity portion in longer period. However, the velocity portion is artificially increased in Chinese code to make sure the safety of high-rise buildings or isolated buildings having long natural period. In the next sections details of each code are introduced.
Table 1: Return period and drift angle corresponding the building codes. Level Japan China Taiwan Return period(yr) Level 50* 50 1 Level 500* 1600~2500 2 475 Story drift angle Level 1/200 1/550 (RC Frame) 1 Level 1/50* 1/50 2 1/50 Place Tokyo Beijing (VIII) Taipei Basin Site class 2nd II *: estimated 2.1.1 Japan In general, the 5% damped spectral acceleration, Sa, shall be obtained by Eq.(1).
S a (T) I Z Gs(T) S0 (T) (1) where: I: occupancy importance factor; Sa (T): the design spectrum on site Z: seismic hazard zoning factor; Gs(T): site amplification coefficient S0(T): the design spectral acceleration at engineering bedrock defined in Eq.2 3.2 30T T 0.16 2 S0 (T )(m / s ) 8.0 0.16 T 0.64 (2) Example 5.12 / T 0.64 T ) 1.2 3.0 2 s /
m 1.0
( 2.5
n o i
t 0.8 2.0 a ) r e T l (
e 0.6
s 1.5 c G c a
l 0.4 1.0
a 1st class ground r t
c 2nd class ground e 0.2 0.5 p 3rd class ground S 0.0 0.0 0.16 0.64 T (s) 0 1 2 3 4 5 Period (s) Period (s)
Fig.1: Spectral acceleration, S0, at the engineering bedrock and site amplification coefficient Gs(T) under different site classes (Japan).
In Fig.1, are shown standard spectral acceleration, S0, at the engineering bedrock and site amplification coefficient Gs(T) under different site classes. The zoning coefficient Z is divided into four levels as 1.0, 0.9, 0.8 and 0.7(Okinawa only) around Japan. There are three different site classes. In practice, the Gs(T) is usually calculated convergently based on the investigated N values and types of the soil profile other than directly using the coefficients defined in the code. continue 4 Conclusions Seismic codes on isolated structures of Japan, China and Taiwan were compared in this paper. After comparing spectral acceleration at a class II site, response analyses were carried out on a typical 14F RC building model base-isolated by lead rubber bearings based on these codes. Conclusions are summarized as follows. Under the assumed places and soil conditions, response spectra in Taipei basin had largest amplitude in long period. Damping deduction factor is introduced in all codes. Comparing other codes, damping effect in Japanese code is largest. Time history analysis method is recommended in all codes, while a simplified design procedure based on the equivalent linear analysis method is also introduced at limited conditions. Good agreement between these two methods was observed in the Japanese code. RF RF RF RANDOM EL_CENTRO NS 14F 14F 14F HACHINOHE NS AVERAGE 13F 13F 13F ELA 12F 12F 12F CAPACITY 11F 11F 11F 10F 10F 10F JAPAN 9F 9F 9F 8F 8F 8F 7F 7F 7F 6F 6F 6F 5F 5F 5F 4F 4F 4F 3F 3F 3F 2F 2F 2F 1F 1F 1F
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0 1000 2000 3000 4000 5000 6000 0 5 10 15 20 25 30 35 40 45 50 RF RF RF SHEAR FORCE COEFFICIENT RANDOM DRIFT ANGLE (H/) STORY DEFLECTION EL_CENTRO (cm) NS 14F 14F 14F HACHINOHE NS JAPAN (Y Direction) AVERAGE 13F 13F 13F ELA 12F 12F 12F CAPACITY 11F 11F 11F 10F 10F 10F CHINA 9F 9F 9F 8F 8F 8F 7F 7F 7F 6F 6F 6F 5F 5F 5F 4F 4F 4F 3F 3F 3F 2F 2F 2F 1F 1F Example1F RF0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 RF 0 1000 2000 3000 4000 5000 6000RF 0 10 20 30 40 50 SHEAR FORCE COEFFICIENT RANDOM DRIFT ANGLE (H/) STORY DEFLECTION EL_CENTRO (cm) NS 14F 14F 14F HACHINOHE NS AVERAGE 13F 13F CHINA (Y Direction) 13F ELA 12F 12F 12F CAPACITY 11F 11F 11F 10F 10F 10F TAIWAN 9F 9F 9F 8F 8F 8F 7F 7F 7F 6F 6F 6F 5F 5F 5F 4F 4F 4F 3F 3F 3F 2F 2F 2F 1F 1F 1F
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0 1000 2000 3000 4000 5000 6000 0 10 20 30 40 50
SHEAR FORCE COEFFICIENT DRIFT ANGLE (H/) STORY DEFLECTION (cm) Fig.9: ResultsTAIWAN of the (Y Direction)response analyses References 1) International Code Council, “International Building Code”, 2000 2) European Standard, “Eurocode 8: Design of structures for earthquake resistance (FINAL DRAFT)”, Dec. 2003 3) MLIT, etc., “The Notification and Commentary on the Structural Calculation Procedures for Building with Seismic Isolation -2000-”, 2000(in Japanese) 4) Ministry of Construction, P.R.China, “Code for seismic design of buildings”, GB50011- 2001, 2001(in Chinese) 5) Ministry of the Interior, Taiwan, “Design Code for Buildings with isolation devices”, 2002(in Chinese) 6) Okamoto, S. etc., “Recent developments in seismically isolated buildings in Japan”, Earthquake Engineering and Engineering Vibration, Vol.1, No.2, Dec. 2002 7) Chang K.C., etc., “Status of Application of Passive Control Technologies in Taiwan”, 13WCEE, No.2993,2004 8) Zhou, F.L., “Seismic Isolation of Civil Buildings in the People’s Republic of China”, Progress in Structural Engineering and Materials, Vol. 3, No. 3, 2001 continue