In the third level document, Evaluation example, a calculation procedure of evaluation is shown for an example building. The building is 12-story reinforced concrete structure, which is a design example in the past AIJ guidelines[2]. The limit state deformations, the seismic capacity index, the probability of exceeding the limit states are calculated for the building numerically in detail. The structure is a regular- shaped, open-frame in X-direction and wall-frame in Y-direction. In accordance with the past guidelines, the building has been designed more carefully than by BSL with design factors, so that the ductile overall mechanism is ensured. Deformability of members are ensured up to the deformation angles of 1/50, 1/67 and 1/100 for beam, column and wall, respectively, although the lateral ultimate lateral load-carrying capacities are made almost equal to the required strength in the BSL, that are determined from the structural characteristics coefficients, Ds=0.3 for open frame in X-dir, and Ds=0.4 for wall-frame in Y-dir.
The calculated overall and story limit deformations are shown in Table 1. The seismic capacity indices, the ratios of the capacity earthquakes to the standard earthquake are also shown in the right column of the table. These estimates by the pushover analysis and CSM are almost equal to the responses calculated from additional time-history analysis. The seismic performance indices, namely the amplification factors of the earthquakes are around 1.0 for the reparable limit I, 1.5 for the reparable limit II, and higher than 2.0 for the safety limit.
Table 1. Limit deformations and seismic capacity indices.
Direction Limit state Base shear coefficient Overall limit deformation Inter-story limit deformation Seismic capacity index Serviceability 0.160 1/412 1/355 (5F) 0.30 Reparability I 0.245 1/151 1/117 (4F) 1.05 Reparability II 0.255 1/98 1/75 (4F) 1.54 X-direction Safety 0.265 1/57 1/45 (4F) 2.35 Serviceability 0.192 1/823 1/631 (9F) 0.26 Reparability I 0.378 1/183 1/146 (9F) 1.00 Reparability II 0.395 1/120 1/120 (9F) 1.74 Y-direction Safety 0.408 1/76 1/67 (9F) 2.75 Skewed direction(60°) Safety - 1/57 - 3.23
Therefore, the ultimate capacity would have enough margin of deformability up to the safety limit, in case of the design with the statically required capacity and the standard design spectrum in the BSL. In other words, the “limit strength design method” allows the design such that the required lateral strengths may be less than required conventionally, if the deformability up to the safety limit is ensured. However, it is not recommended in the Guidelines to make these margins less by selecting less capacity, but to designate these higher performance levels for proper description in the market. It should be noted that this is the result in case of ideally regular type of building with ensured overall mechanism, when the error of estimation might probably be minimum. The factored design of wall and columns based on the capacity design philosophy should be reemphasized. There still need further investigation both on demand and capacity, such as, extreme ground motion, inelastic responses of irregular structures, nonlinear soil-structure interaction and so on.
The risk analysis was carried out for this example with design service life of 50 years: at first, the probabilities of exceeding the capacity earthquake were evaluated in X and Y directions, respectively, as 12% and 7.6% for reparability I, 1.5% and 0.18% for reparability II, 0.21% and 0.13% for safety limit sates. This is the case when the soil amplification is evaluated in detail and reduction of velocity spectrum, i.e., the constant displacement spectrum is assumed over certain period. This could be underestimation, therefore, the constant velocity was assumed over the peak and evaluated alternatively then: 18% and 7.6% for reparability I, 6.5% and 2.0% for reparability II, 0.92% and 0.41% for safety limit sates. Because data were available only for the reliability of safety limit evaluation, the model was applied: the probability of exceeding the safety limit in Y direction was evaluated as 3.6% and 1.4% for the first and the latter assumptions in the spectrum shape. The accuracy in evaluating the limit states must and the earthquake hazard must be made higher in the future. It is expected that the proposed method will be made use of in practice, such as setting rates of earthquake disaster insurance or life-cycle cost analysis.
9. CONCLUSION
The new AIJ Guidelines is outlined, which provides deterministic and probabilistic methods of evaluating the actual seismic performance level of a designed reinforced concrete building. The limit states of the structures are defined based on the residual damage rates of members corresponding to the performance objectives as: (1) serviceability, (2) minor repair, (3) major repair, and (4) safety. The deterministic procedure evaluates the basic seismic capacity index for each limit state, which is defined as the amplitude ratio of the capacity earthquake to the standard earthquake, where the capacity earthquake is to induce the response equal to the limit state. The probabilistic evaluation method is provided as an additional procedure, where the performance level is expressed using the probability of exceeding the limit state by site-specific earthquakes during design service life.
The Guidelines is being translated into English and the English version is to be published from AIJ in the near future. We hope the Guidelines will be referred widely as research and technical documents as well as model code of practice for seismic performance evaluation. It is expected that more sophisticated alternative methods will be proposed based on reliable verification through intensive research in the future.
ACKNOWLEDGEMENT
The Guidelines was drafted by members of the Subcommittee on performance evaluation and limit states, the Steering committee on reinforced concrete structures, the Architectural Institute of Japan, including drafting WG members: Toshimi Kabeyasawa, Toshikatsu Ichinose, Daisuke Kato, Hitoshi Tanaka, Yuuki Sakai, Hiroshi Kuramoto, Hideyuki Kinugasa, Taizo Matsumori, Nobuyuki Izumi, Kazuhiro Kitayama, Masaki Meda, Kazuaki Tsuda, Masaru Teraoka, and Hajime Okano. The efforts of above members as well as reviewers are gratefully acknowledged.
REFERENCES
[1] Architectural Institute of Japan. (1990). Design Guidelines for Earthquake- Resistant Reinforced Concrete Buildings Based on Ultimate Strength Concept 1988(draft), 1990 (the first edition in Japanese), 1994 (in English version), AIJ, Tokyo.
[2] Architectural Institute of Japan. (1999). Design Guidelines for Earthquake- Resistant Reinforced Concrete Buildings Based on Inelastic Displacement Concept 1997 (draft), 1999 (the first edition in Japanese), AIJ, Tokyo.
[3] Architectural Institute of Japan. (2004). Guidelines for Seismic Performance Evaluation of Reinforced Concrete Buildings, 2004 (draft), AIJ, Tokyo.
HAZARD, GROUND MOTIONS AND PROBABILISTIC ASSESSMENTS