長周期長時間地震動に対する免震建物の設計用層せん断力係数増幅率分布の適用性

<p> In June 2016, measure to Nankai trough long period ground motions was announced by MLIT. However, the structural calculation using the response spectrum method indicated by the Ministry of Construction notification Vol. 2009 is out of measure because it is difficult to inspect influence of long period ground motions. Also, we proposed a vertical distribution of seismic design load for seismically isolated buildings (SIBs) using the equivalent isolation ratio which has applicability to various dampers.</p><p> In this paper, we analyze the influence of various structural parameters of SIBs on shear force coefficient distribution. In addition, we investigate whether the effect of adding the fluid damper on the shear force coefficient distribution to suppress the response displacement to the long-period ground motions can be expressed by using I_eq. Furthermore, we verify the applicability of the proposed formula for long-period ground motions amplified by the superficial grounds in the actual ground models and propose a new variation correction coefficient CV. The acquired conclusions are as follows;</p><p> </p><p> 1) Based on the analysis results on the long-period ground motions at engineering base layer, it is found that the influence of the setting of the seismic isolation period on the relationship between I_eq. and the equivalent amplification factor of top floor β_eq is large. When the seismic isolation period is long, the moving average value of β_eq in SZ3 and CH3 obtained from the analysis result tend to exceed the Eq.(13). (Fig. 9).</p><p> 2) When adding fluid dampers to hysteresis dampers whose burden shear force coefficient α_s is 0.01, Eq.(13) cannot capture the change in β_eq. However, if the burden shear force coefficient α_s is 0.02 or more, Eq.(13) can capture the change in β_eq. (Fig. 10).</p><p> 3) The moving average of β_eq for long-period ground motions amplified by the superficial grounds in the actual ground models varies depending on the characteristics of the surface ground and the difference in the seismic motion. However, since the moving average of β_eq calculated collectively from the analytical results of the nine long-period ground motions in all the grounds of Site 1, Site2, and Site3 corresponds well to Eq.(13), it can be said to be able to grasp the response shear force coefficient for nine long-period ground motions on average. (Fig. 13).</p><p> 4) The variation coefficient CV of β_eq is determined by Eq.(17) for long-period ground motions amplified by the superficial grounds in the actual ground models. And as shown in Fig. 15, the applicability of amplification factor of vertical distribution of shear force coefficient for seismically isolated buildings to long-period ground motions is confirmed. (Fig. 15).</p>