1. Introduction
In June 2016, Ministry of Land, Infrastructure, Transport and Tourism has delivered countermeasures against the long-period ground motions caused by strong earthquakes along the Nankai trough3). However, the countermeasures do not cover high-rise buildings equal to or less than 60 m height that are not required earthquake response analyses in the seismic design. Hence, in this study, earthquake response analyses for such high-rise RC buildings were performed under ground motions assumed in the OS1 and OS2 regions to evaluate the base shear coefficients satisfying a safety demand. Furthermore, an estimation method of the required base shear coefficients proposed in the authors’ previous study4) was applied to practically evaluate the results from the earthquake response analyses.
2. Analytical buildings
Design concept of analytical building models are described. Major design parameters were the number of stories (12, 14 and 16) and lateral strengths (with different Ds in Eq. (2)). Table 2 shows the common structural details of the columns and beams for the building models with different numbers of stories. The member bending strengths were designed based on an overall collapse mechanism, as shown in Fig. 1, to satisfy the lateral strength (by Eq. (2)) under assigned Ds.
3. Earthquake response analyses
Analytical methods including modeling and numerical calculation methods are described. Two ground motions in the OS1 and OS2 regions were applied to earthquake response analyses. Within the analytical cases in the present study, in general, the inter-story drift responses were more severe under the OS2 ground motion for high-rise RC buildings. Furthermore, the base shear coefficients satisfying a safety demand of the maximum inter-story drift of 1/75 were identified, which is summarized in Table 5.
4. Estimation of demands on the base shear coefficients by the equivalent linearization method
The equivalent linearization method was applied to estimate the results from the earthquake response analyses. The procedure of the proposed estimation method4) is illustrated, as shown in Fig. 7. It was also implemented for the analytical models. As a result, the estimations with Eq. (8) for practical design for RC buildings underestimated response reductions under hysteretic damping resulting in overestimation of the base shear coefficients to satisfy the safety demand, as shown in Table 6. Therefore, it was modified based on Eq. (12) presented by Kobayashi et al.16) Consequently, the base shear coefficients required by the earthquake response analyses were well estimated by the proposed procedure with Eq. (12a), as shown in Table 8. In addition, suggestions for future study are provided to complete more accurate and simplified estimations.
5. Conclusions
Major findings from the present study are summarized based on the above research outcomes.
